System for locating a mobile unit

• US 7,477,904 B2
• Filed: 07/16/2003
• Issued: 01/13/2009
• Est. Priority Date: 07/31/2002
• Status: Expired due to Term

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Evans, David H., Rankin, Paul J.
• Primary Examiner(s): Nguyen, Duc
• Assistant Examiner(s): PHUONG, DAI
• Application Number:
  US10/522,701
• Publication Number:
  US 20050277426A1
• Time in Patent Office: 2,008 Days
• Field of Search: 455/422.1, 455/456.1, 455/456.2, 455/456.3, 455/452.1, 455/452.2, 455/453, 455/456.6, 340/5.61, 340/991, 340/426.22
• US Class Current: 455/456.1
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: H04B 17/27 for locating or positioning the transmitter
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A wireless local area network (LAN) comprises an access point which transmits a beacon signal at 0 dBm. The detection threshold of the mobile unit is −65 dBm and thus the mobile unit is detected when located within 10 meters of the access point.

Claims

1. A system for locating a mobile unit including:

means for transmitting a first signal at a relatively high power, from an access point;

means for transmitting a second signal at a predetermined, relatively low power, from said access point;

means for receiving said first signal, at a mobile device;

means for determining a first signal strength of said first signal at said means for receiving said first signal;

means for determining whether said first signal strength exceeds a relatively low threshold level so as to determine whether service may be provided;

means for receiving said second signal, at said mobile device;

means for determining a second signal strength of said second signal received at said means for receiving said second signal;

means for determining whether said second signal strength exceeds a relatively high threshold level so as to locate the mobile unit within a known distance of said means for transmitting said second signal.

2. A system according to claim 1, wherein said relatively high power is at least 0 dBm.

3. A system according to claim 1, wherein said relatively high power is at least 6 dBm, 13 dBm or 20 dBm.

4. A system according to claim 1, said relatively low power is no more than 0 dBm.

5. A system according to claim 1, wherein said relatively low threshold level is no more than −

85 dBm.

6. A system according to claim 1, wherein said relatively high threshold level is no less than −

65 dBm.

7. A system according to any claim 1, wherein said means for transmitting said first and second signals transmit said first and second signals at different times.

8. A system according to claim 1, which is a wireless local area network.

9. A system according to claim 8, wherein said means for transmitting said first signal is an access point.

10. A system according to claim 8, wherein said means for transmitting said second signal is an access point.

11. A system according to claim 8, wherein said means (4) for receiving said first signal is a mobile unit.

12. A system according to claim 8, wherein said means (4) for receiving said second signal is a mobile unit.

13. A system according to claim 8, wherein said means for transmitting said first signal is a mobile unit.

14. A system according to claim 8, wherein said means (4) for transmitting said second signal is a mobile unit.

15. A system according to claim 8, wherein said means for receiving said first signal is an access point.

16. A system according to claim 8, wherein said means for receiving said second signal is an access point.

18. An access point configured for use in the system according to claim 1.

17. A system for locating a mobile unit including:

a first transmitter for transmitting a first signal at a relatively high power, from an access point;

a second transmitter for transmitting a second signal at a predetermined, relatively low power, from said access point;

a first receiver for receiving said first signal, at a mobile unit;

a first detector for determining a first signal strength of said first signal at said first receiver;

a first controller for determining whether said first signal strength exceeds a relatively low threshold level so as to determine whether service may be provided;

a second receiver for receiving said second signal, at said mobile unit;

a second detector for determining a second signal strength of said second signal at said second receiver;

a second controller for determining whether said second signal strength exceeds a relatively high threshold level so as to locate the mobile unit within a known distance of said means for transmitting said second signal.