Towards Internet Protocol over seawater (IP/SW): forward error correction (FEC) using Hamming codes for reliable acoustic telemetry

Abstract

Acoustic shallow-water data communications are unreliable. Repeated retransmission of a message received incorrectly often results in transmitter failure due to battery depletion. Internet connectivity to underwater entities via current network protocols does not exist, since most research in data communications has been focused on the physical layer and the underwater channel itself. Therefore, the problems addressed by this thesis are to find a way to increase the reliability of underwater data communications, as well as to specify the steps which need to be taken to enable Internet Protocol (IP) packets to be transmitted over an underwater channel. The approach taken was to add a Hamming forward error-detection and error-correction code to messages, thereby reducing the need for retransmission. This code was implemented in a PC-based communications system which uses commercially available diver's communication and navigation devices as acoustic modems. In a related effort, the internet Protocol stack was analyzed for areas which required modification to enable IP to be reliably passed over an acoustic channel. The results are a low-cost reliable underwater data communications system which can easily be implemented in an AUV or underwater sensor, as well as recommendations for improved protocols required to realize true network communications in an underwater environment.