Coherent acoustic communication in a tidal estuary with busy shipping traffic.

High-rate acoustic communication experiments were conducted in a dynamic estuarine environment. Two current profilers deployed in a shipping lane were interfaced with acoustic modems, which modulated and transmitted the sensor readings every 200 s over a period of four days. QPSK modulation was employed at a raw data rate of 8 kbits on a 12-kHz carrier. Two 16-element hydrophone arrays, one horizontal and one vertical, were deployed near the shore. A multichannel decision-feedback equalizer was used to demodulate the modem signals received on both arrays. Long-term statistical analysis reveals the effects of the tidal cycle, subsea unit location, attenuation by the wake of passing vessels, and high levels of ship-generated noise on the fidelity of the communication links. The use of receiver arrays enables vast improvement in the overall reliability of data delivery compared with a single-receiver system, with performance depending strongly on array orientation. The vertical array offers the best performance overall, although the horizontal array proves more robust against shipping noise. Spatial coherence estimates, variation of array aperture, and inspection of array angular responses point to adaptive beamforming and coherent combining as the chief mechanisms of array gain.

[1]  D. E. Weston,et al.  Studies of sound transmission fluctuations in shallow coastal waters , 1969, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[2]  T.C. Yang.  Measurements of spatial coherence, beamforming gain and diversity gain for underwater acoustic communications , 2005, Proceedings of OCEANS 2005 MTS/IEEE.

[3]  Paul Hursky,et al.  Effects of ocean thermocline variability on noncoherent underwater acoustic communications. , 2007, The Journal of the Acoustical Society of America.

[4]  M Trevorrow.  High-Frequency Acoustic Scattering and Absorption Effects within Ship Wakes , 2005 .

[5]  D. E. Weston,et al.  Interference patterns in shallow‐water reverberation , 1990 .

[6]  T. H. Eggen.  Phase coherent communication in the presence of ship noise , 2000, OCEANS 2000 MTS/IEEE Conference and Exhibition. Conference Proceedings (Cat. No.00CH37158).

[7]  G. Deane,et al.  Channel characterization for communications in very shallow water , 2002 .

[8]  A.B. Baggeroer,et al.  The state of the art in underwater acoustic telemetry , 2000, IEEE Journal of Oceanic Engineering.

[9]  B.S. Sharif,et al.  Combined equalisation and beamforming to achieve 20 kbits/s acoustic telemetry for ROVs , 1996, OCEANS 96 MTS/IEEE Conference Proceedings. The Coastal Ocean - Prospects for the 21st Century.

[10]  Arveson,et al.  Radiated noise characteristics of a modern cargo ship , 2000, The Journal of the Acoustical Society of America.

[11]  W. Hodgkiss,et al.  Effects of tidally driven temperature fluctuations on shallow-water acoustic communications at 18 kHz , 2000, IEEE Journal of Oceanic Engineering.

[12]  D. Farmer,et al.  Acoustical measurements of microbubbles within ship wakes , 1994 .

[13]  Yi Chun Wang,et al.  The Noise Generated by the Collapse of a Cloud of Cavitation Bubbles , 1995 .

[14]  B.S. Sharif,et al.  A computationally efficient Doppler compensation system for underwater acoustic communications , 2000, IEEE Journal of Oceanic Engineering.

[15]  Jeffrey A. Neasham,et al.  Acoustic communication for the monitoring of current and vessel draft , 2006 .

[16]  J. Proakis,et al.  Adaptive multichannel combining and equalization for underwater acoustic communications , 1993 .

[17]  J. Nystuen,et al.  Prediction of underwater sound levels from rain and wind. , 2005, The Journal of the Acoustical Society of America.