Vehicular ad-hoc networks (VANETs) play an important role in intelligent transportation systems for improving security and efficiency. However, due to dynamic characteristics of the vehicular environment, routing remains a significant challenge in the VANETs. While single-layer routing protocols based on the traditional layered open systems interconnection (OSI) model are readily available, they often do not make use of important parameters at the lower three layers of the OSI model when making routing decision. Hence, for making optimal routing decision to gain superior network performance, there is a need to design cross-layer routing that allows information exchange between layers. In this article, a survey of the existing single-layer and cross-layer routing techniques in VANETs is presented, emphasizing on cross-layer routing protocols that utilize information at the physical, medium access control and network layers as routing parameters. An overview and challenges of routing are given, followed by a brief discussion of single-layer routing with more focus on geographic routing. Cross-layer routing protocols are then discussed in detail. The article then elaborates on some advantages and disadvantages of the existing routing approaches, cross-layer routing parameter selection and cross-layer design issues. Finally, some open research challenges in developing efficient routing protocols in the VANETs are highlighted.

Internet of Things (IoT) is the paramount virtual network that enables remote users to access connected multimedia devices. It has dragged the attention of the community because it encompasses real-world scenarios with implicit environs. Despite several beneficial aspects, IoT is surrounded by provocations for successful implementation, as data travels in different layers. One of the critical challenges is the security of the data in these layers. Researchers conducted numerous studies focusing on the level of security at a single technique, creating loopholes to address the entire scenario of securing an IoT network. This study aims to comprehensively review current security issues, wireless communication techniques, and technologies for securing IoT. This work’s utmost significance is addressing all the security perspectives at a glance. For this purpose, research contributions from the previous years are investigated for better understanding. Some countermeasures and snags from security perspectives have also been analyzed in detail concerning the current industry trends. Blockchain, machine learning, fog, and edge computing are possible solutions to secure IoT. After studying these techniques and their immunity to attacks, machine learning can become a hope if incorporated with end-to-end security. This comprehensive review will provide adequate understanding and knowledge in defining security lines of action for the successful implementation of IoT.

Communication in industrial wireless networks necessitates reliability and precision. Besides, the existence of interference or traffic in the network must not affect the estimated network properties. Therefore, data packets have to be sent within a certain time frame and over a reliable connection. However, the working scenarios and the characteristics of the network itself make it vulnerable to node or link faults, which impact the transmission reliability and overall performance. This article aims to introduce a developed multipath routing model, which leads to cost-effective planning, low latency and high reliability of industrial wireless mesh networks, such as the WirelessHART networks. The multipath routing model has three primary paths, and each path has a backup node. The backup node stores the data transmitted by the parent node to grant communication continuity when primary nodes fail. The multipath routing model is developed based on optimal network planning and deployment algorithm. Simulations were conducted on a WirelessHART simulator using Network Simulator (NS2). The performance of the developed model is compared with the state-of-the-art. The obtained results reveal a significant reduction in the average network latency, low power consumption, better improvement in expected network lifetime, and enhanced packet delivery ratio which improve network reliability.

The placement of wireless mesh routers is a significant matter in enhancing the performance of a wireless mesh network. Therefore, it is essential that the mesh routers are optimally placed to guarantee strong connectivity and coverage for ensuring the best network accessibility. The importance of this issue has motivated the researchers to pursue more investigation on optimizing the networks’ performance. Various optimization algorithms have been developed in the literature to identify the trade-offs between network connectivity and client coverage. This work is aimed at implementing a novel application of Harris Hawk’s Optimization (HHO) algorithm to optimally place mesh routers in a wireless mesh network so as to improve connectivity and coverage. The HHO seeks optimal routers placement that leads to maximizing the connection between routers and increasing the number of covered clients. In this study, three network configurations are used with sizes of 40, 60, and 100 mesh routers. The simulation results are statistically analyzed and compared to other population-based algorithms such as Sine Cosine Algorithm (SCA), Gray Wolf’s Optimization (GWO), and Particle Swarm Optimization (PSO). Moreover, the performance of HHO is compared with the state-of-the-art to validate the effectiveness of the proposed approach. The simulation findings and statistical analysis confirm that the HHO outperforms the other algorithms in terms of network coverage and connectivity. The outcomes demonstrate that HHO can be considered an efficacious means to enhance the performance of wireless mesh networks (WMNs).

Evaporation ducts (ED), which are caused by a rapid decrease in the refractive index of the lower atmosphere, are known to trap radio waves between the evaporation duct layer and the sea surface. Although signal propagation and refractivity estimation in evaporation ducts have been well studied, the fading characteristics of ED must be accurately established to help determine fade margin, required for a reliable wireless communication link. In this paper, based on the percentage of occurrences of evaporation ducts, that have been measured and reported in the literature, the statistical distribution of path loss in the South China Sea is calculated for varying distances. These path loss distributions are weather-dependent and time-varying and define several slow time-varying fading characteristics. These slow fading characteristics are, what can be termed as log-lognormal in nature. Propagation in ED, being non-line-of-sight, also has a fast-fading component that is Rayleigh in nature. Once, the complete fading characteristics are known, the overall fade margin due in part; to both slow fading and fast fading can be obtained. For a distance of 100 km, approximately 99% availability can be obtained with an 88-dB fade margin while for a shorter distance of 50 km, the required total margin for 99% availability is only 50-dB.