TIME-VARYING DOPPLER COMPENSATION FOR UNDERWATER ACOUSTIC COMMUNICATION

Abstract

This thesis focuses on time-varying Doppler compensation for underwater acoustic communications using an orthogonal frequency division multiplexing (OFDM) system. An underwater acoustic channel simulator is developed based on the geometry of the system deployment and by considering the statistics of the random variation of the channel. This channel simulator is capable of modelling any relative motion between the transmitter and receiver. The effect of the underwater acoustic (UWA) channel on OFDM system is studied by incorporating a model in system level simulation of the communication link. The time-varying Doppler compensation method is then introduced as an innovative method which is able to compensate for Doppler shift due to time-varying relative velocity between the transmitter and receiver. Finally, the proposed Doppler compensation method is integrated to an ultrasonic OFDM system and the communication reliability is evaluated through simulations and measurements in realistic deployment conditions. Specifically, for a distance of 150 m a net throughput after synchronization, channel estimation and decoding 760 bit/s was demonstrated with a bit error rate of 0.035 for a low SNR of 5.5 dB. More importantly, it will be shown that the assessment of the communication performance realized using simulations is very close to that of the measured performance.