6G mURLLC over Cell-Free Massive MIMO Systems in the Finite Blocklength Regime

In order to support the new service requirements-massive ultra-reliable low-latency communications (mURLLC) in the six-generation (6G) mobile communication system, finite blocklength (FBL) information theory has been introduced. Furthermore, cell-free massive multiple input multiple output (MIMO) has emerged as one of the 6G essential promising technologies. A great quantity of distributed access points (APs) jointly serve massive user equipment (UE) at the same time-frequency resources, which can significantly improve various quality-of-service (QoS) metrics for supporting mURLLC. However, as the number of UE grows, the orthogonal pilot resources in the coherent time are insufficient. This leads to serious non-orthogonal pilot contamination and pilot allocation imbalance. Therefore, we propose an analytical cell-free massive MIMO system model and precisely characterize the error probability metric. In particular, we propose a FBL based system model, formulate and resolve the error probability minimization problem, given the latency requirement. Simulation results verify the effectiveness of the proposed scheme and show that the error probability can be improved by up to 15.9%, compared with the classic pilot allocation scheme.