Variable-rate Retransmissions for Incremental Redundancy Hybrid ARQ

The throughput achievable in truncated Hybrid ARQ protocol (HARQ) using incremental redundancy (IR) in analyzed when transmitting over a block-fading channel whose state is unknown at the transmitter. We allow the transmission lengths to vary, optimize them efficiently via dynamic programming, and show that such a variable-rate HARQ-IR provides gains with respect to a fixedrate transmission in terms of increased throughput and decreased average number of transmissions, reducing at the same time the outage probability. Index Terms Automatic Repeat Request, ARQ, Hybrid ARQ, HARQ, Incremental Redundancy, IR, Block-fading channel, Throughput