Design Criteria for Linear Precoders based on a Bitwise Capacity Argument

The use of linear precoding in bit-interleaved coded modulation with iterative decoding leads to a significant performance improvement on AWGN channels. In this contribution, we approach linear precoding from an information theoretical perspective. We compute the bitwise capacity as seen by each of the precoder inputs in order to investigate the impact of precoding for two scenarios: using (i) a non-iterative decoder and (ii) an iterative decoder under a perfect feedback assumption. When restricting to BPSK signaling, the bitwise capacity reveals simple precoding design rules for both scenarios. Simulation results confirm our analytical findings