I. Introduction
Cell-free massive multiple-input multiple-output (MIMO) has emerged as a cornerstone of the sixth generation (6G) mobile communication systems [1]. However, it suffers from high power consumption, caused by a tremendous amount of high-resolution analog-to-digital converters (ADCs). To address this issue, one prospective solution is reducing the resolution of ADCs, which has been validated in conventional massive MIMO systems [2], [3], [4]. Along this line, considering cell-free networks, many studies have investigated the performance analysis and optimization for uplink maximum ratio combining (MRC) and minimum mean-squared error (MMSE)-based combiners [5], [6].