future of iot research paper

• Survey Paper
• Open access
• Published: 09 December 2019

Internet of Things is a revolutionary approach for future technology enhancement: a review

• Sachin Kumar   ORCID: orcid.org/0000-0003-3949-0302 1 ,
• Prayag Tiwari 2 &
• Mikhail Zymbler 1  

Journal of Big Data volume  6 , Article number:  111 ( 2019 ) Cite this article

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Internet of Things (IoT) is a new paradigm that has changed the traditional way of living into a high tech life style. Smart city, smart homes, pollution control, energy saving, smart transportation, smart industries are such transformations due to IoT. A lot of crucial research studies and investigations have been done in order to enhance the technology through IoT. However, there are still a lot of challenges and issues that need to be addressed to achieve the full potential of IoT. These challenges and issues must be considered from various aspects of IoT such as applications, challenges, enabling technologies, social and environmental impacts etc. The main goal of this review article is to provide a detailed discussion from both technological and social perspective. The article discusses different challenges and key issues of IoT, architecture and important application domains. Also, the article bring into light the existing literature and illustrated their contribution in different aspects of IoT. Moreover, the importance of big data and its analysis with respect to IoT has been discussed. This article would help the readers and researcher to understand the IoT and its applicability to the real world.

Introduction

The Internet of Things (IoT) is an emerging paradigm that enables the communication between electronic devices and sensors through the internet in order to facilitate our lives. IoT use smart devices and internet to provide innovative solutions to various challenges and issues related to various business, governmental and public/private industries across the world [ 1 ]. IoT is progressively becoming an important aspect of our life that can be sensed everywhere around us. In whole, IoT is an innovation that puts together extensive variety of smart systems, frameworks and intelligent devices and sensors (Fig.  1 ). Moreover, it takes advantage of quantum and nanotechnology in terms of storage, sensing and processing speed which were not conceivable beforehand [ 2 ]. Extensive research studies have been done and available in terms of scientific articles, press reports both on internet and in the form of printed materials to illustrate the potential effectiveness and applicability of IoT transformations. It could be utilized as a preparatory work before making novel innovative business plans while considering the security, assurance and interoperability.

General architecture of IoT

A great transformation can be observed in our daily routine life along with the increasing involvement of IoT devices and technology. One such development of IoT is the concept of Smart Home Systems (SHS) and appliances that consist of internet based devices, automation system for homes and reliable energy management system [ 3 ]. Besides, another important achievement of IoT is Smart Health Sensing system (SHSS). SHSS incorporates small intelligent equipment and devices to support the health of the human being. These devices can be used both indoors and outdoors to check and monitor the different health issues and fitness level or the amount of calories burned in the fitness center etc. Also, it is being used to monitor the critical health conditions in the hospitals and trauma centers as well. Hence, it has changed the entire scenario of the medical domain by facilitating it with high technology and smart devices [ 4 , 5 ]. Moreover, IoT developers and researchers are actively involved to uplift the life style of the disabled and senior age group people. IoT has shown a drastic performance in this area and has provided a new direction for the normal life of such people. As these devices and equipment are very cost effective in terms of development cost and easily available within a normal price range, hence most of the people are availing them [ 6 ]. Thanks to IoT, as they can live a normal life. Another important aspect of our life is transportation. IoT has brought up some new advancements to make it more efficient, comfortable and reliable. Intelligent sensors, drone devices are now controlling the traffic at different signalized intersections across major cities. In addition, vehicles are being launched in markets with pre-installed sensing devices that are able to sense the upcoming heavy traffic congestions on the map and may suggest you another route with low traffic congestion [ 7 ]. Therefore IoT has a lot to serve in various aspects of life and technology. We may conclude that IoT has a lot of scope both in terms of technology enhancement and facilitate the humankind.

IoT has also shown its importance and potential in the economic and industrial growth of a developing region. Also, in trade and stock exchange market, it is being considered as a revolutionary step. However, security of data and information is an important concern and highly desirable, which is a major challenging issue to deal with [ 5 ]. Internet being a largest source of security threats and cyber-attacks has opened the various doors for hackers and thus made the data and information insecure. However, IoT is committed to provide the best possible solutions to deal with security issues of data and information. Hence, the most important concern of IoT in trade and economy is security. Therefore, the development of a secure path for collaboration between social networks and privacy concerns is a hot topic in IoT and IoT developers are working hard for this.

The remaining part of the article is organized as follows: “ Literature survey ” section will provide state of art on important studies that addressed various challenges and issues in IoT. “ IoT architecture and technologies ” section discussed the IoT functional blocks, architecture in detail. In “ Major key issues and challenges of IoT ” section, important key issues and challenges of IoT is discussed. “ Major IoT applications ” section provides emerging application domains of IoT. In “ Importance of big data analytics in IoT ” section, the role and importance of big data and its analysis is discussed. Finally, the article concluded in “ Conclusions ” section.

Literature survey

IoT has a multidisciplinary vision to provide its benefit to several domains such as environmental, industrial, public/private, medical, transportation etc. Different researchers have explained the IoT differently with respect to specific interests and aspects. The potential and power of IoT can be seen in several application domains. Figure  2 illustrates few of the application domains of IoTs potentials.

Some of the potential application domains of IoT

Various important IoT projects have taken charge over the market in last few years. Some of the important IoT projects that have captured most of the market are shown in Fig.  3 . In Fig.  3 , a global distribution of these IoT projects is shown among American, European and Asia/Pacific region. It can be seen that American continent are contributing more in the health care and smart supply chain projects whereas contribution of European continent is more in the smart city projects [ 8 ].

Global distribution of IoT projects among America (USA, South America and Canada), Europe and APAC (Asia and Pacific region) [ 8 ]

Figure  4 , illustrates the global market share of IoT projects worldwide [ 8 ]. It is evident that industry, smart city, smart energy and smart vehicle based IoT projects have a big market share in comparison to others.

Global share of IoT projects across the world [ 8 ]

Smart city is one of the trendy application areas of IoT that incorporates smart homes as well. Smart home consists of IoT enabled home appliances, air-conditioning/heating system, television, audio/video streaming devices, and security systems which are communicating with each other in order to provide best comfort, security and reduced energy consumption. All this communication takes place through IoT based central control unit using Internet. The concept of smart city gained popularity in the last decade and attracted a lot of research activities [ 9 ]. The smart home business economy is about to cross the 100 billion dollars by 2022 [ 10 ]. Smart home does not only provide the in-house comfort but also benefits the house owner in cost cutting in several aspects i.e. low energy consumption will results in comparatively lower electricity bill. Besides smart homes, another category that comes within smart city is smart vehicles. Modern cars are equipped with intelligent devices and sensors that control most of the components from the headlights of the car to the engine [ 11 ]. The IoT is committed towards developing a new smart car systems that incorporates wireless communication between car-to-car and car-to-driver to ensure predictive maintenance with comfortable and safe driving experience [ 12 ].

Khajenasiri et al. [ 10 ] performed a survey on the IoT solutions for smart energy control to benefit the smart city applications. They stated that at present IoT has been deployed in very few application areas to serve the technology and people. The scope of IoT is very wide and in near future IoT is able to capture almost all application areas. They mentioned that energy saving is one of the important part of the society and IoT can assist in developing a smart energy control system that will save both energy and money. They described an IoT architecture with respect to smart city concept. The authors also discussed that one of the challenging task in achieving this is the immaturity of IoT hardware and software. They suggested that these issues must be resolved to ensure a reliable, efficient and user friendly IoT system.

Alavi et al. [ 13 ] addressed the urbanization issue in the cities. The movement of people from rural to urban atmosphere resulting in growing population of the cities. Therefore, there is a need to provide smart solutions for mobility, energy, healthcare and infrastructure. Smart city is one of the important application areas for IoT developers. It explores several issues such as traffic management, air quality management, public safety solutions, smart parking, smart lightning and smart waste collection (Fig.  5 ). They mentioned that IoT is working hard to tackle these challenging issues. The need for improved smart city infrastructure with growing urbanization has opened the doors for entrepreneurs in the field of smart city technologies. The authors concluded that IoT enabled technology is very important for the development of sustainable smart cities.

Potential IoT application areas for smart cities

Another important issue of IoT that requires attention and a lot of research is security and privacy. Weber [ 14 ] focused on these issues and suggested that a private organization availing IoT must incorporate data authentication, access control, resilience to attacks and client privacy into their business activities that would be an additional advantage. Weber suggested that in order to define global security and privacy issues, IoT developers must take into account the geographical limitations of the different countries. A generic framework needs to be designed to fit the global needs in terms of privacy and security. It is highly recommended to investigate and recognize the issues and challenges in privacy and security before developing the full fledge working IoT framework.

Later, Heer et al. [ 15 ] came up with a security issue in IP based IoT system. They mentioned that internet is backbone for the communication among devices that takes place in an IoT system. Therefore, security issues in IP based IoT systems are an important concern. In addition, security architecture should be designed considering the life cycle and capabilities of any object in the IoT system. It also includes the involvement of the trusted third party and the security protocols. The security architecture with scalability potential to serve the small-scale to large-scale things in IoT is highly desirable. The study pointed out that IoT gave rise to a new way of communication among several things across the network therefore traditional end to end internet protocol are not able to provide required support to this communication. Therefore, new protocols must be designed considering the translations at the gateways to ensure end-to-end security. Moreover, all the layers responsible for communication has their own security issues and requirements. Therefore, satisfying the requirements for one particular layers will leave the system into a vulnerable state and security should be ensured for all the layers.

Authentication and access control is another issue in IoT that needs promising solutions to strengthen the security. Liu et al. [ 16 ] brought up a solution to handle authentication and access control. Authentication is very important to verify the communicating parties to prevent the loss of confidential information. Liu et al. [ 16 ] provided an authentication scheme based on Elliptic Curve Cryptosystem and verified it on different security threats i.e. eavesdropping, man-in-the-middle attack, key control and replay attack. They claimed that there proposed schemes are able to provide better authentication and access control in IoT based communication. Later, Kothmayr et al. [ 17 ] proposed a two-way authentication scheme based of datagram transport layer security (DTLS) for IoT. The attackers over the internet are always active to steal the secured information. The proposed approach are able to provide message security, integrity, authenticity and confidentiality, memory overhead and end-to-end latency in the IoT based communication network.

Li et al. [ 18 ] proposed a dynamic approach for data centric IoT applications with respect to cloud platforms. The need of an appropriate device, software configuration and infrastructure requires efficient solutions to support massive amount of IoT applications that are running on cloud platforms. IoT developers and researchers are actively engaged in developing solutions considering both massive platforms and heterogeneous nature of IoT objects and devices. Olivier et al. [ 19 ] explained the concept of software defined networking (SDN) based architecture that performs well even if a well-defined architecture is not available. They proposed that SDN based security architecture is more flexible and efficient for IoT.

Luk et al. [ 20 ] stated that the main task of a secure sensor network (SSN) is to provide data privacy, protection from replay attacks and authentication. They discussed two popular SSN services namely TinySec [ 21 ] and ZigBee [ 22 ]. They mentioned that although both the SSN services are efficient and reliable, however, ZigBee is comparatively provides higher security but consumes high energy whereas TinySec consumes low energy but not as highly secured as ZigBee. They proposed another architecture MiniSec to support high security and low energy consumption and demonstrated its performance for the Telos platform. Yan et al. [ 23 ] stated that trust management is an important issue in IoT. Trust management helps people to understand and trust IoT services and applications without worrying about uncertainty issues and risks [ 24 ]. They investigated different issues in trust management and discussed its importance with respect to IoT developers and users.

Noura et al. [ 25 ] stated the importance of interoperability in IoT as it allows integration of devices, services from different heterogeneous platforms to provide the efficient and reliable service. Several other studies focused on the importance of interoperability and discussed several challenges that interoperability issue is facing in IoT [ 26 , 27 , 28 ]. Kim et al. [ 29 ] addressed the issue of climate change and proposed an IoT based ecological monitoring system. They mentioned that existing approaches are time consuming and required a lot of human intervention. Also, a routine visit is required to collect the information from the sensors installed at the site under investigation. Also, some information remained missing which leads to not highly accurate analysis. Therefore, IoT based framework is able to solve this problem and can provide high accuracy in analysis and prediction. Later, Wang et al. [ 30 ] shows their concern for domestic waste water treatment. They discussed several deficiencies in the process of waste water treatment and dynamic monitoring system and suggested effective solutions based on IoT. They stated that IoT can be very effective in the waste water treatment and process monitoring.

Agriculture is one of the important domain around the world. Agriculture depends on several factors i.e. geographical, ecological etc. Qiu et al. [ 31 ] stated that technology that is being used for ecosystem control is immature with low intelligence level. They mentioned that it could be a good application area for IoT developers and researchers.

Qiu et al. [ 31 ] proposed an intelligent monitoring platform framework for facility agriculture ecosystem based on IoT that consists of four layer mechanism to manage the agriculture ecosystem. Each layer is responsible for specific task and together the framework is able to achieve a better ecosystem with reduced human intervention.

Another important concern around the world is climate change due to global warming. Fang et al. [ 32 ] introduced an integrated information system (IIS) that integrates IoT, geo-informatics, cloud computing, global positioning system (GPS), geographical information system (GIS) and e-science in order to provide an effective environmental monitoring and control system. They mentioned that the proposed IIS provides improved data collection, analysis and decision making for climate control. Air pollution is another important concern worldwide. Various tools and techniques are available to air quality measures and control. Cheng et al. [ 33 ] proposed AirCloud which is a cloud based air quality and monitoring system. They deployed AirCloud and evaluated its performance using 5 months data for the continuous duration of 2 months.

Temglit et al. [ 34 ] considered Quality of Service (QoS) as an important challenge and a complex task in evaluation and selection of IoT devices, protocols and services. QoS is very important criteria to attract and gain trust of users towards IoT services and devices. They came up with an interesting distributed QoS selection approach. This approach was based on distributed constraint optimization problem and multi-agent paradigm. Further, the approach was evaluated based on several experiments under realistic distributed environments. Another important aspect of IoT is its applicability to the environmental and agriculture standards. Talavera et al. [ 35 ] focused in this direction and presented the fundamental efforts of IoT for agro-industrial and environmental aspects in a survey study. They mentioned that the efforts of IoT in these areas are noticeable. IoT is strengthening the current technology and benefiting the farmers and society. Jara et al. [ 36 ] discussed the importance of IoT based monitoring of patients health. They suggested that IoT devices and sensors with the help of internet can assist health monitoring of patients. They also proposed a framework and protocol to achieve their objective. Table 1 provides a summary of the important studies and the direction of research with a comparison of studies on certain evaluation parameters.

IoT architecture and technologies

The IoT architecture consists of five important layers that defines all the functionalities of IoT systems. These layers are perception layer, network layer, middleware layer, application layer, business layer. At the bottom of IoT architecture, perception layer exists that consists of physical devices i.e. sensors, RFID chips, barcodes etc. and other physical objects connected in IoT network. These devices collects information in order to deliver it to the network layer. Network layer works as a transmission medium to deliver the information from perception layer to the information processing system. This transmission of information may use any wired/wireless medium along with 3G/4G, Wi-Fi, Bluetooth etc. Next level layer is known as middleware layer. The main task of this layer is to process the information received from the network layer and make decisions based on the results achieved from ubiquitous computing. Next, this processed information is used by application layer for global device management. On the top of the architecture, there is a business layer which control the overall IoT system, its applications and services. The business layer visualizes the information and statistics received from the application layer and further used this knowledge to plan future targets and strategies. Furthermore, the IoT architectures can be modified according to the need and application domain [ 19 , 20 , 37 ]. Besides layered framework, IoT system consists of several functional blocks that supports various IoT activities such as sensing mechanism, authentication and identification, control and management [ 38 ]. Figure  6 illustrates such functional blocks of IoT architecture.

A generic function module of IoT system

There are several important functional blocks responsible for I/O operations, connectivity issues, processing, audio/video monitoring and storage management. All these functional block together incorporates an efficient IoT system which are important for optimum performance. Although, there are several reference architectures proposed with the technical specifications, but these are still far from the standard architecture that is suitable for global IoT [ 39 ]. Therefore, a suitable architecture is still needsvk to be designed that could satisfy the global IoT needs. The generic working structure of IoT system is shown in Fig.  7 . Figure  7 shows a dependency of IoT on particular application parameters. IoT gateways have an important role in IoT communication as it allows connectivity between IoT servers and IoT devices related to several applications [ 40 ].

Working structure of IoT

Scalability, modularity, interoperability and openness are the key design issues for an efficient IoT architecture in a heterogenous environment. The IoT architecture must be designed with an objective to fulfil the requirements of cross domain interactions, multi-system integration with the potential of simple and scalable management functionalities, big data analytics and storage, and user friendly applications. Also, the architecture should be able to scaleup the functionality and add some intelligence and automation among the IoT devices in the system.

Moreover, increasing amount of massive data being generated through the communication between IoT sensors and devices is a new challenge. Therefore, an efficient architecture is required to deal with massive amount of streaming data in IoT system. Two popular IoT system architectures are cloud and fog/edge computing that supports with the handling, monitoring and analysis of huge amount of data in IoT systems. Therefore, a modern IoT architecture can be defined as a 4 stage architecture as shown in Fig.  8 .

Four stage IoT architecture to deal with massive data

In stage 1 of the architecture, sensors and actuators plays an important role. Real world is comprised of environment, humans, animals, electronic gadgets, smart vehicles, and buildings etc. Sensors detect the signals and data flow from these real world entities and transforms into data which could further be used for analysis. Moreover, actuators is able to intervene the reality i.e. to control the temperature of the room, to slow down the vehicle speed, to turn off the music and light etc. Therefore, stage 1 assist in collecting data from real world which could be useful for further analysis. Stage 2 is responsible to collaborate with sensors and actuators along with gateways and data acquisition systems. In this stage, massive amount of data generated in stage 1 is aggregated and optimized in a structured way suitable for processing. Once the massive amount of data is aggregated and structured then it is ready to be passed to stage 3 which is edge computing. Edge computing can be defined as an open architecture in distributed fashion which allows use of IoT technologies and massive computing power from different locations worldwide. It is very powerful approach for streaming data processing and thus suitable for IoT systems. In stage 3, edge computing technologies deals with massive amount of data and provides various functionalities such as visualization, integration of data from other sources, analysis using machine learning methods etc. The last stage comprises of several important activities such as in depth processing and analysis, sending feedback to improve the precision and accuracy of the entire system. Everything at this stage will be performed on cloud server or data centre. Big data framework such as Hadoop and Spark may be utilized to handle this large streaming data and machine learning approaches can be used to develop better prediction models which could help in a more accurate and reliable IoT system to meet the demand of present time.

Major key issues and challenges of IoT

The involvement of IoT based systems in all aspects of human lives and various technologies involved in data transfer between embedded devices made it complex and gave rise to several issues and challenges. These issues are also a challenge for the IoT developers in the advanced smart tech society. As technology is growing, challenges and need for advanced IoT system is also growing. Therefore, IoT developers need to think of new issues arising and should provide solutions for them.

Security and privacy issues

One of the most important and challenging issues in the IoT is the security and privacy due to several threats, cyber attacks, risks and vulnerabilities [ 41 ]. The issues that give rise to device level privacy are insufficient authorization and authentication, insecure software, firmware, web interface and poor transport layer encryption [ 42 ]. Security and privacy issues are very important parameters to develop confidence in IoT Systems with respect to various aspects [ 43 ]. Security mechanisms must be embedded at every layer of IoT architecture to prevent security threats and attacks [ 23 ]. Several protocols are developed and efficiently deployed on every layer of communication channel to ensure the security and privacy in IoT based systems [ 44 , 45 ]. Secure Socket Layer (SSL) and Datagram Transport Layer Security (DTLS) are one of the cryptographic protocols that are implemented between transport and application layer to provide security solutions in various IoT systems [ 44 ]. However, some IoT applications require different methods to ensure the security in communication between IoT devices. Besides this, if communication takes place using wireless technologies within the IoT system, it becomes more vulnerable to security risks. Therefore, certain methods should be deployed to detect malicious actions and for self healing or recovery. Privacy on the other hand is another important concern which allows users to feel secure and comfortable while using IoT solutions. Therefore, it is required to maintain the authorization and authentication over a secure network to establish the communication between trusted parties [ 46 ]. Another issue is the different privacy policies for different objects communicating within the IoT system. Therefore, each object should be able to verify the privacy policies of other objects in IoT system before transmitting the data.

Interoperability/standard issues

Interoperability is the feasibility to exchange the information among different IoT devices and systems. This exchange of information does not rely on the deployed software and hardware. The interoperability issue arises due to the heterogeneous nature of different technology and solutions used for IoT development. The four interoperability levels are technical, semantic, syntactic and organizational [ 47 ]. Various functionalities are being provided by IoT systems to improve the interoperability that ensures communication between different objects in a heterogeneous environment. Additionally, it is possible to merge different IoT platforms based on their functionalities to provide various solutions for IoT users [ 48 ]. Considering interoperability an important issue, researchers approved several solutions that are also know as interoperability handling approaches [ 49 ]. These solutions could be adapaters/gateways based, virtual networks/overlay based, service oriented architecture based etc. Although interoperability handling approaches ease some pressure on IoT systems but there are still certain challenges remain with interoperability that could be a scope for future studies [ 25 ].

Ethics, law and regulatory rights

Another issue for IoT developers is the ethics, law and regulatory rights. There are certain rules and regulations to maintain the standard, moral values and to prevent the people from violating them. Ethics and law are very similar term with the only difference is that ethics are standards that people believes and laws are certain restrictions decided by the government. However, both ethics and laws are designed to maintain the standard, quality and prevent people from illegal use. With the development of IoT, several real life problems are solved but it has also given rise to critical ethical and legal challenges [ 50 ]. Data security, privacy protection, trust and safety, data usability are some of those challenges. It has also been observed that majority of IoT users are supporting government norms and regulations with respect to data protection, privacy and safety due to the lack of trust in IoT devices. Therefore, this issue must be taken into consideration to maintain and improve the trust among people for the use of IoT devices and systems.

