USA As Represented by Secretary of the Navy

John M McCool

Bernard Widrow

James R Zeidler

Robert H Hearn

Douglas M Chabries

Shelby F Sullivan

Guy J Andrews

Jeffrey D Stein

Randall H Moore

The signal appearing at the receiver input of a pulse code active sonar dng a return echo period, is sampled, time compressed and stored in a memory. The time compressed sample is successive read-out of memory, with each individual 'read-out' hetrodyned with a discretely different doppler compensation frequency signal. The successively processed read-outs are passed through an 'on line' correlation detection device to determine presence of a correctly compensated pulse code echo.

Pulse coded sonar having improved doppler determination feature

An acoustic, underwater, telemetry system between two vehicles, a free-rung, deep-operating, sonar platform, or Sonaray vehicle, to overcome refraction, and a surface ship to provide processing of the sonar data gathered by the Sonaray vehicle. The telemetry system is required to communicate analog sonar information, digital command to control the platform, and digital information concerning the status of the platform, between the Sonaray vehicle and the surface ship. The Sonaray concept requires more than 32 channels of analog information for sonar data transmission, each corresponding to a particular received azimuthal beam and each having an information bandwidth of 1 kHz. The output of the analog channels consists of raw data from the search sonar. Because of the long range and very high reliability of the transmission required for the status and control channels, sonar processing by cross-correlation is used to search in both range and doppler. Because the arrival time of the telemetered signal at the surface ship differs from the time of transmission from the Sonaray vehicle, a time-determining code is telemetered simultaneously with the analog information from the Sonaray vehicle. A frequency-diversity encoding scheme overcomes the problem of absorption of acoustic energy in seawater by allowing separate signal normalization in each frequency band. A phase-lock loop overcomes the effects of the large doppler shift which normally occurs. Two maximal length shift-register sequences, often called p-n sequences, are used with phase modulation for the digital information.

Acoustic, underwater, telemetry system

A hook flash actuated telephone control device that is connected into a subscriber's telephone line to permit a user to place an existing call on hold by selectively activating the hook switch of his telephone according to a particular sequence. The control device includes a comparator which senses the line voltage and produces an output signal, the level of which is dependent upon whether or not the telephone handset is in an on-hook or off-hook condition. First timing and logic means are interconnected so as to be triggered by the output signal of the comparator. If the telephone handset is in an off-hook condition and the hook switch flash signal sequence is completed within a first particular predetermined time, a corresponding signal is generated to energize a hold circuit, whereby to place the telephone circuits in a hold condition. Audio signal generating means are also energized in order to provide the user with a tone to indicate that the telephone circuits are rendered in a hold condition. Accordingly, the user may return the handset to the telephone cradle without disconnecting the existing caller. Second timing and logic means are also provided to automatically reset the user's telephone circuits to receive new incoming calls, should the user inadvertently place his telephone circuits in a hold condition for longer than a second predetermined time. To resume an existing telephone call, the user merely raises the handset from the cradle of his telephone or any extension thereof, whereby the line voltage changes and the hold circuit is subsequently de-energized.

Hook flash signal actuated telephone control device

A correlator which is capable of correlating two or more signals of unknown frequency and bandwidth receives inputs on each of two or more channels. For the case of a two-channel, or pairwise, correlator the two channels are designated a first channel and a second channel. For the pairwise correlator, a first adaptive linear predictive (ALP) filter filters the input signal from the first channel and a second ALP filter filters the input signal from the second channel, the two output signals of the filters being x(k) and y(k). The adaptive linear predictive filter is an adaptive time-domain digital filter which adapts its impulse response according to a certain algorithm. The filter output represents an adaptive linear predictive estimate of the current input value, based on many past inputs. The input signals to the two channels of the pairwise correlator may correspond to sensor outputs from two or more widely separated sensors. The two output signals x(k) and y(k), are correlated in a pairwise correlator to result in a signal which corresponds to an estimate of the magnitude-squared coherence between the signal x(k) and a time-delayed, frequency-shifted, version of the signal y(k).

Adaptive correlator

An adaptive detector comprises an adaptive linear prediction filter (ALPF) nd a detection processor. The adaptive filter comprises an input filter, adapted to receive an input signal x(k) and delay it by a time .DELTA.. An L-point, or L-tap, adaptive filter has an input connected to the output of the input filter, a signal r(k) appearing at the output of the filter. A means for summing has two inputs, one for receiving the signal x(k) and the other for receiving an inverted signal from the adaptive filter, the output of the summer being an error signal .epsilon.(k). A feedback amplifier, whose input is connected to the output of the summer, takes a portion 2.mu., of the output signal .epsilon.(k) and feeds it back to the adaptive filter, thereby modifying the tap weights of the adaptive filter. The detection processor comprises a circuit, whose input is connected to the output of the adaptive filter, to receive the signal r(k), for performing a K-point discrete Fourier transform (DFT) on the signal r(k). A spectral analyzer, whose input is connected to the output of the DFT circuit, performs a spectral analysis on the output signal.

Adaptive detector

An input signal X(j) is fed directly to the positive port of a summing function and is simultaneously fed through a parallel channel in which it is delayed, and passed through an adaptive linear transversal filter, the output being then subtracted from the instantaneous input signal X(j). The difference, X(j)-Y(j), between these two signals is the error signal .epsilon.(j). .epsilon.(j) is multiplied by a gain .mu. and fed back to the adaptive filter to readjust the weights of the filter. The weights of the filter are readjusted until .epsilon.(j) is minimized according to the recursive algorithm: ##EQU1## where the arrow above a term indicates that the term is a signal vector. Thus, when the means square error is minimized, W.sub.(j+1) =W.sub.(j), and the filter is stabilized.

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El Cajon, CA, United States of America

John M McCool