SYSTEM AND METHOD FOR CLOCK DISTRIBUTION AND SYNCHRONIZATION AND RADIO LOCATION

• US 20090109956A1
• Filed: 01/05/2009
• Published: 04/30/2009
• Est. Priority Date: 06/10/2004
• Status: Active Grant

• Current Assignee: Clark Carty, James A. Amos
• Original Assignee: Clark Carty, James A. Amos
• Inventors: AMOS, James A., Carty, Clark
• Granted Patent: US 7,957,336 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A system for locating a client in a wireless network. The system includes at least three access points. Each access point is adapted to wirelessly communicate with a client having a location using packeted data, be placed in wired data communication within a selected data network; and to share a common precise time reference using the selected data network. The system further includes a switch adapted to translate the relative position of the access points based on a shared common precise time reference and to calculate the location of the client based on a transmission from the client.

Claims

1. A method for synchronizing clocks in a wireless network, comprising:

determining a distance of a first device from a clock source;

generating a time synchronization packet having a time stamp indicative of a time at the clock source, distance;

distributing an adjusted time stamp to the first device based on the time stamp and the distance to the first device.

2. The method for synchronizing clocks in a wireless network of claim 1, further comprising oversampling the time synchronization packet by the first device.

3. The method for synchronizing clocks in a wireless network of claim 2, wherein the oversampling takes place is at least 500 Megahertz (MHz).

4. The method for synchronizing clocks in a wireless network of claim 1, further comprising:

determining a distance of a second device from the clock source; and

distributing a second adjusted timestamp to the second device based on the time stamp and the distance of the second device from the clock source.

5. The method for synchronizing clocks in a wireless network of claim 4, further comprising:

determining a distance of a third device from the clock source;

distributing a third adjusted timestamp to the third device based on the time stamp and the distance of the third device from the clock source.

6. The method for synchronizing clocks in a wireless network of claim 5, further comprising using a timestamp from the first device, a timestamp from the second device and a time stamp of the third device of a signal received by the first device, second device and third device from a wireless client to determine a location of the wireless client after distributing the adjusted timestamp to the first device, second adjusted timestamp to the second device and third adjusted timestamp to the third device.

7. The method of claim 5, wherein the first device, second device and third device are wireless access points, further comprising:

determining the relative position of the access points;

receiving a packet from a wireless device at the first access point;

oversampling a correlation of the packet;

obtaining a first correlation peak for the packet; and

adjusting the relative position of the first access point using the correlation peak to represent a first coplanar point.

8. The method of claim 7, further comprising:

receiving the packet from the wireless device at the second access point;

obtaining a second correlation peak for the packet; and

adjusting the relative position of the second access point using the second correlation peak to represent a second coplanar point.

9. The method of claim 8, further comprising:

receiving the packet from the wireless device at the third access point;

obtaining a third correlation peak; and

adjusting the relative position of the third access point using the third correlation peak to represent a third coplanar point.

10. The method of claim 9, further comprising determining the equation of a circle using the three coplanar points, wherein the center of the circle corresponds to the location of the wireless device.

11. The method of claim 1, wherein the distance between the clock source and the first device is determined by one of a group consisting of time domain reflectometry and from signals received from a Global Positioning System.

12. An apparatus, comprising:

a clock source;

a first physical interface card communicatively coupled to the clock source and operable to determine a distance to a first device;

wherein the first physical interface is further operable to receive a signal from the clock source indicative of a time at the clock source to generate a first timestamp based on the time at the clock source and the distance to the first device; and

wherein the first physical interface is operable to distribute the first timestamp to the first device.

13. The apparatus set forth in claim 12, further comprising:

a second physical interface communicatively coupled to the clock source and operable to determine a distance to a second device;

wherein the second physical interface is further operable to receive a signal from the clock source indicative of a time at the clock source to generate a second timestamp based on the time at the clock source and the distance to the second device; and

wherein the second physical interface is operable to distribute the second timestamp to the second device.

14. The apparatus set forth in claim 13, further comprising:

a third physical interface communicatively coupled to the clock source and operable to determine a distance to a third device;

wherein the third physical interface is further operable to receive a signal from the clock source indicative of a time at the clock source to generate a third timestamp based on the time at the clock source and the distance to the third device; and

wherein the third physical interface is operable to distribute the third timestamp to the third device.

15. The apparatus set forth in claim 14, further comprising a circuit operable receive a timestamp from the first device, a timestamp from the second device and a time stamp from the third device of a signal received by the first device, second device and third device respectively from a wireless client to determine a location of the wireless client after distributing the first timestamp to the first device, second timestamp to the second device and third timestamp to the third device.

16. A system, comprising:

a network switch having a clock source;

first, second and third access points at first, second and third locations respectively;

wherein the switch is operable to determine a first distance to the first access point, a second distance to the second access point and a third distance to the third access point;

wherein the switch is operable to distribute a first timing synchronization packet to the first wireless access point based on a current time at the clock source and the distance between the switch and the first access point;

wherein the switch is operable to distribute a second timing synchronization packet to the second wireless access point based on a current time at the clock source and the distance between the switch and the second access point; and

wherein the switch is operable to distribute a third timing synchronization packet to the third wireless access point based on a current time at the clock source and the distance between the switch and the third access point

17. The system of claim 16, wherein the switch is operable to determining the relative position of the access points;

wherein a packet is received from a wireless device at the first access point, the first access point is operable to oversampling a correlation of the packet and obtain a first correlation peak for the packet; and

wherein the switch is operable to adjusting the relative position of the first access point using the first correlation peak to represent a first coplanar point.

18. The system of claim 17, wherein the packet is also received from the wireless device at the second access point, the second access point is operable to oversampling a correlation of the packet and obtain a second correlation peak for the packet;

and

wherein the switch is operable to adjusting the relative position of the second access point using the second correlation peak to represent a second coplanar point.

19. The system of claim 18, wherein the packet is also received from the wireless device at the third access point, the third access point is operable to oversampling a correlation of the packet and obtain a third correlation peak for the packet;

and

wherein the switch is operable to adjusting the relative position of the third access point using the third correlation peak to represent a third coplanar point.

20. The system of claim 19, wherein the switch is further operable to determining the equation of a circle using the three coplanar points, wherein the center of the circle corresponds to the location of the wireless device.