  Coarse quantization at the base station (BS) of a massive multi-user (MU)
multiple-input multiple-output (MIMO) wireless system promises significant
power and cost savings. Coarse quantization also enables significant reductions
of the raw analog-to-digital converter (ADC) data that must be transferred from
a spatially-separated antenna array to the baseband processing unit. The
theoretical limits as well as practical transceiver algorithms for such
quantized MU-MIMO systems operating over frequency-flat, narrowband channels
have been studied extensively. However, the practically relevant scenario where
such communication systems operate over frequency-selective, wideband channels
is less well understood. This paper investigates the uplink performance of a
quantized massive MU-MIMO system that deploys orthogonal frequency-division
multiplexing (OFDM) for wideband communication. We propose new algorithms for
quantized maximum a-posteriori (MAP) channel estimation and data detection, and
we study the associated performance/quantization trade-offs. Our results
demonstrate that coarse quantization (e.g., four to six bits, depending on the
ratio between the number of BS antennas and the number of users) in massive
MU-MIMO-OFDM systems entails virtually no performance loss compared to the
infinite-precision case at no additional cost in terms of baseband processing
complexity.
