SYSTEM AND METHOD FOR DETERMINING SIGNAL SOURCE LOCATION IN WIRELESS LOCAL AREA NETWORK

Abstract

A system and method locates a wireless local area network (WLAN) signal source. A wireless LAN signal as an RF signal is propagated from a WLAN signal source at a fixed, known location to a plurality of receivers having unsynchronized clocks. The time-of-arrival is measured at each receiver and the timing relationship from the fixed, known location of the signal source is used to relate time-of-arrival measurements from a signal arriving from an unknown location.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become apparent from the detailed description of the invention, which follows when considered in light of the accompanying drawings in which:

FIG. 1 is a block diagram showing an example of components that could be used with the location system of the present invention and showing unsynchronized receivers that receive an RF signal from a tag transmitter in a wireless local area network (WLAN) where information is forwarded to a processor operative as a time service.

FIG. 2 is a block diagram similar to FIG. 1, but showing the time-of-arrival information that is forwarded to the processor as a time service, including the processing of known propagation and processing delays within the WLAN in accordance with a non-limiting example of the present invention.

FIG. 3 is a high-level flow chart showing a clock tracking loop that can be used in the present invention.

FIG. 4 is an overall system diagram of a wireless local area network using a location system that can be modified for use with the present invention.

FIG. 5 is a high-level block diagram of an example of a circuit architecture that can be used as part of a processor for determining first-to-arrive signals.

FIG. 6 is another high-level block diagram of an example of the circuit architecture that can be used with the present invention for correlation-based RF signal processors.

Claims

1. A system for locating a signal source in a wireless local area network (WLAN), comprising: at least one WLAN signal source positioned at a known location that transmits a wireless radio frequency (RF) signal;a plurality of receivers having unsynchronized clocks that receive the RF signal from the at least one WLAN signal source; anda processor operative with the receivers that measures the time-of-arrival of the RF signal at each receiver and uses a timing relationship from the fixed, known location of the at least one WLAN signal source to relate time-of-arrival measurements from a signal arriving from a WLAN signal source at an unknown location within the WLAN.

2. A system according to claim 1, and further comprising a tag transmitter positioned at each WLAN signal source.

3. A system according to claim 2, wherein each tag transmitter transmits an RF signal having data identifying an object to which the tag transmitter is associated.

4. A system according to claim 1, wherein each receiver comprises a wireless access point of the WLAN.

5. A system according to claim 1, and further comprising a plurality of WLAN signal sources at fixed, known locations.

6. A system according to claim 1, and further comprising a tag transmitter embedded at a receiver and operative as a WLAN beacon.

7. A system according to claim 1, wherein said processor is operative for determining clock timing relationships for clocks based on one of at least the propagation or processing delays in the receivers for synchronizing receiver performance.

8. A system according to claim 1, wherein each WLAN signal source includes a circuit for transmitting a pseudo-random spread spectrum RF signal.

9. A system according to claim 1, wherein said processor is operative for processing first-to-arrive signals at each receiver.

10. A system for locating a wireless station in communication with a wireless local area network (WLAN) comprising: a plurality of wireless mobile devices each forming a WLAN signal source that transmit RF signals;a plurality of cells defining a WLAN and each having a receiver forming an access point in the WLAN and adapted for communicating with WLAN signal sources, wherein at least one WLAN signal source is positioned at a known location; anda processor communicating with each receiver that measures at each receiver the time-of-arrival of the RF signal transmitted from the WLAN signal source at a known location and uses a timing relationship from the fixed, known location of the at least one WLAN signal source to relate time-of-arrival measurements from a signal arriving from a WLAN signal source at an unknown location within the WLAN.

11. A system according to claim 10, and further comprising a tag transmitter positioned at a signal source.

12. A system according to claim 11, wherein each tag transmitter transmits an RF signal having data identifying an object to which the tag transmitter is associated.

13. A system according to claim 11, wherein each tag transmitter includes a circuit for transmitting a pseudo-random spread spectrum RF signal from signal sources.

14. A system according to claim 11, and further comprising a tag transmitter embedded at a receiver and operative as a WLAN beacon.

15. A system according to claim 10, wherein said processor is operative for determining clock timing relationships for clocks based on one of at least the propagation or processing delays in the receivers for synchronizing receiver performance.

16. A system according to claim 10, wherein said processor is operative for processing first-to-arrive signals at each receiver.

17. A method for locating a signal source in a wireless local area network (WLAN), which comprises: propagating a wireless radio frequency (RF) signal from a WLAN signal source at a fixed, known location to a plurality of receivers having unsynchronized clocks; andmeasuring the time-of-arrival of the RF signal at each receiver and using the timing relationship from the fixed, known location of the WLAN signal source to relate time-of-arrival measurements from a signal arriving from a WLAN signal source at an unknown location within the WLAN.

18. A method according to claim 17, which further comprises transmitting RF signals from tag transmitters positioned at the WLAN signal sources at known and unknown locations.

19. A method according to claim 17, which further comprises receiving the RF signals within receivers as access points of the WLAN.

20. A method according to claim 17, which further comprises propagating RF signals from a plurality of WLAN signal sources at fixed, known locations.

21. A method according to claim 17, which further comprises propagating an RF signal from a tag transmitter embedded at a receiver and operative as a WLAN beacon.

22. A method according to claim 17, which further comprises determining clock timing relationships for clocks based on one of at least the propagation or processing delays in the receivers for synchronizing receiver performance.

23. A method according to claim 17, which further comprises maintaining a model of timing relationships of clocks at the receivers.

24. A method according to claim 17, which further comprises transmitting an RF signal from at least one tag transmitter having data identifying the object to which the tag is associated.

25. A method according to claim 17, which further comprises transmitting a pseudo random spread spectrum RF signal from WLAN signal sources.

26. A method according to claim 17, which further comprises processing first-to-arrive signals at each receiver.

27. A method according to claim 17, which further comprises forming a tracking loop to track clock relationships that occur naturally over time.