Bandwidth Efficient Variable Rate HARQ Under Orthogonal Space-Time Block Codes

We propose a bandwidth and power efficient hybrid Automatic Repeat reQuest (HARQ) transceiver system that preserves full retransmission diversity under orthogonal space-time block codes (OSTBC) with low decoding complexity. This new HARQ scheme is built upon traditional OSTBC transmission to achieve full space-time diversity. During retransmissions upon packet losses, space-time encoding can be compressed in time to reduce bandwidth utility and achieve joint detection of multiple transmissions without training. By formulating the joint detection model at the receiver into a Quasi-Orthogonal Space-Time transmission, we can achieve the dual objectives of bandwidth reduction and full transmission diversity. Unlike traditional full ARQ retransmission, our proposed receiver can also apply joint semi-blind channel estimation by omitting training during retransmission to further improve bandwidth efficiency.