MAC rate region of low resolution ADC digital and hybrid beamforming massive MIMO UL

For 5G it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omnidirectional coverage with a similar effective antenna aperture, an antenna array is required at both the mobile and basestation. Due to the large bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog front-end of the transceiver with a large number of antennas is especially power hungry. Two main solutions exist to reduce the power consumption: Hybrid BeamForming (HBF) and Digital BeamForming (DBF) with low resolution ADC. This work compares the uplink rate region for both systems assuming a basestation with a large number of antennas. We show, that in the low SNR regime, the performance of DBF even with about 1-2 bits of resolution outperforms the one of HBF in terms of the achievable sum rate. The higher the SNR, the higher also the required resolution of the ADC to achieve a similar performance compared to HBF. If there is a large spread in receive power of the signal from different users, systems with very low resolution (1-3 bit) suffer from a performance loss.