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 fixed-rate transmission in terms of increased throughput and decreased average number of transmissions, reducing at the same time the outage probability. 
Leszek Szczecinski, Ciro Correa, and Luciano Ahumada
cs.IT math.IT