Communications – electrical: acoustic wave systems and devices – Distance or direction finding – By combining or comparing signals
Reexamination Certificate
1999-05-27
2002-03-05
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
By combining or comparing signals
C367S118000, C367S124000
Reexamination Certificate
active
06353578
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a signal process apparatus and method using generic coherent summation to create informational signals that are in complex form that can apply to passive systems or active systems, applicable to acoustic systems and optical, e.g. in lasers, in terms of light having an amplitude in phase for detection and or enhancing the reception of a laser beam.
It is desirable to provide an easy and rapid technique to align the successive, evenly spaced in time, temporally rotating complex vectors that represent such things as the complex acoustic pressures measured by a sonar hydrophone and spectrum analyzed by a fast Fourier transform (FFT), or the voltage of an electrical signal, in order that a coherent (in phase) calculation of the complex vectors can be accomplished. Phase aligned vector summations and coherent summations are expected to produce larger signal-to-noise ratio (SNR) than either incoherent (magnitude only) and unaligned vector summations because signals, e.g., continuous wave (CW) tonals, are usually more coherent than noise. However, the rotational nature of the complex signal vectors presents a problem in tracking the rotations and phase aligning the vectors to be summed. It is desirable to automatically track the rotations, phase align the vectors, and determine the magnitudes of the contributions to the vector summations. The phases of noise are random, and therefore, do not produce a sensible or trackable progression of noise vectors like that of the signal vectors. The complex signal vectors will generally line-up and contribute constructively to the coherent (using phase alignment) sum, while the complex noise vectors have random phase alignment and will both add to and subtract from the vector sum. This results in a SNR increase of the phase aligned summation over other methods of summation, such as an unaligned vector summation and an incoherent summation of the magnitudes.
In the past, one way of accomplishing such signal processing was through beam forming. It is understood that when forming a beam to look in a given direction or angular elevation, complex coefficients will derive out of the beam former. However, this is problematic because it destroys phase information. Such an algorithm assumes a phase shift of, for example, one degree, and then calculates an error, and then assumes a shift of two degrees and so on, going on up to 180 degrees. Using this method, a shift that renders the least error was used. But the problem with such a system is that it assumes and takes a lot of time and effort and preprocessing. Furthermore, it also assumes a constant shift for the whole time period, and this is not what actually occurs.
Accordingly, an object of the invention is to provide a computationally efficient method for accounting for systematic signal phase rotations.
Another object of the invention is to provide a computationally efficient method for accounting for phase rotations and doing a phase aligned vector summation of the magnitudes (or magnitudes to an given exponent) of the vectors.
Still another object of the invention is to provide a computationally efficient method for accounting for phase rotations and doing a phase aligned “coherent” summation of the magnitudes (or magnitudes to a given exponent) of the vectors.
Another object of the invention is to provide a SNR increase for sinusoidal signals in random noise.
Yet still another object of the invention is to provide an easy and rapid technique for determining the expected phase angle for a vector to be aligned with the previous two vectors.
Further, another object of the invention is to provide an easy and rapid technique for determining the expected phase angle for a rotating vector to be aligned with the previous two vectors and to do a coherent summation of the vectors.
Another object of the invention is to provide a coherent summation that can be used in digital spectrum analyzers including hardware boxes and software computer code, e.g., a fast Fourier transform (FFT).
Still further, another object of the invention is to provide a means for tracking phase rotations and to provide phase aligned data to a processor that requires phase aligned data to improve its performance.
Another object of the invention is to provide a means of increasing the SNR without having to pre-process the data to calculate phase rotations in order to align the vectors for a coherent calculation.
Yet another object of the invention is to provide a means to accomplish phase alignment of the vectors without pre-processing (i.e., on the fly).
Another object of the invention is to provide an easily implemented and computationally efficient method for producing a phase aligned coherent summation spectrogram.
Still, another object of the invention is to provide an easily implemented and computationally efficient method for producing a phase aligned vector summation spectrogramn.
SUMMARY OF THE INVENTION
The invention disclosed herein provides a computationally simple and fast method for aligning the phases of complex signals (real (in phase) and imaginary (quadrature) components) before performing a coherent (in phase components) or vector sum, thus achieving the high gains of in phase summations without pre-processing overhead to determine an optimum progression of phase shifts to enable in phase summations. The method of the invention for aligning the phases, without preprocessing to get an optimum set of phase shifts, uses the temporal relationship that exists in the phase angles of successive vectors that occur evenly spaced in time.
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Mobbs Jackson A.
Wagstaff Ronald A.
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