Method and apparatus for determining global position using almanac information

• US 6,671,620 B1
• Filed: 05/18/2000
• Issued: 12/30/2003
• Est. Priority Date: 05/18/2000
• Status: Expired due to Term

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Schmidt, Kurt Christian, Garin, Lionel Jacques
• Primary Examiner(s): Beaulieu, Yonel
• Assistant Examiner(s): Broadhead, Brian J.
• Application Number:
  US09/575,492
• Time in Patent Office: 1,321 Days
• Field of Search: 701/214, 701/213, 701/215, 342/357.1, 342/357.12, 342/357.13, 342/357.15, 342/357.09
• US Class Current: 701/213
• CPC Class Codes: G01S 19/06 employing an initial estimate of the location of the receiver as aiding data or in generating aiding data
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view

Abstract

In a satellite global positioning system, satellite acquisition and location assistance is based upon shared information between a GPS receiver and a remote server. Satellite position is predicted by satellite almanac data.

Claims

1. A method for determining a location of a mobile station, comprising:

the mobile station computing a tentative satellite visibility list using stored satellite almanac information, wherein the stored satellite almanac information includes a plurality of sub-almanac identifications;

the mobile station transmitting the tentative satellite visibility list and the sub-almanac identifications to a location server;

the mobile station transmitting a computed maximum error parameter to the location server;

the location server calculating at least one actual error between at least one satellite position calculated using the sub-almanac information indicated by the sub-almanac identifications, and at least one satellite position calculated using current ephemeris data; and

the location server transmitting replacement sub-almanac information to the mobile station if an actual error exceeds the maximum error parameter.

2. The method of claim 1, further comprising the location server transmitting a reference position to the mobile station.

3. The method of claim 2, further comprising:

the mobile station computing coarse position information using the stored almanac information and any replacement sub-almanac information received; and

the mobile station transmitting the coarse position information to the location server.

4. The method of claim 3, further comprising the mobile station transmitting a position difference to the location server, wherein the position difference comprises a difference between a position calculated by the mobile station and the reference position.

5. The method of claim 3, further comprising the location server calculating pseudorange corrections to the coarse information using ephemeris data.

6. The method of claim 5, further comprising:

the location server calculating position corrections and time corrections using the pseudorange corrections; and

the location server using the position corrections and time corrections to calculate a corrected coarse position.

7. The method of claim 6, further comprising the location server sending the corrected coarse position to the mobile station.

8. The method of claim 1, further comprising,

the location server computing a true satellite visibility list using complete almanac information;

and

if the true satellite visibility list includes a sub-almanac not included in the tentative satellite visibility list, transmitting the sub-almanac to the mobile station.

9. A system for determining a position of an object, comprising:

a mobile station comprising a global positioning system (“

GPS”

) receiver, wherein the mobile station is configured to compute an approximate GPS satellite visibility list from stored sub-almanacs; and

a position determining entity (“

PDE”

) communicatively coupled to the mobile station, wherein the PDE is configured to receive almanac and ephemeris data, the PDE comprising,

a memory device for storing almanac data and ephemeris data; and

a central processing unit configured to,

calculate an error between a position calculated using the ephemeris data and a position calculated using sub-almanac data received from the mobile station; and

transmit a replacement sub-almanac to the mobile station if an error calculated using a sub-almanac is greater than a pre-determined value;

wherein the mobile station uses the stored sub-almanacs, any replacement sub-almanacs received, and GPS measurements to compute a coarse position.

10. The system of claim 9, wherein the mobile station further uses the stored sub-almanacs and any replacement almanacs received to compute approximate Doppler offset and code offset information.

11. The system of claim 10, wherein the mobile station further uses the approximate Doppler offset and code offset information to acquire and track GPS satellites.

12. The system of claim 9, wherein the mobile station transmits the coarse position and at least one weighting measurement factor to the PDE.

13. The system of claim 12, wherein the PDE computes a position difference between a position calculated using the almanac data and a position calculated using the ephemeris data.

14. The method of claim 13, wherein the computed difference includes a differential GPS correction.

15. The system of claim 14, wherein the PDE corrects the coarse position using the computed difference.

16. An electromagnetic medium containing instructions which, when read by a processor, cause the processor to:

calculate a position using ephemeris data;

calculate a position using sub-almanac data received from a mobile unit;

calculate an error between the positions calculated; and

if the error exceeds a pre-determined error value, sending a replacement sub-almanac to the mobile station for each sub-almanac associated with the error, wherein the replacement sub-almanac is stored with other sub-almanacs as a set of validated sub-almanacs used by the mobile station to calculate a coarse position.

17. The electromagnetic medium of claim 16, wherein the instructions, when read by a processor, further cause the processor to:

receive the coarse position from the mobile station;

compute a pseudorange correction between a position calculated using the validated sub-almanacs and ephemeris data, including consideration of differential GPS corrections;

compute position and time corrections from the pseudorange corrections; and

include the position and time corrections in the coarse position.