On the role of puncturing in hybrid ARQ schemes

In mobile packet data transmission, a special coding/retransmission scheme, known as the type-II hybrid-ARQ (HARQ), achieves higher throughput efficiency then fixed rate codes by adapting their rate to fluctuating channel conditions characteristic for this application. Codes of different rates are obtained by puncturing a chosen low-rate "mother" code. We introduce the notion of random puncturing as a tool to evaluate the performance of punctured codes averaged over a class of puncturing patterns. We illustrate the power of this tool by comparing the throughput performance of an HARQ scheme based on optimized rate compatible puncturing with the throughput performance of an HARQ scheme based on random rate compatible puncturing of the same mother turbo code.