Method and system for location finding in a wireless local area network

• US 20040203870A1
• Filed: 08/20/2002
• Published: 10/14/2004
• Est. Priority Date: 08/20/2002
• Status: Abandoned Application

• Current Assignee: Aeroscout Limited (Stanley Black & Decker, Inc.)
• Original Assignee: Aeroscout Limited (Stanley Black & Decker, Inc.)
• Inventors: Granot, Yair, Aljadeff, Daniel, Tsruya, Shalom
• Application Number:
  US10/225,267
• Publication Number:
  US 20040203870A1
• Time in Patent Office: Days
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• 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: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method and system for location finding in a wireless local area network (LAN) enables enhanced security via network intrusion management and connection access management, as well as providing a mechanism for physically mapping a wireless network. Multiple receivers are employed to determine time-difference-of-arrival (TDOA) of signals transmitted from a wireless device. The location of the transmitting device is determined by triangulating between multiple receivers. The receivers may be devices within the wireless network that have been enhanced to include TDOA capability, or multiple dedicated location units may be employed within the wireless network or a wired network that may be a completely separate infrastructure depending on the requirements of a particular installation.

Claims

1. A method for determining the location of a wireless device within a wireless local area network (LAN), said method comprising:

receiving a wireless LAN signal from said wireless device at multiple location units;

in response to said receiving, determining multiple times of arrival of said standard wireless LAN signal at each corresponding one of said multiple location units;

sending said times of arrival from each of said corresponding multiple location units to a master unit; and

determining, within said master unit, the location of said wireless device by comparing location information for said multiple location units with said multiple times of arrival to determine said location of said wireless device.

2. The method of claim 1, wherein said master unit is one of said multiple location units, whereby said sending said time of arrival is not performed for said time of arrival determined at said master unit.

3. The method of claim 1, further comprising synchronizing a timer in each of said location units, whereby a precise time relationship between said multiple times of arrival is maintained.

4. The method of claim 1, wherein each of said location units is coupled to said master unit via a wired network, and wherein said sending said times of arrival is performed over said wired network.

5. The method of claim 1, wherein said sending is performed over said wireless network.

6. The method of claim 1, further comprising transmitting a request-to-send signal to said wireless device, and wherein said receiving receives a clear-to-send from said wireless device issued in response to said request-to-send signal.

7. The method of claim 1, wherein said receiving further comprises:

filtering said received signal with a matched filter;

sampling and storing quadrature symbol detection outputs of said matched filter; and

subsequently computing an estimate of said time of arrival of said received signal.

8. The method of claim 7, wherein said computing computes said estimate of said time of arrival in conformity with a maximal mean-square profile of said received signal correlated with a spread-spectrum sequence.

9. The method of claim 6, wherein said computing further computes said estimate of said time of arrival in conformity with a maximal mean-square profile of said received signal convolved with a predetermined message sequence.

10. A wireless local area network (LAN), comprising:

a plurality of location units for receiving a wireless LAN signal transmitted by a wireless device within said wireless LAN and determining a time of arrival for said received signal;

at least one master unit for receiving said time of arrival from each of said location units, whereby said location of said wireless devices is be determined in conformity with said time of arrival.

11. The wireless LAN of claim 10, wherein said master unit is one of said multiple location units.

12. The wireless LAN of claim 10, wherein each of said location units comprises a timebase for maintaining precision in said time of arrival among said location units.

13. The wireless LAN of claim 12, wherein said master unit further synchronizes said timebase in each of said location units by sending a synchronization message to said location units.

14. The wireless LAN of claim 10, wherein each of said location units is coupled to said master unit via a wired network, and wherein said time of arrival is sent from said location units to said master unit over said wired network.

15. The wireless LAN of claim 10, wherein said time of arrival is sent from said location units to said master unit over said wireless network.

16. The wireless LAN of claim 10, further comprising an location measurement initiating unit that transmits a request-to-send signal to said wireless device, and wherein said wireless LAN signal is a clear-to-send message sent from said wireless device in response to said request-to-send signal.

17. The wireless LAN of claim 16, wherein said measurement initiating unit is one of said location units.

18. The wireless LAN of claim 16, wherein said measurement initiating unit is said master unit.

19. The wireless LAN of claim 10, wherein each of said location units comprises a receiver including:

a matched filter for filtering said received signal;

a sampler and memory for sampling and storing quadrature symbol detection outputs of said matched filter; and

a signal processor for computing an estimate of said time of arrival of said received signal from said stored samples.

20. The wireless LAN of claim 19, wherein said signal processor further computes said estimate of said time of arrival in conformity with a maximal mean-square profile of said received signal correlated with a spread-spectrum sequence.

21. The wireless LAN of claim 20, wherein said signal processor further computes said estimate of said time of arrival in conformity with a maximal mean-square profile of said received signal convolved with a predetermined message sequence.

22. A location unit, comprising:

a receiver for receiving wireless local area network (LAN) signals from a wireless device in a wireless network;

a time measurement unit coupled to said receiver for determining the time of arrival of said signals from said wireless device; and

an interface for sending said time of arrival information to a master unit.

23. The location unit of claim 22, wherein said receiver comprises a spread-spectrum receiver and wherein said time measurement unit comprises a processor for determining said time of arrival in conformity with samples stored from an output of said receiver.

24. The location unit of claim 23, wherein said processor computes an estimated time of arrival via mean-square estimation.

25. The location unit of claim 22, wherein said wireless LAN signal is a clear-to-send signal received from said wireless device.

26. A master unit, comprising:

a data interface for receiving from multiple external location units, times of arrival of a standard wireless local area network (LAN) signal received from a wireless device by said multiple external location units;

a database including physical location information of said multiple external location units; and

a computation unit for comparing said times of arrival from said multiple external location units in conformity with location information retrieved from said database to determine a location of wireless devices in a wireless LAN.

27. The master unit of claim 26, wherein said computation unit computes differences between pairs of said time of arrival received from pairs of said location units, projects a hyperbolic curve for each of said differences, said curve having foci at physical locations of said pair of location units associated with a corresponding difference, and determines said location of said wireless device in conformity with an intersection of said hyperbolic curves.

28. The master unit of claim 26, wherein said master unit transmits a command to issue a request-to-send signal to said wireless device over said data interface, and wherein said wireless LAN signal is a clear-to-send signal transmitted by said wireless device in response to said request-to-send signal.

29. The master unit of claim 26, wherein said master unit includes a wireless LAN transmitter, and wherein said master unit transmits a request-to-send signal to said wireless device, and wherein said wireless LAN signal is a clear-to-send signal transmitted by said wireless device in response to said request-to-send signal.

30. The master unit of claim 26, wherein said master unit includes a wireless LAN receiver, and wherein said master unit receives said wireless LAN signal and measures a time of arrival at said master unit of said wireless LAN signal, and wherein said computation unit further compares said time of arrival at said master unit of said wireless LAN signal.