Scalability, availability and reliability

A system is scalable if it is possible to add new services, equipments and devices without degrading its performance. The main issue with IoT is to support a large number of devices with different memory, processing, storage power and bandwidth [ 28 ]. Another important issue that must be taken into consideration is the availability. Scalability and availability both should be deployed together in the layered framework of IoT. A great example of scalability is cloud based IoT systems which provide sufficient support to scale the IoT network by adding up new devices, storage and processing power as required.

However, this global distributed IoT network gives rise to a new research paradigm to develop a smooth IoT framework that satisfy global needs [ 51 ]. Another key challenge is the availability of resources to the authentic objects regardless of their location and time of the requirement. In a distributed fashion, several small IoT networks are timely attached to the global IoT platforms to utilize their resources and services. Therefore, availability is an important concern [ 52 ]. Due to the use of different data transmission channels i.e. satellite communication, some services and availability of resources may be interrupted. Therefore, an independent and reliable data transmission channel is required for uninterrupted availability of resources and services.

Quality of Service (QoS)

Quality of Service (QoS) is another important factor for IoT. QoS can be defined as a measure to evaluate the quality, efficiency and performance of IoT devices, systems and architecture [ 34 ]. The important and required QoS metrics for IoT applications are reliability, cost, energy consumption, security, availability and service time [ 53 ]. A smarter IoT ecosystem must fulfill the requirements of QoS standards. Also, to ensure the reliability of any IoT service and device, its QoS metrics must be defined first. Further, users may also be able to specifiy their needs and requirements accordingly. Several approaches can be deployed for QoS assessment, however as mentioned by White et al. [ 54 ] there is a trade-off between quality factors and approaches. Therefore, good quality models must be deployed to overcome this trade-off. There are certain good quality models available in literature such as ISO/IEC25010 [ 55 ] and OASIS-WSQM [ 56 ] which can be used to evaluate the approaches used for QoS assessment. These models provides a wide range of quality factors that is quite sufficient for QoS assessment for IoT services. Table  2 summarizes the different studies with respect to IoT key challenges and issues discussed above.

Major IoT applications

Emerging economy, environmental and health-care.

IoT is completely devoted to provide emerging public and financial benefits and development to the society and people. This includes a wide range of public facilities i.e. economic development, water quality maintenance, well-being, industrialization etc. Overall, IoT is working hard to accomplish the social, health and economic goals of United Nations advancement step. Environmental sustainability is another important concern. IoT developers must be concerned about environmental impact of the IoT systems and devices to overcome the negative impact [ 48 ]. Energy consumption by IoT devices is one of the challenges related to environmental impact. Energy consumption is increasing at a high rate due to internet enabled services and edge cutting devices. This area needs research for the development of high quality materials in order to create new IoT devices with lower energy consumption rate. Also, green technologies can be adopted to create efficient energy efficient devices for future use. It is not only environmental friendly but also advantageous for human health. Researchers and engineers are engaged in developing highly efficient IoT devices to monitor several health issues such as diabetes, obesity or depression [ 57 ]. Several issues related to environment, energy and healthcare are considered by several studies.

Smart city, transport and vehicles

IoT is transforming the traditional civil structure of the society into high tech structure with the concept of smart city, smart home and smart vehicles and transport. Rapid improvements are being done with the help of supporting technologies such as machine learning, natural language processing to understand the need and use of technology at home [ 58 ]. Various technologies such as cloud server technology, wireless sensor networks that must be used with IoT servers to provide an efficient smart city. Another important issue is to think about environmental aspect of smart city. Therefore, energy efficient technologies and Green technologies should also be considered for the design and planning of smart city infrastructure. Further, smart devices which are being incorporated into newly launched vehicles are able to detect traffic congestions on the road and thus can suggest an optimum alternate route to the driver. This can help to lower down the congestion in the city. Furthermore, smart devices with optimum cost should be designed to be incorporated in all range vehicles to monitor the activity of engine. IoT is also very effective in maintaining the vehicle’s health. Self driving cars have the potential to communicate with other self driving vehicles by the means of intelligent sensors. This would make the traffic flow smoother than human-driven cars who used to drive in a stop and go manner. This procedure will take time to be implemented all over the world. Till the time, IoT devices can help by sensing traffic congestion ahead and can take appropriate actions. Therefore, a transport manufacturing company should incorporate IoT devices into their manufactured vehicles to provide its advantage to the society.

Agriculture and industry automation

The world’s growing population is estimated to reach approximate 10 billion by 2050. Agriculture plays an important role in our lives. In order to feed such a massive population, we need to advance the current agriculture approaches. Therefore, there is a need to combine agriculture with technology so that the production can be improved in an efficient way. Greenhouse technology is one of the possible approaches in this direction. It provides a way to control the environmental parameters in order to improve the production. However, manual control of this technology is less effective, need manual efforts and cost, and results in energy loss and less production. With the advancement of IoT, smart devices and sensors makes it easier to control the climate inside the chamber and monitor the process which results in energy saving and improved production (Fig.  9 ). Automatization of industries is another advantage of IoT. IoT has been providing game changing solutions for factory digitalization, inventory management, quality control, logistics and supply chain optimization and management.

A working structure of IoT system in agriculture production

Importance of big data analytics in IoT

An IoT system comprises of a huge number of devices and sensors that communicates with each other. With the extensive growth and expansion of IoT network, the number of these sensors and devices are increasing rapidly. These devices communicate with each other and transfer a massive amount of data over internet. This data is very huge and streaming every second and thus qualified to be called as big data. Continuous expansion of IoT based networks gives rise to complex issue such as management and collection of data, storage and processing and analytics. IoT big data framework for smart buildings is very useful to deal with several issues of smart buildings such as managing oxygen level, to measure the smoke/hazardous gases and luminosity [ 59 ]. Such framework is capable to collect the data from the sensors installed in the buildings and performs data analytics for decision making. Moreover, industrial production can be improved using an IoT based cyber physical system that is equipped with an information analysis and knowledge acquisition techniques [ 60 ]. Traffic congestion is an important issue with smart cities. The real time traffic information can be collected through IoT devices and sensors installed in traffic signals and this information can be analyzed in an IoT based traffic management system [ 61 ]. In healthcare analysis, the IoT sensors used with patients generate a lot of information about the health condition of patients every second. This large amount of information needs to be integrated at one database and must be processed in real time to take quick decision with high accuracy and big data technology is the best solution for this job [ 62 ]. IoT along with big data analytics can also help to transform the traditional approaches used in manufacturing industries into the modern one [ 63 ]. The sensing devices generates information which can be analyzed using big data approaches and may help in various decision making tasks. Furthermore, use of cloud computing and analytics can benefit the energy development and conservation with reduced cost and customer satisfaction [ 64 ]. IoT devices generate a huge amount of streaming data which needs to be stored effectively and needs further analysis for decision making in real time. Deep learning is very effective to deal with such a large information and can provide results with high accuracy [ 65 ]. Therefore, IoT, Big data analytics and Deep learning together is very important to develop a high tech society.

Conclusions

Recent advancements in IoT have drawn attention of researchers and developers worldwide. IoT developers and researchers are working together to extend the technology on large scale and to benefit the society to the highest possible level. However, improvements are possible only if we consider the various issues and shortcomings in the present technical approaches. In this survey article, we presented several issues and challenges that IoT developer must take into account to develop an improved model. Also, important application areas of IoT is also discussed where IoT developers and researchers are engaged. As IoT is not only providing services but also generates a huge amount of data. Hence, the importance of big data analytics is also discussed which can provide accurate decisions that could be utilized to develop an improved IoT system.

Availability of data and materials

Not applicable.

Abbreviations

Internet of Things

Quality of Service

Web of Things

Cloud of Things

Smart Home System

Smart Health Sensing System

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This work was financially supported by the Ministry of Education and Science of Russian Federation (government order 2.7905.2017/8.9).

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Kumar, S., Tiwari, P. & Zymbler, M. Internet of Things is a revolutionary approach for future technology enhancement: a review. J Big Data 6 , 111 (2019). https://doi.org/10.1186/s40537-019-0268-2

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The development of the Internet of Things (IoT) technology and their integration in smart cities have changed the way we work and live, and enriched our society. However, IoT technologies present several challenges such as increases in energy consumption, and produces toxic pollution as well as E-waste in smart cities. Smart city applications must be environmentally-friendly, hence require a move towards green IoT. Green IoT leads to an eco-friendly environment, which is more sustainable for smart cities. Therefore, it is essential to address the techniques and strategies for reducing pollution hazards, traffic waste, resource usage, energy consumption, providing public safety, life quality, and sustaining the environment and cost management. This survey focuses on providing a comprehensive review of the techniques and strategies for making cities smarter, sustainable, and eco-friendly. Furthermore, the survey focuses on IoT and its capabilities to merge into aspects of potential to address the needs of smart cities. Finally, we discuss challenges and opportunities for future research in smart city applications.

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1 Introduction

Due to the tremendous development in communication and sensing technologies, ‘things’ around us are being connected together to provide various smart city applications, enhancing our life quality [ 1 ]. This connectivity between things in the smart city is commonly referred to as the Internet of Things (IoT). IoT includes everything in smart cities, to be connected at any time, anywhere, and using any medium [ 2 , 3 ]. The development of IoT technologies continue to grow, making IoT components smarter through an adaptive communication network, processing, analysis, and storage. For context, some IoT devices include cameras, sensors, Radio Frequency Identification (RFID), actuators, drones, mobile phones, etc. All of these have the potential to communicate and work together to reach common goals [ 1 , 4 ]. With such components and communication technologies, IoT devices are set to provide a broad range of applications for real time monitoring, as seen in environmental monitoring [ 5 , 6 ], e-healthcare [ 7 ], transportation autonomy [ 8 ], industry digitalization and automation [ 9 , 10 ] and home automation [ 11 , 12 ]. Furthermore, IoT is an enabler of software Agents, to help share information, make collaborative decisions, and optimally accomplish tasks [ 10 ].

IoT is capable of collecting and delivering vast amounts of data using advanced communication technologies that can be analyzed for intelligent decision making. The Big data requirements of IoT needs storage capacity [ 13 ], cloud computing [ 14 ], and wide bandwidth for transmission, to make IoT ubiquitous. This big processing and transmitting of data consumes high amounts of energy in the IoT devices. However, using efficient and smart techniques could lead to a decrease in power consumption. Therefore, the combination of IoT and the practical techniques to reduce power consumption of big data processing and transmission can improve the quality of life in smart cities, and contribute to making the world greener, more sustainable, and collectively a safer place to live [ 15 , 16 , 17 ]. Shuja et al. summarized this relationship between green IoT and big data to create sustainable, green, and smart cities by decreasing pollution hazards and reducing energy demand and efficient resource utilization [ 18 ].

Presently there is new potential in smart cities to become even smarter than before with the application of advanced technologies, such as Artificial Intelligence (AI). Examples of this can be seen in smart city components including sensor integrated smart transportation systems, cameras in smart monitoring systems, and so on. Vidyasekar et al. [ 19 ] introduced the critical aspects of potential smart cities in 2020, in which things are smarter through smart energy, smart building, smart mobility, smart citizens, smart infrastructure, smart healthcare, smart technology, and smart education and governance. These aspects are shown in Fig.  1 .

Aspects of smart cities

IoT plays a tremendous role in improving smart cities, affecting in different ways with its numerous applications in enhancing public transformation, reducing traffic congestion, creating cost-effective municipal services, keeping citizens safe and healthier, reducing energy consumption, improving monitoring systems, and reducing pollution, as shown in Fig.  2 . However, IoT environmental issues, such as, energy consumption, carbon emission, energy-saving, trading, carbon labeling and footprint, have attracted researchers’ attention. Therefore, carbon emission reduction and energy efficiency technologies based IoT are summarized [ 20 ]. The study discusses IoT technologies to facilitate real-time intelligent perception of the environment, and generate and collect energy consumption in manufacturing the entire life cycle.

Smart city applications

To fulfill goals of smart cities and sustainability, green IoT is a key technology to decrease carbon emission and power consumption [ 21 , 22 , 23 ]. The increasing number of IoT devices leads to increased energy consumption. For example, wake up protocols and sleep schedules of IoT devices are introduced for energy consumption and resource utilization [ 21 ]. The authors of [ 23 ] provided the techniques that can reduce the energy consumption in IoT via efficient energy of data transmission from IoT devices, data center efficient energy, and design energy-efficient policies. Further, authors in [ 22 ] introduced Information and Communication Technology (ICT) impacts on carbon emissions and smart cities’ energy consumption.

1.1 Related work

The preliminary literature on smart cities based on greening IoT is dispersed [ 23 , 24 , 25 , 26 ], leading to inadequate recognition of the importance of green IoT. There is an apparent lack of depth in current literature which can explain in detail the enabling techniques for IoT systems in smart cities which can reduce C O 2 emission, minimizing power consumption, enhancing QoS [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ], and enabling ICT. Existing surveys are not comprehensively focusing on smart cities strategies strategies and techniques for enabling greener smart cities. To the best of the authors’ knowledge, there is no existing survey dedicated to reviewing the strategies and techniques for greener smart cities, through enabling ICT, reducing energy consumption, reducing C O 2 emissions, reducing waste management, and improving sustainability.

As a comparison, Arshad et al. [ 23 ] discussed green IoT based on minimizing energy consumption. The study focuses only on designing energy efficient policies, energy efficient policies, energy efficient data centers, and data transmission from IoT devices. However, the study does not cover all of the potential ideas, while our survey will focus on techniques and strategies, for enabling IoT to improve the eco-friendly and sustainability of smart cities. The work presented in [ 25 ] discussed the negative impact of IoT technology and suggested solutions to minimize it. Some negative impacts of IoT were included in this study, e.g., greenhouse gas emissions, and energy usage, etc. The study explored the principles of green IoT to improve life quality, economic growth, and environments in smart cities. It showed evidence that green IoT usage can support sustainable natural resource utilization in agriculture, forestry, and aquaculture. However, the authors did not fully discuss all potential negative impacts of IoT technology in various applications. As such, Our work not only includes a broader coverage of the negative impacts, but also focuses on the use of green IoT to improve eco-friendly and sustainability for smart cities.

In [ 24 ], the authors introduced IoT for smart cities, and addressed techniques for minimizing energy consumption for green IoT, and as such, introduced the green ICT principle. However, the authors did not further discuss the green ICT for IoT applications in smart cities. As such, this paper will fill this gap in the literature. Shaikh et al. [ 26 ] presented how to deploy IoT technology efficiently to fulfill a green IoT. They identified IoT applications where energy consumption can be reduced for a green environment. Several techniques were introduced for enabling green IoT to facilitate energy efficiency. The authors of [ 41 ] discussed the concept of IoT for smart cities and their advantages, benefits, and different applications. The study focused mainly on the use of IoT for smart cities such as smart homes, smart parks, smart transports, weather, and pollution management. The authors focused on the benefits and applications of IoT for smart cities applications, however, the study does not discuss the techniques for improving IoT for enhancing the eco-friendlinesss and sustainability of smart cities. A comparison of existing surveys and the present work is summarized in Table  1 .

1.2 Contribution

This literature review is intended to develop smart cities’ strategies and techniques based on collaborative IoT to improve life quality, sustainability, echo-friendliness, citizen safety, and the health of the environment.This work will contribute to the research literature by broadening discussions on:

Enabling IoT techniques for eco-friendly ICT. Specifically the significant impacts of ICT for reducing energy consumption and C O 2 emissions for a sustainable smart city,

Different strategies and techniques used for energy-efficiency, reduced C O 2 , reduced traffic, and reduced resource usage in smart cities,

Waste management techniques to improve smart cities,

Advanced techniques used for smart city sustainability,

Surveyed current ongoing research works and possible future techniques for smart cities’ sustainability and energy efficiency, based on collaborative IoT.

1.3 The scope of study and structure

In a smart city, IoT plays a critical role in improving the life quality, safe environments, sustainability, and ecosystem. This paper will survey the techniques and strategies used to improve smart cities to be eco-friendly and sustainable. The authors focus on techniques which lead to fewer emissions, reduce traffic, improve waste management, reduce resource usage, reduce energy consumption, reduce pollution and improve Quality of Service (QoS) of communication networks. To the authors’ best knowledge, no previous research work in the survey has addressed the techniques and strategies that lead to eco-friendly and sustainable smart cities. Relevant challenges are addressed, and the solutions are conceived for other purposes, yet related work will be introduced.

The rest of this paper is organized as follows (see Fig.  3 ). ICT technology for smart cities is presented in Section  2 . Section  3 discusses energy efficiency. In Section  4 , reducing pollution hazards is considered. Waste management and sustainability are discussed in Sections  5 and  6 , respectively. The future directions and opportunities are discussed in Sections  7 and  8 , respectively. Finally, we conclude the paper in Section  9 .

Paper Organization

2 ICT technology for smart cities

IoT is a global, ambient communication network, immersive, and an invisible computing environment built depending on smart sensors, cameras, software, databases, and data centers in smart cities [ 42 ]. In [ 43 ], the authors presented IoT for constructing a green campus environment based on energy efficiency. Despite prior evidence presented in [ 42 ], IoT elements have been presented in [ 4 ], where the benefits of IoT and how to create a green area by employing efficient techniques were discussed. In [ 44 ], the authors discussed different technical directions towards realizing future green Internet.

Consequently, IoT leads to saving natural resources, minimizing the technological impact on the environments and human health, and reducing costs. Thus, green IoT focuses on green manufacturing, green design, green utilization, and green disposal [ 41 ]. The authors in [ 41 ] discussed all of the above categories and their importance for improving smart cities.

Furthermore, Solutions for green IoT includes reducing C O 2 emissions and reducing IoT energy usage to fulfill the smart world with the sustainability of intelligent everything. Green IoT includes designing and leveraging green aspects. The design elements of green IoT include developing computing devices, energy efficiency, communication protocols, and networking architectures [ 45 ]. Leveraging the IoT element is to reduce the emissions of C O 2 , and enhance energy efficiency. Uddin et al. [ 46 ] presented the techniques for improving energy efficiency and reducing C O 2 for enabling green ICT. Gathering data from smart city environments represents the essential element of smart cities that create an intelligent model for appreciated decision making.

ICT plays an essential role in improving green IoT in smart cities to be friendly and sustainable. ICT can reduce cost, resource consumption, and pollution; interact with city services; and enhance life quality. Therefore, without ICT, the idea of smart cities cannot exist. ICT improves the smart cities’ application by automated, simplified, enabling IoT, automatic security threat isolated, and scalability, as shown in Table  2 . Furthermore, ICT technologies can reduce climate change globally [ 42 , 43 , 44 , 47 , 48 ], with ICT application growth with energy efficiency due to environmental awareness. Greening IoT refers to the advanced technologies that make the IoT environmentally friendly by using facilities and storage that enables subscribers to gather, store, access, and manage various information [ 23 ].

Green ICT enables subscribers to gather, access, store, and manage information [ 24 ]. ICTs play a critical role in greening IoT and providing many benefits to society, i.e., saving energy used for designing, manufacturing, and distributing ICT equipment and devices. Various research have been done on green ICT technologies, such as [ 24 , 49 , 50 , 51 , 52 , 53 ]. These are exciting, but they have been applied for limited applications and ways. In [ 49 ], the authors discussed using ICT applications and strategies to reduce C O 2 emissions and energy consumption. The authors [ 50 ] discussed green IoT principles for enhancing life quality, growth, economy, and environment. They provide the numerous benefits of reducing the negative impact of the latest technology on society, human health, and the environment. In the case of stainability, ICT can manage data centers optimization through techniques of sharing infrastructure, which leads to energy efficiency with reduced C O 2 emissions and e-waste of material disposals [ 54 ]. Furthermore, the authors [ 22 ] discussed the enabling technologies for green IoT, which include RFID, wireless sensor networks (WSN), machine to machine (M2M), data center, cloud computing, and communication networks, as shown in Fig.  4 . However, they did not consider the techniques used for greening IoT by reducing energy consumption and C O 2 emissions. Also, the authors [ 51 ] support the idea of [ 24 ] to satisfy greening IoT by transmitting the needful information, reduce the energy consumption of facilities, and use renewable energy sources. Kai et al. [ 53 ] proved that the Device to Device (D2D) communication plays a key technology to make cities greener and smarter. They investigated the combination of power allocation optimization and uplink subcarrier assignment in the D2D underlying cellular networks. Therefore, all users’ power consumption in network was decreased, while guaranteeing the required throughput of both cellular user and device to the device user equipment.

ICT technologies for smart cities

ICT technologies play a vital role in reducing C O 2 emissions and energy consumption to green IoT applications in smart cities, i.e., smart transportation, smart building, smart parking, and so on [ 55 ]. The authors of [ 56 ] described the green ICT and green IoT depending on green smart grid, green communication, and green computing technologies. The benefits of greening enabling IoT are illustrated in Table  3 . It shows the enhancement of green ICT technologies to reduce energy consumption, reduce C O 2 emissions, reduce costs, and change the climate.

Going towards greening IoT involves finding new resources, exploiting environmental conservation, minimizing the use of available resource and costs, and minimizing negative impacts of IoT on human health and environment (e.g., C O 2 emission , N O 2 and other pollution) [ 45 , 57 , 58 , 59 ]. The authors of [ 49 ] provided the details on how industrial emissions influence the environment over time. Therefore, reducing IoT device energy consumption is required to make the environment healthier [ 20 ]. Furthermore, greening ICT technologies help to support environmental sustainability and economic growth [ 45 , 50 ], and therefore, emerging IoT technologies make the world greener and smarter. Table  4 shows the critical trends in IoT for smart cities applications domains such as smart healthcare, smart transportation, smart retail, smart, smart industries, smart house, smart grid, smart agriculture, smart wearable.

2.1 Smart data center for smart cities

Data Center is a repository and technology for smart city management, data storage, and dissemination gathered from smart cities’ devices. A massive number of IoT devices need permanent internet connectivity over the smart city. However, data management and transformation of data into information over a smart city would not be possible without the data center. It consumes a huge amounts of energy [ 22 ], high costs of operation, and high C O 2 footprints due to dealing with different data from different applications. Furthermore, the production of big data is rising through various ubiquitous things, i.e., mobile devices, actuators, sensors, RFID, etc. For the energy efficiency of the data center, the authors of [ 24 , 60 , 61 ] discussed several techniques (i.e., renewable energy, utilizing efficient dynamic power-management, designing more energy-efficient hardware, constructing efficient, designing novel energy-efficient data center architectures, using accurate data center power models, drawing support from communication and computing techniques, and improving air management, consolidating servers, finding optimal environment, improving the processing technology and boost airflow). An eco-friendly datacenter comprises enhancing the airflow and processing, finding optimal environment, improving the air management, and consolidating the server.

