Full-Duplex User Relaying for NOMA System With Self-Energy Recycling

This paper proposes a self-energy recycling full-duplex cooperative non-orthogonal multiple access (SRF-NOMA) system, where a nearby user can be employed as a decode-and-forward, amplify-and-forward, and quantize-map-forward relay with self-energy recycling protocol to assist a distant user. The relay harvests energy from dedicated energy signal sent by a base station, while it reuses energy from loop self-interference (LI) signal. To characterize the performance of the system proposed, new expressions of exact and asymptotic outage probabilities for two users are derived. Based on analytical results, the diversity orders achieved by the nearby and distant user are one and two, respectively. We confirm that the diversity orders of the distant user are obtained with direct link and relaying link, since the energy from LI is harvested for information transmission at the relay. Numerical results are presented to validate the accuracy of the derived results and demonstrate that: 1) when the DF or AF protocol is employed, the outage behavior of the SRF-NOMA system is superior to orthogonal multiple access; 2) in the high signal-to-noise ratio region, DF relay in the SRF-NOMA system is capable of enhancing the outage performance compared to AF relay; and 3) the distant user in the SRF-NOMA system with QMF relay is able to obtain a better performance than that of DF and AF relays.