SWIPT-Enabled NOMA in Distributed Antenna System With Imperfect CSI for Max-Sum-Rate and Max–Min Fairness

Motivated by the fact that the energy harvesting (EH) of simultaneous wireless information and power transfer (SWIPT) and the system throughput of nonorthogonal multiple access (NOMA) can be greatly increased with the help of the distributed antenna system (DAS), we present a framework for applying the DAS to SWIPT-enabled NOMA. In this article, we jointly optimize power splitting (PS) for SWIPT and power allocation for NOMA signaling in SWIPT-enabled NOMA helped by the DAS for two different following goals: 1) sum-rate maximization; and 2) achieving max–min fairness. Also, we analyze the impact of imperfect channel state information (CSI) on power splitting and power allocation of SWIPT-NOMA with the DAS in both problems. Due to the nonconvexity of the joint optimization problem, we first obtain the optimal PS ratios and use them to convert the problem to a single-variable problem. The joint optimal solution is then obtained in the closed-form by finding and comparing all local extrema of the objective function using the first-order derivative. Numerical results were used to validate the theoretical findings and demonstrate that the proposed framework of using SWIPT-enabled NOMA in DAS achieves higher data rates than the existing SWIPT-enabled NOMA while guaranteeing minimum harvested energy and data rate requirements.