  This paper studies the performance of hybrid-ARQ (automatic repeat request)
in Rayleigh block fading channels. The long-term average transmitted rate is
analyzed in a fast-fading scenario where the transmitter only has knowledge of
channel statistics, and, consistent with contemporary wireless systems, rate
adaptation is performed such that a target outage probability (after a maximum
number of H-ARQ rounds) is maintained. H-ARQ allows for early termination once
decoding is possible, and thus is a coarse, and implicit, mechanism for rate
adaptation to the instantaneous channel quality. Although the rate with H-ARQ
is not as large as the ergodic capacity, which is achievable with rate
adaptation to the instantaneous channel conditions, even a few rounds of H-ARQ
make the gap to ergodic capacity reasonably small for operating points of
interest. Furthermore, the rate with H-ARQ provides a significant advantage
compared to systems that do not use H-ARQ and only adapt rate based on the
channel statistics.