Furthermore, the authors of [ 51 ] introduced many techniques for enhancing and predicting the energy efficiency of the data center and its components. In addition to the work of authors [ 51 ], authors in [ 52 , 53 ] presented the optimization technique for the data center energy efficiency with supporting Quality of Service (QoS). The study in [ 62 ] provided a method to reduce the power consumption without degrading the data center cooling efficiency. Peoples et al. [ 63 ] explored the energy-efficient context-aware broker framework mechanisms to manage data center next-generation. However, the study in [ 64 ] offers a green data center of air conditioning via cloud techniques, consisting of two subsystems (i.e., air conditioning in the data center system and cloud management platform). The air conditioning system’s data center includes environmental monitoring, air conditioning, communication, temperature control, and ventilation. Simultaneously, the cloud platform provides data storage, up-layer application, and big data analysis and prediction. Furthermore, an Ant Colony System (ACS) based virtual machine (VM) can be used for reducing the power consumption of the data center while maintaining QoS requirements [ 65 , 66 ] by a near-optimal solution, while virtual machine is considered to reduce the energy consumption of the cloud data center and maintain the desired QoS [ 67 ]. The authors of [ 50 ] discussed the mitigation of VMs for QoS constraints via bandwidth management and minimalizing energy for 5G networks [ 61 ]. Figure  5 illustrates the required impacts for greening the data center for smart cities.

Required impacts for greening the data center

The dynamic speed scaling technique plays a vital role in reducing power consumption, as discussed in details in [ 68 ]. In the case of speed scaling, various researches have addressed signal processing [ 69 ], and network devices [ 70 , 71 ], and parallel processors [56] for saving energy by speed scaling. However, the authors in [ 72 ] combined sleep state and varying the speed when the tasks are processed for reducing energy usage. The study in [ 72 ] supported by Liu et al. [ 73 ], developed SleepScale for power efficiency and fulfilling QoS agreements. In addition to the work of [ 72 , 73 ], the authors in [ 74 ] used hybrid technology to reduce network energy consumption by using idle periods and adapting the rate of network operators to the requested workload.

The authors in [ 75 ] proposed a centralized network power controller based on collected data of traffic. Statistic servers form, and collected data are used to perform the aggregation of transportation and VM assignment, which was used for migrating the target data center. Authors found that the bandwidth and VM reduced the network power consumption for any data center topology. To optimize the power usage in data center networks with guaranteed connectivity and bandwidth utilization, Zhang et al. [ 76 ] discussed two levels for doing the needful. These levels are core level and pod level, in which the purpose of the core level is to define the core switches, while the pod level defines the aggregation switches. They evaluated the hierarchical energy optimization for various traffic patterns, small, large, or random traffic.

Furthermore, the study [ 77 ] focused on reducing energy by two steps:(i) by allocating VM to the server to minimize the traffic amount and (ii) balancing traffic flows by reducing the number of active switches. Zheng et al. [ 78 ] used PowerNets for improving the energy savings of a data center network. The proposed technique gradually improved VM and traffic consolidation performance with lower VM migration overheads by energy savings for a data center.

For power distribution, Meisner et al. [ 79 ] developed a technique to eliminate idle power waste in servers based on the PowerNap and RAILS.The finding showed that both techniques minimized the average power consumption in the server by 74%. Therefore, the proposed methods supported transitioning quickly between near-zero-power idle and high-performance active states in response to immediate load variations. However, the authors in [ 80 ] proposed a method to reduce the utilized power in installing the infrastructure, and they used power routing across redundant power feed for schedule servers.

Renewable energy is another route towards a green data center which minimizes the negative environmental implications. Therefore, Zhang et al. [ 81 ] designed the middleware system to optimize the dynamically distributed requests through various data centers via linear-fractional programming. They found that the proposed system could significantly increase renewable energy usage at different locations without impacting operational cost budges. Furthermore, authors in [ 82 , 83 ] considered the electrical grid and solar array for data center powering. They proposed two schedulers called GreenHadoop and GreenSlot for data processing jobs and parallel batch jobs, respectively. These schedules are used to predict the solar energy amount to maximize the green energy usage. Both schedulers could increase green energy consumption efficiently. Table  5 illustrates the summary of techniques and strategies for energy efficiency, resource management, thermal control, and green metrics for greening data centers.

Availability and sustainability are the factors that can determine the future of data centers. Therefore, smart cities are required for the data center with the high capacity to process big data coming from sensors dispersed in the city. To enhance the technological infrastructure and reduce the cost, the processing of big data needs communication networks, virtualization systems, and storage access. Here, the smart data center will manage the smart cities effectively and efficiently. Therefore, smart data centers represent smart cities’ core, increasing access security, providing passive sensitometry, achieving balanced sustainability, taking care of the city environment, and providing sustainable development for city development. Furthermore, the smart data center will have the capability to effectively and efficiently coordinate and manage the resources required by smart cities. For instance, they are measuring and controlling energy from renewable resources, managing the mobility and traffic, measuring the emissions and pollutions, managing the growth of resources, i.e., air, water, light, ect., and leading other services such as recycling waste, public safety, health, etc. Smart data centers’ future will help create new technologies and architectures for managing smart cities to improve citizens’ quality of life.

2.1.1 Cloud computing for smart cities

Cloud computing is a critical technology for smart cities’ physical infrastructure. The deployment of smart cities requires the combination of a decentralized cloud and a distributed open-source network.Cloud computing services are essential for smart city applications. Therefore, the massive amounts of heterogeneous data collected from different devices surrounding smart cities require the services of cloud computing. Smart cities refer to the high quality of life, management the natural resources, and economic development. Smart cities should intelligently provide the many facilities to improve smart city applications, such as police transport, public safety, security, electric supply, water supply, internet connectivity, smart parking, etc.

Cloud computing provides unlimited computational service delivery via the internet and unlimited storage. It is shown that different devices (i.e., tablet, camera, laptop, mobile, etc.) are connected to gather via the cloud. The combining of cloud computing and IoT together has a comprehensive research scope. The aim of cloud computing is to promote eco-friendly products, which are facilely reused and recycled. Thus, the authors of [ 18 ] proposed green computing with a focus on ICTs. Also, they discussed the trade-off between green computing and high- performance policies. Furthermore, Baccarelli et al. [ 90 ] introduced a green solution to IoT over the fog-supported network.

Therefore, efficient cloud computing plays a vital role in maximizing energy consumption, reducing hazardous materials, and enhancing old products’ recyclability. Moreover, efficient cloud computing achieves product longevity resource allocation and paperless virtualization due to the management of power used. Furthermore, Sivakumar et al. [ 91 ] introduced the integration of IoT and cloud computing in various architectures, applications, protocols, database technologies, service models, and algorithms.

Further, efficient cloud computing plays a vital role in maximizing energy consumption, reducing the use of hazardous materials, and enhancing the recyclability of old products. Moreover, efficient cloud computing achieves product longevity resource allocation and paperless virtualization due to the management of power used. The idea is supported by a study in [ 47 ], which discusses the various technologies for greening cloud computing by reducing energy consumption. It focused on how the combination of cloud and sensors can be used for green IoT agriculture and healthcare domains. Furthermore, Sivakumar et al. [ 91 ] introduced the integration of IoT and cloud computing in various architectures, applications, protocols, database technologies, service models, and algorithms.

Zhu et al. [ 92 ] presented a multi-method data delivery technique for low cost, sensor-cloud (SC) users, and immediate delivery time. Multi-method data delivery includes four kinds of transportation, i.e., delivery from the wireless sensor network to SC users, delivery from cloudlet to SC users, delivery from cloud to SC users, and delivery from SC users to SC users. Minimizing utility power is the main idea of green cloud computing [ 93 ]. Thus, the authors of [ 93 ] introduced the essential technique for improving the data center’s power performance. Private and public clouds required energy consumption in data processing, switching, transmission, and storage [ 94 ]. Table  6 summaries the used techniques and strategies in cloud computing for smart cities.

Despite the numerous works in [ 22 , 81 , 95 , 96 ] which carried out on green cloud computing and provided potential solutions be shown as the adoption of software and hardware for decreasing energy consumption, power-saving using VM techniques, various energy-efficient resource allocation mechanisms and related tasks, and efficient methods for energy-saving systems. The authors in [ 82 ] explored the trade-off of the energy performance for consolidation, which resulted in the desired workload distribution across servers and saves energy. The authors of [ 83 ] summarized the strategies used for economic and green cloud based on multi-tenancy, dynamic provisioning, server utilization, and data center efficiency.

Regarding green cloud computing, the relationships and similarities are discussed between service rate, packet arrival rate, and response time for efficiency improvement in power cost and server utilization [ 97 ]. However, a VM scheduling algorithm plays a vital role in greening cloud computing, which leads to energy consumption minimization [ 98 , 99 ]. In the case of [ 98 ], a machine algorithm is used for migration of loads of hosts, dynamic voltage frequency scaling, and shutdown of underutilized host features. The result of using algorithms led to improving power consumption. Cloud computing availability in smart cities could help ease big data storage, transforming in real-time data processing, and analyzing in real-time. Therefore, cloud computing will enhance speed, sharpness, and cost savings by providing network access on demand for sharing computing resources, which can be scaled as required and rapidly provisioned. The combination of IoT and cloud computing plays a vital role in healthcare applications such as disease prediction intelligently in smart cities [ 100 ].

Furthermore, [ 101 ] presented an intelligent model for healthcare services in smart cities using parallel particle swarm optimization and particle swarm optimization. The proposed model solves task scheduling, reduce medical requests execution time, and maximize medical resources utilization. The economic benefits and costs were discussed in [ 102 ] based on the combination of AI, cloud computing, and IoT. The authors of [ 91 ] proposed fog, cloud, and IoT to mitigate processing loads, reduce cost and time.

2.2 Communication network for smart cities

Greening wireless communication technologies play a crucial role in making IoT greener. Green communications refer to sustainable, energy-efficient, energy-aware, environmentally aware communications. The idea of a green communication network is referring to low C O 2 emissions, low radiation exposure, and low energy consumption. In [ 103 ], the authors proposed a genetic algorithm optimization for the network planning, where the finding showed significantly C O 2 reduction cost and low radiation exposure. The idea supported by a study in [ 104 ], discussed how to maximize the data rate, minimize C O 2 emissions in cognitive WSNs. In addition to the work of authors [ 103 , 104 ], Chan et al. [ 105 ] provided several models to evaluate the use-phase power consumption and C O 2 emissions of wireless telecommunication networks. The designing of Vehicular Ad hoc NETworks (VANETs) was proposed to decrease energy consumption [ 106 ].

The investigation of the energy efficiency in 5G based mobile communication networks are presented in three aspects, i.e., theory models, application, and technology developments [ 107 ]. Furthermore, Abrol et al. [ 108 ] showed the influence and the growing technologies supporting the energy efficiency of Next Generation Networks (NGN) technology. The need for adopting energy efficiency and C O 2 emission is to increase capacity, enhance data rate, and improve QoS of the NGN. Several researchers have addressed solar for saving energy and enhancing QoS, such as [ 27 , 39 , 109 , 110 , 111 , 112 ], reliable storage for saving energy [ 113 ]. Furthermore, the stochastic geometry approach is applied to achieve energy efficiency and maintaining QoS [ 114 ].

Moreover, the utility-based adaptive duty cycle algorithm proposed to reduce delay, increase energy efficiency, and keep a long lifetime [ 115 ]. However, the hypertext transfer protocol was applied to minimize delay and enhance the lifetime for providing reliability [ 116 ]. The development of wireless communication will improve a next-generation network’s performance according to the requirements based on decreasing energy usage, reducing the emission of C O 2 for providing a healthy environment, and green cities.

5G focuses on reducing energy utilization and results to green communication with healthy environments. In 2020, the prediction of green communication is observed that all communication devices and objects will communicate effectively and efficiently using smart and green techniques for a healthy and green life. 5G technology is essential for enhancing the reliability and improving QoS of communication among machines and humans. Also, 5G technology supports a large area’s connectivity, reduces latency, saves energy, and provides higher data rate. The services of 5G for our society are including robotics communication, e-health, interaction human and robotics, media,transport and logistics, e-learning, public safety, e-governance, automotive and industrial systems, etc.[ 117 , 118 , 119 , 120 ].

Many techniques have been used for energy harvesting and energy-efficient methods discussed in [ 121 ]. Regarding energy-saving methods, Wang et al. [ 122 ] proposed a resource allocation approach for minimizing the network’s energy rate. Maximizing the power-efficiency was by relay station with subcarrier for an orthogonal frequency division multiple access. However, the energy efficiency was optimized by using an energy-efficient incentive resource allocation technique for enhancing the cooperation of communication networks [ 123 ], in which the combination of genetic and water drops method for improving energy consumption effectively and efficiently.

Regarding harvesting energy, many studies focus on greening the communication network based on harvested energy, such as [ 124 , 125 , 126 ]. In [ 124 ], the authors focused on resource allocation techniques used for maximizing the energy efficiency of the green cognitive radio network. Furthermore, Ge et al. [ 125 ] discussed the cognitive radio network secured based on multiple-input single-output using to minim transmit the information signal’s power. However, Zheng et al. [ 126 ] introduced the smart grid’s performance and power consumption based on analyzing IEEE802.11ah. The authors [ 127 ] introduced different techniques for greening communication networks in term of energy-efficiency metrics. The power consumption of the network equipment has taken into account transparency and accuracy [ 128 ]. Yang et al. [ 129 ] differentiated renewable and non-renewable energy for green internet routing. However, Hoque et al. [ 130 ] examined techniques to enhance mobile hand-held devices’ energy efficiency. Table  7 summaries the used techniques and strategies in a communication network for smart cities.

2.2.1 Wireless sensor network for smart cities

The combination of sensing and wireless communication has led to WSNs. WSNs have been used in many applications such as fire detection [ 132 , 133 , 134 ], object tracking [ 135 , 136 , 137 ], environmental monitoring [ 138 , 139 , 140 , 141 , 142 ], evolving constraints in the military [ 143 ], control machine health, and monitoring industrial process [ 121 ]. WSNs represent the critical technology that has made IoT flourish. A sensor combines an enormous number of small, low-power, and low-cost electronic devices [ 139 ]. WSN components are including base stations or sinks and a large number of sensors nodes. The sensor node consists of communication unit, sensing unit, processing unit, and power unit [ 139 ]. Sensor nodes are used to measuring global and local environments such as pollution, weather, healthcare, agricultural fields, and so on. Sensors also communicate via wireless channels and deliver the nearest base station’s sensory data using ad-hoc technology. The authors of [ 144 , 145 ] introduced sleep mode for saving sensor power for a long time and supporting green IoT. For energy conservation of WSNs, Khalil et al. proposed the nearest most used routing algorithm, in which the nearest node is active (transmit and receive data), and the rest of the nodes are in sleep mode and keep sensing in idle mode [ 146 ] . Therefore, any node wanting to send data to another node, it will wake up all the nodes along to its roots and then send data accordingly.

Consequently, when the sending data finished, all the nodes will be reset to sleep mode. Sensors can utilize energy harvested directly from the environment, such as the sun, vibrations, kinetic energy, temperature differentials, etc. [ 147 , 148 , 149 , 150 , 151 , 152 ]. Also, the combination of WSN and energy harvested technologies plays a vital role in the green world [ 153 ], on account of energy harvesting is cost comparable with long batteries life. Many techniques are enabling sensor networks for green IoT, such as sensing selection [ 154 ], energy overheads for context-aware sensing [ 155 ], and sleeping schedule [ 156 ] to save energy, reduce the communication delay between sensors nodes.

Battery power is considered the most critical resource in WSN that directly influences network lifetime. Thus, the main goal is to reduce energy consumption and contribute reliable/robust transmission without compromising the overall QoS [ 203 ]. The idea of energy efficiency is supported by Mehmood et al. [ 157 ], which introduced routing protocols for energy efficiency. Similarly, Rani et al. [ 158 ] discussed flexible IoT and the designing hierarchical network’s energy-efficiency. In addition to [ 58 , 157 ], the authors in [ 159 ] introduced green WSN to improve routing and lifetime of WSN. However, the authors of [ 158 ] discussed green WSN for enabling greening IoT based on increasing energy efficiency, reducing relay nodes, extending the network lifetime, and improving the system budget.

Furthermore, the authors of [ 160 ] investigated a cooperative approach to save energy for greening WSNs. A collaborative approach is based on the cluster technique in which multi-hop works as a relay station to ensure the communication between sensors. Furthermore, energy consumption and network resilience provisioning are discussed for enhancing green WSN for fog computing platforms [ 161 ]. Four steps implemented this work: the creation of hierarchical system frameworks, sensor/actuator nodes localization, nodes clustering, creation of optimization model to realize green IoT, and finally the computing the discovering the minimal energy routing path. The results showed that the proposed approach was pliable, energy-saving, and cost-effective. Furthermore, it applies to the different type of IoT applications such as smart city and smart farming applications.

Mahapatra et al. [ 162 ] introduced wake-up radio, error control coding, wireless energy harvesting to enhance the performance of green WSNs while minimizing the C O 2 emissions. Furthermore, the combination of WSN and cloud computing leads to a decrease in demanded high power consumption and C O 2 emission, which significantly affects the environment [ 163 ]. A balanced tree-based WSN is designed for network lifetime maximization and reduces sensor nodes’ energy consumption [ 164 ]. However, the green cooperative cognitive radio was proposed in WSN [ 104 ]. Also, Araujo et al. [ 165 ] proposed cognitive WSN for reducing a large amount of power. Their work was demonstrated and evaluated in three scenarios to enable the development of power reductions and green protocols for cognitive WSN. Regarding green WSN, the following techniques could be adopted [ 22 , 95 , 116 , 166 ] such as sleep and active sensor nodes to save energy consumption, energy depletion, optimization of radio techniques, data reduction mechanisms and energy-efficient routing techniques, hybrid transmission protocol to maximize lifetime reliability. Table  8 summarizes the used techniques and strategies in WSN for smart cities.

Smart cities are recently suffering from several problems such as traffic, pollution, waste management, and high energy consumption. The rapid development and sustainability solutions demand increasing mobility in order to improve environmental impacts. The authors [ 167 ] introduced smart mobility with autonomous vehicles and connected and discussed smart cities’ challenges. The advantages of mobility for enhancing smart cities’ sustainability are discussed [ 168 ], including increasing people’s safety, reducing noise pollution, reducing pollution, improving transfer speed, reducing traffic, and reducing the transferring costs. Furthermore, [ 169 ] discussed how information shared with IoT help in a sustainable value chain network.

3 Efficient energy for smart cities

The drone plays an essential role in greening IoT. It provides efficient energy utilization and hence reducing IoT device’s power consumption. For sending data over long distances, IoT devices need high transmission power. Therefore, the drone can move towards closer to IoT devices to collect data, processing data, and sending data to another device that is in another place. Authors in [ 170 ] introduced a genetic algorithm for improving drone-assisted IoT devices based on energy consumption, sensor density, fly risk level, and flight time. Furthermore, Mozaffari et al. [ 171 ] evaluated the optimal values for small drone cells’ altitude, which leads to the maximum coverage area and minimum transmit power.

Processing in each machine is the primary object of IoT equipment. Drone-equipped IoT devices are used to capture data, process, analyze, manage, storge, and deliver to the cloud. The combination of drones and WSN was discussed [ 172 ]. The framework of drone and WSN is composed of sensor nodes, fixed-group leaders, and drone-Sink. The finding was that the election process and energy consumption were reduced. The techniques of drone-based WSN for data collection were discussed [ 173 ]. The used procedures were able to reduce flying time, energy consumption, and latency of data collection. The authors in [ 174 ] introduced an algorithm for data collection of WSNs by using mobile agents and drones. Therefore, drones and mobile agents are contributed to save time and reduce sensor nodes’ energy consumption. Also, Zorbas et al. [ 175 ] developed a mathematical model for the energy efficiency of IoT devices. The developed model’s performance detects the events that happened on the ground with minimizing power consumption in the coverage area. Furthermore, Sharma et al. [ 176 ] introduced drones’ cooperation with WSN to provide energy-efficient relaying for a better life.

The power needed for a drone is found that energy-efficient components in emerging technologies can improve the energy efficiency [ 177 ]. Choi et al. [ 178 ] formulated the drone efficient energy based relaying by taking into consideration the traffic load and speed factors. On the other hand, the wired drone docking system was developed to perform several functions via the collaboration of drone and IoT devices for reducing wasted resources, reducing energy consumption, and ensuring transmission security [ 179 ]. Moreover, Seo et al. [ 180 ] proposed drones for IoT monitoring, security platform, and emergency response in buildings by utilizing beacons.The authors in [ 181 ] developed an automatic battery replacement mechanism of drone battery lifetime. An automatic battery was used in drones to operate without battery manual replacement.

The selection of the shortest path for packet transmission plays an important role in conserving energy and high efficiency. Engergy 4.0 fault diagnosis framework was presented based on wind turbines [ 182 ]. For improving WSN efficiency, intelligent path optimization is proposed to maximize the rate of network utilization and create the shortest routing path [ 183 ]. The proposed method shows significant improvement in traffic load and network utilization rate for enhancing network performance.

Mahapatra et al. [ 184 ] discussed smart homes’ energy management for making sustainable and green smart cities. Furthermore, the authors proposed NN-based Q–learning for efficient energy management in Canadian homes by decreasing the peak load. Big data analytics represents the most critical part of developing smart city applications. IoT devices are intended to improve smart cities, where they are connected to improve life quality. Therefore, authors in [ 185 ] introduced a new protocol QoS –IoT to reduce the delay of collecting big data from sensors nodes in smart cities and enhance energy efficiency. The study in [ 91 ] discusses an essential issue related to IoT devices’ hardware lifespan in smart cities and energy conservation. Table  9 summarizes the techniques and strategies for energy-efficient for smart cities.

