  We consider a downlink 1-bit quantized multiuser (MU)
multiple-input-multiple-output (MIMO) system, where 1-bit digital-to-analog
(DACs) and analog-to-digital converters (ADCs) are used at the transmitter and
the receiver for economical and computational efficiency. We end up with a
discrete memoryless channel with input and output vectors belonging to the QPSK
constellation. In the context of massive (MIMO) systems the number of base
station (BS) antennas is much larger than the number of receive antennas. This
leads to high input cardinality of the channel. In this work we introduce a
method to reduce the input set based on the mimimum bit-error-ratio (BER)
criterion combined with a non-linear precoding technique. This method is
denoted as spatial coding. Simulations show that this spatial coding improves
the BER behavior significantly removing the error floor due to coarse
quantization.
