METHODS, DEVICE AND SYSTEM FOR ACCESS POINT FACILITATED FAST HANDOFF

• US 20080062933A1
• Filed: 09/06/2007
• Published: 03/13/2008
• Est. Priority Date: 09/07/2006
• Status: Active Grant

• Current Assignee: NEC Company Limited
• Original Assignee: NEC Company Limited
• Inventors: Xia, Yong, Zhang, Yanfeng, Liu, Yongqiang
• Granted Patent: US 8,023,468 B2
• Time in Patent Office: Days
• US Class Current: 370/332
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 48/12 using downlink control channel

Abstract

Methods, devices and system for access point facilitated fast handoff are provided. Each access point (AP) in a wireless local area network is provided with a primary interface and a secondary interface wherein the primary interface performs normal communication with user terminals and broadcasts standard beacon frames on its working channel, and the secondary interface broadcasts extended beacon frames on working channels of neighbor APs sequentially. The extended beacon frame includes at least information of BSSID, SSID, working channel and the like of the primary interface of the corresponding AP. The user terminal may receive the standard beacons from the serving AP it is communicating with and the extended beacons from the neighbor APs, and according to the two kinds of beacons, the terminal may calculate the signal quality with the primary interface of the serving AP and the signal qualities with the neighbor APs at the current position. By an algorithm of comparing the signal qualities of the best neighbor AP and the serving AP, the terminal may accurately and quickly determine whether to perform handoff with minimized cost.

Claims

1. A method for an access point to facilitate fast handoff of user terminals in a wireless communication network, comprising:

performing communication with user terminals within a coverage area of the access point through a primary interface;

broadcasting standard beacon frames on a working channel of the access point through the primary interface; and

broadcasting extended beacon frames on working channels of one or more neighbor access points of said access point through a secondary interface.

2. The method according to claim 1, wherein the extended beacon frame includes at least information of Basic Service Set Identifier, Service Set Identifier and the working channel of the primary interface.

3. The method according to claim 1, wherein broadcasting extended beacon frames further comprises determining the working channels of said one or more neighbor access points according to a neighbor list and sequentially switching to the determined working channels of said one or more neighbor access points to broadcast the extended beacon frames.

4. The method according to claim 3, wherein each record in the neighbor list includes at least a first field identifying a neighbor access point and a second field identifying the working channel of that neighbor access point.

5. The method according to claim 1, wherein the frequency of broadcasting the extended beacon frames is higher than that of broadcasting the standard beacon frames.

6. The method according to claim 1, further comprising adjusting broadcast interval of the extended beacon frames according to the number of the working channels of said one or more neighbor access points and intervals of standard beacons of said one or more neighbor access points, such that in one period of standard beacon frame of each neighbor access point, one extended beacon frame is sent on the working channel of that neighbor access point.

7. The method according to claim 1, wherein the wireless communication network is a wireless local area network based on 802.11 standard.

8. An access point used in a wireless communication network, comprising:

a standard beacon frame generating unit configured to generate standard beacon frames;

an extended beacon frame generating unit configured to generate extended beacon frames;

a primary interface coupled with the standard beacon generating unit, the primary interface performing communication with user terminals within a coverage area of said access point and broadcasting the standard beacon frames on a working channel of said access point; and

a secondary interface coupled with the extended beacon generating unit, the secondary interface broadcasting extended beacon frames on working channels of one or more neighbor access points of said access point.

9. The access point according to claim 8, wherein the extended beacon frame includes at least information of Basic Service Set Identifier, Service Set Identifier and the working channel of the primary interface.

10. The access point according to claim 8, further comprising a neighbor list storage unit coupled with the secondary interface, the neighbor list storage unit storing a neighbor list of said access point, wherein the secondary interface determines the working channels of said one or more neighbor access points according to the neighbor list, and sequentially switches to the determined working channels of said one or more neighbor access points to broadcast the extended beacon frames.

11. The access point according to claim 10, wherein each record in the neighbor list includes at least a first field identifying a neighbor access point and a second field identifying the working channel of that neighbor access point.

12. The access point according to claim 8, wherein the frequency of broadcasting the extended beacon frames by the secondary interface is higher than that of broadcasting the standard beacon frames by the primary interface.

13. The access point according to claim 8, further comprising a broadcast interval setting unit coupled with the secondary interface, the broadcast interval setting unit adjusting broadcast interval of the extended beacon frames according to the number of the working channels of said one or more neighbor access points and intervals of standard beacons of said one or more neighbor access points, such that in one period of standard beacon frame of each neighbor access point, one extended beacon frame is sent on the working channel of that neighbor access point.

