Efficient Receiver for Cell-Free Massive MIMO Systems with Low-Resolution ADCs

Cell-free massive multiple-input multiple-output (MIMO) is considered as a promising technology for providing uniformly good services in future networks. The aim of this paper is to provide the first comparison of the uplink performance of cell-free massive MIMO systems with low-resolution analogto-digital converters under the zero-forcing (ZF) and maximum ratio combining (MRC) receivers. By utilizing an addictive quantization model, a novel closed-form uplink spectral efficiency (SE) expression is derived for the ZF receiver. Moreover, the energy efficiency (EE) of the considered system is analyzed. In contrast to previous works, it turns out that the ZF receiver outperforms the MRC receiver with a large number of quantization bits in terms of SE and EE. Furthermore, it is interesting to find that a better EE-SE trade-off can be achieved by employing a large number of antennas at the access point. Finally, pilot assignment schemes are used to minimize the pilot contamination and a maxmin power control scheme is proposed to improve both SE and EE performance.