Downlink Outage Probability and Channel Capacity for Cell-Free Massive MIMO Systems

Abstract

In Cell-Free (CF) systems, the users are served simultaneously by a large number of low-cost and low-power distributed antennas, taking advantage of spatial diversity. The scarcity of equations that accurately describe the system performance limits optimization techniques to applications of users Quality of Service (QoS) uniformization. Thus, to accurately characterize the performance of such systems, a simplified model for the downlink received signal is proposed and new expressions are derived for the users Outage Probability (OP) and average channel capacity taking into account the channel gain variations characteristics. Different cell-free scenarios are analyzed and several curves are presented for different parameters that characterize the channels. The new theoretical results are corroborated by Monte-Carlo simulations and compared to literature results, which confirm classical cell-free behavior as well as the saturation on channel capacity and OP curves, and reveal that the proposed expressions describe the systems more accurately.