DSWIPT Scheme for Cooperative Transmission in Downlink NOMA System

In this paper, we focus on the issue how to reduce the throughput performance gap between the cell-center user and the cell-edge user in a downlink two-user non-orthogonal multiple access (NOMA) system. To this end, we apply the Simultaneous Wireless Information and Power Transfer (SWIPT) protocol to the NOMA scheme and propose a dynamic SWIPT (DSWIPT) cooperative NOMA scheme, in which both the time allocation (TA) ratio and power splitting (PS) ratio can be adjusted dynamically to improve the performance of the cell-edge user in the system. Specifically, we derive two analytical expressions for the outage probability (OP) of the cell-center user and the cell-edge user to study the DSWIPT NOMA scheme’s influence on the system. And we also propose an optimization algorithm 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 and the DSWIPT NOMA scheme has a better performance in both the sum-throughput of the system and the OP of the cell-edge user comparing with the non-cooperative NOMA scheme and the SWIPT NOMA scheme.