An effective go-back-N ARQ scheme for variable-error-rate channels

RQ (AUTOMATIC-REPEAT-REQUEST) techniques, A including stop-and-wait, go-back-N, and selective repeat, are widely used for error control in data communication systems. Particularly, the go-back-N ARQ scheme is very popular because it provides higher throughput compared to stop-and-wait ARQ, and its implementation is simpler than selective repeat ARQ since it does not require buffering and resequencing at the receiver end [I]. The operation procedure and throughput efficiency of the basic go-back-N scheme is well known. One disadvantage of this scheme is that its throughput decreases quickly when the error probability increases, especially when the roundtrip delay is large, because of the repeated retransmissions of the N blocks (assuming that the roundtrip delay is equivalent to the N 1 block transmission duration). Sastry modified the basic go-back-N scheme by transmitting the erred block continuously until an ACK (positive acknowledgment) is received [2] which improves the efficiency when the block error probability, P,, is larger than 0.5. Moeneclaey and Bruneel proposed an ARQ scheme [3] which further improves the basid go-back-N efficiency when P, > 0.5. Most studies of ARQ schemes are conducted under the assumption of a fairly constant level of channel noise, i.e., a stationary channel. For example, the approaches given in [2] and [3] result in better performance than the basic go-backN scheme only if the channel stays in a very noisy state. This letter proposes a go-back-N scheme for nonstationary channels where the error rate changes (P, varies from as low as approaching zero to as high as 0.5 or above, possibly in a wireless communication environment). In this scheme, the transmitter estimates the channel state (lowhigh error rate) in a simple manner and adaptively changes its operation mode. It provides higher throughput than other comparable schemes under a wide range of error rate conditions. The idea of dynamically changing the ARQ algorithm was previously considered in the technical literature [4]-[8], and several schemes were proposed for nonstationary channel