Method and apparatus for determining time in a GPS receiver
First Claim
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1. A method for determining time in a global positioning satellite (GPS) receiver, comprising:
- capturing GPS data from a GPS message for a predetermined period of time;
locating a time of arrival of an expected data pattern in said captured GPS data by correlating the captured GPS data with the expected data pattern; and
determining a time offset between a start time of said predetermined period of time and a time of arrival of said expected data pattern.
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Abstract
A method and apparatus for determining time in a GPS receiver is provided according to the invention. The method includes the steps of capturing (304) GPS data in a GPS message for a predetermined period of time, locating (308) a predetermined data sequence in the captured data, and determining (311) a time offset between a data capture start time and a time of arrival of the expected data pattern.
117 Citations
68 Claims
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1. A method for determining time in a global positioning satellite (GPS) receiver, comprising:
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capturing GPS data from a GPS message for a predetermined period of time;
locating a time of arrival of an expected data pattern in said captured GPS data by correlating the captured GPS data with the expected data pattern; and
determining a time offset between a start time of said predetermined period of time and a time of arrival of said expected data pattern. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
correcting said time offset to compensate for a signal propagation time between said GPS satellite and said GPS receiver.
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4. The method of claim 3, wherein the step of correcting further comprises the step of:
modifying said corrected time offset to compensate for a satellite clock offset time.
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5. The method of claim 1, wherein said expected data pattern is a GPS message preamble.
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6. The method of claim 1, wherein said expected data pattern is a hand-over word.
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7. The method of claim 1, wherein said expected data pattern is a subframe ID.
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8. The method of claim 1, wherein said expected data pattern is selected from the group consisting of a GPS message preamble, a hand-over word, and subframe ID, and combinations thereof.
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9. The method of claim 1, wherein said predetermined period of time is approximately one second.
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10. The method of claim 1, wherein the step of capturing comprises the steps of:
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down converting a GPS signal to a predetermined intermediate frequency;
sampling said down-converted GPS signal to produce a plurality of samples; and
storing said plurality of samples into a memory.
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11. A method for determining time in a global positioning satellite (GPS) receiver, comprising:
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capturing post correlation coherent GPS data for a predetermined period of time;
locating a time of arrival of a predetermined data sequence in said captured post correlation coherent GPS data by correlating the captured post correlation GPS data with the predetermined data sequence; and
determining a time offset between a start time of said predetermined period of time and a time of arrival of said predetermined data sequence. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
correcting said time offset to compensate for a signal propagation time between a said GPS satellite and said GPS receiver.
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14. The method of claim 13, wherein the step of correcting further comprises the step of:
modifying said corrected time offset to compensate for a satellite clock offset time.
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15. The method of claim 11, wherein said predetermined data sequence is a GPS message preamble.
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16. The method of claim 11, wherein said p redetermined data sequence is a hand-over word.
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17. The method of claim 11, wherein said predetermined data sequence is a subframe ID.
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18. The method of claim 11, wherein said predetermined data sequence is selected from the group consisting of a GPS message preamble, a hand-over word, and subframe ID, and combinations thereof.
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19. The method of claim 11, wherein said predetermined period of time is about one second.
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20. The method of claim 11, wherein said step of capturing comprises the steps of:
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down converting a GPS signal to a predetermined intermediate frequency;
sampling said down-converted GPS signal to produce a plurality of samples;
coherently correlating said plurality of samples against a predetermined satellite pseudo random noise code; and
storing post correlation coherent in phase and quadrature GPS signal characteristics as post correlation coherent GPS data.
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21. A method for determining time in a GPS receiver, comprising the steps of:
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down converting a GPS signal to a predetermined intermediate frequency;
sampling said down-converted GPS signal to produce a plurality of samples;
storing said plurality of samples in a memory;
selecting a GPS signal from a visible GPS satellite;
measuring and storing in-phase and quadrature coherent characteristics of said selected GPS signal over a plurality of predetermined time periods;
coherently correlating said in-phase and quadrature coherent characteristics to an expected data pattern; and
determining a time offset from a correlation maximum, with said correlation maximum occurring said time offset after a beginning time of said step of storing. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29)
determining a code phase for each visible GPS satellite signal in the memory;
determining a Doppler shift for said each visible GPS satellite signal in the memory; and
choosing a GPS signal having a strongest signal level dependent on the determined code phase for said each visible GPS satellite signal and the determined Doppler shift for said each visible GPS satellite signal.
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23. The method of claim 21, wherein said method determines a capture time from said time offset, a code phase for said selected GPS signal, and a location of a GPS satellite corresponding to said selected GPS signal.
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24. The method of claim 21, wherein said step of determining further comprises:
correcting said time offset for a signal propagation time between said GPS receiver and a GPS satellite corresponding to said selected GPS signal.
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25. The method of claim 24, wherein said step of correcting further comprises:
modifying said corrected time offset to compensate for a satellite clock offset time.
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26. The method of claim 21, wherein said expected data pattern is a GPS message preamble.
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27. The method of claim 21, wherein said expected data pattern is a hand-over word.
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28. The method of claim 21, wherein said expected data pattern is selected from the group consisting of a GPS message preamble, a hand-over word, and subframe ID, and combinations thereof.
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29. The method of claim 21, wherein said step of storing captures about one second of said GPS signal.
