ABSTRACT

Malarkodi, A.; Latha, G., and Srinivasan S., 2020. An experimental study of passive time reversal process of underwater acoustic communication in shallow waters of the Bay of Bengal. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 58-62. Coconut Creek (Florida), ISSN 0749-0208.

Underwater acoustic communication in shallow water is a challenging task due to channel fading, Inter Symbol Interference (ISI) and noise caused by time varying multipath channel. Passive time reversal is a computationally inexpensive technique to mitigate ISI introduced by the channel. This paper describes the effect of passive time reversal technique and its spatial and temporal focal properties to reduce channel fading and inter symbol interference in the received communication signals in a highly reverberant channel. Performance of passive time reversal communications is evaluated for a passive time reversal experiment conducted off Bay of Bengal during September 2017. A single acoustic projector generated linear frequency modulated probe signal and BPSK data packets at a baud rate of 1000 bps with the frequency band of 4 kHz at the center frequency of 11 kHz. These signals were received at a range of approximately 3 km from the source by the vertical hydrophone array of three hydrophones. Since the side lobe leakages are the causes of ISI and bit error for communications, the effectiveness of the temporal focusing is measured by the peak to side lobe ratio of the phase conjugated pulse. The performance of the communication was measured by calculating the BER. The experimental results provide further evidence that the passive time reversal technique can be considered as a good option for reliable underwater communication in a complex acoustic channel.

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