Abstract: The present invention is directed to a global positioning system (GPS) having improved signal-to-noise ratio for reducing the required signal level for which GPS may be implemented in electronic devices or cell phones. The acquisition function of the GPS receiver is improved by inserting new signal processing for broadband noise reduction that allows subsequent improved estimation of critical time shift and frequency shift parameters needed for GPS acquisition at lower received signal levels. The decoding of the navigation bits from the satellite transmissions is improved to provide ephemeris data needed for computing navigation solutions at lower received signal levels, by examining the output of the same new signal processing for broadband noise reduction for spikes in the power of the output time series that correspond to navigation bit flips.

Abstract: A system and method are presented for determining the detection and location of persons and objects using ultrasonic acoustic sensors. The system allows detection of stationary and moving persons and other objects, through atmospheric conditions, to a distance of at least 300 feet. The invention further provides for enhanced signal processing through the use of arrays of transmitters and receivers, where one or more transmitter arrays may be oriented substantially perpendicularly to one or more receiver arrays, allowing high directionality and good rejection of reverberations, background noise, clutter and objects not of interest.

Abstract: An apparatus for destroying a buried object includes a targeting system including a sensor operable to detect the presence and location of an object which is at least partially buried in the ground, a gun system including a gun operable to fire a projectile into the ground, and a control system that aims the gun responsive to the presence and location of the buried object as determined by the targeting system. The sensor also desirably detects the presence and location of the projectile fired by the gun system, and the gun pointer is responsive to the location of the projectile. The sensor thus detects the presence of the buried object, the control system aims the gun at the buried object, and the gun fires the projectile. The sensor detects the relative positions of the buried object and the projectile as it passes near the buried object, the control system corrects the aim of the gun in the event that the prior shot misses, and the gun fires another projectile with a corrected aim.

Abstract: Active sonar apparatus, especially adapted for detecting submarine targets under ice, includes means for providing first and second pulsed, underwater acoustic signals respectfully having a high frequency, f.sub.H, and a low frequency, f.sub.L. The high frequency, f.sub.H, is selected for causing the signal to be reflected at the submerged, water-ice interface and and the low frequency, f.sub.L, selected for enabling the signal to be propagated through the ice with no significant reflection at the water-ice interface while then causing the signal to be reflected at the above-water, air-ice interface. Included are means for separately receiving and processing the reflected signals from the first and second acoustic signals and for detecting possible target reflections (which may include ice reflections) as a function of range and angle cells.

Abstract: Digital logic comprising a high speed analog to digital converter, a high speed analog to digital converter, a digital multiplier, and an infinite impulse response filter and decimation circuit are used to digitize a magnetic signal that is subsequently processed by magnetic data processing algorithms. The high resolution digital to analog converter is directly incorporated in a feedback loop of a magnetometer sensor, and an expensive precision analog to digital converter is replaced by a less expensive, lower power digital to analog converter. The improvement provided by the present invention includes a high speed analog to digital converter coupled between the oscillator and a first input of a multiplier, and a second analog to digital converter that is coupled between the sense coil of the sensor and a second input of the multiplier. The output of the multiplier is coupled to an infinite impulse response filter and decimation circuit that produces the digital output signal from the magnetometer.

Abstract: An active adaptive noise canceller that does not require a training mode and operates over an extended noise bandwidth. The canceller partitions the noise bandwidth into frequency sub-bands, and multiple adaptive filter channels are employed, one for each sub-band, to cancel noise energy in the respective sub-bands. Each channel includes bandpass filters to restrict the channel to operation over only the particular sub-band, and delays are inserted in the operation of the filter weight updating. Because each channel is stable over its sub-band, the canceller operates over the extended noise bandwidth of all the sub-bands.

Abstract: A variable depth sonar is disclosed which is adapted to provide passive multipath target ranging and depth estimates. The sonar employs a novel estimation procedure which is adapted to sonars with relatively small sensors and limited computing power. A novel feature of the invention is the introduction of a change of depth of the sonar receiver, mounted on a mobile platform, into the estimation process. Measurements at the two different depths are combined to provide target range and depth.Other features and improvements are disclosed.

Abstract: An active adaptive noise canceller that inserts delays into the weight update logic of an adaptive filter to keep the filter stable. The noise and residual noise are sensed and the respective sensor signals are digitized at a given sample rate for processing in the adaptive filter. To eliminate the need for high sample rates while maintaining flexibility in the frequency regions over which the adaptive filter is stable, the delay introduced into the weight update logic is a non-integer multiple of the sample period. The non-integer sample delay is obtained by a sample interpolation and decimation procedure.

