Provision of Guaranteed QoS with Hybrid Automatic Repeat Request in Interleave Division Multiple Access Systems

Provision of guaranteed quality of service (QoS) in wireless communication has always been a demanding task. QoS can be ensured by the mechanism of repeat request, however real time systems can tolerate only a finite delay. In this paper we investigate the problem of provision of guaranteed QoS by hybrid automatic repeat request (HARQ) schemes, based on soft outputs of a channel decoder. Focus is on adaptive interleave-division multiple access (IDMA) transmission. Such a system is able to provide virtually arbitrary bit error rates (BER). The proposed HARQ schemes use the reliability information provided by the channel decoder to decide whether a packet satisfies the quality of service (QoS) requirements. QoS can be specified in terms of a minimum required throughput/data rate or a minimum required BER. Effect of truncation of repeat requests on the bit error rate and packet throughput is investigated. An adaptation scheme based upon the bit error rate in the accepted packets is proposed and the effect of the adaptation on the effective throughput is demonstrated