Backscatter Assisted Wireless Powered Non-Orthogonal Multiple Access Systems

Abstract

This work introduces a novel backscatter assisted wireless powered non-orthogonal multiple access (NOMA) net-work for the Internet of things (IoT), where IoT devices harvest energy and take turns to backscatter their information to an information receiver (IR) by passive backscatter communication in the first phase, and then use the harvested energy to transmit information to the IR via uplink NOMA in the second phase. Considering a practical non-linear energy harvesting (EH) model for each IoT device, we maximize the overall throughput of the considered network by jointly optimizing the reflection coefficient during backscatter mode, the time resource for EH, backscattering and uplink NOMA, and the transmit power of each IoT device when performing uplink NOMA, subject to the Quality of Service (QoS) of each IoT device and the energy causality. The formulated problem is, however, non-convex. By introducing a series of auxiliary variables and using an inequality transformation approach, we propose an iterative algorithm to tackle this non-convex problem. Simulation results verify the quick convergence of the iterative algorithm, and show that the proposed backscatter-assisted wireless powered NOMA achieves a higher throughput than the benchmark schemes.