Abstract: A broadband adaptive Doppler estimator and canceller is described for adaptively removing a moving source of near field primary interference that is masking a weaker target. The estimator and canceller employs a distributed field of sensors, through which is moving the source of interference. The estimator and canceller takes the form of a canceller system, wherein the measured reference waveform is a Doppler shifted version of the interference. The estimator and canceller employ interpolating and decimating of the reference waveform to remove Doppler effects over a broadband. The interpolation is performed by oversampling (zero padding) and low pass filtering, and the decimation is a sample rate reduction. The adaption is performed in the decimation to minimize mean square error in the canceller output.

Abstract: An active adaptive noise canceller that inserts delays in the weight update logic of an adaptive filter employed by the canceller to make the filter stable. It has been found that there is a great deal of flexibility regarding the selection of the delay values. This insensitivity permits designing the delays in advance, and not having to adjust them to different situations as they change, thus no longer requiring a training mode. The canceller dramatically reduces the amount of hardward needed to perform active adaptive noise cancelling, and eliminates the need for the training mode, which in some applications, including automobiles, for example, can be as objectionable as the noise sources that are to be suppressed.

Abstract: This invention relates to a technique and system (34) for clustering a set of data points (18) in a data field. Clustering is performed by a set of rules which make no assumptions about the data fields. That is, the number of clusters, the distance between clusters, etc., need not be specified in advance. The invention calculates a distance R that is a function of the distances between each pair of points (18) in a data field. Operating on a chosen point, a parameter is calculated for each neighboring point within distance R from the chosen point. This parameter is proportional to the distance of the neighboring point to the chosen point. The chosen point P is then connected to a neighboring point on the basis of this parameter. All points, in any order are operating on as the new chosen point, so that the additional points may be linked to new chosen points in a similar manner. In this way, a tree-structure (22, 24) of connected points will form the desired clustering.

Abstract: A normalized frequency domain Least Means Square filter. The feedback coefficient for each frequency bin is adjusted separately in the filter by use of an input power estimate. The power estimate is incorporated directly into the filter algorithm as a data-dependent, time-varying stochastic feedback coefficient. The filter is particularly useful in applications in which the input signal has large spectral variations, which could lead to filter instabilities in some frequency bins if a single feedback coefficient were employed in all frequency bins.

Abstract: A channel adaptive active sonar is disclosed, wherein the sonar transmit waveform is adaptively selected in accordance with the measured sonar channel scattering function to reduce the response of the sonar to unwanted reverberation while preserving the response to signal returns. As a result, the sonar target detectability is improved over sonar systems which do not adapt to the variable properties of the ocean channel. The sonar is operable in two modes, the channel measurement mode and the normal active mode. In the channel measurement mode, probe signals are transmitted to test the channel response. From the sonar receive signals resulting from the transmitted probe signals, the channel scattering function is estimated. The transmit waveform for the sonar active mode is then designed to provide a waveform whose ambiguity function overlaps minimally with the estimated channel scattering function.

Abstract: A bistatic sonar employing LMS adaptive spatial prediction is used to process against surface reverberation from the convergence zone (CZ). Hydrophones spatially separated from the primary array are used as references. The critical behavior exploited by the invention is that since the reverberation may be viewed as an extended source for the reverberation, the correlation drops off with separation between the reference and primary sensors, while it stays a constant for the plane wave target return. The reverberation is non-stationary, functionally dependent on the signal (even though the back scatter is statistically uncorrelated with the signal), and spatially extended over the sector of the CZ annulus cut out by the transmitter azimuth beamwidth. The detection of the target is based on the sudden appearance of one strong target point source within a densely packed region of weak point sources that have been constantly present and whose sum is much larger than the target.

Abstract: An adaptive recursive filter is disclosed which, in a preferred embodiment, comprises first and second adaptive transversal filters selectively coupled together to minimize the mean square error of the output data of the recursive filter based upon observations of input data to the recursive filter. Each transversal filter includes a tapped delay line with a variable weight on each tap. The output data of the recursive filter is developed by combining the outputs of the first and second transversal filters. The input data is applied to the first transversal filter, while the output data is applied to the second transversal filter. The output data is also combined with a reference signal to provide an error signal. A function of that error signal is utilized to update the weights of all of the taps in both transversal filters in order to cause the weights to automatically adapt themselves to minimize the mean square error of the output data of the recursive filter.