Constant-Envelope Quantized Precoding with Power Control for Cell-Free Massive MIMO-OFDM

2026-05-22

AI Summary

This work addresses the severe hardware impairments introduced by low-resolution digital-to-analog converters (DACs) in cell-free massive MIMO-OFDM downlink systems, which degrade performance and hinder the deployment of highly energy-efficient power amplifiers. To mitigate these limitations, the paper proposes, for the first time, a constant-envelope quantized precoding scheme tailored to this system architecture, complemented by an innovative dynamic power control mechanism coordinated across access points (APs). This cross-AP power allocation effectively suppresses quantization noise and detrimental inter-AP interference. By jointly incorporating low-resolution DAC modeling, constant-envelope constraints, and per-antenna peak power optimization, the proposed method substantially reduces uncoded bit error rates and significantly enhances both system robustness and energy efficiency under strong quantization conditions.

Abstract

Cell-free massive MIMO has matured into a key candidate technology for 6G and beyond, owing to its ability to provide nearly uniform service quality to many user equipments (UEs) over the same time-frequency resources. Unlike conventional cellular massive MIMO, the core idea is to distribute a large number of low-cost access points (APs) across the network and enable joint coherent transmission and reception. While early works largely assumed ideal hardware, hardware impairments become inevitable when APs are implemented with low-cost components. In this context, this paper investigates the adverse impact of low-resolution digital-to-analog converters (DACs) on the downlink performance of cell-free massive MIMO-OFDM systems. In contrast to prior studies that mainly quantify spectral-efficiency degradation under low-resolution DACs, we consider the design of quantized constant-envelope (CE) precoding, which additionally enables the use of highly power-efficient amplifiers. To the best of our knowledge, this is the first work on quantized CE precoding for cell-free massive MIMO-OFDM. Beyond adapting the classical maximum-antenna-power method, we propose a novel power-control strategy across APs that mitigates the detrimental effects of severely quantized transmitters by reducing the contribution of harmful APs. Simulation results demonstrate that the proposed power-control mechanism significantly improves the uncoded bit error rate performance.

Problem

• cell-free massive MIMO
• low-resolution DACs
• constant-envelope precoding
• hardware impairments
• power control

Innovation

• Constant-Envelope Precoding
• Cell-Free Massive MIMO
• Low-Resolution DACs
• Power Control
• OFDM