Joint Beamforming and Transmission Design for Hybrid Backscatter-HTT Communication System

Backscatter communication and harvest-then-transmit (HTT) communication are regarded as promising technologies for enabling green Internet of Things (IoT). The current works on the joint use of backscatter communication and HTT are limited in single cell scenarios with the fixed backscatter-then-HTT transmission structure. In this work, we propose a transmission scheme with flexible mode selection for the hybrid backscatter-HTT multicell system to achieve much improved communication performance, and then study the joint design for such a system. Specifically, by utilizing multiantenna technology and enabling the flexible mode selecting between backscatter and HTT, a novel transmission scheme is developed. With the aim to maximize the sum rate of the considered system, we formulate a joint optimization problem for the base station transmission beamforming (TB), the transmission mode (TM), and the transmit power (TP) of the hybrid backscatter-HTT devices. To address the formulated nonconvex problem, we propose a block coordinate descent-based algorithm, namely, J3TO, to jointly optimize TB, TM, and TP, by decoupling the original problem into three subproblems. Therein, the weighted minimum mean-square-error approach, matching theory, and the fractional programming technique are leveraged to deal with the subproblems efficiently. Simulation results show that the proposed algorithm flexibly integrates the merits of backscatter and HTT technologies, achieving superior performance across various scenarios, compared with the benchmark schemes, e.g., backscatter-only space division multiple access (SDMA), HTT-only SDMA, and backscatter-HTT TDMA.