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Ultra-linear signal processing for radar and laser radarUltra-linear signal processing for radar and laser radar description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070273863, Ultra-linear signal processing for radar and laser radar. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates generally to signal processing and, more specifically, to systems and methods for processing radar signals. BACKGROUND OF THE INVENTION [0002] Radio detection and ranging (radar) is used to detect, range (that is, determine a distance), and map a wide variety of objects. For example, a weather radar system on an airplane can detect and range rain or other weather events, and a military fire control radar system can detect and track a military target, such as a ship or an aircraft. [0003] Radar can also be used to range and map objects for manufacturing purposes. For example, laser radar is particularly well-suited for manufacturing large-scale objects (such as aircraft) because laser radar allows precise measurement over a large volume. In one approach referred to as a chirped or Frequency Modulated-Continuous Wave (FMCW) radar, the radar frequency is modulated linearly (or nearly linearly). [0004] In an FMCW radar, there is a time delay between the time when the signal is sent to an object and the time when the radiation scattered from the object is collected. As a result, there is a frequency difference between the radiation that is transmitted and the radiation that is collected. If these two signals with different frequencies are mixed, a beat frequency is observed. If the chirp is linear, then the beat frequency is proportional to the time delay and, therefore, to the range to the scattering object. If the chirp is not linear, then measuring range with a chirped radar entails measuring a sinusoidal signal that is varying in frequency (or, equivalently, in phase) in an environment of random noise. [0005] In practical laser radar systems, the frequency or phase of the sinusoidal signal will vary--often by as much as ten percent. Because the frequency or phase of the sinusoid varies in time, a broad peak is obtained via a Fourier transform, such as a Fast Fourier Transform (FFT) of the entire interval. The broad peak reduces accuracy of measurement of frequency or phase of the sinusoid. [0006] It would be desirable to measure accurately parameters of a signal with a narrow frequency that wanders. However, there is an unmet need in the art for a system and method for accommodating wandering in frequency or phase to permit accurately measuring frequency-and/or-phase-related parameters of a laser radar signal. SUMMARY OF THE INVENTION [0007] Embodiments of the present invention provide a system, method, and computer program product for performing accurate measurements of frequency-and/or-phase-related parameters of a sinusoidal signal that varies non-linearly in frequency or phase. Advantageously, according to other embodiments of the present invention, measurements of frequency-and/or-phase-related parameters of such a sinusoidal signal are used to determine range to a target. As a result, embodiments of the present invention are able to provide more accurate range measurements than have been possible in the prior art. [0008] According to an embodiment of the present invention, a measurement indicative of frequency and/or phase of a sinusoidal signal that varies non-linearly in frequency or phase is accurately measured. A sinusoidal signal is sampled over a finite period of time at a plurality of sample points. The sampled signals are pre-processed, and a Fourier transform is performed on the pre-processed sampled signals. Phases of the pre-processed sampled signals are extracted from the Fourier transform, and a measurement indicative of frequency of the sinusoidal signal is determined from slope of the phases of the pre-processed sampled signals. [0009] According to an aspect of the present invention, pre-processing may include filtering (or windowing) the sampled signal. If desired, the filter may include a Kaiser-Bessel window. Pre-processing may also include padding the filtered, sampled signal by adding to the filtered, sampled signal a plurality of sample points that are all zeroes. Pre-processing may also include rotating the filtered padded sample by a predetermined amount, such as without limitation around twenty-five percent or so. [0010] According to another aspect of the present invention, determining frequency from the slope of the phases of the pre-processed sampled signals may include performing a linear fit through a plurality of phase data points. [0011] According to another embodiment of the present invention, range to a target is determined using the exemplary signal processing described above. Two single-mode laser beams having a relative frequency separation are frequency modulated. The two frequency-modulated laser beams are combined, and the combined laser beams are projected onto a target. A return signal from the target and a portion of the combined laser beams are mixed, and the mixed signal is detected. At least one reference signal is generated. The detected mixed signal is pre-processed, and a Fourier transform is performed on the pre-processed signal. Phase of the mixed signal is extracted from the Fourier transform, and a measurement indicative of frequency of the mixed signal is determined from slope of the phase of the mixed signal. Range to the target is determined based on a comparison of either phase or frequency of the mixed signal with either phase or frequency of at least one reference signal. BRIEF DESCRIPTION OF THE DRAWINGS [0012] The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings. [0013] FIG. 1 is a block diagram of a system for determining range to a target according to an embodiment of the present invention; [0014] FIG. 2 is a block diagram of signal processing according to an embodiment of the present invention; [0015] FIG. 3 is a top-level software block diagram of phase calculation according to an embodiment of the present invention; [0016] FIGS. 4A-4D are illustrations of pre-processing of samples according to an embodiment of the present invention; [0017] FIGS. 5A and 5B are illustrations of an exemplary time series interval and its Fourier transform; and [0018] FIG. 6 is an illustration of an exemplary phase-versus-time plot derived from a time series. DETAILED DESCRIPTION OF THE INVENTION [0019] Embodiments of the present invention provide a system, method, and computer program product for enabling accurate measurement of frequency-and/or-phase-related parameters of a sinusoidal signal that varies non-linearly in frequency or phase. Advantageously, according to other embodiments of the present invention, measurements of frequency and/or phase of such a sinusoidal signal are used to determine range to a target. As a result, embodiments of the present invention are able to provide more accurate range measurements than have been possible in the prior art. Continue reading about Ultra-linear signal processing for radar and laser radar... Full patent description for Ultra-linear signal processing for radar and laser radar Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Ultra-linear signal processing for radar and laser radar patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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