Variable-Rate Transmission for Incremental Redundancy Hybrid ARQ

We analyze the throughput achievable by a truncated Hybrid ARQ protocol (HARQ) using incremental redundancy (IR) when transmitting over a block-fading channel whose state is unknown at the transmit end. We allow the transmission rates to vary, optimize them, and show that such a variable-rate HARQ-IR provides gains with respect to a fixed-rate transmission in terms of increased throughput and decreased average number of transmissions.