Eliminating Phase Misalignments in Cell-Free Massive MIMO via Differential Transmission

2025-03-06

AI Summary

In cell-free massive MIMO (CF-mMIMO) downlink joint coherent transmission, severe performance degradation arises from phase misalignment across distributed access points (APs). To address this, this paper pioneers the systematic integration of differential space–time block coding (DSTBC) with differential QPSK/8PSK modulation into the CF-mMIMO downlink architecture, proposing two phase-misalignment-resilient transmission schemes that eliminate the need for channel phase calibration. The proposed methods leverage distributed AP cooperation and noncoherent channel processing, thereby circumventing conventional reliance on stringent inter-AP phase synchronization. Simulation and experimental results demonstrate that, under severe phase misalignment, the proposed schemes achieve spectral efficiency approaching that under ideal synchronization, reduce block error rate by two orders of magnitude, and improve link robustness by 12.8 dB.

Technology Category

• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Machine Learning: Mixture of Experts (MoE)
• Search and Optimization: Distributed Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG

Abstract

This paper proposes two approaches for overcoming access points' phase misalignment effects in the downlink of cell-free massive MIMO (CF-mMIMO) systems. The first approach is based on the differential space-time block coding technique, while the second one is based on the use of differential modulation schemes. Both approaches are shown to perform exceptionally well and to restore system performance in CF-mMIMO systems where phase alignment at the access points for downlink joint coherent transmission cannot be achieved.

Problem

• Addresses phase misalignment in cell-free massive MIMO systems.
• Proposes differential space-time block coding for phase correction.
• Introduces differential modulation to enhance system performance.

Innovation

• Differential space-time block coding technique
• Differential modulation schemes
• Eliminating phase misalignments in CF-mMIMO