uwMIMO-HARQ: Hybrid ARQ for Reliable Underwater Acoustic MIMO Communications

Achieving robust and reliable data communications in the harsh underwater environment is still a challenging issue due to the fast-changing and unpredictable nature of the acoustic channel. Notwithstanding the use of acknowledgement messages at the link layer, data transmission protocols still require more efficient error control strategies so to achieve a higher link reliability. A novel solution based on hybrid automatic repeat request (HARQ) is proposed that exploits the diversity gain offered by independent links in an underwater acoustic Multiple Input Multiple Output (MIMO) system. Irrespective of the channel regime, the proposed scheme aims at reducing the probability of retransmission and at increasing the link reliability via packet-level codeword selection and waterfilling coding. Encoding and decoding algorithms at the transmitter and receiver, respectively, are designed, multiple evaluation metrics are defined, and computer-based simulation results are presented to quantify the performance improvement of the proposed methods.