Hybrid-ARQ Protocols Based on Tornado Codes for the Packet Erasure Channel

Lossless data transfer over communication networks has traditionally been achieved by means of ARQ protocols. However, the last ten years have seen an increasing interest in using erasure-correcting codes as an alternative, with the goal of reducing latency, feedback overhead, etc. Since these two approaches possess advantages as well as drawbacks, several hybrid ARQ schemes have also been proposed as good compromise solutions, in order to attain the “best of both worlds”. Extending this principle, this paper develops new classes of hybrid ARQ protocols for erasure channels that allow for flexible trade-offs between two important cost metrics, viz., the
computational complexity of coding
, and the
amount of feedback
needed. Our hybrid schemes make use of Tornado codes – a class of low-complexity capacity-achieving erasure codes – whose coding structure is well-suited for feedback-based communications. These schemes demonstrate significant cost reductions versus coding-only and feedback-only approaches over a wide region of interest. Moreover, these schemes are easily tuned to achieve different operating points on a trade-off curve. Finally, the proposed schemes showcase novel means of interweaving coding and feedback.