Uplink Performance of Scalable Cell-Free Massive MIMO With Low-Resolution ADCs

This paper investigates the impact of low-resolution analog-to-digital converters (ADCs) on scalable cell-free massive MIMO systems. The ADC quantization distortion is modeled using the additive quantization noise model (AQNM) to derive the minimum mean square error (MMSE) channel estimate. The results show that low-resolution ADCs and pilot contamination lead to error floor of NMSE. Then, to achieve system scalability, a scalable local partial MMSE (LP-MMSE) combining and scalable near-optimal LSFD (no-LSFD) strategies are obtained. The simulation results show that the spectral efficiency (SE) performance of these two schemes is essentially the same as that of the unscalable optimal combining vectors and the optimal LSFD. In addition, we investigate the trade-off between spectral efficiency (SE) and energy efficiency (EE), as well as the effects of the number of quantization bits and the number of antennas at the APs on EE. The resulting observations show that a good tradeoff between SE and EE can be achieved by choosing an appropriate quantization bit.