Table 9.

Contributions and limitation of the literature.

Reference	Title of Article	Proposed Solution	Limitations and Future Work
Sharma et al. [9]	Enhancement of relay nodes communication approach in WSN-IoT for underground coal mine	They designed relay node structures for a wireless sensor network and load balancing to improve network lifetime parameters. They designed an IoT-based WSN to provide advance warning of any natural disaster in coal mines.	There were several analysis parameters to analyze the networks, such as network lifetime, communication and transmission cost, energy consumption, and coverage of the whole area.
Faheem et al. [49]	Bio-inspired routing protocol for WSN-based smart grid applications in the context of Industry 4.0	They designed a comprehensive, optimized, and QoS monitoring multi-hop network system for real-time data transmission in Industry 4.0. This self-optimized smart routing protocol (SIRP) was efficiently used for WSN-based SG applications.	In the future, they will attempt to enhance their developed SIRP routing scheme and communications architecture to collect QoS-aware data for different WSN-based smart grid applications with little data redundancy.
Arslan et al. [52]	IoT and wireless sensor network-based autonomous farming robot	They developed a computer vision-based algorithm used for the classification of weed and a non-image. Wireless sensor nodes detect weed images through image processing methods and gather light, temperature, humidity, and moisture data.	The limitation of this work is that they did not provide any GUI or mobile application control to work robot autonomously.
Chen et al. [53]	Efficient and secure three-party mutual authentication key agreement protocol for WSN in IoT environments	They proposed a practical and secure approach to merge IoT and WSN. Their scheme had high performance, low communication, and computational costs, low energy consumption, and provided effective authentication of the user in IoT.	The limitation of this study is that they did not provide a solution to the security threats in a heterogeneous IoT environment. In the future, they will evaluate the reliability and scalability of their systems of heterogeneous environments.
Rathee et al. [102]	A secure IoT sensors communication in Industry 4.0 using blockchain technology	Wireless sensor network security improved using blockchain and compared security metrics. &It ensured confidentiality and responsibility and tracked each sensor’s operation. The blockchain was used to store IoT artifacts and sensors.	The developed IoT sensor takes time to test a single block before it is put to the blockchain.
Mellado et al. [103]	Prediction of satellite shadowing in smart cities with application to IoT	The technology had a minimal processing load. It was highly desirable to create a coverage map that can optimize network resources in satellites.	There is a lack of evaluation of requirements for satellite-based IoT and output connectivity protocols through simulations in actual situations.
Garg et al. [101]	Towards secure and provable authentication for the internet of things: realizing Industry 4.0	The effectiveness of the developed protocol was evaluated with frequently utilized AVISPA, PUFs, and ECC encryption algorithms. A proposed technique was developed to create a durable, stable, and efficient user architecture that promotes shared authentication for IoT and server nodes and is resistant to cyber threats.	This protocol is for academic and research purposes only, and its implementation has not yet been tested in the real world.
Behera et al. [104]	Residual energy-based cluster-head selection in WSN for IoT application	The method takes into account the intended value of initial energy, residual energy, and cluster heads to choose the specific set of cluster heads in the network that adapts IoT applications to maximize flow, durability, and residual energy.	They did not review existing path selection factors in a node mobility network that altered its role constantly.
Wan  et al.  [105]	Software-defined industrial Internet of Things in the context of industry 4.0	They proposed a new idea of information interaction in Industry 4.0 using software-defined IIoT. They enhanced the network size using IIoT. The IIoT architecture manages physical devices and information exchange methods via a customized networking protocol.	The limitation of the study is the effective coordination between IIoT where the network is heterogeneous for transmission of information.
Tan et al. [106]	Application of IoT-aided simulation to manufacturing systems in cyber-physical systems	They discussed the construction and implementation methods of digital twin (DT). In this study also explained the issues involved in developing DT with the help of IoT manufacturing devices. DT is the simulation tool that can gather and synchronize data for the real world to a real-time environment.	The absence of experimentation and optimization in predicting future locations or results are other essential aspects of DT.
