On ARQ-Based Fast-Fading Channels

Automatic repeat request (ARQ) protocols are normally studied under slow-fading or quasi-static channel assumption where the fading coefficients are assumed to remain fixed during the transmission of a codeword or for the duration of all ARQ retransmission rounds, respectively. This letter investigates the performance of basic ARQ and incremental redundancy hybrid ARQ protocols in fast-fading channels where a number of channel realizations are experienced in each retransmission round. Long-term throughput, delay-limited throughput and outage probability of the ARQ schemes are obtained. Compared to slow-fading and quasi-static channels, a fast-fading channel results in a higher performance for both basic and incremental redundancy ARQ. The fast-fading channel, however, can be mapped to an equivalent slow-fading model at low signal-to-noise ratios. Finally, we show that the efficiency of ARQ protocols is overestimated if the fast-fading variations during a codeword transmission are approximated by their average value.