In this paper we investigate 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. However, the adaptation has to be supported by the automatic repeat request (ARQ) scheme used for error control. 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 in terms of a maximum bit error rate. No additional error detection code is applied. Furthermore, packet combining schemes also employing the reliability information are proposed and their performance is simulated for an IDMA-based transmission system
