Performance Analysis of Repeater-Assisted Massive MIMO Systems With Asynchronous Reception

Abstract

Repeater-assisted massive MIMO (RA-MIMO) provides a cost-effective solution for distributed macro-diversity without the high-capacity fronthaul of cell-free architectures. However, the distributed deployment of repeaters introduces propagation delay differences and timing misalignments, causing asynchronous reception at the base station. To characterize this effect, we derive a closed-form uplink spectral efficiency (SE) expression for asynchronous RA-MIMO, explicitly accounting for phase offsets, inter-carrier interference (ICI), and inter-symbol interference (ISI). The analysis reveals that the performance degradation is primarily driven by phase offsets disrupting coherent transmission, rather than by ICI/ISI. Motivated by this insight, we propose a delay-aware (DA) combining scheme that compensates for phase offsets at the receiver, and derive its closed-form SE. Simulations confirm the derived expressions and show that asynchronous reception severely degrades SE, whereas the proposed DA combining effectively mitigates this impairment and achieves near-synchronous performance.