14. The access point according to claim 8, wherein said access point is an access point of a wireless local area network based on 802.11 standard.

15. A method for handoff of a user terminal in a wireless communication network, comprising:

receiving standard beacon frames from a primary interface of a serving access point on a working channel of the serving access point;

receiving extended beacon frames from secondary interfaces of one or more neighbor access points on the working channel of the serving access point;

calculating signal quality of the serving access point from the received standard beacon frames;

calculating signal qualities of said one or more neighbor access points from the received extended beacon frames; and

selectively performing handoff according to the calculation results of the signal qualities of said serving access point and said one or more neighbor access points.

16. The method according to claim 15, further comprising deriving, from any one of the extended beacon frames, at least Basic Service Set Identifier, Service Set Identifier and the working channel of the primary interface of the corresponding neighbor access point.

17. The method according to claim 15, wherein calculating signal quality of the serving access point comprises calculating a moving average of Received Signal Strength Indicator of the serving access point according to multiple standard beacon frames.

18. The method according to claim 15, wherein calculating signal qualities of said one or more neighbor access points comprises calculating a moving average of Received Signal Strength Indicator of one neighbor access point according to multiple extended beacon frames corresponding to that neighbor access point.

19. The method according to claim 15, wherein selectively performing handoff comprises:

selecting a best neighbor access point according to the signal qualities of said one or more neighbor access points when the signal quality of the serving access point is lower than a predetermined threshold; and

performing handoff from the serving access point to the best neighbor access point when the signal quality of the best neighbor access point is higher than the signal quality of the serving access point by a predetermined margin.

20. The method according to claim 15, wherein the standard beacon frames and the extended beacon frames are received by the same interface.

21. The method according to claim 15, wherein the wireless communication network is a wireless local area network based on 802.11 standard.

22. A terminal used in a wireless communication network, comprising:

a beacon frame receiving unit that receives beacon frames on a working channel of a serving access point of the terminal, the beacon frame receiving unit comprising;

a standard beacon frame acquisition part that acquires, from the received beacon frames, standard beacon frames from a primary interface of the serving access point; and

an extended beacon frame acquisition part that acquires, from the received beacon frames, extended beacon frames from secondary interfaces of one or more neighbor access points;

a serving access point quality calculating unit coupled with the standard beacon frame acquisition part, the serving access point quality calculating unit calculating signal quality of the serving access point from the acquired standard beacon frames;

a neighbor access point quality calculating unit coupled with said extended beacon frame acquisition part, the neighbor access point quality calculating unit calculating signal qualities of said one or more neighbor access points from the acquired extended beacon frames; and

a handoff unit coupled with said serving access point quality calculating unit and said neighbor access point quality calculating unit, the handoff unit selectively performing handoff according to the signal qualities of said serving access point and said one or more neighbor access points calculated by the serving access point quality calculating unit and the neighbor access point quality calculating unit.

23. The terminal according to claim 22, further comprising an extended beacon frame parameter extracting unit coupled with said extended beacon frame acquisition part and said handoff unit, for extracting, from any one of the extended beacon frames, at least Basic Service Set Identifier, Service Set Identifier and the working channel of the primary interface of the corresponding neighbor access point.

24. The terminal according to claim 22, wherein the serving access point quality calculating unit calculates a moving average of Received Signal Strength Indicator of the serving access point according to multiple standard beacon frames.

25. The terminal according to claim 22, wherein the neighbor access point quality calculating unit calculates a moving average of Received Signal Strength Indicator of one neighbor access point according to multiple extended beacon frames corresponding to that neighbor access point.

26. The terminal according to claim 22, wherein the handoff unit selects a best neighbor access point according to the signal qualities of said one or more neighbor access points when the signal quality of the serving access point is lower than a predetermined threshold, and performs handoff from the serving access point to the best neighbor access point when the signal quality of the best neighbor access point is higher than the signal quality of the serving access point by a predetermined margin.

27. The terminal according to claim 22, wherein the beacon frame receiving unit receives the standard beacon frames and the extended beacon frames by the same interface.

28. The terminal according to claim 22, wherein the terminal is a user terminal used in a wireless local area network based on 802.11 standard.

