  We consider the problem of jointly optimizing ADC bit resolution and analog
beamforming over a frequency-selective massive MIMO uplink. We build upon a
popular model to incorporate the impact of low bit resolution ADCs, that
hitherto has mostly been employed over flat-fading systems. We adopt weighted
sum rate (WSR) as our objective and show that WSR maximization under finite
buffer limits and important practical constraints on choices of beams and ADC
bit resolutions can equivalently be posed as constrained submodular set
function maximization. This enables us to design a constant-factor
approximation algorithm. Upon incorporating further enhancements we obtain an
efficient algorithm that significantly outperforms state-of-the-art ones.
