ADAPTIVE HYBRID ARQ PROTOCOL FOR CONTINUOUS-TIME MARKOVIAN CHANNELS.

Abstract

The authors analyze the throughput of an adaptive hybrid automatic repeat request (ARQ) communications protocol used with a continuous-time two-state Markovian channel. The proposed protocol adapts to changes in the channel state, i. e. , changes in noise level, by selecting one of two block error-correction codes for each packet according to an estimate of the next channel state; the estimate, based on the error pattern in the previous packet, is fed back to the transmitter with the acknowledgment. The authors also compare throughputs and computational costs of three next-state estimators. The first, an optimal estimator, is shown to be impractical. A second, suboptimal, estimator is found to require negligible computation and memory. An improved suboptimal estimator is also considered. Throughputs are evaluated and numerical results are presented.