User Scheduling in Massive MIMO

Abstract

Massive MIMO relies on nearly orthogonal user channels to achieve unprecedented spectral efficiency. But in LoS (line-of-sight) environment, some users can be subjected to similar channel vectors. Serving users with similar channel vectors simultaneously can severely compromise the throughput performance to all users. We propose a scheduler that identifies users with similar channels and serves them in separate time slots with properly assigned data rates, while aiming to provide fair service to all users and maximize the system spectral efficiency at the same time. Simulation results show the effectiveness of the scheduler on both downlink and uplink of a single cell Massive MIMO with MR (maximum ratio) processing or ZF (zero-forcing) processing, and that channel correlation threshold for scheduling users is an important design parameter that can be fine-tuned to optimize the user throughput performance.