DSWIPT Scheme for Cooperative Transmission in Downlink NOMA System

Abstract

In this paper, we focus on the issue how to reduce the throughput performance gap between a cell-center user and a cell-edge user in a two-user downlink non-orthogonal multiple access (NOMA) system. To this end, we propose a dynamic Simultaneous Wireless Information and Power Transfer cooperative NOMA (DSWIPT NOMA) scheme. In the proposed scheme, the cell-center user works as a relay to improve the throughput performance of the cell-edge user. The relaying operation is powered by the DSWIPT scheme, in which both the time allocation (TA) ratio and power splitting (PS) ratio can be adjusted dynamically to make full use of the time/power resource in each transfer frame. Specifically, the analytical expressions of the outage probability (OP) corresponding to the cell-center user and the cell-edge user are derived. And a joint optimization algorithm is also proposed to find the optimal TA ratio and PS ratio for maximizing the sum-throughput of the system. The numerical results show that the analytical results are in accordance with the Monte-Carlo simulation results exactly. Compared with the non-cooperative NOMA scheme and the SWIPT cooperative NOMA scheme, the DSWIPT NOMA scheme has a better performance in both the sum-throughput of the system and the OP of the cell-edge user.