Rate Analysis of Full-Pilot Zero-Forcing in Cell-Free Massive MIMO with Low- Resolution ADCs

In contrast to classical zero-forcing (ZF) receiver, a new one called full-pilot zero-forcing (fpZF) receiver is exploited in our work. Based on this, we investigate the achievable uplink rate of a cell-free massive multi-input multi-output (MIMO) system with low-resolution analog-to-digital converters (ADCs) at the access points (APs). In order to carry out the tractable analysis on multiple quantization bits, we advocate the additive quantization noise model (AQNM). Quantization technology is a very effective method to lower the cost of transmission in the case where high data fidelity is not needed. After each AP receiving the payload data transmitted from all users, the quantization procedure is implemented in a distributed manner. Then a closed-form expression of achievable uplink rate is derived, which helps us to investigate system performance. The results in our simulation experiments indicate the fpZF receiver performs much better than the conjugate beamforming (CB) receiver when high-bit ADCs are used to process these received signals. However, when few-bit ADCs are adopted, its performance will decrease a lot and is dramatically inferior to the CB receiver, which is not as well as we expect. This observation demonstrates the fpZF receiver is more sensitive to the quantization operation than the CB receiver.