Repeater-Assisted Massive MIMO Downlink Performance with Calibration Errors

2026-06-12

AI Summary

This work addresses the degradation of downlink beamforming performance in dual-antenna relay-aided massive MIMO systems caused by gain mismatch between the relay’s forward and reverse links, which violates channel reciprocity and exacerbates calibration errors between the base station and users. The paper presents the first unified model that jointly incorporates relay calibration errors and over-the-air channel estimation errors. By leveraging the mechanism of reciprocity impairment, random matrix theory, and spectral efficiency analysis, the authors derive a closed-form expression for downlink spectral efficiency. This expression not only quantifies the impact of calibration errors on system performance but also reveals the critical role of error coupling effects in typical deployment scenarios, thereby providing a theoretical foundation for calibration design in relay-assisted massive MIMO systems.

Abstract

Reciprocity-based downlink beamforming is imperative for a scalable time-division duplex massive multiple-input multiple-output~(MIMO) deployment. Specifically, for a dual-antenna repeater-assisted massive MIMO system, a mismatch between forward and reverse path gains at the repeater can exacerbate the overall calibration error between the user equipments (UEs) and the base station (BS), which potentially also contains calibration errors of their individual radio-frequency chains. This paper models the effects of such calibration errors, underpins the relations between the uplink and downlink channels for repeater-assisted systems with calibration errors clubbed with the over-the-air channel estimation errors, and derives analytical expressions of the downlink spectral efficiency. The presented results can then be simplified to several special cases, underscoring situations wherein such errors can become pronounced.

Problem

• massive MIMO
• calibration errors
• repeater-assisted
• downlink beamforming
• channel reciprocity

Innovation

• massive MIMO
• repeater-assisted
• calibration errors
• spectral efficiency
• channel reciprocity