Cell-free multiple-input multiple-output (MIMO) is a promising distributed network architecture for 5G-and-beyond systems. This paper proposes an access point (AP) selection method that is specific to each user equipment (UE) in downlink cell-free MIMO. The APs are distributed throughout the system coverage area and know only a part of the instantaneous channel state information (CSI). As a beamforming (BF) method based on partial CSI, we use a layered partially non-orthogonal zero-forcing (ZF) method based on channel matrix muting, which is applicable to the case where different transmitting AP groups are selected for each UE under partial CSI conditions. The proposed clustering method initializes the transmitting AP group for each UE based on the conventional signal-to-leakage-and-noise-ratio based method and then updates them for all UEs in an iterative process based on the throughput considering the interference among the UEs. We show that the proposed method achieves higher average and worst-user throughput than those for conventional methods while minimizing the excessive increase in the number of transmitting APs per UE.
Clustering Method in Downlink Cell-Free MIMO Using Layered Partially Non-orthogonal ZF-Based Beamforming
2023-06-01
1356570 byte
Conference paper
Electronic Resource
English