Practical NOMA-Based Coordinated Direct and Relay Transmission

Abstract

This letter puts forth a practical non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) scheme, referred to as network-coded multiple access CDRT (NCMA-CDRT). We consider a two-user uplink scenario, where a near user communicates directly to a base station (BS), whereas a far user needs the assistance of a decode-and-forward relay. While prior NOMA-CDRT studies focused extensively on theoretical analysis, its superiority has not been well investigated through practical communication schemes. In particular, successive interference cancellation (SIC), a predominant NOMA decoding technique, does not work well if transmitters with comparable received powers transmit together. We investigate NCMA-CDRT to tackle this practical issue. A distinguishing feature of NCMA-CDRT is the joint use of physical-layer network coding (PNC) and multiuser decoding at both the relay and the BS. We design packet relaying strategies that can forward the PNC packets decoded at the relay to boost system throughput. Experiments on software-defined radio indicate that the total throughput of NCMA-CDRT significantly outperforms the SIC-based NOMA-CDRT. Overall, NCMA-CDRT is a viable solution for cooperative NOMA systems.