On the Performance of Cell-Free Massive MIMO With Mixed-ADC Under Rician Fading Channels

In this letter, we introduce a mixed analog-to-digital converter (ADC) receiver architecture to cell-free massive multi-input multi-output (mMIMO) system under Rician fading channels. In particular, the mixed-ADC architecture permits some of receiver's antennas to be implemented with economical low-resolution ADCs, while the rests are equipped with high-priced perfect ADCs. Leveraging on the additive quantization noise model (AQNM), a tight approximate uplink spectral efficiency (SE) expression with matched filtering receiver is derived, which provides us with a tool for easily quantifying the impacts of the Rician K-factor, the quantization bit of low-resolution ADCs, and the proportion of the perfect ADCs in the mixed-ADC architecture. Numerical observations demonstrate that the mixed-ADC architecture with a small fraction of perfect ADCs has a great potential to boost the SE compared to the case with pure low-resolution ADCs. Moreover, the mixed-ADC architecture is superior to the full perfect ADCs counterpart in terms of energy efficiency (EE).