Low Complexity Two-Stage Decoders for BAWGN

摘要

The object of the paper is the design of two-stage co-decoders (codecs) with one hard decoded stage to reduce the decoder complexity. It will be shown that properly designed schemes with that structure can yield performance close to the information-theoretical limits while decreasing the decoder complexity. We focus the attention on the design of schemes for the binary input AWGN channel (BAWGN) in a large SNR range. The structure of the designed codec includes two stage encoders and one inner “channel polarizing code”, whose aim is to turn an AWGN channel into a worse and a better channel. The rationale of this operation is that both “very bad channels” and “very good channels” admit simpler hard-input decoders. After showing that for the positive (high) SNR and negative (low) SNR regime the optimal codec has a different optimal structure, the focus is concentrated on the case of low SNR, where binary modulation is indeed the best one. For low SNR regimes, the best solution consists of a very low rate (possibly zero) encoder at first stage coupled with a hard-input decoder, followed by a capacity-achieving encoder associated to a soft-input iterative decoder. The rate splitting between the two stages allows to construct flexible and low complexity encoding schemes for very large SNR ranges.