Performance Analysis of Scalable Pilot Assignment Schemes for Cell-Free Massive MIMO Systems

Cell-free massive multiple-input multiple-output (CF-mMIMO) systems can accommodate the stricter quality-of-service (QoS) and higher data rates required by beyond-5G communications. Scalable cell-free networks are in higher demand as access users grow in number. At present, scalable pilot assignment schemes suitable for general access have been proposed, but whether they can achieve scalable massive access is still a question worth exploring. Therefore, we discuss the computational complexity and performance of three existing scalable pilot assignment schemes for both general access and massive access using maximum ratio (MR) combining. The simulation results show that the Scalable scheme outperforms the others in both throughput and normalized mean square error (NMSE) for the two access situations.