Polar Coded Modulation via Hybrid Bit Labeling

TL;DR

This paper introduces a hybrid polar coded modulation scheme combining BICM and MLC techniques, improving performance and reducing latency for high-order modulation in future communication systems.

Contribution

A novel hybrid labeling scheme that integrates SP and Gray labeling for polar coded modulation, bridging performance gaps between BICM and MLC.

Findings

Hybrid scheme nearly closes performance gap between BICM and MLC.

Significant latency reduction compared to MLC.

Effective for 256-QAM with polar codes at rate 1/2.

Abstract

Bit-interleaved coded modulation (BICM) and multilevel coded modulation (MLC) are commonly used to combine polar codes with high order modulation. While BICM benefits from simple design and the separation of coding and modulation, MLC shows better performance under successive-cancellation decoding. In this paper we propose a hybrid polar coded modulation scheme that lies between BICM and MLC, wherein a fraction of bits are assigned to set-partition (SP) labeling and the remaining bits are assigned for Gray labeling. The SP labeled bits undergo sequential demodulation, using iterative demodulation and polar decoding similar to MLC, whereas the Gray labeled bits are first demodulated in parallel and then sent for decoding similar to BICM. Either polar codes or other channel codes (such as LDPC codes) can be used for the Gray labeled bits. For length 2048 rate 1/2 polar code on 256-QAM, the performance gap between BICM (Gray labeling only) and MLC (SP labeling only) can be almost fully closed by the hybrid scheme. Notably, the hybrid scheme has a significant latency advantage over MLC. These performance gains make the proposed scheme attractive for future communication systems such as 6G.