4 Reducing pollution hazardous in smart cities

Recently, monitoring air pollution has become the ultimate essential issue in our environment, life and society. Smart sensors are utilized for pollution monitoring. However, their transmission power is limited for sending data in real-time. Therefore, these sensors can be carried by drones, and it will be easy for gathering data and sending to the destination in real-time. Thus, Villa et al. [ 187 ] developed the best way for gas sensors and a particle number concentration monitor onboard a hexacopter. The authors showed that developed drone system was capable of identifying the point source emissions. The study focuses on airflow behavior and evaluates CO, NO, C O 2 , and N O 2 sensors for monitoring the pollution emissions in a particular area. The potential drone applications explore for interacting with sensor devices to perform remote crop monitoring, soil moisture sensing, water quality monitoring, infrastructure monitoring, and remote sensor deployment [ 165 , 188 ]. The greenhouse pollution should also be considered for controlling the gas emission from the greenhouse. Hamilton et al. [ 189 ] introduced a solar-powered drone carried C O 2 sensing integrated with a WSN. The authors of [ 190 ] proposed drone for remote autonomous food safety and quality. Due to the dynamic and flexible deployment, air pollution monitoring has been found suitable as one of many applications [ 191 , 192 ]. Authors in [ 193 ], reviewed the existing techniques for drone monitoring applications. Furthermore, author of [ 194 ] proposed drones equipped with off-the-shelf sensors for tracking tasks, but they ignored the guidance system. To solve this issue, few authors suggested adopting the pollution-based drone control system. It was based on the chemotaxis meta heuristic and PSO technique, which monitors certain areas on the most polluted zones [ 195 ]. Authors [ 196 ] proposed drone equipped Pixhawk Autopilot to control the drone and a Raspberry Pi for storing and sensing environmental pollution data. Furthermore, authors in [ 197 ] developed an efficient drone platform model to monitor multiple air pollutants. Also, Šmídl et al. [ 198 ] developed the idea of autonomously navigated drones for pollution monitoring. Authors remonstrated the applications of the drone platform in air pollution. It was focusing on air pollution profiling of roadside and air pollution episodes in emergency monitoring. Furthermore, Zang et al. [ 199 ] demonstrated experiences in applying drones to investigate water pollution in Southwest China because of low air pressure, high altitude, severe weather, strong air turbulence, and clouds over. Furthermore, the prediction of carbon footprint in ICT sectors was discussed in [ 200 ].

Air pollution is one of the impact of climate change. However, drone technology currently represent the key technology for monitoring air pollution in order to improve life quality in smart cities. It is used for many scenarios to monitor air pollution and predict air pollution.

5 Waste management in smart cities

Smart cities are running to become smarter and greener. Therefore, companies and governments are searching for efficient solutions to maximize the collection level using intelligent techniques and smart devices, i.e., smart sensors, cloud platforms, IoT, etc. Therefore, Gutierrez et al. [ 201 ] introduced intelligent waste collection cyber-physical system for smart cities based on IoT sensing prototype. IoT sensing prototype measures the waste level in trash bins and sends data to the cloud over the Internet for processing and storage. Based on the collected data, the optimization process can efficiently and dynamically manage the waste collection by forwarding the worker’s necessary action. The authors focused on improving the strategies of waste collection efficacy in real-time through ensuring that when the trash bins were full, the workers would collect in real-time, and therefore, the waste overflow was reduced. Thus, IoT has enabled waste monitoring and management solutions in smart cities within the connected sensors implemented in the container.

Moreover, creating a comprehensive system can help to make cities smarter, healthier, and greener. Hence, the smart waste management (SWM) system helps in decision-making and processing, ensuring the employers follow the procedures and enhance waste collection services delivery [ 202 ]. The SWM system was analyzed in the public university, such as Oradea University [ 203 ]. The designed system at Oradea University was to reduce pollution, protect the environment, and encourage recycling. Employing the SWM at Oradea University was significantly enhanced. Moreover, the authors in [ 204 ] presented ICT application for smart management in Europe and Italy’s circular economy. Likewise, The authors in [ 205 , 206 , 207 , 208 ] [ 205 , 206 , 207 , 208 ] discussed SWM includes IoT technology for smart cities application.

The smart city development system is essential for automated waste collection. Companies and governments are looking for an efficient solution for collecting all kinds of waste using smart IoT devices, edge intelligence, cloud, etc. Therefore, designing, implementing, and developing an automated system to collect waste is required to increase usage, storage, and production capacity. IoT can improve automated waste collection systems by providing real-time monitoring and communication with the cloud. Furthermore, the authors in [ 209 ] focused on increasing automated waste collection systems and improved productivity and capacity. They studied how the system could be integrated with the infrastructure of the smart city. Here, IoT allowed real-time monitoring and data collection in real-time and connected with a cloud of the automated waste collection system. IoT plays a vital role in enhancing the system’s performance by connecting devices and processing and analyzing data in real-time. Therefore, the proposed system could monitor the different types of waste in the containers in real-time. The proposed system helped provide the total amount of waste collected in containers, and optimal discharging equipment status, the optimized route for waste discharged storage system status. However, exploring the possibilities of increasing profit and productivity in waste collection architectures can be considered for future work. In [ 210 ], the authors introduced the existing Italian legislation tools that aimed toward sustainable waste management for smart cities. The waste management technique should foresee the hazard level and the quantity reduction of waste for sustainable development in smart cities.

To enhance environmental protection, and achieve increased efficiency, handle waste for sustainable smart cities is required. Many technologies control waste, such as automatic waste collection, recycling rate, route optimization, and renewable energy. In the case of automated waste collection, IoT devices such as sensors that produced alarms in case of the container are filled up and need to be serviced, thus mange the waste efficiently. Furthermore, smart in-vehicle monitoring makes the waste process faster and ensuring driver safety. IoT is the new technology that can be used for waste management and provide an efficient solution in different ways such as IoT software in waste management, cost efficiency, waste collection, and reduce Greenhouse gas emissions. Furthermore, advanced technologies such as AI and IoT have immensely contributed to reducing the cost and complexity of automated waste systems via improving efficiency, productivity, and safety and minimizing environmental impacts. Disposed waste represents a challenge due to health issues.

6 Sustainability in smart cities

Urban planning has become essential for our very survival in the development of sustainable and green smart cities. Maintaining the wellbeing of every citizen and health are significant factors. The areas are integrated with human right down to waste disposal. Levels of obesity are low, and then the citizens mental health is positive. The structure and design of sustainable green cities are directly connected with human health as well as wellbeing. Through smart networking and environmentally friendly habitats ecological resources are examined, maintained, and environmental benefits are immense. These technologies applications are not for making human life healthy only but also healthy trees, wildlife, and plants. Energy-efficient practices are the key in a green sustainable city. The smart and green disposal techniques help curtail the catastrophic dilemma of green-house gas emissions.

Furthermore, water and food have an impact on growing sustainable smart cities. The role of clean water is vital to the economy in smart cities’ development. Integrated advanced technologies play a crucial role in creating the relationship between government, citizens, environment, ecosystems, infrastructure, and resource utilization. Therefore, sustainable and green cities lead to change in technical and social innovations. On the other hand, sustainable and green cities are also referring to green spaces and smart agricultural resources. Renewable resources, reducing the ecological footprint, and reducing pollution are necessary to keep the city smart and green. IoT plays a vital role in improving smart cities to become more livable, resilient, green, and sustainable.

IoT and smart city technology represent the critical key for developing society and improving life quality. A smart city is created on an intelligent framework and complex manner of ubiquitous networks, objects, government, and connectivity to send and receive data. The data gathered in a cloud of smart cities of any application is managed and analyzed accordingly, for decision making based on the available data, and transform action in real-time to improve the way we work and live. The study [ 211 ] finds out an analysis of the smart cities’ role in making sustainable cities. It is mainly focused on air quality, green energy, renewable, energy efficiency, water quality, and environmental monitoring.

Green IoT plays a vital role in smart cities to make it a greener and sustainable place for working and living. Green IoT techniques and technologies achieve good performance in big data analysis, making smart cities significantly safer, smarter, and more sustainable. The authors of [ 212 ] discussed the big data achievements in improving life quality by reducing pollution and utilizing resources more efficiently. For managing resources utilized by IoT for sustainable and green smart cities, the authors of [ 213 ] introduced delay tolerant streaming and hybrid adaptive bandwidth and power techniques during media transmission in a smart city. Furthermore, the authors of [ 214 ] discussed a sustainable green-IoT environment. However, in [ 215 ] the authors presented greening the technologies process for sustainable smart cities by exploring the greening IoT in improving the environment, life quality, and economy while minimizing the negative impact on the environment and human health.

A smart sustainable city uses ICT to improve life quality, the efficiency of urban services and operation, and competitiveness while ensuring that it meets present and future generations’ economic, social, and environmental needs. A sustainable smart city is an innovative city that uses ICT and IoT technologies to improve life quality, service quality, and competitiveness. Furthermore, it ensures meeting the need of the present and future people regarding social, economic, cultural, and environmental aspects. Due to many people shifting to live in urban and smart cities, the energy resource management, sustainability and sharing, and utilities of emerging technologies need further discussion. Furthermore, addressing the requirements are the most important such as optimizing resources management, growth of business potential, environmental impact, and improving peoples’ life quality

7 Future directions

The upcoming cutting edge disruptive technologies with efficient techniques and strategies will change our future ambience to become healthier, smarter, and greener, delivering very high QoS. This tomorrow would be sustainable environmentally, socially, and economically. The following research fields will seek in depth investigation to improvise and optimize existing solutions for improving smart cities more efficiently.

7.1 Drones for gathering data from the smart cities

The drone is a promising technology which can improvise many real-time applications. Drone technology is a promising solution for making IoT green from both IoT power consumption and device recharging points of views. For example, drones will reduce power consumption of the IoT devices by getting closer to the nodes during data gathering, capture pollution data from agricultural farm lands, and support real-time traffic monitoring and mitigation. Therefore, drones will lead to greener IoT at low cost and with high efficiency and penetration. For pollution monitoring, few IoT devices can be carried out as payloads on a drone to capture real-time data from a large area, and cover different areas dynamically, in a time division mode for energy saving and economy in management expenditures.

Drones can contribute directly in reducing E-waste by wirelessly recharging the IoT devices, enhancing their lifetime. This is particularly useful in large IoT deployments wherein replacing batteries in the massive number of IoT devices would be impractical, thus new deployments would be considered resulting in producing E-waste.

7.2 Transmission data

The data transmission from sensors to the mobile cloud is more beneficial. Sensor-cloud model is now integrating the WSN with the mobile cloud. It is an upcoming technology for greening IoT to improve the sustainability of smart cities. Furthermore, a green social network as a service (SNaaS) may improve the system’s energy efficiency, service provisioning, sensor networks, and management of the WSN on the cloud.

7.3 Networking

It may be perceived from literature that attaining outstanding performance and high QoS on the network is the future direction for green IoT. Finding suitable and efficient techniques for improving QoS parameters (i.e., bandwidth, delay, and throughput) can efficiently improve the smart city’s eco-friendliness. Furthermore, researches are required to design IoT networks which help in reducing C O 2 emission and energy usage. The most critical tasks requiring urgent attention for smart and eco-friendly environment include energy efficiency, resource utilization, and C O 2 emission reduction.

7.4 Sustainable environment

While shaping up a sustainable and eco-friendly network environment for future, it will require less energy demand, newer resources and minimization of the negative impact of IoT on the health of the humankind without disturbing the environment. While machines are getting connected to machines via the Internet to reduce energy, smart devices have to be smarter and greener to enable automation in smart city. Therefore, machine based automation delays can be reduced in case of traffic and taking immediate action. Furthermore, during the machine to machine communication, energy balancing is required in which the radio frequency energy harvesting should be taken into consideration.

7.5 Waste management

Briefly, the future directions in waste management can be categorized based on enabling impacts, emerging technologies, and objectives. Waste gathering and recovery infrastructure have to focus on the automatizing process, implement the best practices with values. IoT devices and technologies have received enough attention in the smart cities domain. Waste management and smart communities need to be addressed and defined. In emerging technologies, smart cities propose to use many smart devices based on processing and computing capabilities that support green automation, monitoring and data collection. In enabling factors, planning, society, economics are essential to understand the waste management platform and creating value from the controlled collection and disposal of waste. Furthermore, the waste management and collection of smart city infrastructures should be taken into considerations. The connection between waste management and smart communities’ activities need to be addressed in a coherent manner.

7.6 Big data

The challenge in the accumulated big data is the prediction and estimation of the required energy for analysis of the gathered data. Rapid analysis of big data may be taken into consideration. If the volume of big data increases, it will increase the exponential scale-up of the cost and resources required for the analysis. Hence, big data analytics may be considered to enhance the prediction of energy efficiency versus the improvement of the life quality [202]. Deep learning techniques can be applied to getting accurate estimation for energy efficiency and the ways to reduce it further to meet greener ranges of system design and deployments. Table  10 summaries the comparison of recent studies with suggestion for future improvement.

8 Opportunities

Smart cities’ technologies bring many advantages by using IoT devices such as sensors, actuators, wearable devices. To improve smart cities, autonomous cars with potential services enabled by vehicle to vehicle and vehicle to internet wireless communication is a technology disruption. It will change the ways in which taxies have been run and owned thus far. For example, improving traffic flow and reducing accidents via intelligent systems and collaborative IoT devices will enhance communication with autonomous cars. Furthermore, autonomous vehicles can also get passengers in demand based on loading and unloading areas. Moreover, improving traffic flow can allow public service to optimize evacuation planning in natural disasters [ 225 , 226 , 227 ]. In order to make our life easier, machine learning and IoT devices are necessary for improving efficiency. Smarter waste management, using IoT technology, utilizes the consideration of our waste disposal by data gathered and how much waste is produced to collect data and then use collected data to implement models to reduce waste in the nearest future by recycling and separation. Today, IoT technology plays a vital role in making city cleaner, healthier, and happier citizens. Improving healthcare and quality of life via the monitoring of environment, air quality, and reduce health stress. Therefore, there are many opportunities for prospective future to create a smarter, healthier, greener, and happier citizen, leading to a cleaner, greener planet.

9 Conclusion

Tremendous developments of various technologies in the 21 st century has improved life quality in smart cities. Recently, IoT technology has demonstrated heightened benefits in enhancing our life quality in smart cities. However, the technologies development demands high energy accompanied by unintentional e-waste and pollution emissions. This survey studied the strategies and techniques to improve our life quality by making the cities smarter, greener, sustainable, and safer. In specific, we highlighted the green IoT for efficient resource utilization, creating a sustainable, reducing energy consumption, reducing pollution, and reducing e-waste. This survey provided a practical insight for anyone who wishes to find out research in the field of eco-friendly and sustainable city- based on emerging IoT technologies. Based on the critical factors of enabling technologies, the smart things in smart cities become smarter to perform their tasks autonomously. These things communicate among themselves and humans with efficient bandwidth utilization, energy efficiency, mitigation of hazardous emissions, and reducing e-waste to make the city eco-friendly and sustainable. We also identified the challenges and prospective future research direction in developing eco-friendly and sustainable smart cities.

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Acknowledgements

This research has emanated from research supported by a research grant from Science Foundation Ireland (SFI) under Grant Number SFI/16/RC/3918 (Confirm), and Marie Skłodowska-Curie grant agreement No. 847577 co-funded by the European Regional Development Fund.

The authors are grateful to the Deanship of Scientific Research at Taif University, Kingdom ofSaudi Arabia for funding this project through Taif University ResearchersSupporting Project Number (TURSP-2020/265).

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Almalki, F.A., Alsamhi, S.H., Sahal, R. et al. Green IoT for Eco-Friendly and Sustainable Smart Cities: Future Directions and Opportunities. Mobile Netw Appl 28 , 178–202 (2023). https://doi.org/10.1007/s11036-021-01790-w

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DOI : https://doi.org/10.1007/s11036-021-01790-w

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The fifth-generation cellular network (5G) represents a major step forward for technology. In particular, it offers benefits for the network of interrelated devices reliant on wireless technology for communication and data transfer, otherwise known as the Internet of Things (IoT). 

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Yet with more capability comes more complexity, and there are challenges to making 5G connection a full reality. There is global interest in realizing the potential of 5G and IoT integration. Research papers on a wide array of topics are helping to advance the field and bring the vision of 5G technology and IoT connectivity into focus. 

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Making the case for 5G technology

Using millimeter wave technology, 5G connectivity offers increased speed, bandwidth, and reliability of data transfers. These improvements mean that more computing power can be pushed to the cloud, clearing the way for smaller, cheaper, and simpler devices that can do more. Smartphones are a great example of how increased wireless network capacity has allowed devices to get smaller while increasing the range of a user’s cloud-based activities. 

The 5G mobile network also has social justice implications. As Brookings Institute senior fellow Nicol Turner Lee discusses in her research paper “ Enabling Opportunities: 5G, the Internet of Things, and Communities of Color ,” the development of wireless networks will factor heavily in whether mobile-only users can fully participate in the global digital economy. 

Universal benefits, inspired innovations

The 5G network could spur additional IoT innovations such as the following:

• Advancements in edge computing
• Creation of smart cities, smart power grids, and expanded functionality of smart homes
• Improvements in health-care monitoring and delivery of services
• Retail improvements
• Real-time remote control of robots that could improve farming efficiency
• Automated manufacturing
• Supply chain improvements
• Improved transportation and self-driving cars 
• Expanded use of artificial intelligence reliant on machine learning
• More cloud computing
• Expansion of virtual reality and augmented reality

While work to build out 5G has begun, many of the challenges and logistics of completing this vast network still need to be resolved. Some of the challenges include the following:

• Managing disruption to the radio transmission
• Network and wireless security
• Connectivity issues from the network to the internet (known as “backhaul”)
• Assuaging concerns over health impacts of increased high-speed electromagnetic energy
• Cost and logistics of building a vast network of towers across different governmental jurisdictions

Those with a stake in making 5G a reality are investing in researching solutions that explore the possibilities and challenges of 5G deployment and IoT integration. Research is also emerging on how 5G and IoT technology can be utilized to respond and fight the COVID-19 pandemic. 

Two halves of a whole—the relationship between IoT and 5G

5G is revolutionary in that it replaces hardware components of wireless networks with software components that offer increased system flexibility. In doing so, it delivers more power to wireless devices that rely upon fast, uninterrupted data transmission. 

Making IoT smarter

Artificial intelligence (AI) technology, which plays heavily in many IoT applications, relies on smooth and frequent transmission of data. Every disruption in the data transfer process interrupts the feedback loop that facilitates machine learning. 5G’s lower latency eliminates these data hiccups, which translates to better performance over time. 

The 2019 paper “ AI Management System to Prevent Accidents in Construction Zones Using 4K Cameras Based on 5G Network ,” published in the IEEE Xplore digital library, examines how workplace safety can be improved through AI technologies running on the 5G wireless platform. 

Critical and massive IoT

There are two types of IoT devices: Critical IoT devices offer low latency, high uptime benefits. They facilitate bandwidth-hungry applications that include telemedicine, first responder applications, and factory automation. Massive IoT refers to a network of lots of devices using little bandwidth or speed. These devices find use in applications such as wearables, smart agriculture, smart homes, and smart cities. 

5G technology also allows a service provider to dedicate portions of their networks for specific IoT applications. Known as network slicing, the ability to segment a set of optimized resources further improves the ability of 5G to respond to the varying data and bandwidth needs of critical and massive IoT applications. 

The recent paper “ Secure Healthcare: 5G-enabled Network Slicing for Elderly Care,” published in the IEEE Xplore digital library, provides insight into the existing limitations in elder care and discusses a solution that encompasses 5G network slicing techniques and innovations. 

Cybersecurity on the 5G

One fundamental difference between 5G and its predecessors is the shift from a hardware-based system to a software-based system. This shift presents new security challenges as software is more vulnerable to hacking—the same wireless pathways over the 5G that enable IoT can be used to breach it, whereas to hack hardware you need direct physical access. 

Technical solutions to expanding capacity while increasing IoT security, such as those that the IEEE paper “ Wideband Antennas and Phased Arrays for Enhancing Cybersecurity in 5G Mobile Wireless ” discusses, are being researched and discussed worldwide. In addition, the Brookings Institute’s 2019 research paper “ Why 5G Requires a New Approach to Cybersecurity ,” discusses why developing coordinated cybersecurity public policies is of paramount importance.

Investing in the future—top research projects on IoT and 5G integration

Governments and the private sector, including trade associations, service providers, and major tech players are funding research at academic institutions. For example, the University of Texas at Austin’s Wireless Network and Communications Group has an Industrial Affiliates Program that allows companies like Huawei to become stakeholders in the center and to participate in the growth and direction of its research on millimeter waves. Similarly, New York University’s Brooklyn engineering program partners with Nokia, Intel, and AT&T to support its research. 

In the US, the National Science Foundation is supporting advanced wireless research. Research England’s UK Research Partnership Investment Fund (UKRPIF) supports 5G research, including that being done at the University of Surrey’s 5G Innovation Centre . Nonprofit organizations, such as the Brookings Institute , are also conducting research on the logistics and impacts of 5G and IoT. 

Universities, companies, and organizations such as IEEE regularly team up to host conferences around the world that showcase all aspects of 5G. IEEE’s Future Networks is dedicated to enabling 5G and regularly calls for papers related to 5G. 

Opportunities for 5G and IoT—building a sustainable future

The ultimate goal of 5G and IoT integration is for everything to be connected more simply on smaller, less expensive devices. The 5G network has the potential to drive advancements in IoT and to fundamentally change the way humankind operates around the globe with long-term positive impacts possible with respect to sustainability. 

In practical terms, the 5G network provides better efficiency through increased control. At the local level, a smart city would be better able to monitor, through IoT applications, public safety and utilities. This would mean greater conservation and a reduction in their overall carbon impact while improving the lives of its residents. 

