Joint user pairing and power allocation for downlink non-orthogonal multiple access systems

Downlink non-orthogonal multiple access (NOMA), where users are paired as user set and multiplexed in the power domain, is a promising technology for fifth generation (5G) communication system. This paper studies joint optimization of user pairing and power allocation to maximize generalized proportional fair metric subject to transmit power constraints. This problem can be divided into two parts: user pairing and power allocation. In order to reduce the computation burden, we present a pre-defined multi-user pairing criterion to exclude user sets, which are unsuitable for multiplexing. Furthermore, for a given user set, a low complexity multi-user power allocation scheme is proposed by exploiting the convexity of the optimization problem. Simulation results show that the proposed user pairing and power allocation scheme can significantly enhance the downlink system performance and reduce complexity compared to the existing schemes in NOMA systems.