QA-P-MMSE Scalable and High-Performance Receiver for Cell-Free Massive MIMO with Quantized Fronthaul P

Abstract

Cell-free Massive MIMO systems promise unprecedented spectral efficiency by coherently serving users with a large number of distributed Access Points (APs). A key practical challenge, however, is the high capacity required for the fronthaul links connecting these APs to a central processing unit. To reduce cost and power, these links must employ low-resolution quantization, which introduces distortion that can severely degrade system performance. This paper tackles this problem by proposing a novel, scalable receiver scheme: the Quantization-Aware Partial MMSE (QA-P-MMSE) receiver. Unlike conventional methods that either ignore quantization effects or require non-scalable centralized processing, our proposed receiver explicitly incorporates the statistics of the quantization noise into its design. We demonstrate through simulations that the QA-P-MMSE receiver significantly outperforms other scalable schemes, such as Maximum-Ratio (MR) and Partial-MMSE (P-MMSE), in terms of both average spectral efficiency and user fairness. Crucially, it approaches the performance of an ideal, non-scalable MMSE receiver with unquantized fronthaul, proving its efficacy as a practical and high-performance solution for next-generation cellfree networks. Furthermore, energy efficiency analysis reveals that the proposed scheme maximizes bits-per-joule performance at 4-bit resolution, aligning with green 6G targets.