Adaptive Interference Suppressing Multi-User ZF in Cluster-Centric Cell-Free Massive MIMO Systems

In this letter, a cluster-centric (CC)-based cell-free massive multiple-input multiple-output (CF-mMIMO) system is considered, which realizes multi-user multiplexing in each user-cluster formed by neighboring users and served by surrounding antennas. Then, the interference suppressing multi-user zero-forcing (IS-MU-ZF) is considered to further eliminate the inter-cluster interference. But the IS-MU-ZF faces a capacity drop problem. Thus, an adaptive interfering user selection method is proposed to flexibly determine the set of interfering users for each user-cluster. It is confirmed by computer simulation that the proposed CC-based CF-mMIMO system utilizing the IS-MU-ZF with the proposed adaptive interfering user selection method outperforms the well-known user-centric (UC)-based CF-mMIMO system in terms of capacity and computational complexity when the accuracy of channel estimation is guaranteed.