Uplink Performance Analysis of Cell-Free MIMO with Low-Resolution ADCs and ZF Receiver

The cell-free massive multiple-input multiple-output (mMIMO) system is considered in this paper. In contrast to previous works, this paper quantizes the pilot and all the users' signals utilizing low-resolution analog-to-digital converters (ADCs) before they are transmitted to the central processing unit (CPU). The additive quantization noise model (AQNM) is used to characterize the quantization distortion. Moreover, a zero-forcing (ZF) receiver is advocated since it is free from inter-user interference. Based on the AQNM and the ZF receiver, a strict closed-form rate expression is derived, which motivates us to analyse the effect of quantization bits on the system performance. Simulation results show that 6-bit is the minimum quantized bit, which can achieve the same rate as a cell-free mMIMO system with perfect ADCs. In addition, 1-bit ADCs and 2-bit ADCs can result in severe rate degradation.