29. A method for a wireless communication system, the wireless communication system comprising a plurality of access points and at least one user terminal, each one of the plurality of access points comprising a primary interface and a secondary interface, the method comprising:

performing communication by a serving access point, to which the user terminal is currently connected, with the user terminal through its primary interface;

broadcasting standard beacon frames by the serving access point on a working channel of the serving access point through its primary interface;

broadcasting extended beacon frames by one or more neighbor access points of the serving access point on the working channel of the serving access point through secondary interfaces of said one or more neighbor access points;

receiving the standard beacon frames from the serving access point on the working channel of the serving access point by the user terminal;

receiving the extended beacon frames from said one or more neighbor access points on the working channel of the serving access point by the user terminal;

calculating signal quality of the serving access point from the received standard beacon frames by the user terminal;

calculating signal qualities of said one or more neighbor access points from the received extended beacon frames by the user terminal; and

selectively performing handoff by the user terminal according to the calculation results of the signal qualities of said serving access point and said one or more neighbor access points.

30. The method according to claim 29, wherein the extended beacon frame includes at least information of Basic Service Set Identifier, Service Set Identifier and the working channel of the primary interface.

31. The method according to claim 29, wherein broadcasting extended beacon frames further comprises determining working channels of said one or more neighbor access points according to a neighbor list, and sequentially switching to the determined working channels of said one or more neighbor access points to broadcast the extended beacon frames.

32. The method according to claim 29, further comprising adjusting by the serving access point broadcast interval of the extended beacon frames according to the number of working channels of said one or more neighbor access points and intervals of standard beacons of said one or more neighbor access points, such that in one period of standard beacon frame of each neighbor access point, one extended beacon frame is sent on the working channel of that neighbor access point.

33. The method according to claim 29, wherein the method is used in a wireless local area network based on 802.11 standard.

34. A wireless communication system, comprising:

a plurality of access points and at least one user terminal, wherein

each one of the plurality of access points comprises;

a primary interface that performs communication with user terminals within a coverage area of the access point and broadcasts standard beacon frames on a working channel of the access point; and

a secondary interface that broadcasts extended beacon frames on working channels of one or more neighbor access points of said access point, and the user terminal is wirelessly coupled to a serving access point among the plurality of access points, and comprises;

a beacon frame receiving unit that receives standard beacon frames from a primary interface of the serving access point and extended beacon frames from secondary interfaces of one or more neighbor access points of the serving access point on a working channel of the serving access point;

a serving access point quality calculating unit that calculates signal quality of the serving access point from the standard beacon frames;

a neighbor access point quality calculating unit that calculates signal qualities of said one or more neighbor access points from the extended beacon frames; and

a handoff unit that selectively performs handoff according to the signal qualities of said serving access point and said one or more neighbor access points.

35. The system according to claim 34, wherein the extended beacon frame includes at least information of Basic Service Set Identifier, Service Set Identifier and the working channel of the primary interface of the corresponding access point.

36. The system according to claim 34, wherein each one of the plurality of access points further comprises a neighbor list storage unit that stores a neighbor list of the access point, and wherein the secondary interface determines the working channels of said one or more neighbor access points according to the neighbor list and sequentially switches to the determined working channels of said one or more neighbor access points to broadcast the extended beacon frames.

37. The system according to claim 34, wherein each one of the plurality of access points further comprises a broadcast interval setting unit that adjusts broadcast interval of the extended beacon frames according to the number of the working channels of said one or more neighbor access points and intervals of standard beacons of said one or more neighbor access points, such that in one period of standard beacon frame of each neighbor access point, one extended beacon frame is sent on the working channel of that neighbor access point.

38. The system according to claim 34, wherein the system adopts 802.11 standard for the wireless communication.

39. A manufactured article having a machine readable medium with instructions recorded thereon, which, when executed by an access point in a wireless communication system, causes the access point to:

perform communication with user terminals within a coverage area of the access point through a primary interface;

broadcast standard beacon frames on a working channel of the access point through the primary interface; and

broadcast extended beacon frames on working channels of one or more neighbor access points of said access point through a secondary interface.

40. A manufactured article having a machine readable medium with instructions recorded thereon, which, when executed by an user terminal in a wireless communication system, causes the user terminal to:

receive standard beacon frames from a primary interface of a serving access point on a working channel of the serving access point;

receive extended beacon frames from secondary interfaces of one or more neighbor access points on the working channel of the serving access point;

calculate signal quality of the serving access point from the received standard beacon frames;

calculate signal qualities of said one or more neighbor access points from the received extended beacon frames; and

selectively perform handoff according to the calculation results of the signal qualities of said serving access point and said one or more neighbor access points.