Conventional wireless techniques are becoming inadequate for beyond fifth-generation (5G) networks due to latency and bandwidth considerations. To increase the wireless network throughput and improve wireless communication systems’ error performance, we propose physical layer network coding (PNC) in an Intelligent Reflecting Surface (IRS)-assisted environment. We consider an IRS-aided butterfly network, where we propose an algorithm for obtaining the optimal IRS phases. Also, analytic expressions for the bit error rate (BER) are derived. The numerical results demonstrate that the scheme proposed in this thesis significantly enhances the BER performance. The proposed scheme is compared to traditional network coding without IRS. For instance, at a target BER of 10−3, 28 dB and 0.75 dB signal to noise ratio (SNR) gains are achieved at the relay and destination node of the 32-element IRS-assisted butterfly network model.

The limited overcrowded radio frequency spectrum compelled researchers to ex plore higher frequency ranges for wireless transmission. In recent decades, visible light communications (VLC) have gained lots of research attention thanks to the abundant bandwidth and the existing lighting infrastructure they offer. Throughout this dissertation, we study the downlink of multi-user VLC systems with the aim of operation and architecture enhancement. In this context, we accommodate the chal lenges imposed by the visible light nature such as illumination requirements and mod ulation constraints. On the operation optimization front, we investigate three VLC setups: indoor single cell, outdoor energy harvesting enabled single cell, and indoor energy harvesting enabled multi-cell VLC systems. We formulate, and provide low complexity solutions to, resource allocation problems for each setup while accounting for scenario-tailored system objectives and quality of service requirements. For the first setup, the temporal average illumination is maintained fixed while maximizing the system SE and dynamic time-division-multiple-access is employed to serve users in an interference free setup. As for the second setup, owing to the favored joint lighting and SE maximization, we solve a multi-objective optimization problem accounting for both objectives. We found that the severity of the illumination - communications tradeoff increases as the available system power budget decreases or the minimum rate requirements get tighter. In the third setup, transmitters average currents and receivers fields of view tuning strategies are developed to maximize both spectral ef ficiency and energy harvesting objectives in an interference limited scenario, where spatial illumination uniformity is required. It is found that receivers fields of view tuning is substantial to performance enhancement in dense deployments. On the architecture optimization front, we propose two intelligent reflecting surfaces-aided VLC systems and derive their power density distribution in the receiver plane. In addition, we prove their power concentration capability and quantify their relative gain with respect to one another and with respect to the reflector-free VLC systems enjoying direct line of sight. Finally, we study the channel impulse response of the proposed reflecting systems and quantify the incurred delay spread through exact ex pression, simplified bounds and asymptotic expressions when the number of reflecting elements grows unboundedly.

Yes / The world is experiencing an explosion in demand for ultra-high data rates with far greater expectations in the next few years. These expectations, given the bandwidth-demanding applications such as augmented and virtual reality and other beyond-5G applications, motivate the exploration of higher-frequency communication in the terahertz (THz) bands. However, THz communication is faced with many technical challenges, primarily due to the high susceptibility to blockages that limit its applications. Here, reconfigurable intelligent surfaces (RIS) provide alternative paths to circumvent such blockage effects and ensure reliable, spectral, and energy-efficient communication, thus advancing the THz-RIS technology concept. However, the ambitious targets of ubiquitous and global connectivity can only be satisfied by many technologies extending to multiple domains, from terrestrial networks to non-terrestrial network (NTN) domains. The use of airborne and spaceborne networks is considered a potential solution for addressing these challenges due to their dynamism, coverage, and ability to leverage their altitude for achieving line-of-sight communication for enhanced signal quality and network performance. Therefore, unmanned aerial vehicles, high-altitude platform stations, and satellites are poised to use flying THz-based RISs to improve air-to-ground and space-to-ground communication reliability while exploiting novel RIS architectures, techniques and enablers to address the issues regarding the propagation conditions, hardware limitations, network complexity and system performance. The aim in this paper is to present the discussion and a survey on the technical advances on THz-RIS NTNs, in addition to outlining potential applications, architectural variants, influencing properties, as well as its prospects, associated challenges, open issues and future directions towards high-data rate THz-RIS NTN communication for 6G and beyond. / This work was supported in part by the Universiti Kebangsaan Malaysia through Dana Impak Perdana 2.0 under Grant DIP-2022-020; and in part by the Engineering and Physical Sciences Research Council [grant number EP/Z001544/1] through the UK Research and Innovation (UKRI)-funded Marie Skłodowska-Curie Actions (MSCA) Postdoctoral Fellowship