We consider the downlink of an ultra-reliable low-latency communication (URLLC) cell-free (CF) massive multi-input-multi-output (mMIMO) system, with dual-polarized antennas at access point (AP), and user equipments. We assume that APs are equipped with low-quality radio-frequency (RF) chains and low-resolution analog-to-digital converters/digital-to-analog converters (ADC/DACs), which distort their transmit and receive signals. To mitigate these impairments, we propose a novel distortion-aware minimum-mean-square-error (DA-MMSE) precoder by exploiting the knowledge of RF and ADC/DAC impairment correlation matrices. We apply large dimensional random matrix theory to derive a closed-form spectral efficiency expression. We use it to analytically show that RF and ADC/DAC impairment levels increase as the system becomes more distributed, which necessitates the use of DA-MMSE precoder to achieve a desirable URLLC performance. We also show the effectiveness of DA-MMSE precoder and dual-polarized antennas in meeting the strict URLLC constraints.

中文翻译：

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具有双极化天线和硬件损伤的 URLLC CF 大规模 MIMO 系统


我们考虑了超可靠低延迟通信 （URLLC） 无小区 （CF） 大规模多输入多输出 （mMIMO） 系统的下行链路，在接入点 （AP） 和用户设备上具有双极化天线。我们假设 AP 配备了低质量的射频 （RF） 链和低分辨率的模数转换器/数模转换器 （ADC/DAC），这会使它们的发射和接收信号失真。为了减轻这些损伤，我们利用 RF 和 ADC/DAC 损伤相关矩阵的知识，提出了一种新的失真感知最小均方误差 （DA-MMSE） 预编码器。我们应用大维随机矩阵理论来推导出闭式谱效率表达式。我们用它来分析表明，RF 和 ADC/DAC 损伤水平随着系统变得更加分散而增加，这需要使用 DA-MMSE 预编码器来实现理想的 URLLC 性能。我们还展示了 DA-MMSE 预编码器和双极化天线在满足严格的 URLLC 约束方面的有效性。