Randomized code acquisition
First Claim
1. A method for synchronizing an n-chip spreading code of a received spread spectrum radio signal to a local reference code, the method comprising the steps of:
- (i) correlating said n-chip local reference code with n corresponding samples of said received signal, said samples being taken at sampling intervals determined by a chip rate of said received signal and a chip timing position;
(ii) comparing a result of said correlation performed in step (i) with a pre-determined correlation threshold, and providing an output signal indicative of said comparison;
(iii) temporally displacing said n-samples of said received signal by a period representative of one chip period if said threshold has not been exceeded;
(iv) introducing a random time offset into said chip timing position; and
(v) repeating steps (i) to (iv) for each of n-1 possible chip displacements of said received signal with respect to said local reference code until said threshold has been exceeded.
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Accused Products
Abstract
A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received spread spectrum radio signal and an n-chip local reference code generated by a code generator within a receiver, includes a variable delay means which operates to introduce a delay shift into the said received radio signal. A correlator operates to correlate n-chips of the local reference code with n-samples of the received signal communicated thereto, and generates a correlation signal representative of a result of the correlation. A code acquisition controller operates in combination with the correlation signal to maintain the delay shift for at least one correlation and thereafter to change the delay shift, wherein the delay shift is a fraction of one chip period.
89 Citations
29 Claims
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1. A method for synchronizing an n-chip spreading code of a received spread spectrum radio signal to a local reference code, the method comprising the steps of:
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(i) correlating said n-chip local reference code with n corresponding samples of said received signal, said samples being taken at sampling intervals determined by a chip rate of said received signal and a chip timing position; (ii) comparing a result of said correlation performed in step (i) with a pre-determined correlation threshold, and providing an output signal indicative of said comparison; (iii) temporally displacing said n-samples of said received signal by a period representative of one chip period if said threshold has not been exceeded; (iv) introducing a random time offset into said chip timing position; and (v) repeating steps (i) to (iv) for each of n-1 possible chip displacements of said received signal with respect to said local reference code until said threshold has been exceeded.
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2. A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received signal and an n-chip local reference code generated by a code generator within a receiver of said radio signal, said code acquisition circuit comprising:
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variable frequency offset means for introducing a frequency offset into said received signal in accordance with an offset control signal, scaling means for scaling a frequency offset received signal by said local reference code, accumulator means for generating a sub-correlation signal representative of an accumulated result of scaling said frequency offset signal by said reference code for a predetermined correlation period, shift register means comprising a plurality of stages, each stage being arranged to store a sample of said sub-correlation signal communicated thereto, discrete Fourier transformer means for generating a discrete Fourier transform of said sample of said sub-correlation signal stored in each stage of said shift register means, a plurality of comparator means for comparing a magnitude of respective ones of said Fourier transformed sub-correlation samples with a predetermined threshold, and frequency acquisition controller means for generating a frequency lock signal in dependence upon comparison signals generated by said comparator means, said frequency lock signal being indicative of which of said Fourier transformed sub-correlation samples exceeds said predetermined threshold, said frequency acquisition controller means providing said offset control signal fed to said frequency offset means in dependence upon said comparison signals, said frequency offset being maintained for at least one correlation period. - View Dependent Claims (3, 4, 5)
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6. A method of acquiring code synchronization and frequency lock of a received spread spectrum radio signal to a local n-chip reference code, the method comprising the steps of:
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(i) generating a plurality of demodulated versions of said received signal by demodulating said received signal with each of a plurality of de-modulating signals, each de-modulating signal having one of a set of pre-determined frequencies; (ii) correlating said n-chip local reference code with n corresponding samples of each of said demodulated versions of said received signal, said samples being taken at sampling intervals determined by a chip rate of said received signal and a chip timing position; (iii) comparing a result of said correlation with a pre-determined correlation threshold and providing an output signal indicative of said comparison; (iv) introducing a random time offset into said chip timing position; (v) introducing a random frequency offset into said received signal, and (vi) repeating steps (i) to (v) for each or n-1 possible chip displacements of said received signal with respect to said local reference code until said threshold has been exceeded. - View Dependent Claims (7)
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8. A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received radio signal and an n-chip local reference code generated by a code generator within a receiver of said radio signal, the code acquisition circuit comprising:
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variable frequency offset means for introducing a frequency offset into said received signal in accordance with an offset control signal, correlator means for generating a correlation signal representative of a result of correlating a frequency offset received signal with said local reference code during a correlation period, frequency acquisition controller means for providing said offset control signal for said frequency offset means in dependence upon said correlation signal, said frequency offset being changed after at least one correlation period, correlation comparator means for comparing said correlation signal with a pre-determined correlation threshold and for generating a frequency lock signal representative of a result of said correlation and indicative of said correlation signal exceeding said correlation threshold, frequency locking means for maintaining said frequency offset for said received signal in accordance with said frequency lock signal, and discrete frequency shifter means connected to said variable frequency offset means for generating a plurality of frequency shifted versions of frequency offset received signals, each frequency shifted version being representative of said frequency offset received signal shifted in frequency by one of a plurality of predetermined frequencies, said correlator means generating said correlation signal representative of a result of correlating each frequency shifted version of said received signal with said locally generated reference code. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received radio signal and an n-chip local reference code generated by a code generator within a receiver of said radio signal, the code acquisition circuit comprising:
