  We investigate uplink user scheduling for millimeter wave (mmWave) hybrid
analog/digital beamforming systems with low-resolution analog-to-digital
converters (ADCs). Deriving new scheduling criteria for the mmWave systems, we
show that the channel structure in the beamspace, in addition to the channel
magnitude and orthogonality, plays a key role in maximizing the achievable
rates of scheduled users due to quantization error. The criteria show that to
maximize the achievable rate for a given channel gain, the channels of the
scheduled users need to have (1) as many propagation paths as possible with
unique angle-of-arrivals (AoAs) and (2) even power distribution in the
beamspace. Leveraging the derived criteria, we propose an efficient scheduling
algorithm for mmWave zero-forcing receivers with low-resolution ADCs. We
further propose a chordal distance-based scheduling algorithm that exploits
only the AoA knowledge and analyze the performance by deriving ergodic rates in
closed form. Based on the derived rates, we show that the beamspace channel
leakage resulting from phase offsets between AoAs and quantized angles of
analog combiners can lead to sum rate gain by reducing quantization error
compared to the channel without leakage. Simulation results validate the sum
rate performance of the proposed algorithms and derived ergodic rates
expressions.
