On the Capacity of Full-Duplex Diamond Relay Networks Using NOMA

A full-duplex diamond relay network using non-orthogonal multiple access (NOMA) is proposed in this paper wherein a BS communicates with a user through two dedicated decode-and-forward relays. Based on the channel conditions of relays, the BS transmits a superposed NOMA signal by following the downlink NOMA principle. After decoding intended symbols, both relays concurrently transmit their symbols to the user with a slight processing delay by exploiting the uplink NOMA principle. Considering the practical scenario of imperfect interference cancellations, the ergodic sum capacity and ergodic capacities of the proposed system are analyzed over Rayleigh flat-fading channels. Monte-Carlo simulations are provided to substantiate the analysis. The outcomes show the usefulness of the proposed protocol over the corresponding counterparts half-duplex NOMA and half-duplex orthogonal multiple access protocols.