Performance of Cell-Free Distributed Antenna System with Adaptive-Resolution ADCs

In this paper, we propose a cell-free distributed antenna system (DAS) architecture with adaptive resolution-(AR-) analog-to-digital converters (ADCs) in access points (APs). The proposed scheme adopts accurate models of the combined effects of clipping, quantization, and thermal noise in the ADC to analyze the quantization characteristics with different resolutions at different received signal-to-interference-and-noise ratios (SINRs). The proposed resolution bit selection criterion of the AR-ADC scheme is then applied. The AR-ADC scheme is to minimize the ADC resolution bits under allowable quantization distortion, and obtain the corresponding optimal clipping factor of the signal-to-interference -plus-quantization-and-noise ratio (SIQNR) for the desired received signal. The contributions of this paper are as follows; 1) the AR-ADC scheme provides a receiver architecture that realizes better energy efficiency (EE), 2) the spectral efficiency (SE) performance is improved by allocating more resolution bits to the APs closer to each UE with the proposed criterion. Numerical results demonstrate that the proposed AR-ADC scheme improves the EE more than tenfold as compared with the other schemes except the system with only 1???bit ADCs. Moreover, the proposed AR-ADC doubles the SE as compared with the system with only 1-bit ADCs.