Max-Min Fairness for Cell-Free Massive MIMO with Zero-Forcing Receiver

A cell-free massive multiple-input multiple-output (mMIMO) with a large number of antennas, which are randomly distributed in a large area called access points (APs), is a promising technology to provide high data rate, spectral efficiency (SE), and energy efficiency (EE). In this paper, a zero-forcing (ZF) receiver is used to investigate the uplink performance of the cell-free mMIMO system since it is free from inter-user interference. Max-min fairness power control is equivalent to setting all signal-to-interference-plus-noise ratio (SINR) targets to a common value and then finds the maximum possible value of the SINR to ensure that some constraints are met. On this basis, a max-min fairness power control algorithm for the cell-free mMIMO system by optimizing power control coefficient is proposed. In addition, the proposed algorithm is weighted to ensure that some important users get better quality-of-service (QoS). In this paper, the capacity lower bound formula of strict closed-form in the uplink is used for power optimization. Simulation results indicate that the achievable uplink per-user rate of the proposed algorithm are improved considerably compared to the previous algorithm and the weighted algorithm can provide better QoS.