Method and apparatus for acquisition of a spread-spectrum signal
First Claim
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1. In a radiotelephone operable in a code division multiple access (CDMA) system, a method of acquiring a pilot signal, the method comprising:
- storing samples of a received signal;
generating, during the step storing, a PN sequence;
selecting a pseudo-random noise (PN) offset for a PN sequence;
correlating at least a portion of the samples with at least a portion of the PN sequence to produce a correlation energy;
choosing a new PN offset;
comparing the correlation energy to an energy threshold; and
repeating the steps of correlating, choosing, and comparing until any of;
a PN sequence timing is found that produces the correlation energy at least equal to the energy threshold, orthe step of comparing is performed a predetermined number of times; and
wherein during the step of correlating, the PN sequence is re-generated with reference to the PN offset at a faster rate than the step of generating.
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Abstract
An apparatus for acquiring a pseudo-random (PN) sequence timing for a code division multiple access (CDMA) radiotelephone. A buffer stores samples of representations of at least one pilot signal. A correlator coupled to the buffer is operable to correlate at least a portion of the samples with a PN sequence at each of a plurality of different PN offsets to produce corresponding correlation energies. A controller coupled to the correlator interrupts the correlator as soon as the PN sequence at a particular PN offset produces a correlation energy at least equal to an energy threshold.
110 Citations
27 Claims
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1. In a radiotelephone operable in a code division multiple access (CDMA) system, a method of acquiring a pilot signal, the method comprising:
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storing samples of a received signal; generating, during the step storing, a PN sequence; selecting a pseudo-random noise (PN) offset for a PN sequence; correlating at least a portion of the samples with at least a portion of the PN sequence to produce a correlation energy; choosing a new PN offset; comparing the correlation energy to an energy threshold; and repeating the steps of correlating, choosing, and comparing until any of; a PN sequence timing is found that produces the correlation energy at least equal to the energy threshold, or the step of comparing is performed a predetermined number of times; and wherein during the step of correlating, the PN sequence is re-generated with reference to the PN offset at a faster rate than the step of generating. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of activating a radiotelephone operable in a code division multiple access (CDMA) system, the method comprising the steps of:
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activating at least a portion of a searcher receiver; initiating the generation of a pseudo-random noise (PN) sequence; storing samples of a received signal; noting, during the step of storing, a position of the PN sequence; producing, responsive to the step of noting, a reference position of the PN sequence; re-generating the PN sequence using the reference position; correlating, during the step of re-generating, at least a portion of the samples with at least a portion of the PN sequence to produce a correlation energy; incrementing, responsive to the step of regenerating, the reference position; comparing the correlation energy to an energy threshold; and repeating the steps of regenerating, correlating, incrementing, and comparing until any of; a PN sequence timing is found that produces the correlation energy at least equal to the energy threshold, or the step of comparing is performed a predetermined number of times. - View Dependent Claims (8, 9, 10)
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11. In a code division multiple access (CDMA) radiotelephone, a method of acquiring a pilot signal, the method comprising:
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storing a predetermined number of a plurality of samples of a received signal; generating a pseudo-random noise (PN) sequence at each of a plurality of different PN offsets; correlating the samples from the same stored predetermined number of samples with the PN sequence at each of the plurality of different PN offsets to produce corresponding correlation energies at a faster rate than the step of storing; interrupting the correlating when a correlation energy at least equal to a predetermined threshold is produced; and choosing a PN sequence timing based upon the PN sequence and a PN offset that produces a full correlation energy at least equal to the predetermined threshold. - View Dependent Claims (12, 13)
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14. In a code division multiple access (CDMA) radiotelephone, a method of acquiring a pilot signal, the method comprising:
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storing a predetermined number of samples of a received signal; generating a pseudo-random noise (PN) sequence at each of a plurality of different PN offsets; correlating the predetermined number of samples with the PN sequence at each of the plurality of different PN offsets to produce corresponding correlation energies, including a first correlation involving a first portion of the samples and a first portion of the PN sequence, and a second correlation involving a second portion of the samples and a second portion of the PN sequence, wherein if during the step of correlating the first correlation produces an intermediate correlation energy less than an intermediate threshold for a particular PN offset, the second correlation at that particular PN offset is not performed; interrupting the correlating when a correlation energy at least equal to a predetermined threshold is produced; and choosing a PN sequence timing based upon the PN sequence and a PN offset that produces a full correlation energy at least equal to the predetermined threshold.
