Spatial diversity in passive time reversal communications

• Published in: The Journal of the Acoustical Society of America 2006-10, Vol.120 (4), p.2067-2076
• Main Authors: Song, H. C., Hodgkiss, W. S., Kuperman, W. A., Higley, W. J., Raghukumar, K., Akal, T., Stevenson, M.
• Format: Article
• Language: English
• Subjects: Acoustic signal processing; Acoustics; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Physics; Transduction; acoustical devices for the generation and reproduction of sound; Underwater sound
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.2338286

A time reversal mirror exploits spatial diversity to achieve spatial and temporal focusing, a useful property for communications in an environment with significant multipath. Taking advantage of spatial diversity involves using a number of receivers distributed in space. This paper presents the impact of spatial diversity in passive time reversal communications between a probe source (PS) and a vertical receive array using at-sea experimental data, while the PS is either fixed or moving at about 4 knots . The performance of two different approaches is compared in terms of output signal-to-noise ratio versus the number of receiver elements: (1) time reversal alone and (2) time reversal combined with adaptive channel equalization. The time-varying channel response due to source motion requires an adaptive channel equalizer such that approach (2) outperforms approach (1) by up to 13 dB as compared to 5 dB for a fixed source case. Experimental results around 3 kHz with a 1 kHz bandwidth illustrate that as few as two or three receivers (i.e., 2 or 4 m array aperture) can provide reasonable performance at ranges of 4.2 and 10 km in 118 m deep water.