Next generation wireless communication networks demand ultra-high data rates, massive connectivity, robust security, low latency, cost efficiency, spectral efficiency, and energy efficiency amidst challenges posed by obstructions, environmental factors, and random and uncontrollable propagation environments. As such, the terahertz (THz) band holds promise for fulfilling the ultra-high data rates and robust security requirements, but its vulnerability to obstructions and atmospheric factors necessitates effective mitigation techniques. Moreover, to meet the ever-growing data rate demands and support massive connectivity, it is crucial to not only expand the transmission bandwidth but also improve the spectral efficiency through technologies such as full-duplex (FD), non-orthogonal multiple access (NOMA), and rate-splitting multiple access (RSMA), among others. Furthermore, deploying a vast array of antennas is a potential solution to mitigate the impacts of obstructions and randomness in wireless propagation; however, it increases hardware and signal processing complexity, energy consumption, and costs due to the numerous active components. To manipulate and control the wireless environment, reconfigurable intelligent surfaces (RISs), composed of an array of reconfigurable elements, have been introduced as a cost-efficient and energy-efficient solution, revolutionizing the design of future wireless systems. Despite offering significant performance improvements, reflection-only RISs are limited by the necessity for users and base stations (BSs) to be within the reflection space. To overcome this limitation, simultaneously transmitting and reflecting RISs (STAR-RISs) have been proposed, which can simultaneously reflect and transmit signals, providing full-space coverage for users and BSs located in both reflection and transmission spaces. Additionally, backscatter technology, a promising candidate for the Internet of Things (IoT), facilitates low-cost and energy-efficient communications, while integrating it with RISs significantly enhances its inherent short-range coverage and performance. This thesis examines the integration of various technologies mentioned above, with a special focus on RISs under different configurations and protocols. It aims to identify their potential advantages, limitations, and mitigation techniques for meeting the unprecedented demands of next generation wireless communication networks. It investigates the effects of practical factors such as interference, transceiver hardware impairments, antenna beam misalignment, random foggy weather, RIS phase and amplitude quantization errors, various types of noise, the numbers of antennas and RIS elements, and so forth. It derives new accurate expressions for different performance metrics such as ergodic capacity, secrecy capacity, outage probability, diversity order, bit error rate (BER), and symbol error rate for various communication systems. In particular, it presents (i) unified BER expressions for RIS-assisted systems in generalized Gaussian noise and general fading channels, considering arbitrary numbers of RIS elements and antennas; (ii) a unified expression for capacity analysis in general fading channels, applied to equal gain combining, multi-user RSMA, and RIS-assisted systems; and (iii) unified BER expressions for multi-user NOMA with or without RISs and co-channel interference in general fading channels. Numerical and simulation results are provided to verify the derived expressions and offer practical insights essential for the efficient design of future wireless communication networks.
Date of Award | 1 Aug 2025 |
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Original language | English |
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Awarding Institution | - The University of Manchester
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Supervisor | Khairi Hamdi (Supervisor) & Zhirun Hu (Supervisor) |
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