Performance Analysis of Cell-Free Massive MIMO Systems Under Limited Feedback

In this paper, we consider a cell-free massive multiple-input multiple-output (MIMO) system which contains a large number of access points (APs) and a much smaller number of users. Each AP obtains the channel parameters estimated from the uplink quantization bits and applies maximum ratio transmission (MRT) in the downlink transmission. During the transmission of feedback, we consider a quantization technique and limited capacity. We redesign the codebook which contains channel direction information (CDI) and channel quality information (CQI). We derive the closed- form expression for the downlink achievable rate and apply max-min power control algorithm to guarantee the users' data rates. In order to increase the performance, we also propose an optimal bit allocation algorithm. Simulation results show that the proposed algorithms can achieve good system performance.