Pseudorandom noise ranging receiver which compensates for multipath distortion by dynamically adjusting the time delay spacing between early and late correlators
First Claim
1. A receiver for demodulating and decoding a composite radio-frequency ranging signal, consisting of a plurality of transmitted signals, one of which is modulated with a predetermined pseudo-random code, the receiver including:
- A. a code generator for generating the pseudo-random code;
B. a correlation means for synchronizing the output of the code generator with the received version of the code, the correlation means operating in an acquisition mode to synchronize the code generator to within one code chip and operating in a subsequent tracking mode to track the received version of the code, the correlation meansi. when operating in the tracking mode making correlation measurements that correspond to a correlator spacing that is narrower than one-half of one code chip, to reduce the adverse affects of multipath distortion on the code tracking operations; and
ii. when operating in the acquisition mode making correlation measurements that correspond to stepping through the code in steps that are substantially wider than the narrow correlator spacing used in the tracking mode; and
C. pre-correlation filter means that operates at a bandwidth that exceeds 2 MHz.
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Accused Products
Abstract
A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit, multiple carrier and code synchronizing circuits, and multiple digital autocorrelators. The sampling circuit provides digital samples of a received composite signal to each of the several receiver channel circuits. The synchronizing circuits are preferably non-coherent, in the sense that they track any phase shifts in the received signal and adjust the frequency and phase of a locally generated carrier reference signal accordingly, even in the presence of Doppler or ionospheric distortion. The autocorrelators in each channel form a delay lock loop (DLL) which correlates the digital samples of the composite signal with locally generated PRN code values to produce a plurality of (early, late), or (punctual, early-minus-late) correlation signals. The time delay spacing between the (early, late), and (punctual, early-minus-late) correlation signals are dynamically adjusted, such that in an initial acquisition mode, the delay spacing is relatively wide, on the order of approximately one PRN code chip time; once PRN code lock is achieved, the code delay spacing is narrowed to a fraction of a PRN code chip time.
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Citations
13 Claims
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1. A receiver for demodulating and decoding a composite radio-frequency ranging signal, consisting of a plurality of transmitted signals, one of which is modulated with a predetermined pseudo-random code, the receiver including:
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A. a code generator for generating the pseudo-random code; B. a correlation means for synchronizing the output of the code generator with the received version of the code, the correlation means operating in an acquisition mode to synchronize the code generator to within one code chip and operating in a subsequent tracking mode to track the received version of the code, the correlation means i. when operating in the tracking mode making correlation measurements that correspond to a correlator spacing that is narrower than one-half of one code chip, to reduce the adverse affects of multipath distortion on the code tracking operations; and ii. when operating in the acquisition mode making correlation measurements that correspond to stepping through the code in steps that are substantially wider than the narrow correlator spacing used in the tracking mode; and C. pre-correlation filter means that operates at a bandwidth that exceeds 2 MHz. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A receiver for demodulating and decoding a composite radio-frequency ranging signal, consisting of a plurality of transmitted signals, one of which is modulated with a predetermined pseudo-random code, the receiver including:
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A. a code generator for generating the pseudo-random code; B. correlation means for synchronizing the output of the code generator with a version of the code received at the receiver, the correlation means operating in an acquisition mode to synchronize the code generator to the received version of the code and operating in a subsequent tracking mode to track the received version of the code, the correlation means i. when operating in the tracking mode simultaneously making early and late correlation measurements at a spacing of less than one-half of one code chip, in which noise in the measured signals correlates; and ii. when operating in the acquisition mode making correlation measurements in which the noise in the measured signals does not correlate; and C. pre-correlation filter means that operates at a bandwidth that exceeds 2 MHz. - View Dependent Claims (9)
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10. A receiver for demodulating and decoding a composite radio-frequency ranging signal, consisting of a plurality of transmitted signals, one of which is modulated with a predetermined pseudo-random code, the receiver including:
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A. a code generator for generating the pseudo-random code; B. correlation means for synchronizing the output of the code generator with a version of the code received at the receiver, the correlation means operating in an acquisition mode to synchronize the code generator to the received version of the code and operating in a subsequent tracking mode to track the received version of the code, the correlation means i. when operating in the tracking mode making early and late correlation measurements at a spacing of less than one-half of one code chip, in which noise in the measured signals correlates and adverse effects of multipath distortion are minimized; and ii. when operating in the acquisition mode making correlation measurements in which the noise in the measured signals does not correlate; and C. pre-correlation filter means that operates at a bandwidth that exceeds 8 MHz. - View Dependent Claims (11)
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12. A receiver for demodulating and decoding a composite radio-frequency ranging signal, consisting of a plurality of transmitted signals, one of which is modulated with a predetermined pseudo-random code, the receiver including:
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A. a code generator for generating the pseudo-random code; B. a correlation means for synchronizing the output of the code generator with a version of the code received at the receiver, the correlation means operating in an acquisition mode to synchronize the code generator to the received signal and operating in a subsequent tracking mode to track the received version of the code, the correlation means i. when operating in the tracking mode making early minus late correlation measurements at a spacing of less than one-half of one code chip in which noise in the measured signals correlates and adverse effects of multipath distortion are minimized; and ii. when operating in the acquisition mode making early and late correlation measurements in which noise in the measured signals does not correlate; and C. pre-correlation filter means that operates at a bandwidth that exceeds 2 MHz. - View Dependent Claims (13)
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Specification