  Base stations in 5G and beyond use advanced antenna systems (AASs), where
multiple passive antenna elements and radio units are integrated into a single
box. A critical bottleneck of such a system is the digital fronthaul between
the AAS and baseband unit (BBU), which has limited capacity. In this paper, we
study an AAS used for precoded downlink transmission over a multi-user
multiple-input multiple-output (MU-MIMO) channel. First, we present the
baseline quantization-unaware precoding scheme created when a precoder is
computed at the BBU and then quantized to be sent over the fronthaul. We
propose a new precoding design that is aware of the fronthaul quantization. We
formulate an optimization problem to minimize the mean squared error at the
receiver side. We rewrite the problem to utilize mixed-integer programming to
solve it. The numerical results manifest that our proposed precoding greatly
outperforms quantization-unaware precoding in terms of sum rate.
