User Pairing Schemes in Cooperative Downlink NOMA System with SWIPT

Abstract

In this paper, we propose two user pairing algorithms for cooperative downlink non-orthogonal multiple access (NOMA) system, where a base station (BS) equipped with ${N}$ antennas selects ${N}$ pairs of users equipped with single antenna to serve. One pair includes a near user and a far user, whose signals are superposed at the transmitter side, and successive interference cancellation (SIC) is applied to the receiver side. According to SIC, the near user has prior information about the message of the far user, which is exploited to forward the signal of the far user in the proposed NOMA system. Simultaneous wireless information and power transfer (SWIPT) technique is employed at the NOMA system, in which the near user harvests energy from BS to forward the information to the far user. In addition, zero-forcing beamforming (ZFBF) is used to remove the inter-pair interference of the near user, and in order to minimize the inter-pair interference of the far user, the two user pairing algorithms are proposed. To guarantee the performance of users, we propose a power allocation scheme. Simulation results show the proposed algorithms can improve the performance in the cooperative downlink SWIPT NOMA system.