Outage Probability of Uplink Cell-Free Massive MIMO Network with Imperfect CSI Using Dimension-Reduction Method

In this paper, approximate outage probability (OP) expressions are derived for uplink cell-free massive multiple-input-multiple-output (CF-mMIMO) system. The access points (APs) of the system considered have imperfect channel state information (CSI). The approximate expressions are derived first using conditional expectations and then using a novel dimension reduction method that approximates higher-order integration by several single order integrations. Using the same approach, closed-form approximations are also derived for conventional massive MIMO (mMIMO) systems. The OP approximations are then used to characterize the performance of cell-edge users of CF-mMIMO systems and compare the designs of CF-mMIMO and mMIMO systems. The derived expressions have a close match with the simulated expression for OP.