Method and apparatus for assisted GPS

• US 20030011511A1
• Filed: 06/03/2002
• Published: 01/16/2003
• Est. Priority Date: 11/12/1999
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: George J. Geier, Thomas M. King, Yilin Zhao
• Inventors: King, Thomas M., Geier, George J., Zhao, Yilin
• Granted Patent: US 7,064,706 B2
• Time in Patent Office: Days
• US Class Current: 342/357.02
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/071 DGPS corrections
• CPC Class Codes: G01S 19/08 providing integrity information, e.g. health of satellites or quality of ephemeris data
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
• CPC Class Codes: G01S 5/0045 Transmission from base station to mobile station G01S5/009 takes precedence
• CPC Class Codes: G01S 5/009 Transmission of differential positioning data to mobile

Abstract

A cellular network protocol that maintains the reliability of assisted GPS based positioning is taught. An Integrity Monitor (IM) informs mobile stations, their users, or networks of measurement quality and it warns them of failing and failed GPS satellites by isolating them from the effects of these failures. Whenever an unhealthy satellite is detected, its corresponding assistance data will be excluded for delivery or for position determination. In other words, there are two specific aspects to the Integrity Monitor (IM). For DGPS users, it predicts the reliability or quality of the DGPS corrections. For all users, it isolates the mobile position calculation from the effects of GPS satellite failures. The UDRE parameter, nominally output by a reference DGPS receiver, is used to communicate the DGPS quality information, and DGPS corrections are simply excluded for failed satellites. For autonomous GPS users, a special integrity message is required and defined to communicate the satellite failure status information.

Claims

1. A method for maintaining the integrity of a mobile handset'"'"'s location determination in a system comprising the mobile handset, radio communication infrastructure and a Differential Global Positioning System (DGPS) reference receiver coupled to the radio communication infrastructure and installed at a predetermined location, the DGPS reference receiver receiving GPS information from a plurality of GPS satellites, the method comprising:

said radio communication infrastructure receiving DGPS information from the DGPS reference receiver;

deriving differential correction data from said DGPS information;

determining whether one or more of said plurality of GPS satellites have failed/are failing, based on the differential correction data;

generating a failed satellite message when it is determined that one or more of said plurality of GPS satellites have failed/are failing, said failed satellite message identifying the one or more of said plurality of GPS satellites that have failed/are failing; and

transmitting the failed satellite message identifying the one or more of said plurality of GPS satellites that have failed/are failing when it is determined that the one or more of said plurality of GPS satellites has failed/are failing.

2. The method of claim 1 wherein determining whether one or more of said plurality of GPS satellites have failed/are failing comprises determining whether one or more of said plurality of GPS satellites have failed/are failing based on magnitudes of the differential correction data for each of said plurality of GPS satellites.

3. The method of claim 2 wherein determining whether one or more of said plurality of GPS satellites have failed/are failing comprises:

comparing said magnitudes of the differential correction data to a threshold; and

determining that a GPS satellite has failed/is failing when said threshold is exceeded.

4. The method of claim 3 wherein said threshold is based upon an expected level of selective availability (SA).

5. The method of claim 4 wherein said expected level of SA is determined from a User Range Accuracy (URA) parameter communicated in said GPS information.

6. The method of claim 3 wherein transmitting a differential correction message comprises:

for a predetermined period of time, generating the differential correction message by excluding differential correction data corresponding to one or more of said plurality of GPS satellites when it is determined that the one or more of said plurality of GPS satellites have failed/are failing; and

for said predetermined period of time, transmitting the differential correction message to said mobile handset,

wherein said predetermined period of time is a minimum period of time that said differential correction data corresponding to the one or more of said plurality of GPS satellites that have failed/are failing exceeds said threshold.

7. The method of claim 1, determining whether one or more of said plurality of GPS satellites have failed/are failing within a specified time after failure.

8. A method for maintaining the integrity of a mobile handset'"'"'s location determination in a radio communication system, the method comprising:

determining whether one or more of said plurality of GPS satellites have failed/are failing within a specified after failure;

generating an integrity message identifying which of said plurality of GPS satellites have failed/are failing; and

transmitting the integrity message to said mobile handset.

9. The method of claim 8, determining whether one or more of said plurality of GPS satellites have failed/are failing by determining whether one or more of said plurality of GPS satellites have failed/are failing based on a magnitude of residuals of a position solution of each of said plurality of GPS satellites.

10. The method of claim 9, determining the magnitude of said residuals of said position solution by derivation from a set of pseudo ranges generated by a GPS receiver of said mobile handset.

11. The method of claim 8, transmitting the integrity message comprises as a broadcast integrity message addressing more than one mobile handset.

12. The method of claim 8, transmitting the integrity message as a point-to-point integrity message addressing a particular mobile handset.

13. The method of claim 8 wherein generating an integrity message comprises generating an integrity message identifying at least one of said plurality of GPS satellites as having failed/are failing for a predetermined time interval.

15. The method of claim 14, determining whether any satellites have failed, including whether any satellite is failing, by considering magnitudes of the differential correction data.

16. The method of claim 15, determining whether any satellite has failed, including whether any satellite is failing, by comparing said magnitudes of the differential correction data to a threshold.

17. The method of claim 14, determining whether any satellite has failed, including whether any satellite is failing, by considering a selective availability (SA) level.

18. The method of claim 17, determining the SA level from a User Range Accuracy (URA) parameter.

20. The method of claim 19, determining whether a satellite has failed, including whether any satellite is failing, by considering a magnitude of residuals of a position solution of each satellite in the satellite positioning system.

21. The method of claim 20, determining the magnitude of said residuals of said position solution by deriving them from a set of pseudo ranges generated by a satellite receiver.

22. The method of claim 19, transmitting the integrity message as a broadcast integrity message addressing more than one mobile handset.

23. The method of claim 19, transmitting the integrity message as a point-to-point integrity message addressing a particular mobile handset.

24. The method of claim 19, identifying the failed or failing satellites as having failed or are failing for a predetermined time interval.

25. The method of claim 19, determining whether a satellite of the satellite positioning system has failed, including whether any satellite is failing, within a specified time after the failure.

14. A satellite positioning system integrity maintenance method in a mobile handset, comprising:

receiving differential correction data for said mobile handset;

determining whether any satellite of the satellite positioning system has failed, including whether any satellite is failing, based on the differential correction data;

excluding information from any failed and failing satellites from mobile handset position solution determinations.

19. A method for maintaining integrity of a satellite positioning system based location fix in a cellular communications network, comprising:

determining whether any satellite of the satellite positioning system has failed, including whether any satellite is failing;

if a satellite has failed, including if any satellite is failing, generating an integrity message identifying the satellite that has failed/is failing; and

transmitting the integrity message from the cellular communications network.