Spatial diversity processing for underwater acoustic telemetry
First Claim
1. An underwater telemetry system, comprising:
- multiple spatially diverse hydrophones;
means associated with a first one of said spatially diverse hydrophones for receiving underwater acoustic signals transmitted from an underwater acoustic;
source along a first path;
means associated with a second of said spatially diverse hydrophones for receiving underwater acoustic signals transmitted from said underwater acoustic source along a second path, said second path being spatially diverse from said first path;
means for determining an estimate of the relative reliability of the underwater acoustic signals received along said first and second paths;
means for weighting the received underwater acoustic signals in accordance with said reliability estimate; and
means for combining said weighted underwater acoustic signals to recover an accurate representation of the underwater acoustic signals transmitted from said underwater acoustic source.
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Abstract
An underwater acoustic telemetry system uses spatially distributed receivers with aperture sizes from 0.35 to 20 m. Output from each receiver is assigned a quality measure based on the estimated error rate, and the data, weighted by the quality measure, is combined and decoded. The quality measure is derived from a Viterbi error-correction decoder operating on each receiver. The quality estimator exploits the signal and noise differential travel times to individual sensors. The spatial coherence structure of the shallow-water acoustic channel shows relatively low signal coherence at separations as short as 0.35 m. Increasing receiver spacing beyond 5 m offers additional benefits in the presence of impulsive noise and larger scale inhomogeneities in the acoustic field. Diversity combining, even with only two receivers, can lower uncoded error rates by up to several orders of magnitude while providing immunity to transducer jamming or failure.
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Citations
18 Claims
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1. An underwater telemetry system, comprising:
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multiple spatially diverse hydrophones; means associated with a first one of said spatially diverse hydrophones for receiving underwater acoustic signals transmitted from an underwater acoustic;
source along a first path;means associated with a second of said spatially diverse hydrophones for receiving underwater acoustic signals transmitted from said underwater acoustic source along a second path, said second path being spatially diverse from said first path; means for determining an estimate of the relative reliability of the underwater acoustic signals received along said first and second paths; means for weighting the received underwater acoustic signals in accordance with said reliability estimate; and means for combining said weighted underwater acoustic signals to recover an accurate representation of the underwater acoustic signals transmitted from said underwater acoustic source. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An underwater telemetry system, comprising:
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a plurality of spatially diverse hydrophones for receiving signals transmitted underwater; an analog processor associated with each of said hydrophones for recovering signals therefrom; a reliability estimator associated with each of said analog processors for estimating the reliability of the signals received by each of said hydrophones; means for combining the recovered digital signals in accordance with the estimate of reliability associated therewith; and means for correcting the combined recovered digital signals to recovery a replica of the originally transmitted signals. - View Dependent Claims (10, 11, 12)
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13. A method of underwater telemetry comprising the steps of:
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receiving acoustic signals transmitted from a single source underwater in a plurality of frequency channels along a plurality of paths leading to a plurality of spatially diverse hydrophones; determining an estimate of the reliability of the signals received along each of said paths; and combining said signals received along each of said paths in accordance with the estimate of reliability associated therewith to recover a replica of the signals transmitted by the source. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification