Hybrid type-II ARQ schemes with adaptive modulation systems for wireless channels

In this paper, we propose and analyze a scheme for wireless channels which is a combination of a hybrid type-II automatic repeat request (ARQ) scheme and an adaptive modulation system (AMS). In hybrid type-II ARQ schemes, the transmission of redundancy bits for error correction is adapted to the channel variations. Additionally, in the proposed AMS, the modulation is gradually changed from a large constellation to small constellations when the channel bit error probability is high. This is done without any knowledge of the channels at the transmitter. The proposed scheme provides a significant gain in the throughput performance as compared to traditional hybrid type-II ARQ schemes, as verified by simulations