Achieving mURLLC Under Nakagami-m Fading in the CF mMIMO System

Massive ultra-reliable and low latency communications (mURLLC) is emerging as a new important and critical service category in the six generation (6G) mobile communications. However, it is extremely challenging to achieve mURLLC because it needs to fulfill three performance requirements simultaneously, i.e., reliability, latency, and large-scale access requirements. Existing related studies are few and almost all based on the ideal assumption of Rayleigh fading or orthogonal pilots. We considered cell-free massive multiple-input multiple-output (CF mMIMO) and linear precoding to achieve mURLLC under Nakagami-m fading. Firstly, we establish a channel state information (CSI) error model with pilot contamination and analyze statistical properties of estimates and errors for Nakagami-m fading channels. Secondly, in conjunction with maximum ratio transmission (MRT) precoding, we derive the signal-to-interference-plus-noise ratio (SINR) of the downlink of the CF mMIMO system under Nakagami-m fading, which is meaningful but never mentioned in the literature. Then, we calculate the error probability (EP) with the finite blocklength and reveal interaction relationships between different indicators. The simulation results indicate that under pilot contamination, imperfect CSI, and Nakagami-m fading, mURLLC can be achieved by optimizing system configurations.