A green swipt enhanced cell-free massive mimo system for iot networks

Abstract

This paper investigates the downlink performance of a green simultaneous wireless information and power transfer (SWIPT) enhanced cell-free massive multiple-input multiple-output (MIMO) system where the IoT devices are served by the virtual massive MIMO constituted by a large amount of distributed single antenna access points (APs). On the premise of that all the IoT devices can decode the information and harvest energy from the received signals, the closed-form expressions of downlink spectral efficiency (SE) and harvested energy of this system are firstly derived under the time switching (TS) and power splitting (PS) scheme. After that, to maximize the lowest SE of the IoT devices, a joint optimization problem which takes into account the power control coefficients and energy harvesting coefficients simultaneously is formulated and an optimal bisection based algorithm is proposed to solve it. Besides, the network load management problem is also studied to reduce the fronthaul burden and an AP selection method which considers the imbalance of AP transmission ratio is proposed. Simulation results show that compared with the benchmark methods, our proposed schemes can guarantee higher transmission rates for IoT devices as well as a reduction of load for fronthual links.