User Scheduling With Limited Feedback for Multi-Cell MU-Massive MIMO FDD Networks Deployment: From Performance Tradeoff Perspective

Abstract

Feedback of channel state information (CSI) from users to base station (BS) is very vital for efficient user scheduling (US) in frequency division duplexing (FDD)–based massive multiple-input multiple-output (mMIMO) systems. The feedback overhead is one of the major bottlenecks for multi-user (MU) mMIMO systems as it increases with number of antennas and users. In the multicellular scenario, each and every BS schedules appropriate set of users based on the limited CSI feedback received from the users for achieving better throughput and fairness which are the prime objectives for such communication systems. To achieve the higher throughput, better fairness, and better scheduling gain with the least CSI, in this article, user grouping–based scheduling (UGS) strategy for multi-cell MU mMIMO FDD system is considered. The proposed UGS scheme achieves a better trade-off between the two prime objectives, that is, throughput and fairness. Moreover, hybrid precoding architecture is also used for this system as practically radio frequency (RF) chains are usually less in number to support less implementation complexity and budget. Our approach utilizes the angle of departure (AoD)–based adaptive codebook for controlling the amount of feedback. The variation of AoD is slow in nature as compared to path gains of the channel, which controls the feedback overhead. The proposed UGS using AoD codebook with limited channel feedback involves determining the beamspace path co-ordinates of each user from the AoD information fed back by users and then group the users into sets based on the AoD CSI. Specifically, UGS scheme is applied to reduce inter-user and inter-group interferences. By integrating an AoD adaptive subspace codebook with a hybrid precoding architecture and focusing on the dual objectives of maximizing throughput and fairness, we offer a novel solution that addresses the key challenges of inter-cell interference and limited CSI feedback. The numerical experiments show the effectiveness of the proposed UGS scheme for fifth generation and beyond wireless networks deployment.