As Darrel M. West examines in his paper “ Achieving Sustainability in a 5G World ,” IoT innovation in the energy, manufacturing, agriculture and land use, buildings, and transportation sectors coupled with full 5G deployment could allow the global community to meet our long-term sustainability goals. 

Want to learn more about the latest IoT and 5G research? Participate in the 2020 IEEE 3rd 5G World Forum (5GWF'20). The virtual conference, which will be available from September 10–12, aims to bring together experts from industry, academia, and research to exchange their vision as well as their achieved advances towards 5G. In addition, it aims to encourage innovative cross-domain studies, research, early deployment, and large-scale pilot showcases that address the challenges of 5G.

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Internet of Things (IoT): Opportunities, issues and challenges towards a smart and sustainable future

Sandro nižetić.

a LTEF-Laboratory for Thermodynamics and Energy Efficiency, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split, Rudjera Boskovica 32, 21000, Split, Croatia

Petar Šolić

b Department of Electronics, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split, Rudjera Boskovica 32, 21000, Split, Croatia

Diego López-de-Ipiña González-de-Artaza

c Faculty of Engineering, DeustoTech - Fundación Deusto, Universidad de Deusto, Despacho 545 Avda, Universidades 24, 48007, Bilbao, Spain

Luigi Patrono

d Department of Innovation Engineering, University of Salento, Ecotekne Campus - S.P. 6, Lecce, Monteroni, 73100, LECCE, LE, Italy

The rapid development and implementation of smart and IoT (Internet of Things) based technologies have allowed for various possibilities in technological advancements for different aspects of life. The main goal of IoT technologies is to simplify processes in different fields, to ensure a better efficiency of systems (technologies or specific processes) and finally to improve life quality. Sustainability has become a key issue for population where the dynamic development of IoT technologies is bringing different useful benefits, but this fast development must be carefully monitored and evaluated from an environmental point of view to limit the presence of harmful impacts and ensure the smart utilization of limited global resources. Significant research efforts are needed in the previous sense to carefully investigate the pros and cons of IoT technologies. This review editorial is partially directed on the research contributions presented at the 4th International Conference on Smart and Sustainable Technologies held in Split and Bol, Croatia, in 2019 (SpliTech 2019) as well as on recent findings from literature. The SpliTech2019 conference was a valuable event that successfully linked different engineering professions, industrial experts and finally researchers from academia. The focus of the conference was directed towards key conference tracks such as Smart City, Energy/Environment, e-Health and Engineering Modelling. The research presented and discussed at the SpliTech2019 conference helped to understand the complex and intertwined effects of IoT technologies on societies and their potential effects on sustainability in general. Various application areas of IoT technologies were discussed as well as the progress made. Four main topical areas were discussed in the herein editorial, i.e. latest advancements in the further fields: (i) IoT technologies in Sustainable Energy and Environment, (ii) IoT enabled Smart City, (iii) E-health – Ambient assisted living systems (iv) IoT technologies in Transportation and Low Carbon Products. The main outcomes of the review introductory article contributed to the better understanding of current technological progress in IoT application areas as well as the environmental implications linked with the increased application of IoT products.

Graphical abstract

1. Introduction

With rising technological developments in society, new possibilities have occurred and that could simplify our daily life and provide more efficient services or production processes. Digitalization has allowed ‘‘smart’’ ( Zheng et al., 2019 ) to become the epicentre of already ongoing technological developments. In fact, IoT technologies are nowadays assumed to be one of the key pillars of the fourth industrial revolution due to significant potential in innovations and useful benefits for the population. On the other side, each development utilizes limited resources leaving behind different environmental footprints, ( Li et al., 2020a ), especially different kinds of pollutants, ( Zeinalnezhad et al., 2020 ). Internet of things (IoT) based technologies bring a completely new perspective on the further progress of various fields, such as for instance in engineering, ( Zaidan and Zaidan, 2020 ), agriculture ( Farooq et al., 2020 ), or medicine ( Salagare and Prasad, 2020 ), and in other fields that have not been explored yet. Some potential application areas in IoT technologies are still unknown or insufficiently clear on how to approach them which is an evident indication that more intense research activity should be conducted in this challenging field towards new and important potential benefits for society. Therefore, the relevance and importance of IoT technologies in future terms are more than clear and should play an important role.

The rise of IoT technologies is currently intense and according to projections for the next 10 years, over 125 ·10 9 IoT devices are expected to be connected, ( Techradar, 2019 ). The expected investments in IoT technologies are also high with expectations being over 120 ·10 9 USD by 2021, with a compound annual growth rate of about 7.3%, ( Forbes, 2018 ). The general present market structure of IoT technologies is presented in Fig. 1 , where it is evident that the majority of the market is focused on smart cities and industrial IoT.

General market structure of IoT technologies ( Nižetić et al., 2019 ).

If recent projects in IoT technologies are being analysed than most of them are in the field of smart cities and industrial IoT. Other significant potentials are connected buildings, connected cars and energy segments ( Forbes, 2018 ), but lower than the first mentioned fields. It is also found that the most rising trend in the number of IoT projects currently is as expected in smart cities, connected health and smart supply chain segments, with an annual rise over 30% in the EU and USA. Industrial IoT, connected cars and agriculture segments has recorded a decrease in the number of realized projects, i.e. over 25% in the USA and EU, ( Forbes, 2018 ). From a perspective of high upcoming population pressure on cities and because a population of almost 11 ·10 9 is expected by the end of the century ( Pewresearch, 2019 ), the smart city concept could become a vital one to allow for a normal operation of highly populated cities.

In order to support the rapid technical development of IoT technologies, as well as novel potential applications areas, specific technical issues would need to be resolved, ( Techradar, 2019 ). One of the main issues is associated with the development of different tools for the monitoring of network operations ( Kakkavas et al., 2020 ), then issues with security tools and their management, ( Conti et al., 2020 ), issues with software bugs, demanding maintenance of IoT networks, and finally security issues related to IoT networks, ( Almusaylim et al., 2020 ). The important problem linked with the efficient implementation of IoT technologies is linked with the available speed and coverage of wireless networks (Wi-Fi), where expectations are high due to noticeable increases in Wi-Fi network coverage in the period of 2017–2022 as well as increases in Wi-Fi speed Fig. 2 . In a global sense, increases in Wi-Fi speed are expected for more than a factor of two, i.e. from about 24 Mbps to more than 54 Mbps. The most intense increase in Wi-Fi speed is expected in the Asian region, ( Zdnet, 2018 ).

Expected increase in global Wi-Fi speeds in period of 2017–2022 ( Zdnet, 2018 ),

The lowest Wi-Fi speed is noticeable in the Latin America and Middle East&Africa regions, which are an indication of potential problems for the efficient implementation of IoT products or novel more advanced upcoming technologies.

An increased implementation of IoT technologies would lead to a more intense utilization of fossil technologies to ensure the necessary energy supply for IoT production lines. The production of electronic equipment is causing potentially unbalanced waste of limited metals and resources in general, which could become a critical issue in the long run. Unfortunately, the recycling rate of electronic waste is low and currently in the amount of about 20% ( Thebalancesmb, 2020 ) which makes matters questionable regarding the available resource capacity to produce IoT products when taking into accounts the rising market demands. The production of electronic gadgets has led to the consumption of various chemicals, water and finally fossil fuels that have all left environmental impacts. As already tackled, different metals are also being used to produce electronics such as copper, silver, gold, palladium etc. One of the major issues is the led content in e-waste and its severe impact to the environment. Recycling in the previous sense is very important, where the present recycling rate of electronic equipment is certainly not sufficient and must be increased. Globally, the annual rise of the recycling rate ranges from about 4% to 5% ( Thebalancesmb, 2020 ). The legislation related to the e-waste is one of the main drawbacks since more than 50% of world population is still not well covered with proper legislation related to e-waste, ( Globalewaste, 2017 ), which is preventing the further development of e-waste facilities. The market value of raw materials from e-waste is estimated to be more than 50·10 9 Euros, ( Globalewaste, 2017 ). Certainly, more strategic and targeted actions are needed in the e-waste issue to secure a more balanced and sustainable development of IoT technologies. Overall, the annual generation of e-waste is more than 44·10 9 metric tonnes, which is equivalent to more than 6 kg per inhabitant annually, ( Globalewaste, 2017 ). A potential exists and must be better utilized to ensure a sufficient quantity of valuable raw resources.

It should be highlighted that there is no doubt in what IoT technologies would bring to the table, such as various useful benefits to society and an overall improvement in life quality. Each technology has specific issues and drawbacks that need to be detected and closely investigated on time, since IoT technologies have the potential to change our lives and habits. Several important facts need to be emphasized when addressing IoT technologies to be able to understand the long-term effects associated with the fast development of IoT:

• - IoT technologies have caused an increase in the utilization of limited resources or raw materials where some of them have become rare or are already rare (for instance, specific precious metals for electronics),
• - The prices of electronic devices have become more acceptable, which means an increase in production volume, finally more resources are being utilized. A rebound effect is possible in that sense,
• - The long term environmental impacts of IoT technologies are unknown. A noticeable amount of energy would be needed to support the production and operation of IoT devices,
• - An increase in electronic waste is expected due to the large estimated number of IoT based devices in the near future,
• - In some sectors, IoT technologies could have social impacts due to the reduced necessity for labour and limitation of direct social contacts, which is vital and an important aspect for each human being.

The main point of the above raised issues is not to indicate and create a negative attitude towards IoT technologies but to carefully analyze the overall aspects in order to secure a smart and sustainable development of IoT technologies, which are a valuable opportunity for humanity.

1.1. Necessity for smart technologies

The world is rapidly changing, i.e. developing in a technological sense and is being driven by the present economic system globally. Unfortunately, each technological development has got its price, which can be sensed through the intense utilization of limited fossil-based resources and the production of various impacts to the environment, ( Chen et al., 2020a ). The population is constantly growing with an annual rate of about 1.1% per year with the current population being over 7.7·10 9 ( Data.worldbank, 2020 ). As previously addressed, the population concentration is in cities and according to UN projections, about 68% of the population will be living in cities by 2050, ( UN, 2018 ). A significant infrastructure pressure is expected in cities due to boosted urbanization, thus novel technological solutions would be key to secure the normal operation of cities in the given complex and demanding circumstances. In the previous sense, the general application of IoT and smart technologies would have an important role and could help to bridge some major infrastructure related issues in cities. The necessity for IoT technologies is closely linked with ongoing technological advancements and digitalization where a variety of different electronic products need to be somehow connected in a useful manner. There is a necessity for more efficient services and flexible processes in general, which could be obtained with the proper implementation of IoT technologies. IoT technologies have allowed for a variety of efficient services and smart networking, applications or devices that can ensure useful synergic effects and produce benefits. The major advantage of IoT technologies is their connectivity aspect that has enormous potential, Fig. 3 .

General structure of IoT network and connectivity ( Zhang et al., 2018 ).

Various benefits are possible and would be gradually integrated in our lives thorough upcoming years in different application areas and will be briefly discussed in the upcoming section of the introductory review editorial.

1.2. Application areas

The application areas of IoT are various and based on current available technological solutions, the most represented application sectors are shown in Fig. 4 . The most important and most progressing application areas of IoT are related to the industry ( Osterrieder et al., 2020 ) and smart city concept ( Sivanageswara Rao et al., 2020 ), with respect to the number of realized projects.

Application areas of IoT technologies.

The transportation ( Porru et al., 2020 ), smart energy management in buildings ( Douglas et al., 2020 ) or management of power networks ( Martín-Lopo et al., 2020 ), as well as the agriculture sector ( Villa-Henriksen et al., 2020 ) are also promising, having significant potential.

The development of specific IoT application areas strongly depends from several key factors such as:

• - general available advancements in electronic components,
• - available software solutions and user friendly surrounding,
• - solutions related to sensor technologies and data acquisition,
• - quality of network, i.e. network connectivity and infrastructure,
• - sufficient energy supply for production and operation of IoT devices.

In the continuation of the review editorial, some key IoT application areas will be briefly addressed together with the main developments and current challenges.

1.2.1. IoT in industry

The application of IoT technologies in industrial applications would allow for an increase in efficiency regarding the production process and would ensure more efficient communication and networking between operators and machines, Fig. 5 . Finally, it would allow for more competitive companies on the market with more efficient quality control with a minimization in losses. A critical feature would be the development, design and integration of various useful sensors in the industrial applications ( Li et al., 2020b ), to form integral and effective management systems. More intense research efforts are needed towards an efficient application of IoT technologies in the industry and to better understand how IoT technologies could be implemented in specific industries where benefits would be possible. Progress is crucial in the sense of how to connect different industrial sensors, use and process the collected various data to enable enhanced industrial processes, i.e. ensue for instance smart IoT based Computer-Integrated Manufacturing, ( Chen et al., 2020b ).

General concept of IoT industrial application ( Aazam et al., 2018 ).

1.2.2. IoT in smart city concept

The role of IoT technologies in the smart city concept ( Janik et al., 2020 ) is crucial to bridge the already mentioned global infrastructural challenges in cities, which are linked with the current increase of population in cities. IoT technologies in smart cities would enable the utilization of different devices, which would increase the life quality in cities as well as the efficiency of different daily services such as transportation, security (surveillance), smart metering, smart energy systems, smart water management, etc. Different sensing devices would receive information, which would be processed towards efficient and useful solutions. The main benefit of IoT technologies in smart cities would be directed to the early detection of different problems or infrastructural faults (such as issues with traffic jams, energy supply, water shortage, security incidents, etc.). In smart cities, many sensors are installed and linked with many other devices over the internet which gives information to the users as for instance parking spaces, any malfunctions, electrical failure and many other issues. Developing these technologies would help in leading the cities towards smart grids, smart healthcare, smart warehouses, smart transportation, smart waste management, smart communities, etc. Different implementation challenges towards the smart city concept exists, Fig. 6 and should be solved for various applications, ( Fig. 7 ).

Different challenges in Smart City concept ( Bhagya et al., 2018 ).

Various smart home management systems ( Zhou et al., 2016 ).

The most present implementation challenges are linked with the efficient integration of different sensing technologies, development of a suitable network infrastructure, education of population, investigation of the sustainability aspect, such as carbon footprint, etc.

The application of IoT technologies in smart homes, ( Moniruzzaman et al., 2020 ), within the smart city concept allows for an increase in the life quality within residential facilities, bringing novel and attractive technological solutions. Both, energy and fund savings could be reached with more efficient time management, which is a valuable feature in our present economic system. Different control options are possible within the smart home concept and enable an efficient integration of renewable energy technologies in homes ( Stavrakas and Flamos, 2020 ), and their efficient balancing (efficient supply and demand).

1.2.3. IoT in agriculture

Efficient agriculture production is a necessity for our population to prevent the potential lack of food resources in future terms caused by different factors, ( Hussain et al., 2020 ). The first factor is constant population growth, as already emphasized, the second is linked with climate change issues ( Yang et al., 2020 ), which is causing a reduction in the yields of important crops, or some areas are even becoming unsuitable for efficient agriculture production. The food waste issue is one of the major problems ( Keng et al., 2020 ), since it has become a global problem, especially in developed economies. It is estimated that more than 28% of available agriculture areas is ‘‘reserved’’ for food waste and unfortunately more than 800·10 6 people are currently hungry, ( Fao.org, 2020 ). The implementation of IoT technologies in agriculture can certainly help to secure sufficient food demands and increase the efficiency of agricultural production processes in general. Various useful data about crops could be collected and used for yield monitoring and the detection of potential diseases in advance that can significantly reduce the yields of specific crops. The monitoring of soil and nutrients would rationalize agricultural production processes and lead to water savings that are precious in some specific geographical regions, which could be utilized through smart irrigation systems, ( Xin et al., 2020 ). A more precise seeding could also be ensured and fertility crop management in general, Fig. 8. There are some issues linked with the efficient application of IoT technologies in agriculture production. Different sensing and monitoring technologies should be developed and a better education of farmers should be provided (i.e. development of standard education modules for farmers). Due to a large quantity of collected data, farmers could be potentially overwhelmed, ( Ec.europa, 2017 ). Therefore, there is a necessity for the development of standard trainings (education modules) for farmers coupled with the development of more user-friendly software solutions.

IoT in agricultural production from farmer’s perspective.

The application of IoT technologies in the agricultural sector would lead to advancements that could drastically modify current production procedures in agriculture, ( Shafi et al., 2020 ) ( Fig. 8 ).

1.2.4. IoT in waste management

Waste management towards a circular economy concept ( Fan et al., 2019 ) is a vital current population problem, where there is certainly a role for IoT technologies that could help provide more efficient waste management in specific areas ( Voca and Ribic, 2020 ) and recycling of different limited resources, ( Qiu et al., 2020 ). Currently, various technological solutions are being developed to support the smart waste management concept, ( Das et al., 2019 ). Some of them are already available on the market for wide implementation, ( Iot.farsite, 2020 ). The developed solutions are mostly directed towards the smart monitoring of waste bins ( Dhana Shree et al., 2019 ), i.e. bin filling level detection, waste temperature and fire detection, bin vibration occurrence and bin tilt, presence of waste operators, waste humidity, bin GPS location etc. In general, smart waste management systems, can be effectively supported by IoT devices, Fig. 9 . IoT technologies could also be used for the smart coordination of waste trucks ( Idwan et al., 2020 ) and efficiency waste utility companies could be ensured in that manner, which would be followed by a reduction of harmful emissions (pollutants) created by garbage trucks, ( Kozina et al., 2020 ). From the perspective of smart technologies, the proper and IoT based waste management of electronic waste is very important ( Kang et al., 2020 ) to secure sufficient raw resources to produce electronic equipment as already highlighted. IoT technologies could also be used for the reduction of food waste through intelligent appliances and a developed management structure in that sense, ( Liegeard and Manning, 2020 ).

IoT in smart waste management system, ( Quamtra, 2020 ).

Innovative IoT based technological solutions are expected to be developed in upcoming years, especially from a smart city concept perspective and that could support smart waste management systems and a circular economy concept.

1.2.5. IoT in healthcare

One challenging implementation field of IoT technologies has been detected in the healthcare system in general, through the e-health concept, ( Farahani et al., 2020 ). An increase in the service quality of healthcare systems could be utilized through IoT support (mainly collection of patient health data) and finally with the improvement of patient safety and care since it could also lead to an increase in patient life expectancy. There is an enormous potential in smart medical devices for different purposes ( Papa et al., 2020 ) that can be utilized for the monitoring of various vital and valuable human functions such as heart rate, skin temperature, movement monitoring, etc. Remote health monitoring is also an interesting perspective that could be utilized with the proper support of IoT devices and products. The prediction of different symptoms and prevention of potentially life hazardous states and diseases could generally be enabled, ( Muthu et al., 2020 ). Assistance to the elderly could also be ensured by monitoring a patient’s general health condition and nutrition status ( Nivetha et al., 2020 ), that would be supported via IoT devices. Rehabilitation after a serious disease could also be efficiently supported with IoT technologies, especially in cases of home rehabilitation circumstances, ( Bisio et al., 2019 ). One of the main issues and challenges in this specific IoT application field would be to ensure proper cyber safety due to potential attacks that could occur within healthcare monitoring systems, ( John et al., 2019 ). Significant progress in upcoming years is expected in the field of software development for health care systems, i.e. especially in hospitals. Namely, different devices could be linked via advanced software solutions as for example MRIs or CT devices and connected with laboratory data to create a smart hospital information system. The previously mentioned approach would allow for the better treatment of patients, detection of medical priorities and support for medical staff in monitoring and therapy decisions. IoT systems could also be used in hospitals for the efficient maintenance of a large number of medical devices ( Shamayleh et al., 2020 ). Equipment costs could be reduced in hospital systems due to the early detection of severe equipment malfunctions that could affect the accuracy of specific readings from medical devices. The development of smart and based IoT solutions in healthcare systems could also be very useful in the case of severe global pandemic states (data collection and fast data diversity, resources of medical staff and resources, medical triage, etc.), such as is the recent corona virus situation that has severely threatened the global population, ( WHO, 2020 ). The healthcare sector is probably one of the most challenging areas for IoT, thus important progress is expected in the upcoming year with serious benefits for the population.

1.2.6. IoT in transportation

Transportation modes will be significantly changed in upcoming decades, ( Jonkeren et al., 2019 ), especially due to the expected rising implementation of electric cars on the market, ( Capuder et al., 2020 ). The upcoming ban of Diesel based vehicles due to environmental issues ( Li et al., 2020c ) and finally development of alternative transportation technologies, such as hydrogen based vehicles for example ( Ajanovic and Haas, 2019 ), would change the shape of future transportation systems. In general, there is a demand for more environmentally suitable transportation options that are already being gradually developed with an expected penetration on the market. A necessary development of transportation infrastructure is needed for specific vehicle technologies to ensure desirable vehicle autonomy. Nowadays, the IoT emerged in the ‘‘internet of vehicles’’ concept ( Shen et al., 2020 ), which just proves its potential in this important area. The most significant IoT application area is in the case of the smart car (vehicles) concept, ( Chugh et al., 2020 ). The smart car concept considers the utilization and optimization of different internal functions in the car that are supported by IoT technologies. The application of IoT would upgrade driver experience and increase in comfort and safety. Specific data are collected in the smart car and associated with the main operating parameters such as tyre pressure, fuelling, early detection of potential failures, regular maintenance indicators, etc. In general, improved service as well as added value for customers could be obtained with a targeted utilization of IoT technologies, which finally can improve competition in the automobile industry between vehicle manufacturers. The challenging aspect of IoT application is in the case of autonomous vehicles, ( Padmaja et al., 2019 ). Location, direction as well as a planned path of the autonomous vehicle could be efficiently supported with IoT in general as well as the monitoring of safety systems for autonomous vehicles, ( Bylykbashi et al., 2020 ). The most important issue with autonomous vehicles is the prevention and avoidance of crash vehicle accidents, which could be solved with a targeted utilization of IoT devices, ( Abdou et al., 2019 ). Smart parking is also currently one of the most developing IoT areas when considering the transportation sector in general terms. Different research efforts are provided in that sense with the main goal being to enable the latest status of available parking space, control and monitoring of different useful parking space information in real time, ( Luque-Vega et al., 2019 ). Again, the development of sensor technologies, i.e. smart parking sensors is very important to enable efficient and accurate service, ( Perković et al., 2020a ). The maintenance and failure prevention of different vehicles could also be supported by IoT ( Saki et al., 2020 ), which could improve security and the lifetime of vehicles. Taking all the previously addressed into account, IoT technologies could completely change the driving experience and generally improve the quality of transportation systems from various aspects.

