PERFORMANCE AND PHYSICAL LAYER SECURITY OF RF AND FSO LINKS FOR 5G WIRELESS-POWERED NETWORKS AND BEYOND

Abstract

The introduction of high-speed wireless technologies has fueled the growth of the number of potential mobile users at a rapid pace, leading to the escalation in demand for energy efficiency and reliability in wireless communication. Meeting these demands is the major challenge for the design engineer in designing wireless systems over error-prone wireless radio channels due to the crucial constraints, including scarcity in spectrum and openness and harshness in channel nature. Therefore, it is a primary requirement to accurately characterize the fading in wireless radio channels to design the system and enhance system performance. The signal propagation mechanism formed by both the multipath and shadowed effects may induce fading after interacting with the transmitted signal. The receiver can take advantage of fading by estimating the channel parameters to detect the transmitted symbols. However, the perfect channel estimation cannot be feasible in practical wireless systems. This fading creates severe problems in long-distance wireless systems where multipath fading is superimposed on shadowing fading, referred to as composite multipath/shadowing fading. Several fading distribution functions have been proposed to encapsulate these channel disturbances, highlighting the statistical characteristics of channel behavior and allowing us to further investigate the information-theoretic aspects of communication over the radio channels. On the other hand, the fading-induced effects can be trounced by deploying fiber optic-based links between transmitters and receivers. However, broad-scale implementation of these technologies is constrained by high deployment costs, especially where they are deployed in high-density urban and rugged areas (for example, the area surrounded by solid rocks and mountains) for backhaul connections. Therefore, free-space optical (FSO) communication has been considered a cost-effective and wide-bandwidth solution for next-generation backhaul networks compared to traditional backhaul solutions. FSO links are contemplated as a potential paradigm to yield efficient point-to-point communication in wireless systems. Notably, these links provide proficient wireless connectivity between the radio frequency wireless network and the fiber optic-based network. However, FSO links are sensitive to various impairments, including fading induce by atmospheric turbulence, path loss, and pointing errors. Moreover, the inherent openness of wireless mediums induced more concerns about information security and the privacy of the users. Therefore, the investigation into the performance of physical layer secrecy is increasingly becoming the center of attention of recent studies. Physical layer security (PLS) is the pivotal notion of enhancing the secrecy of mobile communication wireless networks against malicious abuses and security attacks by utilizing the intrinsic randomness of the wireless channel. The thesis aims to provide a novel mathematical framework to examine the fundamental performance of the RF and mixed FSO-RF systems. Moreover, the thesis contributes towards the enhancement of the physical layer secrecy of wireless communication and privacy of the intended users. Firstly, the system performance is investigated over combined (time-shared) shadowed (i.e., Nakagami-m/lognormal) and unshadowed fading (i.e., Rician) environments by deriving various performance metrics. The approach uses an efficient procedure to approximate the composite function proposed by Holtzman. We then conduct the performance analysis for effective capacity (EC) over double shadowed Rician (DSR) and α-η-κ-μ fading channels. To achieve this, the expression for the EC is derived in the closed-form. A truncation error of the expression for the corresponding EC is also derived, which is considerably tight. Furthermore, the consequences of channel and system parameters on the quality-of-service (QoS) performance of the wireless network are revealed by conducting an asymptotic EC analysis under the sovereignty of a high signal-to-noise ratio (SNR). It is found that the asymptotic bound for EC is notably tight, and asymptotic EC matches with the analytical EC when SNR is large. Additionally, the expressions for the EC of well-known fading scenarios (i.e., Rician and Nakagami-q fading) are deduced as special cases.