A Turbo-Like Iterative Decoding Algorithm for Network Coded HARQ

This paper proposes a turbo-like decoding algorithm for network coded HARQ (NC-HARQ) retransmission scheme. Instead of retransmission erroneous packets individually, we send a network coded packet formed by XOR of two incorrectly received packets in the NC-HARQ retransmission. With respect to the two initial packets and one network coded packet, this retransmission scheme can be viewed as a product code based on the Turbo coding principle. We develop an iterative decoding algorithm for the proposed NC-HARQ scheme. The algorithm uses the log-likelihood ratios generated by decoding any two packets to calculate a priori information for the third one. This approach is applicable for both Chase Combing (CC) and Incremental Redundancy (IR). Furthermore, a link adaptation algorithm is investigated for the proposed network coded HARQ scheme. LTE link-level simulations confirm the throughput enhancement by the proposed scheme compared to common HARQ transmission.