Method and system for improved wlan location

• US 7,412,246 B2
• Filed: 10/06/2003
• Issued: 08/12/2008
• Est. Priority Date: 10/06/2003
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Lewis, Thomas P., Barr, Russell A.
• Primary Examiner(s): Beamer; Temica M
• Application Number:
  US10/679,524
• Publication Number:
  US 20050075118A1
• Time in Patent Office: 1,772 Days
• Field of Search: 4554561-4566, 455/457, 455/404.2, 455/67.11, 455/226.2, 342/357.08, 342/357.09, 342/357.1, 342/357.17
• US Class Current: 455/456.1
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Mobile units within an area are located using a wireless local area network. Reference signal transmitters are provided at selected fixed locations within the area. Reference signals are transmitted using the reference signal transmitters using a first selected channel of the wireless local area network. A computer is provided having a database relating signal characteristics of signals transmitted by the reference signal transmitters to location within the area At least one access point is coupled to the computer and provides wireless data communications between the computer and the mobile unit using one or more channels of the wireless data communications system that are different from the first data communications channel. A selected plurality of the reference signals are received at the mobile unit, signal characteristics of the received reference signals are determined and data representing the received reference signal characteristics is transmitted to the computer via the access point using the one or more data communications channels. The data representing reference signal characteristics is received at the computer and position of the mobile unit is determined using the database.

Claims

1. A method for locating mobile units within an area using a wireless local area network, comprising:

providing reference signal transmitters at selected fixed locations within said area;

transmitting reference signals using said reference signal transmitters using a first selected channel of said wireless local area network;

providing a computer having a database relating signal strengths of signals transmitted by said reference signal transmitters to location within said area;

providing at least one access point coupled to said computer and providing wireless data communications between said computer and at least one mobile unit in said area using one or more channels of said wireless local area network that are different from said first selected channel;

receiving a selected plurality of said reference signals at said at least one mobile unit, determining signal strengths of said received reference signals and transmitting data representing said received reference signal strengths to said computer via said at least one access point using said one or more data communications channels; and

receiving said data representing reference signal strengths at said computer and determining position of said mobile unit using said database.

2. A method as specified in claim 1 wherein said wireless local area network is an IEEE Standard 802.11 network and wherein determining signal strength comprises determining RSSI value at said at least one mobile unit.

3. A method as specified in claim 1 wherein said transmitting reference signals comprises periodically transmitting reference beacon signals at selected beacon intervals.

4. A method as specified in claim 3 wherein said beacon intervals are selected to be different for each of said reference signal transmitters.

5. A method as specified in claim 1 wherein said reference signals are transmitted in response to request signals transmitted by a mobile unit on said first selected channel.

6. A method as specified in claim 1 wherein said data communications channels are selected to be non-overlapping with said first selected channel.

7. A method as specified in claim 1 wherein said reference signal transmitters receive signals on said first selected channel and delay said reference signal transmissions if a signal is detected on said first selected channel.

8. A system for locating mobile units within an area using a wireless local area network, comprising:

a selected plurality of reference signal transmitters located at selected fixed locations within said area, said reference signal transmitters being arranged to transmit reference signals using a first selected channel of said wireless local area network;

a computer having a database relating signal strengths of signals transmitted by said reference signal transmitters to location within said area;

at least one access point coupled to said computer and providing wireless data communications between said computer and one or more mobile units in said area using one or more channels of said wireless local area network that are different from said first selected channel; and

at least one mobile unit arranged to receive a selected plurality of said reference signals, determine signal strengths of said received reference signals and transmit data representing said signal strengths to said computer via said at least one access point using said one or more data communications channels; and

wherein said computer is arranged to receive said data representing signal strengths and determine position of said mobile unit using said database.

9. A system as specified in claim 8 wherein said wireless local area network is an IEEE Standard 802.11 network and wherein said mobile unit is arranged to determine signal strength using an RSSI function.

10. A system as specified in claim 8 wherein said reference signal transmitters are arranged to periodically transmit said reference signals as reference beacon signals at selected beacon intervals.

11. A system as specified in claim 10 wherein said reference signal transmitters are arranged to transmit said reference signal beacons at different beacon intervals.

12. A system as specified in claim 8 wherein said reference signal transmitters are arranged to transmit said reference signals in response to request signals transmitted by a mobile unit on said first non-overlapping channel.

13. A system as specified in claim 8 wherein said data communications channels are selected to be non-overlapping with said first selected channel.

14. A system as specified in claim 8 wherein said reference signal transmitters are arranged to receive signals on said first selected channel and delay said reference signal transmissions if a signal is detected on said first selected channel.