Time synchronization system and method for synchronizing locating units within a communication system using a known external signal

• US 20070053340A1
• Filed: 08/09/2005
• Published: 03/08/2007
• Est. Priority Date: 08/09/2005
• Status: Active Grant

• Current Assignee: Keysight Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Guilford, John
• Granted Patent: US 7,411,937 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

A time synchronization system synchronizes local clocks of locating units within a communication system using a known external signal. Each of the locating units receives a radio frequency (RF) signal from a transmitter at a known geographical location and measures the RF signal to produce a respective measurement of the signal and a respective timestamp of the measurement recorded at substantially the same time of the local clocks of the locating units. A controller determines a measured time difference of arrival between the locating units using the measurements and timestamps, computes a time synchronization error between the locating units from a difference between the measured time difference of arrival and an expected time difference of arrival and provides a respective time adjustment to each of the locating units to offset the time synchronization error.

Claims

1. A controller for synchronizing locating units in a radio communication system, comprising:

a receiver connected to receive from two or more locating units respective measurements of a radio frequency (RF) signal transmitted from a transmitter at a known geographical location and respective timestamps of said respective measurements, wherein each of said timestamps are recorded at substantially the same time of a respective local clock of said two or more locating units; and

a processor operable to determine a measured time difference of arrival between said two or more locating units using said measurements and said respective timestamps, to compute a time synchronization error between said two or more locating units from a difference between said measured time difference of arrival and an expected time difference of arrival and to provide a respective time adjustment to each of said two or more locating units to offset said time synchronization error.

2. The controller of claim 1, wherein said processor is further operable to determine said expected time difference of arrival from a respective distance between each of said two or more locating units and said transmitter.

3. The controller of claim 1, wherein said processor is further operable to compare said measurements of said measured signals to determine said measured time difference of arrival.

4. The controller of claim 3, wherein said processor is further operable to determine a time offset between highest correlation points of said measurements and to adjust said time offset using said respective timestamps to determine said measured time difference of arrival.

5. The controller of claim 1, wherein said processor is further operable to divide said time synchronization error between said two or more locating units to determine said respective time adjustment for each of said two or more locating units;

wherein each said respective time adjustment is used to synchronize said local clocks of said two or more locating units.

6. The controller of claim 5, wherein said processor is further operable to divide said time synchronization error equally between said two or more locating units to determine said respective time adjustment for each of said two or more locating units.

7. The controller of claim 5, wherein said processor is further operable to set said local clock of one of said two or more locating units as a reference clock and to determine said respective time adjustment for other ones of said two or more locating units based on said time synchronization error from said reference clock.

12. The system of claim 1, wherein each of said locating units is further operable to adjust said respective local clock using said respective time adjustment to synchronize said local clocks of said locating units.

13. The system of claim 12, wherein said controller is further operable to divide said time synchronization error between said locating units to determine said respective time adjustment for each of said locating units.

14. The system of claim 12, wherein said controller is further operable to set said local clock of one of said locating units as a reference clock and to determine said respective time adjustment for other ones of said locating units based on said time synchronization error from said reference clock.

8. A time synchronization system, comprising:

locating units within a radio communication system and configured to receive a radio frequency (RF) signal from a transmitter at a known geographical location, each of said locating units measuring said RF signal to produce respective measurements and respective timestamps of said measurements recorded at substantially the same time of a respective local clock of each of said locating units; and

a controller operable to determine a measured time difference of arrival between said locating units using said measurements and said respective timestamps, to compute a time synchronization error between said locating units from a difference between said measured time difference of arrival and an expected time difference of arrival and to provide a respective time adjustment to each of said locating units to offset said time synchronization error.

9. The system of claim 8, wherein said controller is further operable to determine said expected time difference of arrival from a respective distance between each of said locating units and said transmitter.

10. The system of claim 8, wherein said controller is further operable to compare said measurements to determine said measured time difference of arrival.

11. The system of claim 10, wherein said controller is further operable to determine a time offset between highest correlation points of said measurements and to adjust said time offset using said respective timestamps to determine said measured time difference of arrival.

15. The system of claim 8, wherein each of said locating units is further operable to periodically measure said RF signal for a predetermined time interval.

16. The system of claim 8, wherein said locating units provide respective signals for use in locating radio devices within the radio communication system using time difference of arrival.

17. A method for synchronizing locating units within a communication system, comprising:

receiving from two or more locating units respective measurements of a radio frequency (RF) signal transmitted from a transmitter at a known geographical location and respective timestamps of said measurements recorded at said two or more locating units, wherein each of said timestamps are recorded at substantially the same time of a respective local clock of said two or more locating units;

determining a measured time difference of arrival between said two or more locating units using said measurements and said respective timestamps;

computing a time synchronization error between said two or more locating units from a difference between said measured time difference of arrival and an expected time difference of arrival and;

providing a respective time adjustment to each of said two or more locating units to offset said time synchronization error.

18. The method of claim 17, further comprising:

determining said expected time difference of arrival from a respective distance between each of said locating units and said transmitter.

19. The method of claim 17, wherein said determining said measured time difference of arrival further includes:

comparing said measurements to determine a time offset between highest correlation points of said measurements; and

adjusting said time offset using said respective timestamps to determine said measured time difference of arrival.

20. The method of claim 17, further comprising:

splitting said time synchronization error equally between said locating units to determine said respective time adjustment for each of said locating units.

21. The method of claim 17, wherein said local clock of one of said locating units is a reference clock, and further comprising:

determining said respective time adjustment for other ones of said locating units based on said time synchronization error from said reference clock.