1.2.7. IoT in smart grids and power management

Energy transition ( Biresselioglu et al., 2020 ) has become a necessity due to the potential shortcomings of fossil fuel resources in future terms and for the reduction of different pollution impacts that are associated with the utilization of various fossil-based technologies, ( Bielski et al., 2020 ). Since a more intense implementation of renewable energy technologies has already been occurring, the efficient and advanced power management of electric grids has become an important aspect. Efficient demand side management with accurate and flexible smart metering technologies are key factors to enable smart power management in smart grids, ( Mendes et al., 2020 ). The most important role of IoT technologies in smart grids is to save electricity ( Rishav et al., 2019 ), with efficient distribution of electricity, Fig. 10 . The collection of specific grid data through IoT devices, and later their analysis with the proper software, could help improve grid reliability and efficiency. The economic aspect of electricity could also be improved with IoT due to the already mentioned efficiency improvement as previously highlighted. Useful benefits could be ensured both for customers and service providers.

Concept of smart grids ( Tuballa and Lochinvar Abundo, 2016 ),

A demand side management in households is also an important application area of IoT, ( Rahimi et al., 2020 ). Homes are typically equipped with different appliances that are becoming more advanced, creating the possibility for an efficient operation with the regulation of IoT, ( Tawalbeh et al., 2019 ). The efficient and smart forecasting of electricity demands for households could also be effectively supported by IoT technologies, ( Nils et al., 2020 ). An expected higher penetration of renewables in households through hybrid energy systems as an example ( Gagliano et al., 2019 ), would also require a smart operation strategy that could be utilized by IoT through integrated smart nano-grids, ( Kalair et al., 2020 ). A growth of IoT products and technologies in smart power management is expected to enable accurate forecasting and different load strategies in the case of renewable generation, ( Pawar et al., 2020 ). The elaborated main issues and challenges above just reflect the importance of IoT devices in smart grids and power management.

1.3. Review methodology

By addressing all the above raised general challenges towards an efficient and suitable implementation of IoT technologies, it is evident that more intense research efforts are needed to lead to further advancements in this dynamic research topic, with a strong application potential. A synergy of different research efforts in the field, mainly focused on the targeted topical area is needed. The main contribution and novelty of this review editorial is in line with that. Further main topical areas are addressed in the herein review introductory editorial;

• - IoT technologies in sustainable energy and environmental issues,
• - IoT enabled Smart City
• - E-health – Ambient assisted living systems
• - IoT technologies in Transportation and Low Carbon Products

The main objective of the herein presented review editorial is to address and discuss the latest advancements in the above specified and key IoT application areas. This review editorial serves as an introduction to the Virtual Special Issue (VSI) of JCLEPRO devoted to the 4th International Conference on Smart and Sustainable Technologies (SplTtech 2019) held on 18–21 June 2019, in Bol (Island of Brač) and Split, at the University of Split, (Croatia). The herein presented introductory review editorial was directed to the selected and accepted publications from the international conference SpliTech2019 and published papers were divided into four main topical areas as already specified above. Overall 38 papers were initially selected and invited for potential inclusion in the VSI SpliTech 2019. After conducted peer-review process, based on the JCLP procedures, 29 of them were selected for inclusion in the VSI SpliTech 2019. Authors from following countries have contributed VSI SpliTech 2019: China, India, Australia, Canada, Italy, Croatia, Serbia, Greece, Poland, Czech Republic, Spain, Cyprus, Turkey, Norway, Iran, Germany, Brazil, Malaysia, Pakistan, Dubai and United Kingdom. Besides the selected VSI SpliTech2019 works published in the JCLEPRO, the other relevant and latest works from the existing literature in the field were also addressed using the Scopus database, ( Scopus, 2020 ). Based on the conducted review as well as selected contributions in this VSI the key issues were identified, discussed and highlighted in the conclusion section.

2. IoT technologies in sustainable energy and environment

The rapid development of information technologies caused in one sense the necessity for ‘‘energy digitalization’‘. The increasing application of renewable energy technologies and development of efficient policies will be key points in upcoming decades to be able to secure global energy transition goals, ( Tzankova, 2020 ). Referring to the previous, the development of alternative renewable energy sources would also be valuable, ( Nižetić, 2010 ). Different energy scenarios or options have been considered in recent years involving a high share of renewables via hybrid energy options ( Nizetic et al., 2014 ), or for instance the possible application of alternative energy sources such as hydrogen technologies in different implementation fields ( El-Emam et al., 2020 ), or vehicle applications ( Matulić et al., 2019 ). The focus of the research is to investigate the techno-economic viability of different energy concepts in order to secure a suitable mix of energy technologies that would support an efficient energy transition. An improvement in the energy efficiency of different renewable energy technologies is also important, especially in the case of photovoltaics ( Grubišić-Čabo et al., 2019 ) and wind generation technologies ( Marinić-Kragić et al., 2020 ), to secure large scale projects. The efficiency of specific production processes ( Giama et al., 2020 ), is also vital and certainly needs to be carefully investigated and analysed, to reduce energy intensity and provide a circular economy concept in specific application areas, ( Xu et al., 2020 ). The main research efforts should be directed towards the upgrade of energy saving technologies followed with the increasing utilization of renewable energy sources, ( Klemeš et al., 2019 ). Recent technological progress in the field of IoT technologies has enabled different opportunities for the possible application of IoT concepts in the energy sector and environmental protection to secure a sustainable development.

Energy and environment are two of the most important elements of Smart Cities and are very often closely interrelated concepts. The available challenges in energy management to use and generate energy in the most efficient manner possible, and the development of a sustainable energy structure can take advantage of Internet of Things (IoT) and Internet of Energy (IoE) technologies, Fig. 11 ( Mohammadian, 2019 ) or in the case of battery charging protocols ( Fachechi et al., 2015 ).

IoE architecture ( Mohammadian, 2019 ).

The climate change and global warming impose a paradigm shift in the exploitation of resources and in more efficient energy resource management: production, distribution and consumption, as an integral part of this vision. The energy transition must point to an infrastructure change at the center of which there are the so-called smart grids. With the advent of smart grids and new technologies, the energy industry is inexorably changing. The most interesting aspect is that smart grids ensure flexibility in demand and allow consumers to participate in the energy system, as prosumers. Smart grids exploit digital and innovative technologies to manage and monitor the transport of electricity from all sources of generation to promptly, quickly and effectively satisfy the demand of end users. Smart grids are raising reliability, system resilience and stability, and minimizing disruptions, costs and environmental impacts. Some of these new technologies such as Distributed Generation (DG) and microgrids provide energy locally, creating larger and more reliable networks and reducing the line overload. Energy storage complements the energy from renewable sources while microgrids help reduce any blackouts by providing energy locally. Unlike the existing power system of a unidirectional system, which distributes electricity generated from a power plant to the consumer, the microgrid is equipped with a local power supply and storage system centered on independent distributed power sources. It is an energy network that can connect with an existing power system as needed and the self-sufficiency of energy such as electricity and heat by using multiple distributed power sources independently. In addition to giving owners the ability to generate their own energy, microgrids also reduce the dependency on energy providers by helping reduce costs and avoid peak usage charges. The microgrid can produce revenue if it were to produce a surplus of power, which could be sold to the energy provider. Recent works in the energy related field are discussed in the upcoming section of the paper to highlight IoT implementation areas and clarify the benefits in specific engineering applications.

In microgrids, IoT technologies are introduced mainly to realize a smart system able to autonomously schedule loads and/or detect system faults and then improving the efficiency of the energy consumption. The work ( Nayanatara et al., 2018 ) proposes a renewable energy based microgrid management strategy to use renewable energy (solar energy from a photovoltaic panel and wind energy from a wind turbine) effectively reducing the energy usage from the power grid. IoT technologies are used to realizing a smart scheduling algorithm able to control schedulable loads as per the needs of the consumer. Authors demonstrate that the proposed energy management system installed in an institution enables low power consumption and reduced costs. In ( Sujeeth et al., 2018 ) an IoT-based automated system that constantly monitors the current and voltage flowing through various branches of a DC microgrid, detects and controls the fault clearance process during fault conditions that has been developed. The system is capable to alert the user during overcurrent faults, ground faults and short circuit faults. As the operation of a microgrid is automated, the need for human decision making is eliminated and the minimum reaction time to react to fault conditions is drastically reduced. The work ( Majee et al., 2018 ) is also focused on the issue of fault management within a microgrid exploiting the IoT. The concept of IoT is used to solve the issues of microgrid reconfiguration occurring due to faults, changing energy usage patterns and the inclusion and removal of distributed energy resources.

Smart grids can automatically monitor energy flows and adapt to changes in energy demand and supply in a flexible and real-time manner. These smart systems can benefit from technologies such as machine learning ( Chou et al., 2019 ) and artificial intelligence ( Bose, 2017 ) to perform predictive analyzes and better configure all the devices. To do this, however, smart grids require adequate and equally intelligent measuring instruments. Here, smart metering tools could be efficient solution, reaching the consumers and suppliers, providing them with information on consumption in real-time. With smart meters, consumers can adapt - in terms of time and volume - their energy consumption to different energy prices during the day, saving on their energy bills by consuming more energy in periods of lower prices. In this perspective, the possibilities generated by improved digitization and sensorization, utilizing to the Internet of Things solutions, has led many research works to focus on realizing innovative IoT-based hardware and software solutions. These solutions are capable of providing real-time information about the quality usage of appliances, data consumption, and energy flow information ( Morello et al., 2017 ). present an interesting study on the role of advanced smart metering systems in the electric grid of the future through the realization and the experimental validation of a smart meter, Fig. 12 . The cost effective three phase smart energy meter, IoT enabled, multi-protocol and modular, capable to collect, process, and transmit several electric energies related information, mainly focused on consumer-side, to any smart energy control system was proposed by ( Avancini et al., 2018 ), Fig. 13 .

Proposed smart power meter, ( Morello et al., 2017 ).

Photo of created IoT enabled smart energy meter ( Avancini et al., 2018 ).

Several solutions are also based on the use of the Arduino platform ( Arduino, 2020 ) and a few sensors for the realization of low-cost smart meters ( Patel et al., 2019 ) or for instance Arduino based solutions ( Saha et al., 2018 ). Although smart grids are fundamental elements when it comes to energy sustainability, it is reductive to identify the concept of smart energy only in them. In fact, smart buildings also play a crucial role. The energy efficiency of building structures using smart technologies provides an increasingly intelligent management of resources, avoiding waste, improving the life quality of people and making the buildings themselves more resilient in the face of current climate changes. Thanks to building automation and IoT not only individual buildings but also entire neighborhoods can be controlled remotely from an energy point of view and in terms of the security. For example, it is possible to carry out checks on air pollution remotely ( Becnel et al., 2019 ), monitor fire systems ( Cavalera et al., 2019 ) or, furthermore, immediately detect any intrusion by outsiders ( Dasari et al., 2019 ).

Smart buildings are able to monitor actual energy needs, optimizing consumption and therefore counting not only on green energy, but also on a high degree of energy efficiency. The virtuous process that passes from smart energy allows to count on Nearly (Net) Zero Energy Building (NZEB) ( Rushikesh Babu and Vyjayanthi, 2017 ) and on a wider energy sustainability.

The most common use of IoT for energy and environmental sustainability is in the home automation systems, which allow homeowners to live comfortably and manage energy consumption through connected devices. In this field, numerous applications have been implemented and, despite the common goal of creating an Energy Management System (EMS) for home, the techniques used to achieve it can be very different. For example ( Li et al., 2018 ), propose a self-learning home management system that exploits computational and machine learning technologies, Fig. 14 . The proposed system has been validated by collecting real-time power consumption data from a Singapore smart home. In ( Al-Ali et al., 2017 ), an EMS for smart home is realized exploiting off-the-shelf Business Intelligence (BI) and Big Data analytics software packages to better manage energy consumption and meet consumer demands. In this work, the proposed system has been validated realizing a case study based on the use of HVAC (Heating, Ventilation and Air Conditioning) Units. Smart energy solutions such as those analysed provide real-time visibility of consumption and billing data, helping consumers to save resources, while energy and service companies can better balance production to meet actual demands, reducing potential problems. As the main effect, the energy consumption of families is reduced, also decreasing our impact on climate change.

Self-learning home management system architecture ( Li et al., 2018 ).

In addition to buildings and homes, industrial facilities and enterprises also deal with the adoption of innovative energy efficiency solutions to optimize resource consumption and reduce costs, but they need to evaluate a high number of factors to adopt the best energy efficiency measures. The work ( Suciu et al., 2019 ) proposes an IoT and Cloud-based energy monitoring and simulation platform to help companies monitor energy production and consumption, forecast the energy production potential and simulate the economic efficiency for multiple investment scenarios.

The concept of sustainability is increasingly linked to that of circular economy, which is now considered the key to this new paradigm. Unlike the traditional linear economy, based on the so-called “take-make-dispose” scheme, which provides for a complete utilization of resources, the circular economy model promotes reparability, durability and recyclability. In practice, the circular economy aims to minimize waste through reuse, repair, refurbishment and recycling of existing materials and products, focusing attention on designs that last over time. In this system, the IoT is considered an essential element, as it offers new opportunities in various sectors, such as manufacturing, energy and public services, infrastructure, logistics, waste management, fishing and agriculture. Especially in the field of waste management, research has made great strides through the creation of innovative systems capable of concretizing the concept of digital economy. In the work ( De Fazio et al., 2019 ) the activities related to the research project called POIROT were discussed, which exploit innovative hardware and software technologies, aiming to realize a platform for the inertization and traceability of organic waste. In detail, the main project objective is to realize a targeted transformation, through technological processes, regarding the organic fraction of urban solid waste, into inert, odorless and sanitized material, identified and traced to be employed for building applications or as thermal acoustic insulator, Fig. 15 .

Architecture of proposed identification and traceability system, ( De Fazio et al., 2019 ).

Several works propose solutions to support waste management at a domestic level, simplifying the waste separation to avoid problems due to improper waste management including hazards for human health or environmental issues. For example ( Al-Masri et al., 2018 ), propose a server-less IoT architecture for smart waste management systems able to identify waste materials prior to the separation process. This allows reducing costs related to the waste separation process from hazardous materials such as paint or batteries ( Kumar et al., 2017 ). propose a hygienic electronic system of waste segregation. The proposed approach eases the segregation of wastes at source level and thereby reducing the human interaction and curbs the pollution caused by improper segregation and management of wastes at source level.

The role of IoT supported smart meters was considered in the work ( Mendes et al., 2020 ) to address different demand side management scenarios. The novel and adaptive compression mechanism was proposed in the same work to improve the communication infrastructure for the given case, i.e. complete controlling structure, Fig. 16 . The proposed mechanism can reduce the quantity of data sent to utility companies and can automatize energy consumption management.

Proposed general controlling structure ( Mendes et al., 2020 ).

The proposed and tested control solution showed to be efficient with respect to the considered application, since compression rates were satisfactory and the proposed concept showed potential for other applications. The demand side management of a hybrid rooftop photovoltaic system was discussed in ( Kalair et al., 2020 ) where the system was integrated in a smart Nano grid. The smart monitoring system was presented in detail for residential purposes, together with a developed experimental setup that contains specific electronic components, Fig. 17 . The developed controller can automatically detect any frequency and voltage changes and link them with specific loading patterns. The proposed solution demonstrated efficiency since the power supply reliability was up to 97%. The proposed home management system could lead to the reduction of carbon footprints in the case of residential facilities.

Experimental setup with pre-processing unit (a) and smart controller (b) ( Kalair et al., 2020 ).

A machine learning-based smart home energy system was investigated in ( Machorro-Cano et al., 2020 ), using big data with the support of IoT. The home automatization system was coupled with IoT devices that enabled energy savings for the given purpose. A machine learning algorithm was used to study user behaviour and was later linked with energy consumption, i.e., with the proposed approach, specific user patterns were revealed. The developed monitoring system, Fig. 18 allowed specific recommendations to lead towards an improvement of energy efficiency in households, which were somehow personalized for the specific household. The system was successfully validated via the provided case study where the main strength of the conducted research was the personalized approach for the specific household. A step further could be to network and balance other households in the specific building facility. The importance of the BIM (Building Information Modelling) systems was discussed and analysed in the review paper ( Pantelia et al., 2020 ). An overview of the recent works focused on the building smart operation was elaborated in detail with use of IoT technologies. In the same work the renovation projects were also tackled as well as interoperability problems caused by data sharing with respect to the BIM related applications.

Concept of proposed IoT supported smart home system ( Machorro-Cano et al., 2020 ).

An application of smart wearable sensors was reported in the study ( Pivac et al., 2019 ) that were used for the monitoring of thermal comfort data as well as for the modelling of occupant metabolic response in office buildings. The smart and IoT supported monitoring system allowed the collection of useful data from the wearable sensors. The readings helped for the better understanding of thermal comfort issues in office buildings from a personalized thermal comfort point of the view. The experimental readings were compared with a subjective response from the occupants, where a successful modelling of personal metabolic responses was enabled with an accuracy of over 90%. Industrial facilities could also be improved with the implementation of IoT technologies as already briefly addressed in the introduction section. Legislation support is important to ensure smart electricity utilization in the households, especially from the perspective of the smart city concept. Study ( Grycan, 2020 ) discussed legislative for electricity consumption for the case of the Polish residential sector. Lack of legislative was detected and mainly in the smart metering solutions that are slowing down development of the smart infrastructure. There is necessity for the new regulations to ensure adaptability to the novel desired goals towards smart cities. Development of the novel business models is important to ensure smart driven business in the energy sector. The case of the smart energy driven model was elaborated in ( Chasin et al., 2020 ) as well as implications and necessary changes in the energy sector. Eight smart business models were discussed with introduction of desired changes. Presented knowledge and development business scenarios could be useful guideline for energy utility companies. The possibility of IoT based smart solutions was discussed in the review paper ( Bagdadee et al., 2020 ), where the focus of the work was on IoT-based energy management systems in the industry. IoT based energy management systems were elaborated for industrial applications as well as for smart energy planning in industrial facilities. The energy management systems in factories were addressed from a perspective of energy demand and supply. The focus of IoT applications could also be used on a level of single or multiple devices or appliances. The scheduling and optimal power management of the transformers was analysed and discussed in ( Sarajčev et al., 2020 ). The Bayesian approach was applied to detect an optimal controlling strategy to ensure benefits for power utility companies. The proposed and demonstrated model can predict the transformer health index with an accuracy of about 90%. The solution could be applied on the fleet of the power transformers where with the application of IoT technologies, further savings could be ensured for the specific application. The efficiency of the lighting system could also be improved with IoT devices. The work ( Mukta et al., 2020 ) discussed and reviewed the possible application of IoT technologies for the energy efficiency improvement of highway lighting systems. The results of the conducted review revealed that the development of smart and IoT supported highway lighting systems lack a systematic approach, quality and comprehensiveness. Possible framework was proposed to bridge the mentioned gap and secure an efficient pathway for the improvement of energy efficiency in IoT based lighting smart and green highway systems. The necessity for the environmental suitability of the proposed smart lighting system was also raised in the same study and noted as an important factor that needs to be further investigated. Energy harvesting is also interesting topic and closely linked with the possible application of IoT technologies, especially since IoT devices require energy for their operation. An underwater piezoelectric energy harvesting system was discussed in ( Kim et al., 2020 ) for the case of autonomous IoT sensor production. The proposed solution was fully designed and provided in the form of a prototype and demonstrated an autonomous energy source that could be further linked with IoT devices. The harvesting of waste energy could also be considered with the implementation of IoT devices. The possibility for waste energy harvesting supported by IoT was addressed and discussed in ( Kausmally et al., 2020 ) for the case of an industrial chimney. The complete design procedure was reported, i.e. the conceptual approach for the waste heat recovery where the prototype was successfully developed and demonstrated. Energy storage systems are also interesting for the application of IoT technologies. A renewable energy storage system was analysed in ( Sathishkumar and Karthikeyan, 2020 ), where a power management strategy was supported by IoT. The optimal design of a hybrid energy system coupled with energy storage was discussed based on solar and wind renewable energy resources.

The IoT approach allows successful monitoring and managing of complex energy systems. The main advantage of IoT for the considered application is the energy efficiency improvement, better synchronization of different energy systems and improvement of the economic aspect. A significant development of IoT products would lead to a rapid increase of big data that are usually processed by data centres. The energy load of data centres is increased, so efficiency improvements are necessary in the case of data centres to minimize load power as well as utilization of other limited resources. The issue related to data centres, power demands and the possible application of IoT technologies in order to reduce the mentioned unwanted impacts was discussed in ( Kaur et al., 2020 ). The authors proposed a specific framework in the same work that is applicable for data centres and could lead to efficiency improvement of over 27% (proposed approach was based on empirical evaluations).

IoT technologies could also be successfully implemented in a circular economy concept as above already mentioned, especially in smart waste management systems and environment protection as already mentioned. The role of IoT technologies in e-waste was discussed in ( Kang et al., 2020 ) for the case of the Malaysian recycling sector. A novel smart waste collection box was designed together with a user friendly mobile application, Fig. 19 . The concept was successfully demonstrated. The developed solution could be further optimized and fitted for possible market implementation. A discussion of possible IoT framework, based on the developed IoT supported smart e-waste bin was elaborated for the Sunway city in Malaysia. The proposed approach could be a helpful guideline for other cities. The remaining issue with the proposed concept is its economic feasibility that should be further investigated via a detailed user survey, detecting user willingness for the acceptance of the proposed concept. The innovative IoT supported platform for the transformation of organic waste into inert and sterilized material was reported in ( Ferrari et al., 2020 ). The specific Arduino-electronic platform was developed to control process parameters and link them with user responses and traceability. Novel and low cost sensors were developed and successfully applied for the given purpose. The proposed prototype of the device was presented and was used for the mechanical treatment of waste. The developed IoT supported framework for the identification and traceability of products was presented in Fig. 20 .

