The performance of NOMA-based cooperative wireless networks with best relay selection over nakagami-M fading channels

5G and beyond wireless systems, which enable very high speed data transfer and extremely low latency, are expected to play an important role in meeting the increasing wireless communication demands. Since the classical orthogonal multiple access methods are inefficient to provide high user access aimed with 5G and beyond communication networks, the non-orthogonal multiple access technique (NOMA) in which many users simultaneously transmit signals using the same channel but different transmission power levels has been proposed. On the other hand, cooperative diversity approach, which provides antenna diversity gain by obtaining virtual antenna arrays in the wireless network, is another principal technology used to increase the quality of service. The combination of cooperative communication technique and NOMA technology provides significant spectral efficiency increases in 5G and beyond mobile networks. In this master's thesis, a NOMA-based cooperative network consisting of a source, L relays and a destinationis considered and a system model, where the source communicates with the destination directly and through the selected best relay is examined. The relay selection criterion has been proposed as choosing a relay that maximizes the achievable rate of the system. Nakagami-m fading is assumed for all the channels in the system and the average achievable rate of the system is determined by computer simulations for different values of L-total number of relays, m-fading parameter and link average signal-to-noise ratios. It has been seen by simulation results that in many cases the NOMA-based cooperative networks with the best relay selection outperforms the conventional cooperative systems with relay selection.