Decoupling scanning from handoff for reduced delay over wireless LAN

• US 20080186917A1
• Filed: 02/02/2007
• Published: 08/07/2008
• Est. Priority Date: 02/02/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Tan, Kun, Zhang, Yongguang, Wu, Haitao
• Granted Patent: US 8,929,328 B2
• Time in Patent Office: Days
• US Class Current: 370/331
• CPC Class Codes: H04W 36/10 Reselecting an access point controller
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information

Abstract

Methods and systems for handing off a wireless client between access points wherein the scanning for access points in decoupled from the handing off, thus reducing the delay in the handing off.

Claims

1. A method for use in a wireless communication system comprising a wireless client (1400) and a plurality of wireless access points (1411, 1412, 1413), wherein the wireless client associates with one of the plurality of wireless access points (1410) to enable communication therethrough, the method comprising acts of:

a) in response to a first set of at least one triggering condition (1420), scanning to detect which of the plurality of access points is within range to enable association with the client (1401); and

b) in response to a second set of at least one triggering condition (1421) that differs from the first set of at least one triggering condition, associating with at least one of the plurality of wireless access points (1402).

2. The method of claim 1, wherein the method is performed by the wireless client.

3. The method of claim 1, wherein the scanning in step (a) comprises active scanning.

4. The method of claim 1, wherein the scanning in step (a) further comprises acts of:

a1) the wireless client switching to a new channel other than a channel of a currently associated wireless access point;

a2) the wireless client detecting wireless access points on the new channel;

a3) the wireless client switching back to the channel of the currently associated wireless access point;

a4) after a predefined time interval, repeating steps (a1) through (a3).

5. The method of claim 1, wherein the first set of at least one triggering condition and the second set of at least one triggering condition each depends on a plurality of indicators detected by the wireless client.

6. The method of claim 5, wherein the plurality of indicators includes one or more of the Received Signal Strength Indicator as defined by IEEE, a number of retransmitted packets, a loss of beacons, an uplink bitrate, and a downlink bitrate.

7. The method of claim 5, wherein the first set of at least one triggering condition uses different indicators than does the second set of at least one triggering condition.

8. The method of claim 1, wherein the association delay incurred in step (b) is less than one second.

9. The method of claim 1, wherein the association delay incurred in step (b) is less than 500 ms.

10. The method of claim 1, wherein the association delay incurred in step (b) is less than 50 ms.

11. The method of claim 1, wherein the association delay incurred in step (b) is less than 10 ms.

12. A wireless client comprising:

at least one processor programmed (1302) to implement

a scanning module (1401) for detecting access points (1411, 1412, 1413) in response to a first set of at least one triggering condition (1420); and

a handoff module (1402) for handing off the client station between access points in response to a second set of at least one triggering condition (1421),

wherein the first set of at least one triggering condition (1420) differs from the second set of at least one triggering condition (1421).

13. The client of claim 12, further comprising a network interface card and a software driver for the network interface card, wherein the scanning module and the handoff module are implemented the software driver.

14. The client of claim 12, wherein the scanning module and the handoff module are implemented in hardware in the wireless client.

15. The client of claim 12, wherein the wireless client is a personal digital assistant, a cell phone, or a laptop computer.

16. The client of claim 12, wherein the wireless client communicates using one or more of the following IEEE standards:

802.11(a), 802.11(b), 802.11(g), 802.11 (n).

17. A computer-readable medium having computer-readable signals stored thereon that define instructions that, as a result of being executed by a device, instruct the device (1400) to perform a method comprising:

a) associating with a first access point (1410),

b) scanning to detect access points (1401) in response to a set of at least one indicator of connectivity with the first access point (1420),

c) associating (1402) with a second access point (1412) in response to a set of at least one indicator of connectivity with the first access point (1421).

18. The computer-readable medium of claim 17, wherein the scanning to detect access points is active scanning.

19. The computer-readable medium of claim 17, wherein the scanning to detect access points is passive scanning.

20. The computer-readable medium of claim 17, wherein the associating with a second access point is completed in less than one second.