METHODS AND APPARATUS FOR LOCATIONING IN A WIRELESS NETWORK USING STATISTICAL WEIGHTING

• US 20090005064A1
• Filed: 06/28/2007
• Published: 01/01/2009
• Est. Priority Date: 06/28/2007
• Status: Active Grant

• Current Assignee: Extreme Networks, Inc.
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: MALIK, Ajay, VANGATI, Mahender, LE, Vinh-Phuong
• Granted Patent: US 7,873,367 B2
• Time in Patent Office: Days
• US Class Current: 455/456.100
• CPC Class Codes: G01S 5/02524 Creating or updating the radio-map
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Methods and systems are provided for determining the location of a first wireless device (e.g., a mobile unit) within a wireless network comprising a plurality of second wireless devices (e.g., access points). The method includes identifying an overlap area corresponding to the intersection of RF ranges for the one or more second wireless devices then computing a set of signal strength values, each associated with a measure of RF signal strength (e.g., RSSI) received by the plurality of second wireless devices from the first wireless device. A decision metric is evaluated for a plurality of locations within the overlap area based on the set of signal strength values. The location of the first wireless device is determined by selecting, from the plurality of locations, a location having the optimum value of the decision metric within the overlap area. The decision metric may utilize a minimum mean square error (MMSE) calculation. A weighting function may be used to remove redundant or weak signal strength values. The systems and methods are applicable, for example, to networks operating in accordance with 802.11, RFID, WiMax, WAN, Bluetooth, Zigbee, UWB, and the like.

Claims

1. A method for locating a first wireless device having a first type within a wireless network comprising a plurality of second wireless devices having a second type, comprising the steps of:

identifying an overlap area corresponding to the intersection of RF ranges for the one or more second wireless devices;

computing a set of signal strength values, each associated with a measure of RF signal strength received by the plurality of second wireless devices from the first wireless device;

evaluating a decision metric for a plurality of locations within the overlap area based on the set of signal strength values; and

determining the location of the first wireless device by selecting, from the plurality of locations, a location having the optimum value of the decision metric within the overlap area.

2. The method of claim 1, wherein the first type of wireless device is a mobile unit, and the second type of wireless device is an access port.

3. The method of claim 1, wherein the first type of wireless device is an access port, and the second type of wireless device is a mobile unit.

4. The method of claim 1, wherein the first and second types of wireless devices are configured to operate within a wireless environment selected from the group consisting of 802.11, RFID, WiMax, WAN, Bluetooth, Zigbee, and UWB.

5. The method of claim 1, wherein computing the set of signal strength values includes computing signal strength based on a receiver signal strength indicator (RSSI).

6. The method of claim 1, wherein the step of evaluating a decision metric includes evaluating a statistical measure selected from the group consisting of minimum mean square error (MMSE), maximum log likelihood, and least mean square.

7. The method of claim 6, wherein the decision metric is defined by

8. The method of claim 7, wherein the weighting function is used to remove or reduce the weighting of particular RSSI values from the set of signal strength values.

9. The method of claim 8, wherein the weighting function is used remove duplicate RSSI values associated with the same second wireless device.

10. The method of claim 1, wherein the plurality of locations within the overlap area are defined in accordance with a regular grid.

11. The method of claim 1, wherein time stamp information associated with the plurality of signal strength values is used in conjunction with the decision metric to select the optimum value.

12. A wireless network system comprising:

a first wireless device having a first type;

a plurality of second wireless devices having a second type, wherein an overlap area exists for RF ranges of the one or more second wireless devices; and

a locationing module configured to identify the overlap area, compute a set of signal strength values associated with a measure of RF signal strength received by the plurality of second wireless devices from the first wireless device, evaluate a decision metric for a plurality of locations within the overlap area based on the set of signal strength values; and

determine the location of the first wireless device by selecting, from the plurality of locations, a location having the optimum value of the decision metric within the overlap area.

13. The system of claim 12, wherein the first type of wireless device is a mobile unit, and the second type of wireless device is an access port.

14. The system of claim 12, wherein the first type of wireless device is an access port, and the second type of wireless device is a mobile unit.

15. The system of claim 12, wherein the first and second types of wireless devices are configured to operate within a wireless environment selected from the group consisting of 802.11, RFID, WiMax, WAN, Bluetooth, Zigbee, and UWB.

16. The system of claim 12, wherein computing the set of signal strength values includes computing signal strength based on a receiver signal strength indicator (RSSI).

17. The system of claim 16, wherein the decision metric is defined by

18. A locationing module configured to communicate with a first wireless device and a plurality of second wireless devices, the locationing module configured to identify an overlap area associated with the plurality of second wireless devices, compute a set of RSSI signal strength associated with the plurality of second wireless devices from the first wireless device, evaluate a decision metric for a plurality of locations within the overlap area based on the set of signal strength values, and determine the location of the first wireless device by selecting, from the plurality of locations, a location having the optimum value of the decision metric within the overlap area.

19. The module of claim 18, wherein the decision metric is defined by

20. The module of claim 19, wherein the weighting function is used to remove or reduce the weighting of particular RSSI values from the set of signal strength values.