Blind Recognition of Polar Codes Using Successive Cancellation List Decoding

TL;DR

This paper introduces a blind recognition method for polar codes using successive cancellation list decoding, exploiting statistical differences in soft information to improve recognition success rates.

Contribution

The proposed method uniquely leverages soft decision log-likelihood ratios and path reliability to enhance blind recognition of polar codes with known length.

Findings

Achieves at least 2.5 dB gain over previous methods for certain polar codes.

Recognition success rate improves with larger list sizes.

Effective in non-cooperative scenarios for polar code recognition.

Abstract

Blind recognition of polar codes remains challenging in non-cooperative scenarios, particularly for information-set recognition with known code length. Existing methods mainly rely on threshold decisions determined by the generator-matrix structure and channel bit error probability, without fully exploiting the soft information in received signals. In this letter, we propose a blind recognition method using successive cancellation list (SCL) decoding for polar codes with known code length. The proposed method exploits the distinct statistical behaviors of frozen and information bits in source-side decision log-likelihood ratios (LLRs) over multiple received vectors: frozen bits tend to favor zero decisions, whereas information bits exhibit nearly equiprobable $0/1$ decisions. Based on this property, the decoder expands candidate paths under the frozen-bit and information-bit hypotheses at each bit position, evaluates their reliabilities using the corresponding average path metrics, and retains only the $L_{\mathrm{list}}$ most reliable paths for subsequent recognition. Finally, the information-set pattern corresponding to the most reliable surviving path is selected as the recognition result. Simulation results show that the proposed scheme improves the recognition success rate as the list size increases. For the $(32,16)$, $(64,32)$, and $(128,64)$ polar codes, it achieves at least $2.5$ dB gain over the previous method when $L_{\mathrm{list}}=64$.