Reliability considerations of a selective-repeat ARQ policy for a data communication system

Abstract

This paper considers the following selective-repeat ARQ (automatic-repeat-request) policy which is mainly used in a data communication system: We transmit a block of data successively to a receiver. A negative (NAK) or positive (ACK) acknowledgement is returned from a receiver, depending on whether errors of data have occurred or not. When we have received NAK, we retransmit the erroneous block, otherwise we continue to send new blocks waiting for transmission. The expected numbers of ACK's and retransmitted blocks and the mean time until the first successive N + 1 NAK's are derived. Using these results, the optimal numbers N ∗ which minimize the mean time per successful blocks and the mean loss time in the mean time are discussed.