Basin-scale acoustic communication: a feasibility study using tomography m-sequences

Tomography transmissions made over a 3250 km path in the North Pacific as part of the Acoustic Thermometry of Ocean Climate (ATOC) program are analyzed as data communications signals in order to estimate the rate and reliability of very long range undersea telemetry. The ATOC tomography signal is a phase-encoded maximal-length shift-register sequence transmitted at 37.5 symbols per second using a 75 Hz carrier. It may be interpreted as a BPSK data signal at 37.5 bits per second, or as a direct sequence spread spectrum signal with a spreading rate 1023 (the m-sequence period) and a resulting data rate of 1 bit every 27 seconds. The multipath arrivals observed at the receiver span nearly 8 seconds, with the majority of the energy occupying the last two seconds. The data are processed using an adaptive multi-channel decision feedback equalizer with integrated phase tracking and Doppler compensation. Equalization of the signal on one hydrophone is sufficient to extract the low-rate spread spectrum modulation, while joint use of all twenty hydrophone channels provides near symbol-rate communications. The excellent results may be attributed to the short term stability (several minutes) of the deep-ocean sound channel at low frequencies.

[1]  Robert C. Spindel,et al.  Comparisons of measured and predicted acoustic fluctuations for a 3250-km propagation experiment in the eastern North Pacific Ocean , 1999 .

[2]  Lee Freitag,et al.  Multiuser undersea acoustic communications in the presence of multipath propagation , 2001, MTS/IEEE Oceans 2001. An Ocean Odyssey. Conference Proceedings (IEEE Cat. No.01CH37295).

[3]  A. Plaisant.  Long range acoustic communications , 1998, IEEE Oceanic Engineering Society. OCEANS'98. Conference Proceedings (Cat. No.98CH36259).

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

[5]  W. Munk,et al.  Ocean Acoustic Tomograpthy: Notation , 1995 .

[6]  T. Birdsall,et al.  A review of recent results on ocean acoustic wave propagation in random media: basin scales , 1999 .

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

[8]  Lee Freitag,et al.  Channel-estimation-based adaptive equalization of underwater acoustic signals , 1999, Oceans '99. MTS/IEEE. Riding the Crest into the 21st Century. Conference and Exhibition. Conference Proceedings (IEEE Cat. No.99CH37008).

[9]  V. Capellano,et al.  Performance improvements of a 50 km acoustic transmission through adaptive equalization and spatial diversity , 1997, Oceans '97. MTS/IEEE Conference Proceedings.

[10]  Lee Freitag,et al.  Hypothesis-feedback equalization for direct-sequence spread-spectrum underwater communications , 2000, OCEANS 2000 MTS/IEEE Conference and Exhibition. Conference Proceedings (Cat. No.00CH37158).

[11]  Carl Wunsch,et al.  Multimegameter-range acoustic data obtained by bottom-mounted hydrophone arrays for measurement of ocean temperature , 1999 .

[12]  J. A. Catipovic,et al.  Performance limitations in underwater acoustic telemetry , 1990 .

[13]  Milica Stojanovic,et al.  Recent advances in high-speed underwater acoustic communications , 1996 .

[14]  Robert C. Spindel,et al.  A test of basin-scale acoustic thermometry using a large-aperture vertical array at 3250-km range in the eastern North Pacific Ocean , 1999 .

[15]  Lee Freitag,et al.  High-rate acoustic communications for ocean observatories-performance testing over a 3000 m vertical path , 2000, OCEANS 2000 MTS/IEEE Conference and Exhibition. Conference Proceedings (Cat. No.00CH37158).

[16]  Walter Munk,et al.  Ocean Acoustic Tomography , 1988 .

[17]  Hyuck M. Kwon,et al.  Digital waveform codings for ocean acoustic telemetry , 1991 .

[18]  Ross Williams,et al.  Coherent Recombination of Acoustic Multipath Signals Propagated in the Deep Ocean , 1971 .