Location system for wireless local area network (WLAN) using RSSI and time difference of arrival (TDOA) processing

• US 7,899,006 B2
• Filed: 12/03/2007
• Issued: 03/01/2011
• Est. Priority Date: 12/05/2006
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Zebra Enterprise Solutions Corp. (Zebra Technologies Corporation)
• Inventors: Boyd, Robert W.
• Primary Examiner(s): Cho; Hong
• Assistant Examiner(s): Choi; Eunsook
• Application Number:
  US11/949,080
• Publication Number:
  US 20080130604A1
• Time in Patent Office: 1,184 Days
• Field of Search: None
• US Class Current: 370/328
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/02216 Timing or synchronisation of the receivers
• CPC Class Codes: G01S 5/02524 Creating or updating the radio-map
• 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 24/00 Supervisory, monitoring or testing arrangements
• 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]
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
• CPC Class Codes: H04W 88/10 adapted for operation in multiple networks, e.g. multi-mode access points

Abstract

A wireless local area network includes a plurality of access point stations that receive and transmit communications signals within the wireless local area network. A first set of access point stations are WiFi compliant and measure signal strength and determine the received signal strength indication (RSSI). A second set of access point stations are operable in accordance with the time of arrival (TOA) real time location standard (RTLS). A dual mode mobile station is operative for multimode communication with both the WiFi and RTLS compliant access point stations. A location processor is operatively connected with each of the access point stations and processes the RSSI and creates a RSSI locate map and processes communication signals from the second set of access point stations and determines which signals are first-to-arrive signals to locate the mobile station and update the RSSI locate map and locate any non-dual mode WiFi devices.

Claims

1. A wireless local area network, comprising:

a plurality of access point stations that receive and transmit communications signals within the wireless local area network, wherein a first set of said access point stations comprise WiFi compliant access point stations that measure signal strength and determine the received signal strength indication (RSSI) and a second set of said access point stations are operable in accordance with a time of arrival (TOA) real time location standard (RTLS);

a dual mode mobile station within the wireless local area network and operative for multimode communications with both said WiFi and RTLS compliant access point stations; and

a location processor operatively connected with each of said access point stations and operative for processing the RSSI from said first set of access point stations and creating a RSSI locate map and processing communication signals from the second set of access point stations and determining which signals are first-to-arrive signals to locate the mobile station and update the RSSI locate map to locate any non-dual mode WiFi devices.

2. The wireless local area network according to claim 1, wherein said dual mode mobile station comprises a tag transceiver.

3. The wireless local area network according to claim 1, wherein said dual mode mobile station and WiFi compliant access point stations are operative in compliance with said IEEE 802.11 standard.

4. The wireless local area network according to claim 3, wherein said dual mode mobile station and WiFi compliant access point stations are operative in a CCX mode for 802.11 tag transceivers.

5. The wireless local area network according to claim 1, wherein said location processor is operative for processing the maximum likelihood estimation for determining location probabilities and updating the RTLS locate map.

6. The wireless local area network according to claim 1, wherein said location processor is operative for correlating a signal as a first-to-arrive signal and conducting differentiation of the first-to-arrive signals to locate the dual mode mobile station.

7. The wireless local area network according to claim 1, wherein said access point stations are positioned at known locations within said wireless local area network.

8. The wireless local area network according to claim 1, wherein said dual mode mobile station is operative for transmitting spread spectrum communications signals.

9. The wireless local area network according to claim 1, wherein said location processor further comprises a matched filter correlator.

10. The wireless local area network according to claim 1, wherein said dual mode mobile station comprises a receiver operative for receiving an interrogation signal and in response, transmitting an RF communications signal to said access point stations.

11. The wireless local area network according to claim 1, wherein said receiver comprises a magnetic receiver.

12. A system for locating an object within a monitored environment, comprising:

a dual mode tag transceiver associated with the object, said dual mode tag transceiver operative for transmitting RF communications signals;

a plurality of receivers within the monitored environment for receiving RF communications signals from the dual mode tag transceiver, wherein a first set of said receivers comprise WiFi compliant receivers that measure signal strength and determine the received signal strength indication (RSSI) and a second set of said receivers are operable in accordance with a time of arrival (TOA) real time location standard (RTLS); and

a location processor operatively connected with each of said receivers and operative to process the RSSI from said first set of receivers and create a RSSI locate map and process communication signals from the second set of receivers and determine which signals are first-to-arrive signals to locate the dual mode tag transceiver and associated object and update the RSSI locate map to locate any non-dual mode WiFi devices.

13. The system according to claim 12, wherein said dual mode tag transceiver and WiFi compliant receivers are operative in compliance with the IEEE 802.11 standard.

14. The system according to claim 12, wherein said dual mode tag transceiver and WiFi compliant receivers are operative in a CCX mode for 802.11 tag transceivers.

15. The system according to claim 12, wherein said location processor is operative for processing the maximum likelihood estimation for determining location probabilities and updating the RTLS locate map.

16. The system according to claim 12, wherein said location processor is operative for correlating a signal as a first-to-arrive signal and conducting differentiation of the first-to-arrive signals to locate the dual mode tag transceiver.

17. The system according to claim 12, wherein said receivers are positioned at known locations within said monitored environment.

18. The wireless local area network according to claim 12, wherein said dual mode tag transceiver comprises a receiver operative for receiving an interrogation signal and in response, transmitting an RF communications signal.

19. The wireless local area network according to claim 18, wherein said receiver comprises a magnetic receiver.

20. A method of locating a dual mode mobile station within a wireless local area network, comprising:

transmitting wireless communications signals from a dual mode mobile station to a plurality of access point stations that comprise WiFi compliant access point stations that measure signal strength and determine the received signal strength indication (RSSI) and a second set of access point stations operable in accordance with a time of arrival (TOA) real time location standard (RTLS);

processing the RSSI from the first set of access point base stations;

creating a RSSI locate map;

processing communications signals from the second set of access point stations to determine which signals are first-to-arrive signals for locating the dual mode mobile station; and

updating the RSSI locate map to locate any non-dual mode WiFi devices.

21. The method according to claim 20, which further comprises processing a maximum likelihood estimation for determining location probabilities and updating the RTLS locate map.

22. The method according to claim 20, which further comprises correlating a signal as a first-to-arrive signal and conducting differentiation of the first-to-arrive signals to locate the dual mode mobile station.

23. The method according to claim 20, which further comprises positioning the access point stations as known locations.

24. The method according to claim 20, which further comprises transmitting an interrogation signal to the dual mode mobile station, and in response, transmitting the wireless communications signals.