GRAND-Assisted Demodulation

We propose a novel demodulation technique that leverages developments in guesswork-based forward error correction decoders and variable-length bit-to-symbol mappings. For most common channel models, the optimal modulation schemes are known to require nonuniform probability distributions over signal points, which presents practical challenges. An established way to map uniform binary sources to non-uniform symbol distributions is to assign a different number of bits to different constellation points. Doing so, however, means that erroneous demodulation at the receiver can lead to bit insertions or deletions, turning a channel with Hamming-type errors into an insertion-deletion channel. The demodulator we propose provides error detection and correction through the use of a low-overhead padding bit sequence. We evaluate the performance of the proposed demodulator in various channel models and various communication settings. We verify that the demodulator successfully corrects the insertion-deletion errors. Using the proposed demodulator, we study different constellation design schemes and how they behave in different channel conditions. Overall, we observe considerable gains that suggest, in some circumstances, one may improve the throughput while keeping the error rate the same.