Rahman et al. [107]	DistB-SDoIndustry: enhancing security in Industry 4.0 services based on the distributed blockchain through software-defined networking-IoT enabled architecture	In this work, the authors develop a distributed blockchain-based security system integrated with the help of IoT and SDN. Blockchain is used for data security and confidentiality, while SDN-IoT incorporates sensor networks and IoT devices to improve the security services in Industry 4.0.	Limitations of this study are that the developed model SDN-IoT was still in the initial stage, so it was not able to detect different types of risks, such as service denial (DoS) and flood attack and packet filtering. The developed system had no proper GUI, so the throughput, packet arrival time, and response time were rarely challenging to analyze.
Haque et al. [108]	Comparative study of IoT-based topology maintenance protocol in a wireless sensor network for structural health monitoring	They developed a computer-based monitoring system to analyze the vibration or earthquake measurement. WSN are used to sense structural damages and identify their pinpoint location. They also proposed a topology-based maintenance system to analyze network architecture. Their system was an energy-efficient system that automatically turned off nodes where no traffic was detected.	The limitation of this study is that WSN nodes are not capable enough to provide scalability for large coverage areas.
Wan et al. [109]	Toward dynamic resources management for IoT-based manufacturing	To build a fully interactive environment and dynamic management of resources, an ontology-based technology, SDN, communication technology device to device combined with ontology modeling and multi-agency technology were used to accomplish sophisticated administration of resources. They solved load secluding problems using Jena logic reasoning and contract-net protocol-based technology in Industry 4.0.	The limitation of this work was the high time complexity of the load balancing algorithm to complete the task efficiently. It was challenging to refine the process due to the complex nature of multi-agent technology, and referencing rules were much more complex.
Bulaghi et al. [110]	SENET: a novel architecture for IoT-based body sensor networks	Multiple algorithms, such as particle swarm optimization (PSO), ant colony optimization (ACO), and genetic algorithms (GA) were used to save energy of WSN. They evaluated WSN energy consumption using optimization algorithms and calculated the total number of uncovered points, their stability, and dependability.	The design meets some disadvantages and does not work in real-time data.
Thiago et al. [111]	A comprehensive dependability model for QoM-aware Industrial WSN	When performing visual area coverage in occluded scenarios. They proposed a mathematical model named quality of monitoring parameter (QoM) to assess the dependability of WSN, their availability, and reliability considering hardware, networking, and visual coverage failures.	Their developed method was inefficient at analyzing the system’s dependability in real-time applications due to failures or repairs happening as soon.
Patricia et al. [112]	Wireless sensor network combined with cloud computing for air quality monitoring	They designed a small size, low cost, and efficient system to monitor the air quality using wireless sensor nodes. They performed multiple algorithms such as multi-layer perceptron, SVM, and PCA to discriminate and quantify the volatile organic compounds.	The limitation of this study is that sensor nodes are less efficient at covering a large area to monitor and cannot do real-time testing and the field measurements of sensors.
Li et al. [113]	Edge computing-enabled wireless sensor networks for multiple data collection tasks in smart agriculture	They designed a data collection algorithm considering data quality factors in smart agriculture. Then modeled the data collection process by merging WSN and IoT.	The developed edge computing driven framework [47] and data collection algorithm were not capable of collecting data in a real agriculture environment.
Kumar et al. [114]	Cluster centroid-based energy-efficient routing protocol for WSN-assisted IoT	They developed a system that was capable of self-organization of local nodes to save energy. Their system adopted new algorithms to rotate head clusters based on centroid locations in IoT using WSN. The technique exceeds conventional protocols for efficiency criteria, such as the consumption of energy by the network, intermediate sensor node, packet distribution ratio, packet failure percentage, and network output. Their work was best for the base station located in the network.	The routing protocol was not optimal, routing strategies were lacking, and packet loss was caused if the base stations were even in the network. In the future, they will enhance this work by using a multi-hop path strategy to the base station. In this technique, the cluster head will transmit data to the base station, even outside the network.
Haseeb et al. [115]	An energy-efficient and secure IoT-based WSN framework: an application to smart agriculture	They proposed an IoT-based WSN framework that collected data from agriculture and transmitted it to the nearest base station. They enhanced network throughput, low latency rate, energy consumption, and packet drop ratio. They also provided security to the data transmission channel using the recurrence of the linear generator.	The limitation of this work is that they did not assess the device consistency in a mobile IoT. Therefore, they will analyze the performance and reliability of developed frameworks in the transportation system and mobile-based IoT network.