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A method of and computer system for assisting GPS position determination is described. Ephemeris and updated almanac information for a GPS satellite is received over a datalink. Based on the received updated almanac information and GPS parity algorithms, data bits of the GPS signal are reconstructed

A method of and computer system for assisting GPS position determination is described. Ephemeris and updated almanac information for a GPS satellite is received over a datalink. Based on the received updated almanac information and GPS parity algorithms, data bits of the GPS signal are reconstructed. Based on the current time, the reconstructed data bits are synchronized with the time of reception of a GPS signal from a satellite currently in view. The reconstructed data bits are subtracted from the received GPS signal at the synchronized time. A coherent integration of the received GPS signal over the time period corresponding to the reconstructed data bits is performed to obtain a GPS pseudo-range measurement. The GPS receiver position is determined using the generated, synchronized pseudo-range measurement and the ephemeris information received over the datalink.

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What is claimed is: 1. A method of assisting GPS position determination comprising: receiving ephemeris information for a GPS satellite over a datalink; receiving updated almanac information for a GPS satellite over a datalink; based on the received updated almanac information and GPS parity algori

What is claimed is: 1. A method of assisting GPS position determination comprising: receiving ephemeris information for a GPS satellite over a datalink; receiving updated almanac information for a GPS satellite over a datalink; based on the received updated almanac information and GPS parity algorithms, reconstructing data bits of the GPS signal; based on the current time, synchronizing the reconstructed data bits with the time of reception of a GPS signal from a satellite currently in view; subtracting the reconstructed data bits from the received GPS signal at the synchronized time; coherently integrating the received GPS signal over the time period corresponding to the reconstructed data bits to obtain a GPS pseudo-range measurement; and determining the GPS receiver position using the generated, synchronized pseudo-range measurement and the ephemeris information received over the datalink. 2. The method as claimed in claim 1, wherein the datalink is a one-to-many broadcast. 3. The method as claimed in claim 1, wherein the information received over the datalink is formatted for transmission over the datalink. 4. The method as claimed in claim 1, wherein the step of reconstructing data bits reconstructs 240 contiguous data bits. 5. The method as claimed in claim 4, wherein the contiguous data bits are words 3 through 10 of sub-frame 5 of the GPS signal. 6. The method as claimed in claim 4, wherein the contiguous data bits are words 3 through 10 of sub-frame 4 of the GPS signal. 7. The method as claimed in claim 1, wherein the subtracting step removes a plurality of bits of data from the received GPS signal. 8. The method as claimed in claim 1, wherein the subtracting step removes a plurality of seconds of data from the received GPS signal. 9. The method as claimed in claim 1, wherein the step of coherently integrating is performed for more than one satellite. 10. The method as claimed in claim 1, wherein the received ephemeris information is received from a periodic broadcast. 11. The method as claimed in claim 10, wherein the periodic ephemeris broadcast is broadcast at least once per hour. 12. The method as claimed in claim 1, wherein the received almanac information is received from a periodic broadcast. 13. The method as claimed in claim 12, wherein the periodic almanac broadcast is broadcast at least once per 24 hours. 14. The method as claimed in claim 1, further comprising the steps of: storing the reconstructed data bits of the GPS signal; and subsequent to storing the reconstructed data bits, performing the synchronizing, subtracting, integrating, and determining steps using the stored reconstructed data bits. 15. The computer system of claim 1, wherein all of the steps are performed by a mobile GPS receiver. 16. The computer system of claim 17, wherein the computer system is a mobile GPS receiver. 17. A method of assisting GPS position determination comprising: receiving ephemeris information for a GPS satellite currently in view from a GPS signal transmitted by the GPS satellite at a GPS receiver; receiving almanac information for a GPS satellite from a GPS signal transmitted by the GPS satellite at a GPS receiver; after receipt of ephemeris information and almanac information, moving the GPS receiver to a covered environment; based on the received almanac information, ephemeris information, and GPS parity algorithms, reconstructing data bits of the GPS signal; based on the current time, synchronizing the reconstructed data bits with the time of reception of a GPS signal from a satellite currently in view; subtracting the reconstructed data bits from the received GPS signal at the synchronized time; coherently integrating the received GPS signal over the time period corresponding to the reconstructed data bits to obtain a GPS pseudo-range measurement; and determining the GPS receiver position using the generated, synchronized pseudo-range measurements and the received ephemeris information. 18. The method as claimed in claim 17, wherein the step of reconstructing data bits reconstructs 240 contiguous data bits. 19. The method as claimed in claim 18, wherein the contiguous data bits are words 3 through 10 of sub-frame 5 of the GPS signal. 20. The method as claimed in claim 18, wherein the contiguous data bits are words 3 through 10 of sub-frame 4 of the GPS signal. 21. The method as claimed in claim 17, wherein the subtracting step removes a plurality of bits of from the received GPS signal. 22. The method as claimed in claim 17, wherein the subtracting step removes a plurality of bits of from the received GPS signal. 23. The method as claimed in claim 17, wherein the step of coherently integrating is performed for more than one satellite. 24. A computer system for assisting GPS position determination comprising: one or more processors for receiving and transmitting data; and a memory coupled to said one or more processors, said memory having stored therein received ephemeris information and updated almanac information for a GPS satellite over a datalink, GPS parity algorithms, and sequences of instruction which, when executed by one of said one or more processor, cause one of said one or more processors to reconstruct data bits of the GPS signal based on the stored almanac information and GPS parity algorithms, synchronize the reconstructed data bits with the time of reception of a GPS signal from a satellite currently in view based on the current time, coherently integrate the received GPS signal over the time period at the synchronized time, coherently integrate the received GPS signal over the time period corresponding to the reconstructed data bits to obtain a GPS pseudo-range measurement, and determine a position using the generated, synchronized pseudo-range measurement and the stored ephemeris information. 25. The computer system as claimed in claim 24, wherein the data bits reconstructed comprise 240 contiguous data bits. 26. The computer system as claimed in claim 24, wherein the received ephemeris information is received from a periodic broadcast. 27. The computer system as claimed in claim 26, wherein the periodic ephemeris broadcast is broadcast at least once per hour. 28. The computer system as claimed in claim 24, wherein the received almanac information is received from a periodic broadcast. 29. The computer system as claimed in claim 28, wherein the periodic almanac broadcast is broadcast at least once per 24 hours. 30. The computer system of claim 24, wherein the processor is in a mobile GPS receiver. 31. A computer system for assisting GPS position determination comprising: one or more processors for receiving and transmitting data; and a memory coupled to said one or more processors, said memory having stored therein received ephemeris information and updated almanac information for a GPS satellite from a GPS signal transmitted by the GPS satellite, GPS parity algorithms, and sequences of instructions which, when executed by one of said one or more processors after determining that the computer system is in a covered environment, cause one of said one or more processors to reconstruct data bits of the GPS signal based on the stored almanac information, ephemeris information, and GPS parity algorithms, synchronize the reconstructed data bits with the time of reception of a GPS signal from a satellite currently in view based on the current time, subtract the reconstructed data bits from the received GPS signal at the synchronized time, coherently integrate the received GPS signal over the time period corresponding to the reconstructed data bits to obtain a GPS pseudo-range measurement, and determine a position using the generated, synchronized pseudo-range measurement and the stored ephemeris information. 32. The computer system as claimed in claim 31, wherein the data bits reconstructed comprise 240 contiguous data bits. 33. The computer system of claim 31, wherein the processor is in a mobile GPS receiver.