Max-Min Throughput in Hybrid of Wireless Powered NOMA and Backscatter Communications

This article proposes a hybrid of backscatter communication (BackCom) and wireless powered non-orthogonal multiple access (NOMA) network for Internet of Things (IoT) applications, which consists of one power beacon (PB), multiple energy-constrained IoT devices, and one information receiver (IR). In the proposed network, the IoT devices harvest energy and backscatter their information to the IR in turn when PB broadcasts energy signals, and then use the harvested energy to transmit information to the IR via uplink NOMA when PB keeps silent. Considering the non-overflowing energy constraint, a max-min throughput optimization problem is formulated to ensure the throughput fairness among different IoT devices by jointly optimizing the time resource for operating BackCom and uplink NOMA, the reflection coefficient of BackComs, the transmit power for uplink NOMA and the transmit power of the PB. Although the formulated problem is non-convex and challenging to solve, we first transform the original non-convex problem into an equivalent convex one with the aid of an inequality transformation approach and introducing several kinds of auxiliary variables, and then devise a two-layer iterative algorithm to obtain the optimal resource allocation. Simulation results are provided to verify the convergence of the devised iterative algorithm and validate that the proposed scheme achieves the highest max-min throughput by comparing it with three baseline schemes.