On the delay statistics of SR ARQ over Markov channels with finite round-trip delay

In this paper, the packet delay statistics of a fully reliable selective repeat automatic repeat request (SRARQ) scheme is investigated. The study is carried out assuming that the packet error process can be characterized by means of a discrete time Markov channel. The packets transmitted by the sender are checked for errors at the receiver´s side, and acknowledgment messages (ACK or NACK), assumed error free, are sent back accordingly. It is assumed that the feedback message is known at the transmitter m channel slots after the packet transmission started. First, an analytical exact approach is described, in which an appropriate Markov model is developed in order to find the exact delay statistics. This allows to write close formulas related to the delivery delay experienced by ARQ packets. Moreover, in order to reduce the computational complexity of this analysis, an approximate model is presented. The results obtained from the approximate approach are in good agreement with the ones derived from the exact analysis.