Communications link time transfer to improve navigation system accuracy

• US 7,679,554 B1
• Filed: 07/03/2008
• Issued: 03/16/2010
• Est. Priority Date: 03/06/2006
• Status: Active Grant

• Current Assignee: Rockwell Collins, Inc. (Rtx Corporation)
• Original Assignee: Rockwell Collins, Inc. (Rtx Corporation)
• Inventors: Anderson, David A., Hwang, Patrick Y, McGraw, Gary A., Schnaufer, Bernard A.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): LIU, HARRY K
• Application Number:
  US12/167,897
• Time in Patent Office: 621 Days
• Field of Search: 342/357.03, 342/357.06
• US Class Current: 342/357.24
• CPC Class Codes: G01S 19/15 Aircraft landing systems
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]

Abstract

A method and apparatus for improving differential navigation accuracy uses time transfer over a two-way communications link. The communications link transmits an overall time offset between a differential reference station and a remote user. A differential navigation position solution is modified at the remote user with the overall time offset to improve the differential navigation accuracy. A first time offset between a first communications device and a first navigation receiver at the remote user is determined. A second time offset between the first communications device at the remote user and a second communications device at the differential reference station is determined. A third time offset between the second communications device and a second navigation receiver at the differential reference station is determined. An overall time offset from the first time offset, the second time offset, and the third time offset is computed and used to improve the differential navigation accuracy.

Claims

1. A differential navigation system using time transfer to improve accuracy comprising:

a first navigation receiver configured to;

receive and process navigation signals to determine position and provide a first navigation time mark;

a first communications device configured to;

provide a first communications time mark, and compare the first communications time mark to the first navigation time mark to compute a first time offset;

a two-way communications link over which the first communications device communicates messages and computes time offset via two-way time transfer;

a second navigation receiver configured to;

receive and process navigation signals to determine position, which position is compared with a known position of the second navigation receiver and used to determine differential correction signals to be transmitted to said first navigation receiver, and provide a second navigation time mark; and

a second communications device, which is time offset with respect to said first communications device by a second time offset, said second communications device being configured to;

receive messages from the two-way communications link,

provide a second communications time mark, and

compare the second navigation time mark to the second communications time mark to obtain a third time offset, and for transmitting the third time offset over the two-way communications link to the first communications device;

the first communications device is further configured to;

receive the third time offset from the two-way communications link,

compute the second time offset, and

compute a first navigation receiver to second navigation receiver time offset to provide clock aiding to the first navigation receiver.

2. The differential navigation system using time transfer to improve accuracy of claim 1 further comprising a first time interval counter in the first communications device for computing the first time offset and for computing the first navigation receiver to second navigation receiver time offset.

3. The differential navigation system using time transfer to improve accuracy of claim 1 further comprising a second time interval counter in the second communications device for comparing the second communications time mark and the second navigation time mark.

4. The differential navigation system using time transfer to improve accuracy of claim 1 wherein the second time offset is determined by performing a time transfer measurement between the first communications device and the second communications device over the two-way communications link.

5. The differential navigation system using time transfers to improve accuracy of claim 1 wherein the first navigation receiver and the first communications device comprise a remote user with unknown location.

6. The differential navigation system using time transfer to improve accuracy of claim 5 wherein the second navigation receiver and second communications device comprise a different reference station for transmitting differential position corrections to the remote user.

7. The differential navigation system using time transfer to improve accuracy of claim 1 wherein the first navigation receiver uses the clock aiding to improve vertical accuracy.

8. The differential navigation system using time transfer to improve accuracy of claim 1 wherein the first navigation receiver uses the clock aiding to improve horizontal accuracy.

9. A differential navigation system using time transfer to improve accuracy of a calculated position determination of a mobile roving navigation receiver;

the system comprising;

a mobile roving navigation receiver configured to;

receive and process navigation signals to determine position and,

provide a first navigation time mark;

a first communications device configured to;

provide a first communications time mark, and

make a comparison of the first communications time mark to the first navigation time mark to compute a first time offset;

where the comparison has level of resolution is as fine as on an order of 10 nanoseconds;

a two-way communications link over which the first communications device communicates messages;

a second navigation receiver configured to;

receive and processing navigation signals to determine position, which position is compared with a known position of the second navigation receiver and used to determine differential correction signals to be transmitted to said mobile roving navigation receiver and

provide a second navigation time mark; and

a second communications device, which is time offset with respect to said first communications device by a second time offset, said second communications device being configured to;

receive messages from the two-way communications link,

provide a second communications time mark, and

compare the second navigation time mark to the second communications time mark to obtain a third time offset, and for transmitting the third time offset over the two-way communications link to the first communications device;

wherein the first communications device is further configured to;

receive the third time offset from the two-way communications link,

compute the second time offset, and

compute a mobile roving navigation receiver to second navigation receiver time offset to provide clock aiding to the mobile roving navigation receiver.

10. The differential navigation system using time transfer to improve accuracy of claim 9 further comprising a first time interval counter in the first communications device for computing the first time offset and for computing the mobile roving navigation receiver to second navigation receiver time offset.

11. The differential navigation system using time transfer to improve accuracy of claim 9 further comprising a second time interval counter in the second communications device for comparing the second communications time mark and the second navigation time mark.

12. The differential navigation system using time transfer to improve accuracy of claim 9 wherein the second time offset is determined by performing a time transfer measurement between the first communications device and the second communications device over the two-way communications link.

13. The differential navigation system using time transfers to improve accuracy of claim 9 wherein the mobile roving navigation receiver and the first communications device comprise a remote user with unknown location.

14. The differential navigation system using time transfer to improve accuracy of claim 9 wherein the second navigation receiver and second communications device comprise a different reference station for transmitting differential position corrections to the remote user.

15. The differential navigation system wherein the first time offset has a resolution on an order of one nanosecond.

16. The differential navigation systems wherein the first time offset has a sub-nanosecond resolution.