The analysis of the adaptive three-mode ARQ GBN scheme using retransmission cycles mechanism

This paper presents the new throughput analysis of the adaptive three-mode automatic-repeat-request (TM-ARQ) system. TM-ARQ system adapts to the channel operating conditions by following one of the “Go-back N” (GBN) procedures: standard GBN (SGBN), n  -copy GBN (nnGBN) and continuous GBN (CGBN), depending on channel drawback intensity (low, moderate or high). Channel state estimation is based on counting the ACK/NAK acknowledgements. The throughput analysis of this model is conducted using new, exact method, which is based on determination of the time cycles duration required for successful packet transmission–retransmission cycles. By applying this method, the number of approximations in TM-ARQ model analysis has been reduced to minimum, thus obtaining the more accurate results, compared to the mathematical methods used so far. The validity of the proposed calculation method has been proved on examples of GBN-based protocols. The results obtained through exact analysis match the expressions known for throughput of these protocols. In that way, it has been shown that the method that is based on determination of retransmission cycles duration, can be applied on all kinds of adaptive protocols with aim of obtaining the most accurate results.