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15. An apparatus for acquiring a pseudo-random (PN) sequence timing for a code division multiple access (CDMA) radiotelephone, the apparatus comprising:
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a buffer to store a plurality of samples of a received signal; a correlator coupled to the buffer and operable to correlate at least a portion of the same stored samples with a PN sequence at each of a plurality of different PN offsets to produce corresponding correlation energies; a controller coupled to the correlator and operable to interrupt the correlator from correlating portions of the samples with further PN sequences of different PN offsets, when the PN sequence at a particular PN offset produces a correlation energy at least equal to an energy threshold; and a memory coupled to the correlator for storing a predetermined number of highest correlation energies and corresponding PN offsets; and wherein if after a predetermined number of correlations none of the produced correlation energies at least equal the energy threshold, the controller chooses from the memory a PN offset corresponding to a highest correlation energy. - View Dependent Claims (16, 17, 18, 19)
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20. A code division multiple access (CDMA) cellular telephone system comprising:
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at least one base station for transmitting a pilot signal having a particular time alignment; a cellular telephone operable to receive representations of the pilot signal, the cellular telephone including; a buffer to store a plurality of samples of the representations of the pilot signal; a correlator coupled to the buffer and operable to correlate at least a portion of the same stored samples with a pseudo-random noise (PN) sequence at each of a plurality of different PN offsets to produce corresponding correlation energies; a controller coupled to the correlator and operable to interrupt the correlator from correlating portions of the samples with further PN sequences of different PN offsets, when the PN sequence at a particular PN offset produces a correlation energy at least equal to an energy threshold; and a memory coupled to the correlator for storing a predetermined number of highest correlation energies and corresponding PN offsets; and wherein if after a determined number of correlations none of the produced correlation energies at least equal the energy threshold, the controller chooses from the memory a PN offset corresponding to a highest correlation energy. - View Dependent Claims (21, 22, 23, 24)
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25. A method of activating a code division multiple access (CDMA) cellular telephone, the method comprising:
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turning on the cellular telephone; activating a searcher receiver; receiving representations of a pilot signal; generating a pseudo-random noise (PN) sequence; storing, during the step of generating, digital samples of the representations of the pilot signal; re-generating the PN sequence at each of a plurality of PN offsets; correlating the digital samples with the PN sequence at each of the plurality of PN offsets to produce corresponding single correlation energies; storing a predetermined number of highest single correlation energies and corresponding PN offsets; comparing after each correlation each of the single correlation energies to an energy threshold; suspending the step of correlating responsive to finding a particular PN offset producing a single correlation energy at least equal to the energy threshold and using the particular PN offset as a PN sequence timing of a demodulation branch in a receiver of the cellular telephone; and if, after the step of correlating is performed a predetermined number of times without producing the single correlation energy at least equal to the energy threshold, then choosing a PN offset corresponding to a highest stored single correlation energy for the PN sequence timing.
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26. In a radiotelephone operable in a code division multiple access (CDMA) system, a method of acquiring a pilot signal, the method comprising:
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(a) generating a pseudo-random noise (PN) sequence at a first rate; (b) storing samples of a received signal at the first rate; (c) nothing, during the step of storing, a reference position of the PN sequence; (d) storing the reference position; (e) re-generating at a second rate the PN sequence starting from the reference position, the second rate faster than the first rate; (f) correlating, during the step or re-generating, at least a portion of the samples with at least a portion of the PN sequence to produce a correlation energy; (g) selecting, responsive to the step of re-generating, a new reference position; (h) comparing the correlation energy to an energy threshold; and (i) repeating steps (e) through (h) until any of; a correlation results in the correlation energy at least equal to the energy threshold, wherein a reference position corresponding to the correlation energy at least equal to the energy threshold is assigned to at least one demodulation branch of a receiver of the radiotelephone, or the step of comparing is performed a predetermined number of times, wherein a reference position corresponding to a highest correlation energy is assigned to the at least one demodulation branch.
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27. In a radiotelephone operable in a code division multiple access (CDMA) telephone system, a receiver circuit for acquiring a pseudo-random noise (PN) sequence timing, the receiver circuit comprising:
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a buffer to store samples of representations of at least one pilot signal; a first PN generator coupled to the buffer to produce a PN sequence at a first rate; a second PN generator coupled to the buffer to produce the PN sequence at a plurality of PN offsets at a second rate, the second rate faster than the first rate; a correlator coupled to the buffer and operable to correlate at least a portion of the samples with the PN sequence at each of the plurality of PN offsets to produce a correlation energy for each correlation; a comparator coupled to the correlator to compare each of the correlation energies to an energy threshold; and an energy post-processor coupled to the comparator and operable to note a highest correlation energy; wherein responsive to a particular PN offset resulting in a correlation energy at least equal to an energy threshold, the correlator suspends correlating and the particular PN offset is useful as a PN sequence timing, and wherein responsive to the correlator performing a predetermined number of correlations and none of the plurality of PN offsets results in the correlation energy at least equal to the energy threshold, a PN offset corresponding to the highest correlation energy is selected as the PN sequence timing.
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Specification