Uplink Cell-Free Massive MIMO URLLC Systems with User Mobility and Imperfect CSI

Abstract

The cell-free massive multiple-input and multiple-output (CF-mMIMO) communication technology has the ability to handle inter-cell interference in MIMO systems, making it a potential candidate for sixth-generation (6G) wireless communication. A CF-mMIMO system is investigated in this paper for mission-critical ultra-reliable low latency communication (URLLC) applications involving a central processing unit (CPU), many distributed access points (APs), each with multiple antennas, and multiple single-antenna user equipment (UEs). In order to maximize energy efficiency (EE) and throughput gains, each AP is linked to the CPU through a fronthaul link with limited capacity, which handles the quantized uplink data to the CPU. We assume that each AP serves fewer UEs. Our approach has a minimal signal processing complexity and offers UEs uniform quality of service (QoS) as well as improved EE. Closed-form expression for outage probability (OP) in the uplink of the CF-mMIMO system considering Welch-Satterthwaite approximation is derived using a variety of Doppler power spectra (DPS) models that consider imperfect channel state information (CSI) and mobility of UEs. Our numerical simulations validate the correctness of the derived expressions.