Accurate approximation of ARQ packet delay statistics over Markov channels with finite round-trip delay

In this paper the packet delay statistics of a fully reliable selective-repeat ARQ scheme is investigated. The sender transmits packets whose error process is characterized by means of a two-state discrete time Markov channel (DTMC). At the receiver, these packets are checked for errors and ACK/NACK messages are sent back to the sender accordingly. It is assumed that the feedback message is known with no errors at the transmitter m channel slots (round-trip delay) after the packet transmission started. An appropriate Markov model has been previously developed in order to find exact statistics of the delays experienced by ARQ packets. In this work, in order to reduce the computational complexity of such analysis, an appropriate model is presented. The results obtained from the approximate approach are shown to be in excellent agreement with the ones derived from the exact analysis.