Multi-Rate CRC-Aided TBCC via Bit Repetition: Construction and Decoding

Abstract

Cyclic redundancy check-aided tail-biting convolutional codes (CRC-TBCCs) have shown strong potential for hyper-reliable and low-latency communications (HRLLC), particularly due to their excellent performance in short block lengths. However, their ability to support variable input lengths remains underexplored. This work addresses that gap by introducing a novel framework for flexible-length encoding using CRC-TBCC. The proposed scheme combines a fixed-length cyclic redundancy check (CRC) with bit repetition, enabling the encoder to accept variable-length input sequences while maintaining a fixed output length. Two novel techniques are proposed to fully exploit the potential of CRC. First, we prioritize the repetition of CRC bits. Second, the CRC bits, including their repetitions, are evenly multiplexed with the information bits. To support the proposed encoding method, we introduce a tailored pre-processed list Viterbi decoding algorithm. In the proposed decoder, pre-processing is first applied to enhance the reliability of the edges of the TBCC trellis by exploiting the constraint of repetition. After pre-processing, the serial list Viterbi algorithm (SLVA) is then executed to identify the candidate paths, which are subsequently checked by both the repetition and CRC constraints. We also propose an erasure-aided pre-processed SLVA to further improve the decoding performance. Extensive simulation results demonstrate the effectiveness of the proposed repetition and multiplexing techniques and the two-stage decoder. In particular, compared to existing flexible coding schemes, the proposed multi-rate CRC-TBCCs with the pre-processed SLVA show notable performance gains. These results make CRC-TBCC a promising solution for 6G HRLLC, where high flexibility and high performance are both required.