Cooperative Non-Orthogonal Multiple Access Transmission Through Full-Duplex and Half-Duplex Relays

We investigate the beamforming for cooperative non-orthogonal multiple access (NOMA) transmission through a decode-and-forward relay either with full-duplex (FD) mode or with half-duplex (HD) mode. The beamforming vectors at the source and at the relay are optimized to maximize the end-to-end sum rates of the NOMA transmission. The optimal beamforming for the second-hop of the NOMA transmission is present, from which the beamforming algorithms for the two relay modes are derived. For the FD case, the removal of self interference from the feedback loop is important and a two dimensional (2-D) search algorithm based on semi definite relaxation (SDR) is provided, where the 2-D search range is narrowed down as the algorithm iterates. For the HD mode, no iteration is necessary and only one implementation of SDR is required since the SI suppression is not needed. Simulation results show the performance advantage of the proposed FD mode system over that of HD mode in various parameter settings. This justifies the cost and complex hardware circuitry of FD mode.