Outage Performance of User-Assisted Energy Harvesting Full Duplex MIMO-NOMA Networks

This work focuses on analyzing the outage probability (OP) in a downlink multi-user multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) system, specifically employing the maximum-ratio transmission/receive antenna selection structure. In the investigated system, the user close to the base station (BS) acts as a full-duplex (FD) (or half-duplex [HD]) energy harvesting (EH) relay adopting decode-and-forward (DF) protocol for transmission to the far user. With and without a direct link, we derive the exact and asymptotic OP expressions in closed form for Nakagami-$m$ fading channels. The analytical results are validated through simulations, which show that the presence of a direct link in the system significantly enhances the performance of the far user. This improvement occurs because the direct link mitigates the performance degradation caused by the self-interference of the near-user. Additionally, the far user exhibits superior performance when the near user operates in the FD mode to the HD mode. Moreover, as the number of transmit antennas of the BS increases, the signal-to-noise ratio gains are more pronounced in FD mode than in HD mode. For both HD and FD modes, the performance is better when the number of antennas at the BS is higher than that of the users.