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30. A method for determining time in a GPS receiver, comprising the steps of:
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down converting a GPS signal to a predetermined intermediate frequency;
sampling said down-converted GPS signal to produce a plurality of samples;
non-coherently correlating said plurality of samples against each visible GPS satellite pseudo random noise code and each visible GPS satellite Doppler;
selecting a GPS satellite signal;
measuring and storing an in-phase and quadrature coherent characteristics of said selected GPS satellite signal over a plurality of predetermined time periods;
coherently correlating said in-phase and quadrature coherent characteristics to an expected data pattern; and
determining a time offset from a correlation maximum, with said correlation maximum occurring said time offset after a beginning time of said step of measuring and storing. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 38, 39)
determining a real-time code phase for said each visible GPS satellite from said each visible GPS satellite pseudo random noise code;
determining a real-time Doppler shift for said each visible GPS satellite from said each visible GPS satellite Doppler; and
choosing a GPS satellite signal having a strongest signal level dependent on the determined real-time code phase for said each visible GPS satellite and the determined real-time Doppler shift for said each visible GPS satellite.
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32. The method of claim 30, wherein said method determines a capture time from said time offset, said code phase for said selected GPS satellite signal, and a location of a GPS satellite corresponding to said selected GPS satellite signal.
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33. The method of claim 30, wherein said step of determining further comprises:
correcting said time offset to compensate for a signal propagation time between said GPS receiver and a GPS satellite corresponding to said selected GPS satellite signal.
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34. The method of claim 33, wherein the step of correcting further comprises:
modifying said corrected time offset to compensate for a satellite clock offset time.
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35. The method of claim 30, wherein said expected data pattern is a GPS message preamble.
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36. The method of claim 30, wherein said expected data pattern is a hand-over word.
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37. The method of claim 30, wherein said expected data pattern is selected from the group consisting of a GPS message preamble, a hand-over word, and subframe ID, and combinations thereof.
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38. The method of claim 30, wherein said step of measuring and storing captures about one second of said selected GPS satellite signal.
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39. The method of claim 30, wherein said step of measuring and storing captures post correlation data at a rate of one sample per millisecond.
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40. An apparatus for determining time in a GPS receiver, comprising:
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a down converter for down converting a plurality of GPS signals to an intermediate frequency;
an analog-to-digital converter coupled to said down converter for converting said down-converted plurality of GPS signals to digital data;
a digital intermediate frequency (IF) switch coupled to said analog-to-digital converter and coupled to a clock, said digital IF switch controlled by said clock to periodically close for a predetermined sample time period;
an IF memory coupled to said digital IF switch for storing a plurality of digital IF data available when said digital IF switch is closed;
a non-coherent GPS correlator coupled to said IF memory for determining a code phase characteristic, determining a Doppler characteristic, determining a signal strength characteristic for a plurality of GPS signals in said plurality of digital IF data, and selecting a GPS satellite signal based on said determined code phase characteristics, determined Doppler characteristics, and determined signal strength characteristics;
a coherent GPS correlator coupled to said IF memory and said non-coherent GPS correlator for producing in-phase and quadrature coherent measurements;
a memory storage switch coupled to said coherent GPS correlator, said memory storage switch periodically closing to produce a plurality of in-phase and quadrature coherent measurement samples;
a samples memory coupled to said memory storage switch for storing said plurality of in-phase and quadrature coherent measurement samples;
a correlator coupled to said samples memory and to a predetermined expected data pattern storage, said correlator coherently correlating said plurality of in-phase and quadrature coherent measurement samples to a predetermined expected data pattern in said predetermined expected data pattern storage to produce a correlation output;
a coherent integrator coupled to said correlator for integrating said correlation output to produce an integration output;
a magnitude determiner coupled to said coherent integrator for detecting a magnitude of said integration output and generating a plurality of integration magnitudes;
a magnitude versus delay memory coupled to said magnitude determiner and storing said plurality of integration magnitudes; and
a maximum integration magnitude determiner coupled to said magnitude versus delay memory and capable of determining a maximum integration magnitude and a time offset representative of a delay period from a starting time of storing a plurality of digital IF data to said maximum integration magnitude. - View Dependent Claims (41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53)
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54. An apparatus for determining time in a GPS receiver, comprising:
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a down converter for down converting a GPS signal to an intermediate frequency;
an analog-to-digital converter coupled to said down converter for converting said down-converted GPS signal to digital data;
a non-coherent GPS correlator coupled to said analog-to-digital converter for determining a code phase characteristic, determining a Doppler characteristic, determining a signal strength characteristic for said digital data, and selecting a GPS satellite signal based on said determined code phase characteristics, determined Doppler characteristics, and determined signal strength characteristics;
a coherent GPS correlator coupled to said analog-to-digital converter and said non-coherent GPS correlator for producing in-phase and quadrature coherent measurements;
a memory storage switch coupled to said coherent GPS correlator and coupled to a clock, said memory storage switch controlled by said clock to periodically close to produce a plurality of in-phase and quadrature coherent measurement samples;
a samples memory coupled to said memory storage switch for storing said plurality of in-phase and quadrature coherent measurement samples;
a correlator coupled to said samples memory and to a predetermined expected data pattern storage for coherently correlating said plurality of in-phase and quadrature coherent measurement samples to a predetermined expected data pattern in said predetermined expected data pattern storage to produce a correlation output;
a coherent integrator coupled to said correlator for integrating said correlation output to produce an integration output;
a magnitude determiner coupled to said coherent integrator for detecting a magnitude of said integration output and generating a plurality of integration magnitudes;
a magnitude versus delay memory coupled to said magnitude determiner for storing said plurality of integration magnitudes; and
a maximum integration magnitude determiner coupled to said magnitude versus delay memory for determining a maximum integration magnitude and a time offset representing a delay period from a start time of storing said plurality of in-phase and quadrature measurement samples and said maximum integration magnitude. - View Dependent Claims (55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68)
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Specification