# Circular Buffer Rate-Matched Polar Codes

## TL;DR

This paper introduces a practical circular buffer rate-matching scheme for polar codes, enabling flexible, capacity-approaching transmissions on various channels with HARQ support and higher order modulations.

## Contribution

It proposes a novel rate-matching method based on two-stage polarization, suitable for any code length, rate, and modulation, with low complexity and capacity-achieving performance.

## Key findings

- Achieves symmetric capacity of BICM channels.
- Competitive performance against LDPC and turbo codes.
- Supports flexible rate and length adaptation with low complexity.

## Abstract

A practical rate-matching system for constructing rate-compatible polar codes is proposed. The proposed polar code circular buffer rate-matching is suitable for transmissions on communication channels that support hybrid automatic repeat request (HARQ) communications, as well as for flexible resource-element rate-matching on single transmission channels. Our proposed circular buffer rate matching scheme also incorporates a bit-mapping scheme for transmission on bit-interleaved coded modulation (BICM) channels using higher order modulations. An interleaver is derived from a puncturing order obtained with a low complexity progressive puncturing search algorithm on a base code of short length, and has the flexibility to achieve any desired rate at the desired code length, through puncturing or repetition. The rate-matching scheme is implied by a two-stage polarization, for transmission at any desired code length, code rate, and modulation order, and is shown to achieve the symmetric capacity of BICM channels. Numerical results on AWGN and fast fading channels show that the rate-matched polar codes have a competitive performance when compared to the spatially-coupled quasi-cyclic LDPC codes or LTE turbo codes, while having similar rate-dematching storage and computational complexities.