RELIABILITY-BASED HYBRID ARQ WITH REDUCED FEEDBACK OVERHEAD

Reliability-based hybrid ARQ (RB-HARQ) is a recently developed form of incremental-redundancy ARQ. In RB-HARQ, the bits that are to be retransmitted are adaptively selected at the receiver based on the estimated bit reliabilities. This technique has the potential to improve performance and minimize retransmission size by targeting those bits that are likely to be in error. However, previous versions of the RB-HARQ algorithm have resulted in large request (NACK) packets that made the technique appropriate only for systems that can tolerate large request packets on the feedback link. Therefore, in this paper, by exploiting the high correlation of reliabilities of information bits mapping to same modulation symbol, we propose a symbol-based unreliable bits feedback scheme for RB-HARQ, in which instead of the indices of information bits, the indices of symbols are selected and fed back. The performance of the proposed technique is evaluated in terms of feedback overhead, packet error rate and spectral efficiency. The results show that the proposed technique can reduce the feedback overhead significantly with no or negligible performance loss.