SYSTEM AND METHOD FOR ACCESS POINT BASED POSITIONING

• US 20120063340A1
• Filed: 09/12/2011
• Published: 03/15/2012
• Est. Priority Date: 09/13/2010
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: WATERS, Deric W., RAMAKRISHNAN, Sthanunathan, XHAFA, Ariton E., BALAKRISHNAN, Jaiganesh, PANDE, Tarkesh, KASARGOD, Sandeep, THUKRAL, Saket
• Granted Patent: US 8,924,155 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: G01S 5/0242 Determining the position of transmitters to be subsequently used in positioning G01S5/0289 takes precedence
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Apparatus and methods for scanning for access points (APs) for wireless local area network (WLAN) positioning. In one embodiment a wireless device includes a WLAN positioning system. The WLAN positioning system includes an AP scanner. The AP scanner is configured to determine which WLAN channels are being used by APs proximate to the wireless device. The AP scanner is also configured to scan for AP transmissions only the WLAN channels determined to be used by APs proximate to the wireless device. The AP scanner is further configured to extract signal strength and AP identification information for WLAN positioning from the AP transmissions on the scanned channels.

Claims

1. A wireless device, comprising:

a wireless local area network (WLAN) positioning system, comprising;

an access point (AP) scanner configured to;

determine, prior to execution of a WLAN positioning scan, which WLAN channels are being used by APs proximate to the wireless device; and

execute a WLAN positioning scan for AP transmissions based on the prior determination of WLAN channels used by APs proximate to the wireless device; and

extract signal strength and AP identification information for WLAN positioning from the AP transmissions on the scanned channels.

2. The wireless device of claim 1, wherein the AP scanner is configured to determine the WLAN channels being used based on at least one of:

information retrieved from an AP database that identifies the WLAN channels;

energy levels of non-overlapping WLAN channels detected by the AP scanner;

a beacon report identifying an AP not visible to the wireless device; and

geographic location of the wireless device.

3. The wireless device of claim 1, wherein the AP scanner is configured to discontinue scanning for APs based on identifying a number of APs sufficient to position the wireless device with a predetermined accuracy.

4. The wireless device of claim 1, further comprising a motion sensor;

wherein the AP scanner is configured to scan for AP transmissions based on the motion sensor indicating that the wireless device has moved.

5. The wireless device of claim 1, wherein the AP scanner is configured to refrain from scanning for AP transmissions based on the position of the wireless device being determined to predetermined accuracy by via a non-WLAN positioning system.

6. The wireless device of claim 1, wherein the AP scanner is configured to adjust scan interval length based on a number of APs identified during the interval.

7. The wireless device of claim 1, wherein the AP scanner is configured to scan for AP transmission at a time derived from a previously received beacon frame.

8. The wireless device of claim 7, wherein the time comprises a scanning interval having a length based on times of predicted beacon transmissions by a plurality of APs.

9. The wireless device of claim 8, wherein the AP scanner is configured to select the plurality of APs based on a geometry metric derived from locations of the APs.

10. The wireless device of claim 9, wherein the AP scanner is configured to base the geometry metric on at least one of:

a dilution of precision computation applied to the plurality of APs;

an area defined by a geometric contour of the plurality of APs;

mutual distance between the plurality of APs; and

angles of arrival of the plurality of APs to a predicted position of the wireless device.

11. The wireless device of claim 1, wherein the AP scanner is configured to select which of an active scan and a passive scan to perform based on at least one of:

network information retrieved from an AP database;

an amount of network traffic detected by the wireless device; and

a scheduled wireless medium access by co-located wireless communication system disposed in the wireless device.

12. The wireless device of claim 1, wherein the wireless device is associated to a basic service set (BSS) and the wireless device is configured to transfer packets via the BSS, and the AP scanner is configured to scan for AP transmissions based on at least one of:

an inactive interval defined by a communication schedule of the BSS; and

an inactive period caused by a delay in transfer control protocol acknowledgement transmission by the wireless device.

13. The wireless device of claim 1, wherein the AP scanner is configured to:

determine, prior to execution of a WLAN positioning scan, an order for scanning WLAN channels, the order determined to minimize scanning time applied to identify a predetermined number of APs; and

execute the WLAN positioning scan based on the determined order.

14. A method, comprising:

scanning, by a wireless device, a wireless network channel for a transmission from an access point (AP);

identifying, by the wireless device, an AP based on a transmission detected by the scanning;

computing, by the wireless device, a position uncertainty value for the wireless device based on the identified AP;

comparing, by the wireless device, the position uncertainty value to a predetermined uncertainty threshold; and

terminating scanning based on the uncertainty threshold exceeding the position uncertainty value.

15. The method of claim 14 further comprising determining which of an active scan and a passive scan to perform based on at least one of wireless medium use scheduled for a coexisting wireless transceiver in the wireless device, and a level of traffic on the WLAN.

16. The method of claim 14, further comprising changing the WLAN channel used in the scanning based on the uncertainty threshold not exceeding the position uncertainty value and one of:

all APs on the previously scanned WLAN channel being identified; and

a predetermined percentage of the APs on the previously scanned WLAN being identified.

17. The method of claim 14, further comprising:

setting a time interval to scan the WLAN channel; and

extending the time interval based on the uncertainty threshold not exceeding the position uncertainty value and all APs on the WLAN channel not being identified.

18. The method of claim 14, further comprising changing the network radio frequency modulation mode based on the uncertainty threshold not exceeding the position uncertainty value and all APs on the WLAN using the previous network radio frequency modulation mode being identified.

19. The method of claim 14, further comprising accessing an AP database and retrieving from the database a value indicating a number of APs proximate to the wireless device.

20. The method of claim 14, further comprising adjusting a scan time interval during the scanning based on a percentage of APs on a channel identified prior to the adjusting.

21. A method, comprising:

executing, by a wireless device, a passive scan and identifying a set of all visible access points (APs) based on the passive scan;

selecting a sub-set of the set of all visible APs based on predicted beacon frame transmission times for the APs of the subset;

scanning for APs during a time interval defined based on the predicted beacon frame transmission times for the APs of the subset.

22. The method of claim 21, wherein the selecting comprises excluding from the sub-set APs having a received signal strength lower than a predetermined value.

23. The method of claim 21, wherein the selecting comprises excluding from the sub-set APs positioned less than a predetermined distance from the wireless device.

24. The method of claim 21, wherein the selecting comprises:

identifying all combinations of APs of the set;

wherein each AP of each combination is at least a predetermined distance from each other AP of the combination;

computing a dilution of precision value for each combination; and

discarding each combination having a dilution of precision value greater than a predetermined value.

25. The method of claim 21, further comprising extending the time interval based on not receiving a beacon from transmission from each AP of the sub-set.

26. The method of claim 21, further comprising executing a scan for all visible APs responsive to either of not receiving a beacon from transmission from each AP of the sub-set and receiving a beacon from an AP having a signal strength value greater than a predetermined value not in the sub-set.

27. The method of claim 21, wherein the selecting comprises choosing APs transmitting on the same WLAN channel.

28. The method of claim 21, further comprising determining, based on APs identified by the scanning, whether the wireless device has moved since the passive scan was executed.