Analyzing Ultra-Low Latency, Ultra-High Reliable and Ultra-Large Connectivity Communication in Scalable CF mMIMO Systems

The sixth-generation mobile communication systems are faced with the challenge of supporting massive user access while satisfying massive ultra-reliable and low latency communications (mURLLC). Although the cell-free massive multiple input multiple output (CF mMIMO) has significant advantages, seamless coverage is still challenging. Moreover, mURLLC is limited by the mutual constraints of latency, reliability and connection density for a scalable CF mMIMO system. In this paper, we first develop an analytical model of mURLLC based on a scalable CF mMIMO architecture. By introducing the access point planning matrix and combining it with the maximum-ratio combining method, we derive the user's post-processing signal-to-noise ratio. Second, we employ the finite blocklength theoretical analysis tools to derive the latency and error probability, which can quantify system reliability, and use the connection density metric to portray scalability. Furthermore, we analyze the interplay mechanism between latency, reliability and connection density. Through simulation experiments, we verify the constraints among latency, reliability and connection density, and find that the scalable CF mMIMO can effectively meet mURLLC requirements for massive user access with appropriate parameters.