Impact of Receiver Orientation on Full-Duplex Relay Aided NOMA Underwater Optical Wireless Systems

In this paper, we consider a non-orthogonal multiple access (NOMA) underwater optical wireless communication system in which a full-duplex decode-and-forward relay is used to assist the far user with weak channel conditions. Full-duplex operation introduces interference to the near user with strong channel conditions and our model covers several practical assumptions such as imperfect interference cancellation and random receiver orientation at the near/far user. In particular, we derive the exact outage probability at the near user and far user valid for log-normal weak turbulence conditions. An accurate outage approximation for the near user is also derived in closed-form. The correctness of the analysis has been verified through simulation results where they both match closely. Moreover, the derived expressions are useful to investigate the impact of various system and channel parameters such as the access point/relay transmit power, node locations, strength of the residual interference and random receiver orientation at the near and far user. Our results reveal that the outage probability of the near user is more sensitive to receiver orientation errors as compared to the far user.