GPS receiver having a fast time to first fix
First Claim
1. A global positioning system (GPS) receiver, comprising:
- a correlator for despreading a GPS signal including a GPS bit stream including a GPS message synchronized to a GPS clock time and providing said GPS bit stream;
a clock for providing an approximate local clock time;
a processor including a variable memory for storing an expected GPS message and a program memory including an executable code for receiving said GPS bit stream and executing said executable code; and
a GPS synchronization code for inclusion in said executable code for generating a replica bit stream including said expected GPS message having a timing based upon said local clock time and for aligning said local clock time to said GPS time for providing a GPS-based clock time by adjusting said local clock time to synchronize said replica bit stream to said GPS bit stream.
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Accused Products
Abstract
A global positioning system (GPS) receiver and a method having a fast time to first fix (TTFF) using GPS signal Doppler frequency shifts for correcting the local clock time and using information for an expected GPS message for synchronizing the corrected local clock time to GPS time. The GPS receiver includes radio frequency (RF) circuitry for receiving and downconverting a spread spectrum GPS satellite signal, a correlator for despreading the downconverted GPS signal and providing a GPS bit stream, a clock for providing a local time, and a processor including an executable code. The executable code includes a Doppler correction code for improving the accuracy of the local time by comparing a measured and a calculated Doppler frequency shift for the GPS satellite signal from three or more GPS satellites, and a GPS synchronization code for synchronizing the local time so that the timing of a replica bit stream based upon information for an expected GPS message matches the timing a GPS bit stream received in the GPS satellite signal.
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Citations
16 Claims
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1. A global positioning system (GPS) receiver, comprising:
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a correlator for despreading a GPS signal including a GPS bit stream including a GPS message synchronized to a GPS clock time and providing said GPS bit stream; a clock for providing an approximate local clock time; a processor including a variable memory for storing an expected GPS message and a program memory including an executable code for receiving said GPS bit stream and executing said executable code; and a GPS synchronization code for inclusion in said executable code for generating a replica bit stream including said expected GPS message having a timing based upon said local clock time and for aligning said local clock time to said GPS time for providing a GPS-based clock time by adjusting said local clock time to synchronize said replica bit stream to said GPS bit stream. - View Dependent Claims (2, 3, 4)
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5. A global positioning system (GPS) receiver, comprising:
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a correlator for despreading a GPS signal including a GPS bit stream and providing said GPS bit stream; a clock for providing an approximate local clock time; a processor including a program memory including an executable code for receiving said GPS bit stream and executing said executable code; and a Doppler correction code for inclusion in said executable code for improving an accuracy of said local clock time by adjusting said local clock time according to a difference between a calculated Doppler frequency shift and a measured Doppler frequency shift for said GPS signal and providing a Doppler-corrected local time. - View Dependent Claims (6, 7, 8)
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9. A method in a global positioning system (GPS) receiver for receiving a spread spectrum GPS signal including a GPS bit stream including a GPS message synchronized to a GPS time, comprising steps of:
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despreading said GPS signal for providing said GPS bit stream; generating an approximate local clock time; retrieving information for an expected GPS message from a memory; generating a replica bit stream including said expected GPS message having a timing based on said local clock time; and aligning said local clock time to said GPS time for providing a GPS-based clock time by adjusting said local clock time to synchronize said replica bit stream to said GPS bit stream. - View Dependent Claims (10, 11, 12)
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13. A method in a global positioning system (GPS) receiver for receiving a spread spectrum GPS signal including a GPS bit stream including a GPS message synchronized to a GPS time, comprising steps of:
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despreading said GPS signal for providing said GPS bit stream; generating an approximate local clock time; and improving an accuracy of said local clock time by adjusting said local clock time according to a difference between a calculated Doppler frequency shift and a measured Doppler frequency shift for said GPS signal and providing a Doppler-corrected local time. - View Dependent Claims (14, 15, 16)
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Specification