Method of doppler searching in a digital GPS receiver

Claim 2

In a spread-spectrum receiver, for receiving one or more direct-sequence-coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, an improved method of Doppler frequency search for each desired signal, and for each code delay search trial, comprising the steps of: a. inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of the desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequency of said down-converted received signal; b. calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of the samples input in step a; c. calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; and d. performing steps a through c M times, summing the M power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective N search frequency, the maximum of said average power quantities exhibiting indicia of the presence and approximate Doppler frequency shift of said desired signal.

Claim 3

In a spread-spectrum receiver, for receiving one or more direct-sequence-coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, an improved method of Doppler frequency search for each desired signal, and for each code delay search trial, comprising the steps of: a. inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of the desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f 2 /2 to +f s /2), f s being the sampling frequency of the samples input in step a; c. calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. performing steps a through c M times, summing the M power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective N search frequency; e. selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. comparing the maximum average power quantity to a threshold, the fact of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power found in step e indicating the approximate Doppler frequency shift, and the fact of said threshold not being exceeded signifying that the current code delay is not approximately correct, and that another code delay should be tried.

Claim 4

In a spread-spectrum receiver, for receiving one or more direct-sequence-coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, an improved method of Doppler frequency search for each desired signal, and for each code delay search trial, comprising the steps of: a. inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of the desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f 2 /2 to +f s /2), f s being the sampling frequency of the samples input in step a; c. calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. performing steps a through c M times, summing the M power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective N search frequency; e. selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. comparing the maximum average power quantity to a threshold, the fact of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power found in step e indicating the approximate Doppler frequency shift, and the fact of said threshold not being exceeded signifying that the current code delay is not approximately correct, and that another code delay should be tried.

Claim 5

In a global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, an improved method of Doppler frequency search for each desired signal, and for each code delay search trial, comprising the steps of: a. inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of the desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of the samples input in step a; c. calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; and d. performing steps a through c M times, summing the M power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency, the maximum of said average power quantities exhibiting indicia of the presence and approximate Doppler frequency shift of said desired signal.

Claim 6

In a global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, an improved method of Doppler frequency search for each desired signal, and for each code delay search trial, comprising the steps of: a. inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of the desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of the samples input in step a; c. calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; and d. performing steps a through c M times, summing the M power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency, the maximum of said average power quantities exhibiting indicia of the presence and approximate Doppler frequency shift of said desired signal.

Claim 7

In a global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out to activation of delay-tracking and carrier-recovery loops, an improved method of Doppler frequency search for each desired signal, and for each code delay search trial, comprising the steps of: a. inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of the desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. calculating the N-point discrete Fourier transform of said block of N samples of produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of the samples input in step a; c. calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. performing steps a through c M times, summing the M power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency; e. selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. comparing the maximum average power quantity to a threshold, the face of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power found in step e indicating the approximate Doppler frequency shift, and the fact of said threshold not being exceeded signifying that the current code delay is not approximately correct, and that another code delay should be tried.

Claim 8

In a global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out to activation of delay-tracking and carrier-recovery loops, an improved method of Doppler frequency search for each desired signal, and for each code delay search trial, comprising the steps of: a. inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of the desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. calculating the N-point discrete Fourier transform of said block of N samples of produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of the samples input in step a; c. calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. performing steps a through c M times, summing the M power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency; e. selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. comparing the maximum average power quantity to a threshold, the face of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power found in step e indicating the approximate Doppler frequency shift, and the fact of said threshold not being exceeded signifying that the current code delay is not approximately correct, and that another code delay should be tried.

Claim 10

The method of claim 1, 2, 3 or 4, wherein step (d) in performed 8 times

Claim 11

A spread-spectrum receiver for receiving one or more direct-sequence-coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequency of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; and d. means for summing, M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective N search frequency, the maximum of said average power quantities exhibiting indicia of the presence and approximate Doppler frequency shift of said desired signal.

Claim 12

A spread-spectrum receiver for receiving one or more direct-sequence-coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequency of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; and d. means for summing, M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective N search frequency, the maximum of said average power quantities exhibiting indicia of the presence and approximate Doppler frequency shift of said desired signal.

Claim 13

A spread-spectrum receiver, for receiving one or more direct-sequence-coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. means for summing, M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective N search frequency; e. means for selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. means for comparing the maximum average power quantity to a threshold, the fact of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power indicating the approximate Doppler frequency shift, and the fact of said threshold not being exceeded signifying that the current code delay is not approximately correct, and that another code delay should be tried.

Claim 14

A spread-spectrum receiver, for receiving one or more direct-sequence-coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. means for summing, M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective N search frequency; e. means for selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. means for comparing the maximum average power quantity to a threshold, the fact of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power indicating the approximate Doppler frequency shift, and the fact of said threshold not being exceeded signifying that the current code delay is not approximately correct, and that another code delay should be tried.

Claim 15

A global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; and d. means for summing M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency, the maximum of said average power quantities exhibiting indicia of the presence and approximate Doppler frequency shift of said desired signal.

Claim 16

A global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out prior to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples to produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; and d. means for summing M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency, the maximum of said average power quantities exhibiting indicia of the presence and approximate Doppler frequency shift of said desired signal.

Claim 17

A global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples of produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. means for summing, M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency; e. means for selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. means for comparing the maximum average power quantity to a threshold, the face of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power found in step e indicating the approximate Doppler frequency shift, and the fact of

Claim 18

A global positioning system receiver, for receiving one or more course/access (C/A) coded signals, each of which may be Doppler shifted from its nominal carrier frequency, wherein for each signal a code delay/Doppler frequency search procedure must be carried out to activation of delay-tracking and carrier-recovery loops, said receiver comprising: a. means for inputting N consecutive digitized samples of a signal equal to a filtered product of a down-converted received signal multiplied by a locally-generated code of a desired signal, the code delay of said locally-generated code being that of the current code delay search trial, said filtering passing, at least, the band of frequencies corresponding to the entire range of possible Doppler-shifted carrier frequencies of said down-converted received signal; b. means for calculating the N-point discrete Fourier transform of said block of N samples of produce N complex-valued transformed output samples, each corresponding to one of N equally-spaced search frequencies in the band from zero Hertz to fs (or, equivalently, in the band from -f s /2 to +f s /2), f s being the sampling frequency of said N samples; c. means for calculating the square of the magnitude of each of said N complex-valued output samples to produce N power quantities, corresponding to the N said search frequencies; d. means for summing, M times, the power quantities produced for each of the N said search frequencies, to produce N quantities proportional to the average power of each respective search frequency; e. means for selecting the maximum of the N average power quantities, and calculating the corresponding frequency; and f. means for comparing the maximum average power quantity to a threshold, the face of said threshold being exceeded signifying that the current code delay is approximately correct (local code approximately time-aligned to received code), with the frequency of maximum average power found in step e indicating the approximate Doppler frequency shift, and the fact of