Reliability-based hybrid ARQ and rate-compatible punctured convolutional (RCPC) codes

Abstract

Reliability-based hybrid ARQ (RB-HARQ) is a recently developed form of incremental-redundancy ARQ. The RB-HARQ technique can be used with codes that use soft-input, soft-output (SISO) decoders, such as convolutional codes and turbo codes. In RB-HARQ, the bits that are to be retransmitted are adaptively selected at the receiver based on the estimated bit reliabilities at the output of a SISO decoder. This technique has the potential to improve performance and minimize retransmission size by targeting those bits that are likely to be in error. It has already been shown that RB-HARQ achieves significant performance improvement provided that large retransmission-request (NACK) packets can be afforded on the feedback link. In this paper, we propose and evaluate the performance of a RB-HARQ technique that uses rate-compatible punctured convolutional (RCPC) codes in the forward channel and source coding in the feedback link. The proposed technique uses source coding to achieve small request packets, thus leading to better performance. The performance of the proposed technique is evaluated in terms of probability of bit error, probability of packet error and throughput. We also compare the performance of the proposed scheme with the common approach to hybrid-ARQ that uses punctured convolutional codes and code combining. The results show that the proposed RB-HARQ scheme achieves better performance than a hybrid-ARQ scheme that uses only RCPC codes.