Performance analysis of uplink massive MIMO systems with variable-resolution ADCs using MMSE and MRC detection

In this paper, we analyze the performance of uplink massive multiple-input-multiple-output (MIMO) systems with variable-resolution analog-to-digital converters (ADCs), ie, each receive antenna uses a pair of ADCs with arbitrary resolution. Given that the minimum mean square error (MMSE) or the maximum ratio combining (MRC) detection can be employed at the base station (BS); using perfect channel state information (CSI) and results from the random matrix theory, we first derive the closed-form approximate expression of sum achievable rate for these two type detectors, respectively. Suppose that only imperfect CSI is available at the BS. We then provide a scheme to estimate the equivalent channel based on the classical linear MMSE technique and derive the sum achievable rate using the estimated equivalent channel. Moreover, to improve the system performance, we take the impacts of channel estimation error and quantization noise into account and achieve the corresponding analytical results. Finally, simulation results are presented to validate our theoretical analysis and provide some insights on the massive MIMO systems with variable resolution ADCs. Additionally, for the MMSE and MRC detector with perfect and imperfect CSI in the considered architecture, the trade-off between the spectral efficiency and the energy efficiency is investigated as well.