Quantized Power Allocation Algorithms in Cell-Free Massive MIMO Systems

Abstract

Cell-Free Massive Multiple Input Multiple Output (M-MIMO) is a system where a large number of low-cost single antenna Access Points (APs) are distributed over a specific area. The APs are connected to a Network Controller (NC) and serve all the existing users simultaneously. This work proposes two power allocation algorithms for Conjugate Beamforming (CB) and Zero-Forcing (ZF) pre-coders in downlink scenario. They are based on quantizing the transmitted powers of APs to reduce the system complexity. The performance of the proposed algorithms is evaluated under the most common practical scenarios such as channel errors, pilot contamination and correlated shadowing channel model. The results show that the proposed algorithms have closer solution to the optimal one for both pre-coders. Moreover, ZF pre-coder significantly outperforms CB pre-coder with and without pilot contamination effect under both correlated and uncorrelated shadowing channel models.