Joint Design of Channel Coding and Modulation Toward 6G: Probabilistically-Shaped Polar-Coded Modulation

The forthcoming sixth-generation (6G) wireless system brings forth the need to meet increasingly stringent performance criteria, necessitating refinement and advanced design of channel coding and modulation techniques. Within this context, polar codes stand out as a competitive candidate due to their favorable attributes. This study delves into probabilistically-shaped polar-coded modulation (PS-PCM) for its potential to enhance spectral efficiency and error-correction performance, offering a pragmatic design geared toward standardization. Specifically, we present a coding chain for PS-PCM that ensures backward compatibility with legacy 5G polar codes. We also propose, for the first time, a channel-independent method for constructing PS-PCM that eliminates the need for on-the-fly computations, which is an imperative attribute for practical system implementation. The core of this code construction method is the utilization of a surrogate channel to allocate rates to each component code while considering the varying probability distributions and protection levels of label bits. The assigned component code rates can be seamlessly integrated into the modulation and coding scheme (MCS) table to facilitate rapid construction for both base stations and user equipment. Furthermore, we devise flexible rate matching methods to allow fine granularity adjustment of rates and blocklengths for PS-PCM. Simulation results validate the efficacy of our proposed approaches, which also provide insights and benchmarks for the capability of PS-PCM to meet requirements for enhanced spectral efficiency, higher reliability, and more flexibility.