Phase Rotated Non-Orthogonal Multiple Access for Superposition of 3-User Signals Employing Joint MUD and SIC

Abstract

Non-orthogonal multiple access (NOMA) has attracted much attention in 5G, for its high usage efficiency of spectrum. Successive interference cancellation (SIC) cancels dominant interference and detects desired signals on the receiver side. However, when transmit power levels allocated to the users let some superposed constellation points get close to others, the bit error rate (BER) performance deteriorates severely. To alleviate such degradation, this paper proposes a novel phase rotated NOMA scheme, and analyzes the optimum angle of the phase rotation in 3-user NOMA signals. Even when multiuser detection (MUD), which simultaneously detects both desired and interfering signals, is employed, the BER performance is still degraded due to short minimum distance between the superposed constellation points. To improve the BER performance furthermore, this paper also proposes a joint MUD and SIC scheme, which exploits the advantages of both the schemes. Computer simulations demonstrate that the joint detection scheme with the phase rotation outperforms other detection schemes with or without the phase rotation.