Efficient Receiver Design for Uplink Cell-Free Massive MIMO With Hardware Impairments

This paper investigates the effect of hardware impairments on the achievable performance of cell-free (CF) massive multiple-input multiple-output (MIMO) systems with four low-complexity receiver cooperation among the multiple antennas access points (APs), included large scale fading decoding (LSFD), simple LSFD, simple centralized decoding and small cell. Taking into account the joint hardware impairment (HI) effects brought by both APs and user equipments, we derive closed-form expressions for uplink spectral efficiency (SE) of CF massive MIMO systems. It is found that LSFD can achieve the largest SE. Furthermore, a novel hardware-quality scaling law is presented to reveal the relationship between the number of antennas and HI. Based on these results, we provide important insights into the practical impact of HI. For example, the impact of HI at the APs vanishes as the number of APs grows. Finally, numerical results validate our derived results.