On the Performance Analysis of Full-Duplex Cell-Free Massive MIMO With User Mobility and Imperfect CSI

One of the disruptive communication technologies for sixth-generation (6G) wireless networks is cell-free massive multiple-input multiple-output (CF-mMIMO), which is capable to control inter-cell interference in MIMO systems. This paper investigates the performance of a full-duplex (FD) CF-mMIMO systems with practical limited-capacity fronthaul links. The proposed system employs a large number of M distributed FD APs, arbitrarily distributed K_d downlink (DL) and K_u uplink (UL) half-duplex (HD) single-antenna equipped user terminals (UEs), and a central processing unit (CPU). To exploit the energy efficiency and potential throughput gains of FD systems, each AP is linked to the CPU through a fronthaul link with limited capacity that handles the quantized UL/DL data to/from the CPU. Each AP is expected to support K HD UEs on the same spectrum resource, where K = (K_u + K_d) . Imperfect channel state information and the mobility of the UEs are also considered. A closed-form expression for the outage probability is derived using the optimal uniform quantization and maximum-ratio combining/maximum-ratio transmission considering the Welch-Satterthwaite approximation. Additionally, the asymptotic and infinite-M outage expressions for the proposed system are analytically studied and verified via Monte Carlo simulation. Simulation results demonstrate the relationship between the improved outage performance and uniform quality of service (QoS) for all UEs. Moreover, this analysis provides valuable insights into the behavior of FD-CF-mMIMO system and underscores the importance of providing a uniform QoS to all UEs in improving the overall performance of the system.