Security and latency are crucial aspects in the design of future wireless networks. Physical layer security (PLS) has received a growing interest from the research community in recent years for its ability to safeguard data confidentiality without relying on key distribution or encryption/decryption, and for its latency advantage over bit-level cryptographic techniques. However, the evolution towards the fifth generation (5G) technology and beyond poses new security challenges that must be addressed in order to fulfill the unprecedented performance requirements of future wireless communication networks. Among the potential key-enabling technologies, reconfigurable intelligent surface (RIS) has attracted extensive attention due to its ability to proactively and intelligently reconfigure the wireless propagation environment to combat dynamic wireless channel impairments. Consequently, the RIS technology can be adopted to improve the information-theoretic security of both radio frequency (RF) and optical wireless communications (OWC) systems. It is worth noting that the configuration of RIS in RF communications is different from the one in optical systems at many levels (e.g., RIS materials, signal characteristics, and functionalities). This survey paper provides a comprehensive overview of the information-theoretic security of RIS-based RF and optical systems. The article first discusses the fundamental concepts of PLS and RIS technologies, followed by their combination in both RF and OWC systems. Subsequently, some optimization techniques are presented in the context of the underlying system model, followed by an assessment of the impact of RIS-assisted PLS through a comprehensive performance analysis. Given that the computational complexity of future communication systems that adopt RIS-assisted PLS is likely to increase rapidly as the number of interactions between the users and infrastructure grows, machine learning (ML) is seen as a promising approach to address this complexity issue while sustaining or improving the network performance. A discussion of recent research studies on RIS-assisted PLS-based systems embedded with ML is presented. Furthermore, some important open research challenges are proposed and discussed to provide insightful future research directions, with the aim of moving a step closer towards the development and implementation of the forthcoming sixth-generation (6G) wireless technology.

This letter investigates a reconfigurable intelligent surfaces (RIS)-aided wireless communication system in an inband underlay Device-to-Device (D2D) communication, where the direct link between D2D users is unavailable. An RIS is used to adjust its reflecting elements to enhance the D2D communication data transmission while improving the cellular network's secrecy performance concurrently. Specifically, analytical results for the secrecy outage probability and the probability of non-zero secrecy capacity are derived for the cellular network. Moreover, the D2D outage probability is also provided. Simulation and analytical results are presented to verify the derived expressions' correctness and the effectiveness of the proposed scenario. Moreover, the asymptotic results are presented.

Network coding and opportunistic routing are two recognized innovative ideas to improve the performance of wireless networks by utilizing the broadcast nature of the wireless medium. In the last decade, there has been considerable research on how to synergize inter-flow network coding and opportunistic routing in a single joint protocol outperforming each in any scenario. This paper explains the motivation behind the integration of these two techniques, and highlights certain scenarios in which the joint approach may even degrade the performance, emphasizing the fact that their synergistic effect cannot be accomplished with a naive and perfunctory combination. This survey paper also provides a comprehensive taxonomy of the joint protocols in terms of their fundamental components and associated challenges, and compares existing joint protocols. We also present concluding remarks along with an outline of future research directions.

Reconfigurable intelligent surface (RIS) technology is considered one of the leading technologies for sixth-generation wireless communication, and it has also been revealed to be effective in enhancing secure and reliable communications. This article investigates using RIS to improve physical layer security and data transmission in underlay cognitive radio networks (CRNs). Because of its capability to control the wireless environment, RIS can enhance the security of the primary network (PN) and increase the reliability of the secondary network (SN) data transmission. This approach is practical and beneficial for both the PN and SN in terms of reliability and security. The study focuses on a scenario where the eavesdropper is passive and uses either selection or maximal ratio combining to combine the signals from the PN. Analytical expressions for the secrecy outage probability and the probability of nonzero secrecy capacity of the PN are derived. Additionally, an expression for the SN outage probability is also provided. The results from simulations and the numerical analysis confirm the benefits of the proposed system model and validate the accuracy of the derived expressions. This work provides valuable insights into the integration of RIS with CRNs and highlights the potential role of RIS in the future of wireless communication systems.

In this paper, we study the underlay relay-aided Device-to-Device (D2D) communications to improve the physical layer (PHY) security of the cellular network. We propose a cooperative scheme, whereby the D2D pair, in return of being allowed to share the spectrum band of the cellular network, serves as a friendly jammer, through its multiple-input multiple-output relay, to degrade the wiretapped signal at an eavesdropper. This paper aims to show that spectrum sharing is advantageous for both D2D communications and cellular networks with respect to reliability and robustness for the former, and the physical layer security enhancement for the latter. To assess the proposed cooperative system model, closed-form expressions for the D2D outage probability, the secrecy outage probability, and the probability of non-zero secrecy capacity are derived. More importantly, the benefits due to the cooperation scheme are verified through numerical and simulation results.

Smart ambulance is a novel system where modern communication, computation, and sensing technologies are employed to revolutionize ambulance and emergency systems. We propose a smart system that aims to minimize the ambulance response time, travel time from patient’s location to the hospital, and the waiting time at the hospital. We utilize the road traffic conditions and hospital loading information (collected in real-time basis) to make optimal decisions (which hospital responds to the patient’s request and which ambulance it sends, which route the ambulance takes to reach the patient, which hospital the ambulance heads to after picking up the patient, and which route it should take to the selected hospital). The first two decisions are used to minimize the response time while the last two decisions are employed to minimize the door-to-needle time. We analyze the performance of the proposed algorithm; both analytically and by simulation for verification. The results showed very good consistency between simulation results and analytical results, which confirms the correctness and accuracy of the analysis. In addition, we compare the performance of our proposed smart algorithm with a previous algorithm that is reported in the literature and that minimizes the drop-off delay. The results confirmed the superiority of our smart algorithm under considered operating conditions and scenarios.