Non-Orthogonal Multiple Access with Phase Rotation Employing Joint MUD and SIC

As a multiple access technique candidate of 5G, non-orthogonal multiple access (NOMA) has attracted much attention for its high spectral efficiency. On its receiver side, successive interference cancellation (SIC) cancels the dominant interference and detects the desired signal. When a transmit power level allocated to one user is roughly equal to those allocated to other users, however, the bit error rate (BER) performance degrades severely. To alleviate such a problem, this paper proposes a novel NOMA scheme with phase rotation, and analyzes the optimum angle of the phase rotation in the case of two modulation schemes. Even when multiuser detection (MUD) that simultaneously detects both desired and interfering signals is employed, the BER performance still degrades due to low minimum distance between the superposed constellation points. To improve the BER performance, this paper also proposes a joint MUD and SIC scheme that exploits the advantages of both MUD and SIC. Computer simulations demonstrate that the joint MUD and SIC scheme with the phase rotation outperforms other detection schemes with or without the phase rotation.