Method for GPS positioning in a weak signal environment
First Claim
1. A method for processing a global positioning system (GPS) signal at a GPS receiver, comprising the steps of:
- converting the GPS signal to an intermediate frequency signal, wherein the GPS signal being modulated by a carrier signal, a pseudorandom code and a predicted navigation data;
obtaining the predicted navigation data for the GPS signal;
generating a local carrier signal and a local pseudorandom code; and
correlating the intermediate frequency signal with the predicted navigation data, the local carrier signal and the local pseudorandom code at a starting time.
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Accused Products
Abstract
The present invention is a method for GPS positioning in a weak signal environment. The method includes obtaining assistance data for a GPS signal from a satellite at a predetermined time, wherein the assistance data including predicted navigation data, Doppler shift and Doppler shift rate and the GPS signal being modulated by a carrier signal, a pseudorandom code and navigation data, estimating a predicted receiving time for the GPS signal reaching the GPS receiver, capturing the GPS signal, converting the GPS signal to an intermediate frequency signal, acquiring a code phase of the pseudorandom code from the intermediate frequency signal by using the assistance data and the predicted receiving time, and obtaining a position for the GPS receiver based on the predicted navigation data and the code phase of the pseudorandom code. To acquire the code phase of the pseudorandom code, the GPS receiver corrects a real time clock to one millisecond accuracy and process the intermediate frequency signal through coherent correlation of one second.
25 Citations
25 Claims
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1. A method for processing a global positioning system (GPS) signal at a GPS receiver, comprising the steps of:
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converting the GPS signal to an intermediate frequency signal, wherein the GPS signal being modulated by a carrier signal, a pseudorandom code and a predicted navigation data; obtaining the predicted navigation data for the GPS signal; generating a local carrier signal and a local pseudorandom code; and correlating the intermediate frequency signal with the predicted navigation data, the local carrier signal and the local pseudorandom code at a starting time. - View Dependent Claims (2, 3, 4)
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5. A method for synchronizing a GPS receiver with a satellite, comprising the steps of:
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obtaining assistance data for a GPS signal received from the satellite at a predetermined time, wherein the assistance data including predicted navigation data, Doppler shift and Doppler shift rate and the GPS signal being modulated by a carrier signal, a pseudorandom code and navigation data; estimating a predicted receiving time for the GPS signal reaching the GPS receiver; capturing the GPS signal through channels of the GPS receiver; acquiring the GPS signal at each channel by using the assistance data to obtain a local receiving time for the GPS signal, wherein the GPS signal at each channel has a starting point and a predetermined search period; and correcting a real-time clock of the GPS receiver based on the local receiving time and the predicted receiving time. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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12. A method for positioning of a GPS receiver in a weak signal environment, comprising the steps of:
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a) obtaining assistance data for a GPS signal from a satellite at a predetermined time, wherein the assistance data including predicted navigation data, Doppler shift and Doppler shift rate and the GPS signal being modulated by a carrier signal, a pseudorandom code and navigation data; b) estimating a predicted receiving time for the GPS signal reaching the GPS receiver; c) capturing the GPS signal; d) converting the GPS signal to an intermediate frequency signal; e) acquiring a code phase of the pseudorandom code from the intermediate frequency signal by using the assistance data and the predicted receiving time; and f) obtaining a position for the GPS receiver based on the predicted navigation data and the code phase of the pseudorandom code. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method for controlling a GPS receiver, comprising the steps of:
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initiating the GPS receiver to a stand-alone mode; determining whether the GPS receiver succeeded to acquire GPS signals from at least four satellites; shifting the GPS receiver to a self-assisted mode if the GPS receiver failed to acquire the GPS signals from the at least four satellites; determining whether valid assistance data are stored in memory of the GPS receiver; and shifting the GPS receiver to an assisted-GPS mode if no valid assistance data are stored in the memory of the GPS receiver. - View Dependent Claims (24, 25)
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Specification