Coverage Probability of Cell-Free Massive MIMO Systems

Abstract

Despite that ongoing and future networks become denser and increasingly irregular, prior works in the area of cell-free (CF) massive multiple-input-multiple-output (mMIMO) systems relied on the strong assumption of uniformly distributed access points (APs). Actually, this randomness was accounted for only during the simulation and not in the analysis. Consequently, the direction of this paper is towards the application and investigation of a more realistic model for the spatial randomness of the APs in terms of a Poisson point process (PPP). Specifically, we derive the downlink coverage probability (CP) of CF mMIMO systems by means of stochastic geometry and deterministic equivalent tools. Notably, it is the only work having derived the CP for CF mMIMO systems. Among the results, we highlight the outperformance of CF mMIMO systems against small cells (SCs), which increases with the density of the APs due to channel hardening, favorable propagation, and interference suppression. Moreover, we observe the saturation of the CP at high AP density.