USA As Represented by Secretary of the Navy

David J Pistacchio

G Clifford Carter

Peter A Child

Mary H Johnson

A system and method and system for receiving communications signals coded at transmission in a frequency hopping waveform includes a sensor that receives acoustic data. A detector joined to the sensor receives the data and separates signals from background noise. Logic determines when the signal ends. Clusters of signals are processed and grouped into combinations of symbols. A computer translates these symbols into messages using a codebook. When multiple possibilities exist, the message is selected from the codebook that maximizes a similarity score. Additional logic is provided to handle situations where unwanted signals are mixed into an otherwise valid symbol sequence, to find the best subset of signals forming a valid message. Selected messages are provided as output to users. In further details, the detector filters the acoustic data and transforms it to the frequency domain. A power spectrum is calculated for detecting signals in specific frequency bands. Integrations are performed over groups of frequencies. A detection is indicated when one integrator has a large variation from the expected background level.

Acoustic receiver for underwater digital communications

A system for close range sonar is provided. The system provides sufficient warning to permit maneuvering to avoid a close encounter even in the forward starboard/port regions, which have been problematic in the past due to ownship noise. The system utilizes a hull mounted sonar array and a towed sonar array which may be controlled in position to provide sufficient separation of noise received by both sonar arrays such that the noise is largely uncorrelated. The system utilizes beamformers for each array to supply a cross-correlator section which is able to minimize the ownship noise and maximize the signal thereby providing more time for maneuvering. The system also provides a LOFAR display and other displays that are highly sensitive to detecting close encounters.

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Narragansett, RI, United States of America

David J Pistacchio