Inter-Access Point Coordinated User and Beam Selection for mmWave Distributed MIMO Systems

Millimeter wave (mmWave) distributed multiple-input multiple-output (MIMO), which is also known as cell-free massive MIMO, is a promising technology for beyond 5G. To improve system capacity in mmWave distributed MIMO systems, a coordinated scheme between distributed access points (APs) is required. In this paper, we evaluate the throughput performance of precoding across multiple APs under channel aging and compare it with that of inter-AP coordinated user and beam selection to clarify the inter-AP coordinated scheme suitable for practical mmWave distributed MIMO systems. Simulation results show that the inter-AP coordinated user and beam selection achieves a higher throughput performance than the precoding. Moreover, to make the inter-AP coordinated user and beam selection more practical, we propose a coordinated selection method using reference signal received power (RSRP) database. Simulation results show that the proposed method improves the 5%-tile user throughput by 17% compared to the coordinated selection without using the RSRP database.