User Association in User-Centric Hybrid VLC/RF Cell-Free Massive MIMO Systems

A continuous goal in all communication systems is to enhance users’ experience and provide them with the highest possible data rates. Recently, the concept of cell-free massive MIMO (CF-mMIMO) systems has been considered to enhance the performance of systems that operate solely with radio-frequency (RF) or visible light communication (VLC) technologies. In this paper, a hybrid VLC/RF cell-free massive MIMO system is proposed where an RF cell-free network and a VLC cell-free network coexist to serve the users. The idea is to utilize the benefits of each network and balance the load with the aim of maximizing the system’s sum-rate. The system is evaluated using zero-forcing (ZF) precoding scheme. Two distinct user association algorithms are proposed for assigning users to either the VLC network or the RF network. In addition, two user-centric clustering approaches are proposed and evaluated. Simulation results show that the proposed association algorithms significantly outperform a random network association of users in terms of sum-rate. Results also show great potential for the proposed system compared to standalone cell-free networks.