Coarse Network Coding: A Simple Relay Strategy for Two-User Gaussian Interference Channels

Reminiscent of the parity function in network coding for the butterfly network, it is shown that forwarding an even or odd indicator bit for a scalar quantization of a relay observation recovers 1 bit of information at the two destinations in a noiseless interference channel where interference is treated as noise. Inspired by this observation, a scalar quantization-binning strategy for a two-user interference relay channel is proposed where the relay simultaneously helps both users using an out-of-band link of constant rate R₀. For the proposed strategy, we devise practical coding schemes using low-density parity-check codes for two scenarios: 1) a matched scenario where the input alphabet of the interference signal is known to the destination decoder, and 2) a mismatched scenario that assumes no such knowledge. In both scenarios, we show that our strategy significantly improves the performance. We also present a theoretical analysis of our coding scheme using generalized mutual information.