Energy-Efficient Power Control for Simultaneous Wireless Information and Power Transfer—Nonorthogonal Multiple Access in Distributed Antenna Systems

A simultaneous wireless information and power transfer (SWIPT)-enabled nonorthogonal multiple access (NOMA) system has been recognized as a promising technology for enabling the Industrial Internet of Things (IIoT), as it extends the lifetime of small battery-driven sensors. However, its energy efficiency significantly decreases with distance from the central controller. This article proposes a framework for applying SWIPT-aided NOMA system to a distributed antenna system (DAS) to improve the spectral efficiency and energy efficiency of the IIoT. Moreover, we jointly optimize the power allocation for the NOMA signaling and power splitting for SWIPT in the DAS to maximize energy efficiency while reaching the minimum harvested energy and data rate requirements. Owing to the nonconvexity of the joint optimization problem, we divide the optimization problem into subproblems and present an iterative algorithm for finding the optimal solution. To verify the effectiveness of the proposed method, extensive simulation results are presented, and we show improvements in energy efficiency relative to conventional schemes. Particularly, the proposed SWIPT-NOMA-DAS system provides energy efficiency of more than five times that of SWIPT-NOMA without DAS, and more than 10% improvement compared with SWIPT-OMA-DAS.