Stochastic Geometry Based Performance Characterization of SWIPT in Cell-Free Massive MIMO

Abstract

This paper investigates the integration of wireless information and power transfer (SWIPT) and cell-free massive multiple-input multiple-output (MIMO) technologies for a cell-free spatially random network, where the access points (APs) are located randomly and modeled using a Poisson point process, and the users' energy and data transfers are separated in time. For the time-division-duplexing mode of operation, the uplink channel state information is acquired locally at the distributed APs via user pilots, and the APs utilize conjugate beamforming for downlink transmissions by exploiting channel reciprocity. In addition, line-of-sight and non-line-of-sight scenarios, which arise from link blockages due to objects are considered along with the corresponding path loss and fading parameters in our performance analysis of the above system set-up. We characterize the harvested energy at a user for both linear and non-linear energy harvesting models, and derive expressions for the average achievable downlink rate for the energy harvesting users. Subsequently, we propose a multi-slot energy storing scheme, and thereby, derive the probability of a user being fully charged at any given time. The throughput and the harvested energy are investigated under different system parameters. We show that a higher mean energy can be harvested by energy users with limited impact on non-energy users through allocating a higher portion of power for the energy users. Furthermore, we reveal that increasing the AP power level has diminishing effect on the probability of being within the fully charged state.