This paper considers the secure transmission in a cell-free massive MIMO system with imperfect radio frequency (RF) chains and low-resolution analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) at both access points (APs) and legitimate users, where an active eavesdropper attempts to wiretap the confidential data. The Gaussian RF impairment model (GRFIM) and additive quantization noise model (AQNM) are used to evaluate the impacts of the RF impairments and low resolution ADCs/DACs, respectively. The analytical results of the linear minimum mean square error (MMSE) channel estimation show that there is nonzero floor on the estimation error with respect to the RF impairments, ADC/DAC precision and the pilot power of the eavesdropper which is different from the conventional case with perfect transceiver. Then, a tractable closed-form expression for the ergodic secrecy rate is obtained with respect to key system parameters, such as the antenna number per AP, the AP number, user number, quality factors of the ADC/DAC and the RF chain, pilot signal power of the eavesdropper, etc. Moreover, a compensation algorithm between the imperfect RF components and the inexpensive coarse ADCs/DACs is also presented. Finally, numerical results are provided to illustrate the efficiency of the achieved expressions and the devised algorithm, and show the effects of RF impairments and low resolution ADC/DAC on the secrecy performance.

中文翻译：

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具有射频损伤和低分辨率 ADC/DAC 的无蜂窝大规模 MIMO 中的安全传输


本文考虑了无小区大规模 MIMO 系统中的安全传输，该系统在两个接入点均具有不完善的射频 (RF) 链以及低分辨率模数转换器 (ADC) 和数模转换器 (DAC)（ AP）和合法用户，其中活跃的窃听者试图窃听机密数据。高斯 RF 损伤模型 (GRFIM) 和加性量化噪声模型 (AQNM) 分别用于评估 RF 损伤和低分辨率 ADC/DAC 的影响。线性最小均方误差(MMSE)信道估计的分析结果表明，对于RF损伤、ADC/DAC精度和窃听者的导频功率，估计误差存在非零下限，这与传统情况不同具有完美的收发器。然后，针对关键系统参数，例如每个 AP 的天线数量、AP 数量、用户数量、ADC/DAC 和 RF 链的质量因数、导频，获得遍历保密率的易于处理的封闭式表达式。此外，还提出了不完善的射频元件和廉价的粗ADC/DAC之间的补偿算法。最后，提供数值结果来说明所实现的表达式和设计的算法的效率，并显示 RF 损伤和低分辨率 ADC/DAC 对保密性能的影响。