  All-digital basestation (BS) architectures for millimeter-wave (mmWave)
massive multi-user multiple-input multiple-output (MU-MIMO), which equip each
radio-frequency chain with dedicated data converters, have advantages in
spectral efficiency, flexibility, and baseband-processing simplicity over
hybrid analog-digital solutions. For all-digital architectures to be
competitive with hybrid solutions in terms of power consumption, novel
signal-processing methods and baseband architectures are necessary. In this
paper, we demonstrate that adapting the resolution of the analog-to-digital
converters (ADCs) and spatial equalizer of an all-digital system to the
communication scenario (e.g., the number of users, modulation scheme, and
propagation conditions) enables orders-of-magnitude power savings for realistic
mmWave channels. For example, for a 256-BS-antenna 16-user system supporting 1
GHz bandwidth, a traditional baseline architecture designed for a 64-user
worst-case scenario would consume 23 W in 28 nm CMOS for the ADC array and the
spatial equalizer, whereas a resolution-adaptive architecture is able to reduce
the power consumption by 6.7x.
