PHY Transceiver Design Based on Cooperative NOMA

The upcoming next generation of wireless networks is expected to offer ultra-reliable and low-latency communication, and other features due to the unprecedently high growth of timely mobile data traffic and stringent quality-of-service (QoS) requirements. These features will make a range of applications possible, including multiple access strategies (e.g., non-orthogonal multiple access (NOMA)), cooperative communications, energy harvesting (EH), reconfigurable intelligent surfaces (RISs), and unmanned aerial vehicle (UAV). NOMA is one of the most exciting approaches to improve spectrum efficiency in the next generations of wireless networks. Cooperative communication is integrated with NOMA (CNOMA) to offer an effective approach to mitigate challenges in channel conditions, extend the coverage area, and enhance spectral efficiency. Moreover, to enhance energy efficiency and prolong battery life for devices, CNOMA is empowered with EH. Furthermore, RIS enhances wireless communication by controlling radio propagation with low-cost passive elements, adjusting reflection coefficients for altered electromagnetic wave propagation. NOMA has been integrated with RIS to effectively provide efficient transmission in next-generation networks. Besides, UAV communication is a beneficial option for maintaining connectivity during brief events and after natural disasters. The UAV is adapted with RIS (UAV-RIS) and can serve as a reflective layer between ground base stations and devices, enhancing wireless communication. This thesis aims to investigate the interplay of NOMA with cooperative communication to improve the performance and extend the coverage area. To this end, we use several technologies for the CNOMA system, such as cooperative with and without direct links, multiple relays (multi-hop relay), EH, and UAV-RISs.


First, we investigate the downlink CNOMA without direct links (WDL). We derive the closed-form ergodic capacity (EC), outage probability (OP), and bit error rate (BER) over the Rayleigh fading channel. We evaluate the power allocation factor and helper user distance. We compare our scheme with traditional cooperative orthogonal multiple access (COMA) WDL. Then, we investigate the downlink CNOMA with DL. We derive the OP and BER with imperfect successive interference cancellation (ISIC) and channel state information (ICSI) over the Rayleigh fading channel. We assess the power allocation factor and the helper user distance. Thereafter, we investigate the multi-hop CNOMA with two schemes WDLs and DLs under the ICSI and ISIC. We derive the end-to-end (e2e) OP and BER expressions for the considered systems under ICSI and ISIC. We discuss the influence of power allocation, the number of relays, ICSI, and SIC on the performance of the systems. We compare our findings with single relay CNOMA. Moreover, we investigated two CNOMA with EH schemes: Firstly, we obtained the BER of CNOMA with time switching (TS) and power splitting (PS) protocols over the Rayleigh fading channel with ICSI, ISIC, and ICI. We explore the impact of ISIC and CSI on BER performance within the parameters of EH. Secondly, we obtained the OP and BER of CNOMA with three EH protocols (TS, PS, and hybrid) over the Nakagami-$m$ fading channel. We discuss optimal values for EH parameters and the power allocation coefficient. Besides, we examine the performance of the wireless-powered cooperative communication network with linear/non-linear EH in the presence of in-phase and quadrature-phase imbalance (IQI) and SIC imperfections over the Rayleigh fading channel in terms of OP, EC, and throughput. We assess the impact of IQI and SIC imperfections on the proposed scheme using various WPCCN parameters. We compare our system to conventional UL NOMA without EH. Finally, we examine the BER and energy efficiency (EE) of UAV-RIS NOMA in the presence of practical constraints. We compare our results with two schemes: UAV without RIS and conventional UAV-RIS OMA. We validate our numerical derivations through simulation results.

The results show the following. The best relay location is between the base station and users to achieve higher performance. Increasing the number of relays reduces the OP and BER. Multi-hop NOMA achieves high-performance gain compared to single relay schemes. The ICSI and ISIC decrease the system performance at the high signal-to-noise ratio (SNR). The EH schemes achieve higher performance compared to those without EH and the hybrid protocol is superior to all benchmarks, which are in the range of 1-3 dB and 0.5-1.5 dB for OP and BER performances, respectively. The non-linear EH limits system performance in high SNR regions and is significantly impacted by IQI and SIC imperfections. IQI negatively affects RF impairment, highlighting the necessity of IQI mitigation to maximize system capabilities. Finally, HWI, ICI, and ISIC degrade performance at high SNR, however, increasing the number of RIS reflecting elements at low SNR achieves satisfactory results. The UAV-RIS system outperforms UAVs without it, and OMA performs better than NOMA due to no inter-user interference IUI issues.