A Soft Combining Hybrid-ARQ Technique Applied to Throughput Maximization Within 3G Satellite IP Networks

Abstract

This paper deals with the application of Hybrid-Automatic-Repeat-reQuest (H-ARQ) techniques to reliable end-to-end data communications in satellite networks, whose applications have to cope with accurate Quality-of-Service (QoS) requirements. Particularly, we face this problem by introducing a modified H-ARQ scheme based on the use of the turbo codes' error-correction capabilities. According to our scheme, each packet is turbo coded, and packet retransmissions are lowered by keeping track of previous erroneous packet-decoding results. Moreover, two kinds of these techniques are proposed and applied, respectively, to consecutive received packet replicas or to decoding algorithm outputs. The benefits achieved through this approach have a positive effect both on the error-recovery strategies and, above all, on the congestion-control protocols, since they rely on a retransmission scheme. By means of analytical derivations carried out under the assumption of a wideband-code-division multiple-access communications, it has been possible to highlight noticeable performance improvements in terms of bit- and frame-error rates and link throughput. Computer simulations performed focusing on a typical satellite-universal-mobile-telecommunication-system environment validate analytical predictions and point out a remarkable gain without requiring a significant hardware-complexity increase. As a result, it has been possible to allow active users a better QoS, in terms of error rate, throughput, and delivery delay, or to increase access-network capacity, besides avoiding transmitted-power wasting