Prototype of smart e-waste bin ( Kang et al., 2020 ).

Conceptual IoT supported framework for waste processing ( Ferrari et al., 2020 ).

The implementation of IoT technologies in a circular supply chain framework was elaborated in ( Garrido-Hidalgo et al., 2020 ) for the waste management of Li-ion battery packs from used electric vehicles. A novel and IoT supported supply chain framework was proposed, which is compatible with the information infrastructure. The approach could be further used for the recovery process of Li-ion batteries. Due to a planned increase in electric car fleets globally, intensive research was also directed for the potential usage of IoT technologies for the smart charging of electric vehicles. Real time IoT based forecasting applications were proposed in ( Savari et al., 2020 ) for a more efficient charging process of electric vehicles. The application allowed better scheduling management where the waiting time was minimized, which improved the overall charging economy as well as charging time.

Environmental protection and sustainable behaviour could also be improved with the targeted application of IoT technologies. In the study ( Irizar-Arrieta et al., 2020 ), long-term field investigation was presented with the main goal being to investigate how IoT technologies could help ensure the sustainable behaviour of users in office building facilities. The results of the conducted directed study could lead to the improvement of energy efficiency at workplaces with IoT utilization in different aspects. The impact of IoT technologies on a sustainable perspective and society was addressed in ( Mahmood et al., 2020 ). The study was focused on addressing the impacts of home systems on the environment and sustainability in general. A survey was conducted for specific users and the investigation showed that the impact of home automatization on sustainability and environment is significant. However, the environmental effects should be discussed in more detail and quantified to get realistic indicators that would later be used for sustainable planning.

Besides the obvious potential impact of IoT technologies to the environment, IoT products could on the other side be used for environmental protection. The design and concept of a systematic framework for the massive deployment of IoT-based PM (Particulate Matter) sensing devices was elaborated in ( Chen et al., 2020c ). The proposed framework was applied for the monitoring of air quality. Compressed spatiotemporal data were used and that allowed for the efficiency improvement of air quality monitoring systems, energy savings and improved data saving ratio. In order to improve the interoperability between different sensor networks, as well as data sources, a novel IoT data framework was proposed in ( Duy et al., 2019 ). The proposed analytical framework was used as a useful tool to improve the data management of environmental monitoring systems. The developed framework enabled a more efficient utilization of the gathered environmental data and improved knowledge extraction later. IoT platforms could also be used for environmental planning as it was demonstrated in the study ( Wu et al., 2019 ). In the conducted research, a building information model was integrated successfully with IoT and used for environmental planning for environmental protection reasons. Moreover, the system was used for environmental protection in a specific construction project (tunnel utility). Different impacts to the environment were monitored during the construction project such as dust falling control, temperature monitoring, visual monitoring etc. The overall findings directed that the proposed IoT supported system showed to be effective for the considered application. The application of an IoT based data logger was presented in ( Mishra et al., 2020 ), for the monitoring of equipment for environmental protection. The developed monitoring system ensured accurate and reliable work of the equipment used for the environmental protection. Potential equipment faults were detected in advance (prevention of serious failure), the equipment energy consumption was rationalized and scheduled maintenance was enabled. The accurate prediction of particulate matter (PM 2.5 ) concentrations is very important, especially in urban areas. Usually, there is a network of sensors used for the monitoring of PM 2.5 concentrations but they are not well connected and harmonized in some situations, which is vital. An IoT framework was used, together with a fusion technique, to improve the data utilization from the PM measuring stations in the work ( Lin et al., 2020 ). A novel multi-sensor space-time data fusion framework was proposed that ensured better accuracy, i.e. a more reliable model was ensured with a higher spatial-temporal resolution. Regarding the current progress of specific application areas in IoT devices for environmental protection, it can be conducted that the studies were mostly focused on air quality monitoring. Water-Energy-Carbon (WEC) nexus was analysed in detail for EU27 countries, in the recent work ( Wang et al., 2020 ) by implementation of the Environmental Input-Output model (EIO). Study was important since contributed to the better understanding of the environmental performance in EU27 and could serve as important basis for future considerations or planning for policymakers.

Based on the previously conducted overview of latest research findings related to the application of IoT technologies in sustainable energy and environment, the further main findings could be highlighted:

• - IoT technologies are intensively investigated from a perspective of smart monitoring in different devices or engineering components that are associated with energy applications. Better usage and networking of various collected data could lead to noticeable efficiency improvements, energy savings, improved safety, improved equipment maintenance and finally the general improved operation of devices in different engineering applications,
• - The economic aspect associated with the application of IoT technologies was not addressed in most studies, which is a significant drawback,
• - The environmental impacts associated with the implementation of IoT technologies for specific use were not addressed, which is serious and an important issue that should be carefully considered and investigated when discussing specific IoT concepts. Moreover, an integral techno-economic-environmental conceptual approach (TEE) should be applied when considering an IoT application for specific cases,
• - The main advantages (benefits) of IoT technologies enable a personalized approach in specific engineering applications such as smart homes (level of single user), which lead to different possibilities for both energy and fund savings,
• - There is significant potential in IoT technologies for environmental protection; however, rare studies have been conducted in that sense. More intense research efforts are needed in that direction to be able to utilize all the potential benefits of IoT technologies and improve the environmental suitability of IoT in one sense,
• - The waste management and circular economy concept could be well supported with IoT technologies, where the main issue is the development of integral and conceptual smart waste management frameworks that would efficiently support the circular economy concept in different economies.

3. IoT enabled smart city

To enable the IoT-based smart city concept, Fig. 21 , is described in the form of a tree that can be considered to further understand what the possible applications or functionalities the IoT-enabled Smart City can provide. The branches of the given tree are dedicated to applications, wherein the leaves of the given branch are dedicated to the functionalities that each application can have. As the more leaves a branch contains, the more functionalities it has. Fig. 16 represents the different functionalities of a smart parking system for instance. Further on, for example, smart homes can have many functionalities: smart metering (electricity, water consumption, gas monitoring), smart lock control, smart room temperature monitoring, smart kitchens and other appliances, etc. The root of the given tree (enabler and information source of these systems) is dedicated to the hardware whose system uses to accomplish any of the given possible functionalities. This section considers an overview of the most important hardware technologies, and software architectures that can enable and present functionalities for different applications in the smart city concept.

Generalized concept of IoT enabled Smart City Architecture ( Perković et al., 2020b ).

3.1. Hardware overview and state-of-the-art

To enable Smart Cities, an infrastructure that uses sensing hardware acting as an information source is of crucial importance. As this sensing hardware is located in remote areas, often without access to an electrical network, an almost zero-energy use is needed and therefore can prolong battery lifetime and possibly enable self-powering through ambient power sources, e.g. solar cells. This is crucial for improving the usability of the whole system as a battery replacement in these circumstances is difficult, expensive and a time-consuming activity. To understand power consumption issues, an overview of state-of-the-art technologies to build the hardware is provided.

A standard sensing node, presented in Fig. 22 is consisted of a sensor component that delivers the sensed information to a microcontroller unit (MCU) for its further processing. To reduce power needs, the node is usually equipped with a related power management unit, while there is a given power source. Once the MCU acquires the data from the sensor, it gives data to a radio unit that uses an antenna to transmit the data over a wireless channel. In the next sections, the components are described in depth by referencing the relevant literature, while the specific original work was done in current technology investigations that can enable these functionalities.

Block scheme of standard sensing node architecture in IoT enabled Smart City.

Sensors vary in terms of design and functionalities. A good overview of sensing technologies, and its power consumption is given in Fig. 23 . It can be noticed that each of them has its own power consumption pattern, where the more functionalities they have, the more consumption will appear. Using it in an optimal way is of the highest importance for reducing battery lifetime.

Most popular sensors and their power requirements in active and power-down (i.e. sleep mode, Perković et al., 2020b ).

3.2. Efficient IoT radio units

To achieve data transmission, a critical part is to deliver the data in an efficient manner. For this, the major idea and enabler is to provide data links between sensing nodes and receiving stations for transmitted data. To satisfy different applications and related functionalities, it is important that these radios can timely transmit the data over larger distances while consuming less energy. The major competitors in this area are Low-Power Wide Area Networks (LPWAN) with their technology competitors: LoRa, NB-IoT and Sigfox. According to Fig. 24 LPWAN can satisfy long ranges wherein the data rate is sacrificed, just suitable for sensorial application. In these cases, sensor devices send several data packets containing only the sensed information.

Overview of technologies that can satisfy different usage scenarios ( Mekki et al., 2019 ).

When considering LPWANs, the competitive technologies are also orthogonal in terms of different application points of view. A good overview of these technologies is given in Fig. 25 and Fig. 26 , also by providing the costs for each of them. In addition, Figs. 25 and ​ and26 26 give the technological comparison between each of them, so the deployers can understand which technology better fits which need. These mostly refer to which kind of infrastructure is required to match needs, what distance can be covered, what the overall system latency is when considering the number of nodes, etc.

Overview of performances and deployment costs for different LPWAN technologies ( Mekki et al., 2019 ).

Pros and cons for each of LPWAN competitors ( Mekki et al., 2019 ).

3.3. Power management

The basic mechanism that allows for the long lifetime of battery-operated devices (up to a couple of years) is to keep the device in low-power state during inactive periods. IoT devices, especially battery-operated ones, spend only a small fraction of time within active state, in which MCU performs sensor readings, and communicates data over wireless channels using a radio peripheral, while during inactive periods, the MCU along with other components is kept in deep-sleep state. Such a period between two active states, i.e. active - sleep - active is referred to as a duty cycle. Intuitively, to increase the lifetime of an IoT device, it is necessary to minimize its consumption during inactive periods. Logically, within inactive periods, it is necessary to place all active components into sleep. Some components, such as sensors, and radio modules, already come with libraries that support low-power consumption in sleep state (around 1uA per component or less). Using built-in functions, the MCU triggers external components to enter sleep once the sensor reading and radio transmission is done. On the other hand, the MCU also has to be kept in deep-sleep during the sleep period. However, to trigger the MCU waking from deep-sleep, some form of interrupt has to be sent to it. This is usually accomplished with some form of low-power timer. Depending on the MCU that is used in the implementation of an IoT device, there are many ways to accomplish this.

An MCU such as ATmega328P, found on Arduino boards, comes with a built-in Watchdog timer (WDT), with consumption up to couple of Ua, ( ATmega328P, 2020 ). Some external timers, like TPL5010 come with Watchdog functionalities, however, with nA scale consumption ( TPL5010, 2020 ). Unfortunately, the maximum time WDT can hold the MCU in low-power mode is around 8 s ( Tutorial - Atmega328p, 2020 ). One way to increase sleep time using WDT would require a loop that periodically triggers the MCU waking up every 8 s, after which the MCU immediately enters deep-sleep. Within deep-sleep period, the consumption of MCU and WDT is only a few uA. To increase sleep time for ATmega328P, an external RTC clock could be employed, such as a cheap and precise RS3231 RTC clock, with ±2 ppm stability and 1uA of consumption (Datasheet - RTC3231, 2020 ). Other MCUs, such as STM32 or SAMD21, already come with built-in RTC clocks that can be used to trigger an alarm for waking up from deep sleep (Libraries - Arduino low-power, 2020 ), ( STM32, 2020 ). All these components (MCU, sensor, RTC clock, radio peripheral, voltage regulators, capacitors, etc.), although in low-power mode, combined may consume tens to even couple of hundred of uA while being placed in deep-sleep. Moreover, it may happen that some boards equipped with components that adopt low-power modes have a hardware problem that prevent them from achieving low deep-sleep currents, such as found in MKRWAN1300 (Arduino LoRa with SAMD21) and ( MKRWAN1300, 2020 ).

To reduce even more consumption regarding all components, it is suggested to use an external timer component that will completely cut-off power for predefined periods. The TPL5110 is a low power timer where an alarm clock is regulated with resistors, allowing for the duration of sleep mode to be up to 2 h ( TPL5110, 2020 ). Within the sleep period, the TPL5110 simply cuts-off power from other components leaving overall consumption to be equal to the consumption of the timer only. Since the TPL5110 is low power by nature, the overall consumption falls to only 50 nA. The drawback of such a solution is that the MCU is no longer in deep-sleep but is instead powered off, which means that possible variables that were held in volatile memory during deep-sleep will not be available to the MCU when it wakes up. For this reason, it is suggested to use EEPROM or flash memory to write the variables before cutting off power from the MCU. A Tega328P may use built-in EEPROM, while STM32 or SAMD21 can use flash memory or RTC backup RAM ( Flash storage, 2020 ). The RS3231 RTC clock has an EEPROM that can be used for saving variables. The main drawback of EEPROM and flash memory is the limited number of writes (around 10,000), hence some external EEPROM or flash memory may be used with a larger number of writings, or either an external specialized chip like ATECC508A ( ATECC508A, 2020 ) that supports secure storage (of key for example) (ATEC). It must be noted that when the MCU wakes from deep-sleep, the code runs from where it left off, which usually requires a couple of mS. On the other hand, powering the MCU with an external timer such as TPL5110 requires a fresh restart of code, which in some scenarios may indicate running the bootloader. For ATmega328P, by default it may take up to 2 s for the bootloader to start ( Tutorial - Low-power nodes, 2020 ). Hence, to reduce consumption, it is suggested to either completely wipe out the bootloader or flash faster bootloader ( Bootloader, 2020 ). It must be mentioned that battery capacity, along with its input voltage may vary during sensor lifetime or could be larger than the operating voltage of some components. A good quality voltage regulator that may deliver enough current to a sensor device while consuming itself small current is required. For example, MCP1700 ( MCP1700, 2020 ) is a family of CMOS low dropout (LDO) voltage regulators that can deliver up to 250 mA of current while consuming only 1.6 μA, with input operating ranging from 2.3V to 6.0V, making it ideal for battery operated devices.

3.4. Microcontrollers for IoT: scouting and comparison

The Microcontroller (MCU hereafter) is the core of any Internet of Things (IoT) device and embedded system. Indeed, its role is to coordinate, according to a specific pre-programmed logic, all the peripherals of the IoT node thus providing sensing, actuation, and connectivity in an as low power mode as possible. In other words, the MCU sets the “smart-ability” of a certain object in relation with its cost, computational capability, power consumption, memory, communication interfaces and other features to accurately select during the design phase. It is worth highlighting that a “perfect” microcontroller does not exist, but just the most suitable one for the specific application. For this reason, the role of the designer in selecting the microcontroller for a specific IoT application is never simple. Some “universal” microcontroller key features are useful to drive the designer towards the right choice according to the requirements of the considered IoT application.

The proposed analysis aims at comparing some microcontrollers as potentially useful for the IoT by considering the following objective parameters.

• • Register Memory Bits : This parameter refers to the number of internal register bits and buffer. The higher the number of MCU bits, the higher the number of operations that the MCU itself can sustain. This parameter sets different families of Microcontrollers.
• • Maximum Clock Frequency: is the maximum frequency on the internal/external clock of the microcontroller. It is useful because it sets the number of operations of an MCU in a single time unit.
• • RAM : RAM is the volatile memory of an MCU which is useful for performing quick operations, actions or data buffering. The absence of powering resets this kind of memory
• • Flash Type : It is the static memory of an MCU that retains data in the absence of power. The quality of this memory in terms of writing operation figures and writing/reading speed determines a consistent part of the microcontroller cost.
• • Number and Type of GPIOs : GPIO is the acronym of a general-purpose input/output interface. It is referred to as the presence of pins that can be configured to act as the analog or digital input/output of the MCU. The higher the number of MCU GPIOs, the higher the number of external devices (sensors, actuators, transceivers) that can be controlled.
• • Serial Bus : Presence of an SPI/I2C bus for communication
• • Integrated Wireless Connectivity Interfaces: This key feature is useful in the IoT to wirelessly connect the MCU by using Wi-Fi, Ethernet, or BLE interfaces.
• • Power Consumption: Power Consumption is the most important aspect of IoT-oriented Microcontrollers. This parameter should be optimized by controlling the Active time and Sleeping time of the MCU according to the specific application.
• • Development board/Launchpad: The availability of a development board is helpful during the design phase to test the targeted IoT solution before realizing a prototype. Providing this board is an added value for MCUs.
• • Arduino IDE Programming Interface: Multi-brand MCUs implement an Arduino-compatible convergence programming language useful to simplify the programming operations and modular implementation of IoT applications.
• • Cost: IoT applications are often cost-sensitive. In many cases, functionalities could not be implemented to maintain a low-cost IoT system design. Generally, both MCUs and the presence of specific sensors determine the cost of the whole solution.

In addition to the above-mentioned parameters, the computational capability of a microcontroller can be evaluated by considering the presence of an on-board Operating System. If supported, this feature helps in managing complex IoT embedded applications where several peripherals must be managed. In this regard, three different typologies of microcontrollers can be summarized:

• • No-Operating system: The operating system is not present. In this case the microcontroller can be programmed in a “canonical” manner, by developing a code for low-level operations (Assembler of C are the main programming languages). A software-level connection cannot be implemented, however, the cost-effectiveness of these kinds of microcontrollers as well as reduced power consumption, make this MCU typology quite diffused.
• • RTOS : namely “Real-Time Operating System”. An RTOS Operating system enables a multi-task approach by introducing priority levels among the tasks running under the operating system. Moreover, this Operating System guarantees the correct timing of single events.
• • Linux/UNIX : This feature allows high-level programming in a way similar to a canonical computer. Open source software can be run on the MCU thus enabling connectivity and port management. Real-time and low-power operations are never guaranteed so that this kind of MCU is often not compatible with IoT applications, except for hi-level management IoT node systems.

Underneath, selected multi-brand MCUs will be compared by using the above-mentioned metrics in order to have a quick perspective useful in selecting the right MCU for a specific IoT application. After a quick overview of the microcontrollers based on manufacturer descriptions, which is useful to understand the different categories, a table summarizing their main features will be provided. Being low-power, “No-Operating system” devices will be considered in this comparison, Fig. 27 .

Comparison of microcontroller devices.

3.4.1. Texas instruments G series MSP430G2x13 and MSP430G2x53

The MSP430G2x13 and MSP430G2x53 series are ultra-low-power microcontrollers with built-in 16-bit timers, up to 24 I/O capacitive-touch enabled pins, a versatile analog comparator, and built-in communication capability using a universal serial communication interface. In addition, the MSP430G2x53 family members have a 10-bit analog-to-digital (A/D) converter. This is an entry-level microcontroller useful for general purpose low-power and low-cost IoT applications. The availability of a development board for the MSP43G2553 MCU, called “Launchpad”, makes the design easy for simple IoT sensing nodes.

3.4.2. Texas instruments F series MSP430F552x

The MSP430F5529, MSP430F5527, MSP430F5525, and MSP430F5521 microcontrollers have an integrated USB and PHY supporting USB 2.0, four 16-bit timers, a high-performance 12-bit analog-to-digital converter (ADC), two USCIs, a hardware multiplier, DMA, an RTC module with alarm capabilities, and 63 I/O pins. The MSP430F5528, MSP430F5526, MSP430F5524, and MSP430F5522 microcontrollers include these peripherals but have 47 I/O pins. This MCU family is compatible with low-power hi-performance IoT applications where hi-speed communication, port availability, and USB connectivity is required. Also in this case, the availability of a “Launchpad”, for the MSP430F5529 MCU makes the design easy for rather advanced and low-cost IoT smart nodes.

3.4.3. Texas instruments FR series MSP430FR572x and MSP430FR59xx

The TI MSP430FR572x and MSP430FR59xx families of ultra-low-power microcontrollers consist of multiple devices that feature an embedded FRAM nonvolatile memory, ultra-low-power 16-bit MSP430™ CPU, and different peripherals targeted for various applications. The architecture, FRAM, and peripherals, combined with seven low-power modes, are optimized to achieve extended battery life in portable and wireless sensing applications. FRAM is a new nonvolatile memory that combines the speed, flexibility, and endurance of SRAM with the stability and reliability of flash, all at lower total power consumption. Peripherals include a 10-bit ADC, a 16-channel comparator with voltage reference generation and hysteresis capabilities, three enhanced serial channels capable of I2C, SPI, or UART protocols, an internal DMA, a hardware multiplier, an RTC, five 16-bit timers, and digital I/Os.

3.4.4. Microchip PIC18F family PIC18F26K22

The PIC18 microcontroller family provides PICmicro® devices in 18-to 80-pin packages, that are both socket and software upwardly compatible to the PIC16 family. The PIC18 family includes all the popular peripherals, such as MSSP, ESCI, CCP, flexible 8- and 16-bit timers, PSP, 10-bit ADC, WDT, POR and CAN 2.0B Active for a maximum flexible solution. Most PIC18 devices will provide a FLASH program memory in sizes from 8 to 128 Kbytes and data RAM from 256 to 4 Kbytes; operating from 2.0 to 5.5 V, at speeds of DC to 40 MHz. Optimized for high-level languages like ANSI C, the PIC18 family offers a highly flexible solution for complex embedded applications.

3.4.5. Microchip PIC24F family PIC24F16KA102

The PIC24F is a cost-effective, low-power family of microcontrollers (MCUs) based on eXtreme Low Power (XLP) technology and 16-bit architecture. The flash memory ranges from 16 KB to 1 MB. The PIC24F family is a suitable solution for many space-constrained, low-power, cost-sensitive industrial, IoT and consumer applications.

3.4.6. STMicroelectronics STM32L0 family – STM32L053x8

The STM32L053x6/8 devices provide high power efficiency for a wide range of IoT applications. It is achieved with a large choice of internal and external clock sources, an internal voltage adaptation and several low-power modes. The STM32L053x6/8 devices offer several analog features, one 12-bit ADC with hardware oversampling, one DAC, two ultra-low-power comparators, several timers, one low-power timer (LPTIM), three general-purpose 16-bit timers and one basic timer, one RTC and SysTick which can be used as time bases. The MCU is provided with SPI, I2C, UART and USB 2.0 busses. This kind of MCU is studied for Ultra Low Power IoT applications and is provided with an effective development Arduino-compatible modular kit, called NUCLEO, allowing for easy interconnection with connectivity (BLE, Wi-Fi, Lo-Ra, etc) modules for IoT.

