Distortion-Aware Clustering for Cell-Free Massive MIMO Under Backhaul Capacity Limitation

This paper investigates the uplink transmission of cell-free massive MIMO with multiple central processing units (CPUs) interconnected to each other by capacity-limited backhaul links. Considering the unavoidable effect of quantization noise through backhaul links, we study two different signal detection approaches: two-stage detection based on local combining (TDLC) and centralized detection (CD). We then propose a distortion-aware clustering (DAC) for both detection schemes and a deterministic combining vector for TDLC. Simulation results prove that the proposed clustering outperforms the conventional proximity-based clustering (PC). Moreover, the results reveal that CD is not always the best choice, depending on the capacity of backhaul links connecting CPUs.