Method and apparatus for assisted GPS integrity maintenance

• US 6,429,808 B1
• Filed: 01/10/2000
• Issued: 08/06/2002
• Est. Priority Date: 11/12/1999
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: King, Thomas M., Geier, George J., Zhao, Yilin
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/480,380
• Time in Patent Office: 939 Days
• Field of Search: 342/357.03, 342/357.05, 342/357.1, 342/357.02, 455/456
• US Class Current: 342/357.44
• 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 which 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 isolats 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 method comprising the steps of:

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

deriving differential correction data from said DGPS information;

determining whether said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination by calculating a location of the DGPS reference receiver based on said differential correction data and measurement data generated by the DGPS reference receiver; and

transmitting a measurement quality indicator identifying off-nominal errors to said mobile handset when said determining step determines that said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination.

2. The method of claim 1 wherein the step of determining whether said differential correction data will produce off-nominal errors comprises the step of determining at the radio communication infrastructure whether said differential correction data will produce off-nominal errors.

3. The method of claim 1 wherein the step of determining whether said differential correction data will produce off-nominal errors comprises the steps of:

calculating a location determination; and

comparing the location determination with a surveyed location of the DGPS reference receiver to generate a location error.

4. The method of claim 3 wherein the step of determining whether said differential correction data will produce off-nominal errors further comprises the step of comparing the location error to a location error threshold to determine whether said off-nominal errors will be produced.

5. The method of claim 4 wherein the step of determining whether said differential correction data will produce off-nominal errors further comprises the step of calculating the location error threshold based on a covariance matrix of a Weighted Least-Square (WLS) solution for the location of the DGPS reference receiver.

6. The method of claim 5 wherein the step of calculating the location error threshold based on the covariance matrix of the WLS solution comprises the step of calculating the covariance matrix based on User Differential Range Error (UDRE) values determined by the DGPS reference receiver to compute measurement error variances for GPS pseudo ranges.

7. The method of claim 1 wherein the step of transmitting said measurement quality indicator comprises the step of transmitting said measurement quality indicator as a broadcast measurement quality indicator addressing more than one mobile handset.

8. The method of claim 1 wherein the step of transmitting said measurement quality indicator comprises the step of transmitting said measurement quality indicator as a point-to-point measurement quality indicator addressing only the mobile handset.

9. The method of claim 1, transmitting said measurement quality indicator identifying off-nominal errors with a scaled User Differential Range Error (UDRE) accuracy predictor to compensate for said off-nominal errors.

10. The method of claim 1, transmitting said measurement quality indicator identifying off-nominal errors with a scaled User Differential Range Error (UDRE) scale factor to reflect the appearance of said off-nominal errors.

11. A method for maintaining the integrity of assisted satellite positioning system based location fixes for a mobile handset in a cellular communication network including a satellite positioning system reference receiver, comprising:

deriving differential correction data from satellites;

determining whether said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination by calculating a location of the reference receiver based on said differential correction data and measurement data generated by the reference receiver; and

transmitting a measurement quality indicator identifying off-nominal errors to said mobile handset if said determining step determines that said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination.

12. The method of claim 11, determining whether said differential correction data will produce off-nominal errors at the cellular communication network.

13. The method of claim 11, transmitting said measurement quality indicator as a broadcast measurement quality indicator addressing more than one mobile handset.

14. The method of claim 11, transmitting said measurement quality indicator as a point-to-point measurement quality indicator addressing only the mobile handset.

15. The method of claim 11, transmitting said measurement quality indicator identifying off-nominal errors with an adjusted User Differential Range Error (UDRE) accuracy predictor to compensate for said off-nominal errors.

16. The method of claim 11, transmitting said measurement quality indicator identifying off-nominal errors with an adjusted User Differential Range Error (UDRE) scale factor to reflect appearance of said off-nominal errors.

17. A method for maintaining the integrity of assisted satellite positioning system based location fixes for a mobile handset in a cellular communication network including a satellite positioning system reference receiver, comprising:

deriving differential correction data from satellites;

determining whether said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination by calculating a location determination and comparing the location determination with a surveyed location of the reference receiver to generate a location error; and

transmitting a measurement quality indicator identifying off-nominal errors to said mobile handset if said determining step determines that said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination.

18. The method of claim 17, determining whether said differential correction data will produce off-nominal errors by comparing the location error to a location error threshold.

19. The method of claim 18, determining whether said differential correction data will produce off-nominal errors by calculating the location error threshold based on a covariance matrix of Weighted Least-Square (WLS) solutions for the location of the reference receiver.

20. The method of claim 19, calculating the location error threshold based on the covariance matrix of the WLS solution by calculating the covariance matrix based on User Differential Range Error (UDRE) values determined by the reference receiver to compute measurement error variances for satellite pseudo ranges.

21. A method for maintaining the integrity of assisted satellite positioning system based location fixes for a mobile handset in a cellular communication network including a satellite positioning system reference receiver, comprising:

deriving differential correction data from satellites;

determining whether said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination;

adjusting User Differential Range Error (UDRE) of a differential correction based on the off-nominal error;

transmitting the adjusted UDRE to said mobile handset if said differential correction data will produce off-nominal errors in said mobile handset'"'"'s location determination.