Alocação adaptativa de potência, seleção de relay e pareamento de usuários em redes cooperativas com múltiplo acesso não-ortogonal.

Abstract

Diverse services and applications ranging are foreseen for beyond fifth-generation (B5G) wireless systems which will impose strict requirements to the system designers, such as reliable communications, low latency, seamless connectivity, and high spectral efficiency. In particular, non-orthogonal multiple access (NOMA) has been regarded as a key technique to attend these heterogeneous demands due to its promising gains when compared to the orthogonal counterpart. The combination of the resources of NOMA and cooperative communication techniques can provide even greater gains for the network in terms of coverage, latency, fairness, capacity and spectral efficiency. However, system performance can still be degraded and the communication reliability affected due to the deep fading. In order to increase the performance of NOMA cooperative networks, it is necessary to find appropriate strategies for power allocation, relay selection (RS), and user pairing (UP). In this context, methods of the power allocation, RS and UP are proposed in this dissertation. Specifically, two scenarios are considered. In the first scenario, a downlink cooperative full-duplex relaying NOMA (CFR-NOMA) with multiple relays and two users is projected and evaluated. In order to maximize the achievable rate and ensure rate fairness between the two users, an RS method is developed and the optimal solution for power allocation is derived at the relays. In the second scenario, a cooperative half-duplex relaying NOMA (CHR-NOMA) with multiple relays and multiple users is designed. Based on rate fairness, for each phase of the cooperative system a power optimization problem is formulated to maximize the minimum rate among mobile users. Firstly, the optimization problem is formulated at the base station and then a joint RS and UP scheme is proposed to reduce the complexity of the system. Finally, the second problem of power optimization for user pairs is formulated at the relays. The performance of the proposed schemes is validated through numerical simulations and significant discussions are provided, which proves the superiority of the proposed solutions in terms of outage probability, rate fairness and achievable rate.