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variable frequency offset means for introducing a frequency offset into said received signal in accordance with an offset control signal, correlator means for generating a correlation signal representative of a result of correlating said frequency offset received signal with said local reference code during a correlation period, frequency acquisition controller means for providing said offset control signal for said frequency offset means in dependence upon said correlation signal, said frequency offset being changed after at least one correlation period, and variable delay means for introducing a delay shift into said received radio signal in accordance with a time control signal fed thereto from a code acquisition controller means and arranged to maintain said delay shift for at least one correlation period to provide both code and frequency acquisition. - View Dependent Claims (15, 16)
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17. A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received spread spectrum radio signal and an n-chip local reference code generated by a code generator within a receiver of said radio signal, the code acquisition circuit comprising:
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variable delay means for introducing a delay shift into said received radio signal, said delay shift being a randomly selected fraction of one chip period for randomly varying chip timing position of said received radio signal; correlator means for correlating n-chips of the local reference code with n-samples of said delayed received signal, said n-samples being taken at sampling intervals determined by said chip timing position and a chip rate for said delayed received signal, said correlator means being provided with means for generating a correlation signal representative of a result of said correlation, said correlator means comprises scaling means for generating a product signal representative of scaling said delayed received signal fed to a first input thereof by said local reference code fed to a second input thereof, accumulator means for generating an accumulation signal representative of accumulating said product signal over a predetermined period, magnitude calculation means for generating a magnitude signal representative of said accumulation signal at the end of said predetermined period, and comparison means for comparing said magnitude signal with a predetermined threshold to generate said correlation signal; and code acquisition controller means for maintaining said delay shift in dependence upon said correlation signal. - View Dependent Claims (18)
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19. A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received spread spectrum radio signal and an n-chip local reference code generated by a code generator within a receiver of said radio signal, the code acquisition circuit comprising:
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variable delay means for introducing a first delay shift into said received radio signal, said first delay shift being a randomly selected fraction of one chip period for randomly varying chip timing position of said received radio signal; correlator means for correlating n-chips of the local reference code with n-samples of said delayed received signal, said n-samples being taken at sampling intervals determined by said chip timing position and a chip rate for said delayed received signal, said correlator means being provided with means for generating a correlation signal representative of a result of said correlation, said correlator means comprising first shift register means having a plurality of stages for providing a sample of said delayed received signal at an output of said plurality of stages in dependence upon a chip rate clock and said samples of said received signal fed thereto;
a plurality of scaling means each having a first input connected to the output of one of the stages of said first shift register means for scaling said received signal sample provided at the output of one of said stages with a sample representative of a chip of said local reference code provided at a second input thereof, and summer means connected to an output of each of said scaling means for generating said correlation signal in accordance with a sum of said scaled samples of said received signal; andcode acquisition controller means for maintaining said delay shift in dependence upon said correlation signal. - View Dependent Claims (20, 21)
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22. A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received spread spectrum radio signal and an n-chip local reference code generated by a code generator within a receiver of said radio signal, the code acquisition circuit comprising:
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variable delay means for introducing a delay shift into said received radio signal said delay shift being a randomly selected fraction of one chip period for randomly varying chip timing position of said received radio signal; correlator means for correlating n-chips of the local reference code with n-samples of said received signal, said n-samples being taken at sampling intervals determined by said chip timing position and a chip rate for said delayed received signal, said correlator means being provided with means for generating a correlation signal representative of a result of said correlation; code acquisition controller means for maintaining said delay shift in dependence upon said correlation signal; and variable frequency offset means for introducing a frequency offset into said delayed received radio signal in accordance with an offset control signal fed thereto from said code acquisition controller means and arranged to maintain said frequency offset for at least one correlation period to provide both code and frequency acquisition. - View Dependent Claims (23, 24)
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25. A code acquisition circuit for acquiring code synchronization between an n-chip spreading code of a received spread spectrum radio signal and an n-chip local reference code generated by a code generator within a receiver of said radio signal, the code acquisition circuit comprising:
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variable delay means for introducing a delay shift into said received radio signal, said delay shift being a randomly selected fraction of one chip period for randomly varying chip timing position of said received radio signal; correlator means for correlating n-chips of the local reference code with n-samples of said delayed received signal, said n-samples being taken at sampling intervals determined by said chip timing position and a chip rate for said delayed received signal, said correlator means being provided with means for generating a correlation signal representative of a result of said correlation; and code acquisition controller means for maintaining said delay shift in dependence upon aid correlation signal, said code acquisition controller means comprising a random number generator which generates a control signal in accordance with a random number generated thereby, said control signal being communicated to said variable delay means to introduce said delay shift in accordance therewith. - View Dependent Claims (26, 27, 28, 29)
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Specification