Taking into the account the above elaborated recent works, application scenarios and the enabling technology overview, following can be emphasized:

• - all kinds of services that are used to enable smart cities highly depend on the deployed hardware sensing infrastructure. Less infrastructure implies limited functionalities for given application scenarios. On contrary, many different application scenarios can be considered but this increases implementation and maintenance costs,
• - many different sensing techniques were proposed, and research community is intensively working to provide more reliable and cost-effective sensing technologies that can be easily implemented in IoT sensing nodes,
• - to enable different functionalities of the given application scenarios it is important to have the technology which can deliver sensed data on a greater distance, while preserving the energy in order to improve battery lifetime. For their products, many vendors specify 2–10 years of lifetime for their products, and it can be concluded that the battery lifetime depends on how frequently data is sensed and sent to the receiving station. Two-years span can certainly be considered as not enough, ten years’ horizon could be enough as by then, new technologies may arise and substitute currently implemented technologies. In any case, providing new technologies from any point of view: radios, MCUs, sensing techniques that can preserve battery lifetime is of crucial interest for both current and future IoT deployment,
• - currently available radios can fulfil today’s needs in terms of delivering data from remote areas in smart cities/villages. The NB-IoT, LoRa and Sigfox are overlapping in part, but can be considered as orthogonal for specific use-cases. Smart usage of given radios can further improve battery lifetime. However, it is always of the high interest to consume even less energy and provide larger communication distances and it provides the space for further analysis and technology improvements.

4. E-health – ambient assisted living systems

In recent years, the exploitation of new assisted living technologies has become necessary due to a rapidly aging society. In fact, it is estimated that 50% of the population in Europe will be over 60 years old in 2040, while in the USA it is estimated that one in every six citizens will be over 65 years old in 2020 ( Corchado et al., 2008 ). In addition, in 75-year-olds, the risk of Mild Cognitive Impairment (MCI) and frailty increases and people over 85 years of age usually require continuous monitoring. This suggests that taking care of elderly people is a challenging and very important issue. People with limited mobility are increasingly looking for innovative services that can help their daily activities. Ambient Assisted Living (AAL) encompasses technological systems to support people in their daily routine to allow an independent and safe lifestyle as long as possible. AAL (or simply assisted living) solutions can provide a positive influence on health and quality of life, especially with the elderly. An AAL approach is the way to guarantee better life conditions for the aged and people with limited mobility, chronic diseases and in recovery status with the development of innovative technologies and services.

Modern assistive technologies constitute a wide range of technological solutions aimed at improving the well-being of the elderly, Fig. 28 . These technologies are used for personalized medicine, smart health, health tracking, telehealth, health-as-a-service (HaaS), smart drugs and multiple other applications ( Maskeliunas et al., 2019 ).

IoT technology applications for AAL domain, ( Maskeliunas et al., 2019 ).

AAL technologies can also provide more safety for the elderly, offering emergency response mechanisms ( Lin et al., 2013 ), fall detection solutions ( Kong et al., 2018 ), and video surveillance systems ( Meinel et al., 2014 ). Other AAL technologies were designed in order to provide support in daily life, by monitoring the activities of daily living (ADL) ( Reena and Parameswari, 2019 ), by generating reminders ( Uribe et al., 2011 ), as well as by allowing older adults to connect with their families and medical staff. The recent advancements in mobile and wearable sensors helped the vision of AAL to become a reality. All novel mobile devices are equipped with different sensors such as accelerometers, gyroscopes, a Global Positioning System (GPS) and so on, which can be used for detecting user mobility. In the same way, recent advances in electronic and microelectromechanical sensor (MEMS) technology promise a new era of sensor technology for health ( Vohnout et al., 2010 ). Researchers have already developed noninvasive sensors in the form of patches, small holter-type devices, wearable devices, and smart garments to monitor health signals. For example, blood glucose, blood pressure, and cardiac activity can be measured through wearable sensors using techniques such as infrared or optical sensing. User localization is another key concept in AAL systems because it allows tracking, monitoring, and providing fine-grained location-based services for the elderly. While GPS is the most widespread and reliable technology to deal with outdoor localization issues, in indoor scenarios it has a limited usage due to its limited accuracy due to the impact of obstacles on the received signals. The number of alternative indoor positioning systems have been proposed in the literature ( Mainetti et al., 2014 ) that can be exploited in order to support AAL systems. Among all technologies, Bluetooth (BT) technology represents a valid alternative for indoor localization ( Yapeng et al., 2013 ) or specifically in museums ( Alletto et al., 2015 ). It is able to guarantee a low cost since it is integrated in most of daily used devices such as tablets and smart phones. The spread of the emerging Bluetooth Low Energy (BLE) technology makes the BT also energy-efficient, which is a key requirement in many indoor applications. An interesting investigation regarding the state-of-the-art and adaptive AAL platforms for older adult assistance was provided in ( Duarte et al., 2018 ). The authors present an overview of AAL platforms, development patterns, and main challenges in this domain.

In recent years, a large number of solutions have been proposed in the literature in order to create smart environments and applications to support elderly people. The main purpose is to provide a level of independence at home and improve elderly quality of life. In ( Dobre et al., 2018 ), an architecture which constitutes the base for the development of an integrated Internet of Things (IoT) platform to deliver non-intrusive monitoring and support for older adults to augment professional healthcare giving is presented, Fig. 29 . The proposed architecture integrates proven open-data analytics technology with innovative user-driven IoT devices to assist caregivers and provide smart care for older adults at out-patients clinics and outdoors.

Proposed modular architecture, ( Dobre et al., 2018 ).

A solution for monitoring patients with specific diseases such as diabetes using mobile devices is discussed in ( Villarreal et al., 2014 ). The proposed system provides continuous monitoring and real time services, collecting the information from healthcare and monitoring devices located in the home environment which are connected to BT mobile devices. The sensor data are transmitted to a central database for medical server evaluation and monitoring via 3G and Wi-Fi networks. An ad hoc application, installed on a mobile phone, allows the remote control of a patient’s health status whilst the patient can receive any notifications from the health care professionals via the application running on her/his mobile phone, Fig. 30 .

Proposed system for continuous monitoring and real time services, ( Villarreal et al., 2014 ).

The work ( Villarrubia et al., 2014 ) proposes a monitoring and tracking system for people with medical problems whose system architecture is shown in Fig. 31 . The solution includes a system for performing biomedical measurements, locomotor activity monitoring through accelerometers and Wi-Fi networks. The interactive approach involves the user, through a smart TV. The locomotor activity of the elderly is deduced through the analysis of Received Signal Strength Indication (RSSI) measurements, i.e. through an algorithm, the received signal power from different access points located in the house is determined. Mobile accelerometers are used to analyze the movement of users and detect steps. Single board computers, such as Raspberry Pi, are used to collect data coming from the different sensors wirelessly connected to obtain real-time context-aware information such as gas, temperature, fire, etc. or to get information from biomedical sensors such as, oxygen meter, blood pressure, ECG, accelerometer, etc. The Raspberry Pi can be connected to a TV to transmit warnings or notifications coming from health care professionals.

Virtual organization of system, ( Villarrubia et al., 2014 ).

The work ( Mainetti et al., 2016 ) proposes an AAL system for elderly assistance applications able to provide both outdoor and indoor localization by using a single wearable device. A prototypal device has been developed exploiting GPS technology for outdoor localization and BLE technology for indoor localization. The proposed system is also able to collect all information coming from heterogeneous sensors and forward it towards a remote service that is able to trigger events (e.g., push notifications to families or caregivers and notifications to the same indoor environment that will change its status). In an enriched work ( Mainetti et al., 2017 ), presents an architecture that exploits IoT technologies to capture personal data for automatically recognizing changes in the behaviour of elderly people in an unobtrusive, low-cost and low-power manner, Fig. 32 . The system allows performing a behavioral analysis of elderly people to prevent the occurrence of MCI and frailty problems.

Overall logical architecture ( Mainetti et al., 2017 ).

Based on the recent analysed research works on the use of IoT technologies in the e-health and for the creation of AAL systems, it is possible to draw the following general observations:

• - an extensive research is aimed at creating AAL systems intended primarily for the elderly or for people with physical or mental diseases,
• - current challenges deal with the use of IoT technologies in order to capture the habits of the people monitored both in indoor and outdoor environments for behavioral analysis purposes. The behavioral analysis can be useful for monitoring people, scheduling interventions and providing notifications directly to the user,
• - increasing efforts are needed in order to unobtrusively capture habits by favoring the use of wearable devices.

5. IoT technologies in Transportation and Low Carbon Products

The issue of security and traceability of goods is increasingly important in the logistics sector, with repercussions in terms of supply chain management and goods transport. In this case, information technologies and in particular the IoT can offer valuable support, increasing the degree of visibility and control over the entire supply chain. Transportation is a good example of how IoT technologies can bring value. In fact, this sector needs systems that on the one hand allow for the planning, management and optimization of flows (both along the supply chain and within complex logistics hubs such as intermodal ones) and, on the other hand, allow for the traceability of goods (products or containers) in real time along the entire supply chain. A further requirement concerns the check of goods integrity. In this context, it is clear how IoT technologies can contribute to the remote monitoring of flows and assets, providing a series of information useful for their management and optimization. This is possible through identification (e.g., via RFID or barcode), location (e.g., via GPS), monitoring of parameters and status variables of the assets (e.g., via sensors) and their transmission (e.g., via Wi-Fi or GSM/GPRS network).

The advent of IoT technologies allows to organize, automate and control processes remotely and from any device connected to the Internet. By definition, an efficient supply chain is responsible for delivering the goods, from the manufacturer to the end user, at the agreed time and under the specified conditions. Through the use of IoT technologies, it is possible to track the entire process in real time, promoting speed and efficiency in automated processes, reducing time and personnel costs. IoT technologies such as sensors, embedded and mobile devices, and cloud storage systems allow for the connection of “things” (warehouses, vehicles or goods) to the Internet so that the manufacturer, the logistics service provider and even the end user can thoroughly know at any time the status of products, their location and estimated delivery time.

Logistics can benefit from the use of IoT technologies in all the following sectors:

• • efficient inventory and warehouse management
• • automation of internal business processes
• • fast and efficient delivery of products (e.g., route planning)
• • conservation and quality of transported goods (e.g., monitoring of cold chain)
• • location, monitoring and tracking of vehicle fleets
• • interactive communication between vehicles and manufacturers/distributors of goods
• • certification of both deliveries and transport phases

The basic principles of logistics always remain valid: transfer the right product, in the right quantity and condition, at the right time and right price, in the right place and to the right customer. As carrying out each of these tasks has become much more complicated in an increasingly globalized and interconnected world, the need for innovative solutions to achieve these objectives also increases. As mentioned above, the IoT is revolutionizing the logistics sector, offering many advantages and opportunities. Supply chain monitoring, vehicle tracking, inventory management, secure transport and process automation are the cornerstones of IoT applications as well as the main elements of interconnected logistics systems.

In the logistics sector, the IoT allows creating smart location management systems, which allow companies to easily monitor driver activities, vehicle location and delivery status, ( Brincat et al., 2019 ). This solution is indispensable in the planning of deliveries and the organization of timetables and reservations. It is possible to detect any changes in real time and this is precisely the reason behind the success of the IoT: the ability to improve the management of good movement and therefore streamline business processes. Inventory and warehouse management is another important element of the connected logistics ecosystem. The positioning of small sensors allows companies to easily track items in warehouses, monitor their status, position and create a smart control system. In fact, with the help of IoT technology, employees will be able to successfully prevent any loss, ensure the safe storage of goods and efficiently locate the product needed. Even the minimization of human error becomes possible thanks to the IoT. In this scenario ( Wang et al., 2015 ), proposes a layered architecture for the realization of an automation enterprise asset management system using IoT and RFID technologies, Fig. 33 .

Layered architecture of proposed automation enterprise asset management system ( Wang et al., 2015 ).

The sustainable and IoT supported business model was discussed in ( Gao and Li, 2020 ) for the case of the bike-sharing services. Novel framework was developed that links sustainable indicators as well as social aspects of the business concept. The case studies for dockless bike-sharing services were discussed and presented for China and UK. Practical findings extended knowledge needed for improvement of the sharing economy to achieve sustainably goals through IoT enabled support. The work ( Zhang et al., 2016 ) proposes an inventory management system for a warehousing company. The system adopts the concept of IoT using RFID technology to track the material and provide messages or warnings when incorrect behaviors are detected. In particular, it integrates RFID technology and a self-Adaptive distributed decision support model for inbound and outbound actives, inventory location suggestions and incident handling. In ( Guptha et al., 2018 ), the authors design an IoT architecture for order picking processes in a warehouse that allows the inventory real time tracking and visibility into the reduction of warehouse operation costs, improved safety and reduced theft. IoT and RFID technologies are again exploited in ( Valente et al., 2017 ) to improve productivity in the value chain of a steel mill. In this work, an existing RFID solution architecture based on the reference EPCGlobal/GS1 framework was modified in order to be extended to the IoT domain, Fig. 34 .

RFID/IoT solution architecture for steel mill (Valente et al., 2017).

The internet-connected devices collect large amounts of data which can be transmitted to a central system for further analysis. In this context, the integration between IoT and predictive analysis systems can help companies to create effective business development strategies, improve decision-making and manage risks. In the logistics sector, this integration finds application to plan routes and deliveries as well as identify various defects before something goes wrong. An integrated framework to track and monitor shipped packages, Fig. 29 was proposed in ( Proto et al., 2020 ). Framework relies on a network of IoT-enabled devices, called REDTags, allowing courier employees to easily collect the status of package at each delivery step. The framework provides back-end functionalities for smart data transmission, management, storage, and analytics. A machine-learning process is included to promptly analyze the features describing event-related data to predict the potential breaks of goods in the packages ( Fig. 35 ).

Framework architecture, ( Proto et al., 2020 ).

Ensuring product quality and integrity is an interesting challenge that in recent years has led to the creation of smart systems that integrate IoT solutions and block chain technology. The Blockchain technology associated with IoT sensors could allow the creation of a temporal “stamp” inside which a series of information is kept such as product delivery date, product characteristics and status, and origin of product. By positioning the sensors, for example, it is possible to monitor parameters such as product temperature and humidity, vehicle position and phases of the transport process and save this data in the block chain. Block chain infrastructure can also revolutionize company logistics in the field of document management (i.e., invoices, transport documents, etc.), traceability of goods (origin of products, monitoring of vehicle fleets, etc.), and play a substantial role in fighting counterfeiting. Imeri and Khadraoui (2018) showed a conceptual approach to the security and traceability of shared information in the process of dangerous goods transportation using block chain technology based on smart contracts. IoT and block chain technologies are exploited in ( Arumugam et al., 2018 ) where a smart logistics solution encapsulating smart contracts, logistics planner and condition monitoring of the assets in the supply chain management area is presented, Fig. 36 . Moreover, a prototype of the proposed solution is implemented.

High-level architecture of proposed solution, ( Arumugam et al., 2018 ).

The block chain-IoT-based food traceability system (BIFTS) to integrate the novel deployment of block chain, IoT technology, and fuzzy logic into a total traceability shelf life management system for the managing of perishable food, Fig. 37 was proposed in ( Tsang et al., 2019 ). Challenges in the adoption of the proposed framework in the food industry are analysed and future research planned to improve the proposed work.

Modular framework of BIFTS, ( Tsang et al., 2019 ).

Taking into account above discusses recent research findings further main findings could be highlighted:

• - The studies analysed previously show how the hardware and software technologies enabling the Internet of Things are leading to a digital transformation process that aims at an intelligent and advanced management of the entire logistics and transportation system.
• - The main scientific challenges in this field aim to use sensors in order to monitor the status of the goods transported, to ensure traceability and above all to safely and reliably collect telemetry data and offer them to Artificial Intelligence modules for advanced processing.
• - Furthermore, recently the interest has focused on the next generation of blockchain systems (the so-called blockchain 3.0) which aims to apply the benefits of the classic blockchain in typical scenarios of the Internet of Things, such as logistic and transportations.

6. Concluding remarks and future directions in the field

This review paper discussed and presented latest research findings that were included within the JCELPRO VSI SpliTech2019 and dedicated to the 4th International Conference on Smart and Sustainable Technologies (SpliTech 2019). The contributions as well as herein presented knowledge is summarized and discussed in upcoming sections.

The Intense digitalization in recent years has allowed for different technological possibilities that have already gradually been changing the main economic sectors and societies in general. Digitalization in different economic sectors enabled various possibilities for advancements and for a more efficient utilization of limited resources, systems or processes. The main driver for an efficient digitalization in various sectors is information technology, i.e., IoT supported smart technologies. In the previous sense, the energy sector is one of the key sectors where ‘‘energy digitalization’’ has already been rapidly developing in various energy related fields. Currently, one of the most progressing implementation areas of IoT technologies is related to the energy sector. The developing solutions are focused on smart homes, i.e. advanced automatization of home energy systems, development of smart and adaptive micro-grids, or advancements in efficient demand-side management of power systems. A circular economy concept has also been intensively worked on where various concepts have been investigated, which can support smart waste management and help bridge one of the main challenges in society. Recently, different concepts have been tested where IoT technologies could be used for environmental protection, primarily for the monitoring of air quality, which is a big potential in that sense.

Healthcare systems can also be significantly improved with the application of IoT devices, i.e. via the E-health concept. An improved quality of services and patient safety could be enabled with an advanced IoT supported monitoring system. The prediction of life threatening states could be efficiently detected with a better treatment of patients, such as timely therapy decisions and qualitative rehabilitation. In general, large healthcare systems could also benefit from IoT, both in efficiency and from a cost aspect, which is important for hospitals. The current pandemic state with COVID-19 allowed for the consideration of different IoT applications or devices that could help in efficiently monitoring and controlling the pandemic, which proves the added value of IoT products.

The transportation sector is currently in gradual transition where a mix of transportation vehicle technologies is expected in upcoming decades with the involvement of electric vehicles primarily along with hybrid or hydrogen based vehicles. The main advancements of IoT in transportation are the support of the smart car concept where different vehicle operating parameters can be monitored in an efficient manner. The main advantage is early detection of severe failures, then regular maintenance, improved fuelling and finally improvement of safety and driving experience in general. The most challenging IoT application area is in the case of autonomous vehicles, where safety is the main goal and in that sense, significant research advancements are expected to occur in the near future.

The smart city concept is the most progressing IoT application area since cities have been vastly populated, which causes severe infrastructural issues. The main benefit of IoT technologies in the smart city concept is to bridge severe infrastructural challenges in highly populated cities. The improvement of life quality in cities is also expected thanks to the efficiency improvement of various convectional services in cities. The early detection of various and common daily problems in cities could be efficiently solved with IoT as with transportation issues, energy and water shortage supplies, security issues, etc. The biggest challenge in the smart city concept is directed to the efficient networking and operation of different sensing technologies, which must be followed with the proper education of the population.

Each technology that is rapidly progressing has got specific potential drawbacks that need to be carefully analysed and addressed. Since IoT devices are measured in billions, and with large potential impacts on the population, specific challenges need to be addressed, which were detected based on the herein conducted review. The main goal is to secure a sustainable and balanced development of IoT technologies. Therefore, further issues are briefly discussed below and should be carefully considered during the further development of IoT technologies:

• - the rapid development of IoT technologies causes fast consumption of raw materials to produce different electronic devices where unfortunately some of raw materials are already rare or becoming,
• - electronic devices are becoming more economically acceptable where a potentially large population would be affected. High production volumes are expected which can finally cause a rebound effect and a more rapid unwanted utilization of already limited resources,
• - the sustainability aspect and long-term effects of IoT technologies are not clear and insufficiently investigated. A noticeable amount of energy would be needed to operate IoT devices and the electronic industry is leaving different unfavourable environmental footprints that also need to be carefully investigated,
• - electronic waste will become one of the major issues caused with the planned rise of IoT products. Recycling rates must be improved and better e-waste management should be secured,
• - IoT technologies can cause social impacts in specific industrial branches or businesses since working labour could be reduced and direct social contacts have also been reduced. In that sense, the application of IoT technologies should be carefully considered taking the raised issues into account,
• - significant advancements in both specific electronic components as well as user-friendly software solutions are required,
• - further development in sensing technologies and advanced data acquisition systems is also required,
• - the minimization of energy consumption in IoT devices is a crucial target, i.e. reduction of energy supply.

From the herein addressed recent research findings within the VSI SpliTech 2019, it is obvious that developments in various IoT application sectors are promising but further advancements are expected and that are mainly focused on maximizing the efficiency of specific IoT supported processes or technologies, minimizing resource utilization (raw materials and energy) and environmental footprints. IoT technologies are an opportunity for humanity and can bring important as well as useful benefits to the population. The authors contributions within the JCLEPRO VSI SpliTech2019 provided quality discussion and presentation of the latest advancements in the field, and most important, they contributed to the better understanding of IoT application areas, technological possibilities, but also potential drawbacks and issues that should be carefully monitored in future terms. The crucial and important aspects are linked with sustainability where the rapid developments in IoT technologies must be carefully monitored from a resource and environmental point of view to ensure balanced and sustainable development of IoT products. Herein presented knowledge and published works in the Journal of Cleaner Production are serving as important foundations for researchers dealing with this challenging and dynamic research field.

CRediT authorship contribution statement

Sandro Nižetić: Conceptualization, Methodology, Supervision. Petar Šolić: Conceptualization, Methodology, Supervision. Diego López-de-Ipiña González-de-Artaza: Supervision. Luigi Patrono: Conceptualization, Methodology, Supervision.

Declaration of competing interest

We wish to confirm that there are no known conflicts of interest associated with this publication in Journal of Cleaner Production ( Internet of Things (IoT): Opportunities, issues and challenges towards a smart and sustainable future ) and there has been no significant financial support for this work that could have influenced its outcome.

We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us.

We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property.

We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author and which has been configured to accept email from ( [email protected] ).

Acknowledgments

This work has been supported in part by Croatian Science Foundation under the project “Internet of Things: Research and Applications”, UIP-2017-05-4206, Croatia.

Handling editor: Cecilia Maria Villas Bôas de Almeida

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