Method and Apparatus for Access Point Selection in Wireless LAN

• US 20080102852A1
• Filed: 10/09/2007
• Published: 05/01/2008
• Est. Priority Date: 10/25/2006
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Du, Lei, Bai, Yong, Chen, Lan, Yamada, Akira, Watanabe, Fujio
• Granted Patent: US 7,907,582 B2
• Time in Patent Office: Days
• US Class Current: 455/453
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

A method and an apparatus select an access point (AP) in a wireless LAN to associate or reassociate, based on considerations that take into account the quality-of-service (QoS) status of the stations (STAs) and the potential hidden terminal effect. The method utilizes advertised or requested information obtained from an AP which includes the QoS status in each basic service set (BSS) and estimates the potential hidden terminal (HT) effect based on local channel sensing by the STA. The method selects the AP in a manner that reduces the possibility of collision from equal and higher priority HTs, thus providing greater transmission throughput and improving performance.

Claims

1. A method for selecting an access point for a mobile station to associate, comprising:

in each of a plurality of channels;

(i) obtaining, from an access point associated with the channel, load information at the access point for each of a plurality of access categories;

(ii) calculating a load metric based on the load information; and

selecting the access point that is associated with the channel having the least of the load metrics among the channels.

2. A method as in claim 1, further comprising:

(i) obtaining from the data packets transmitted by other mobile stations in the channel a measure of channel activity, for each access category; and

(iii) calculating a hidden terminal effect metric based on a bandwidth requirement of the mobile station, the obtained measure of channel activity, and the load information; and

wherein selecting the access point further include taking into consideration the channel having the least of the calculated hidden terminal effect metrics among the channels.

3. A method as in claim 1, wherein the load information is derived from beacon frames received at the mobile station operating under a passive scanning mode.

4. A method as in claim 1, wherein the load information is derived from probe-request transactions conducted between the mobile station and the access point according to an active scanning mode.

5. A method as in claim 1, wherein the load information is derived from administrative frames exchanged between the mobile station and the access point according to an administrative function.

6. A method as in claim 1, wherein the load information comprises the numbers of mobile stations associated with the access point by access categories.

7. A method as in claim 1, wherein the load information comprises channel utilization measures by access categories.

8. A method as in claim 1, wherein the load information is provided as a combination of:

a bitmask indicating the access categories represented, and (ii) a listing of the load information according to access categories.

9. A method as in claim 1, wherein the load information is provided as a combination of (i) load information pertaining to a specified category, and (ii) load information pertaining to access categories other than the specified category.

10. A method as in claim 1, further comprising calculating a data rate based on the measured signal strength received in a transmission from the access point.

11. A method as in claim 1, wherein the method takes into consideration load information pertaining only to access categories that has an equal or higher priority than an access category associated with the mobile terminal.

12. A method as in claim 1, wherein the measure of channel activity is obtained by:

overhearing in the channel frames that are not addressed to the mobile station;

extracting from each overheard frame an identity of a sending station and an associated access category;

for each access category, accumulating a number of stations based on the identities extracted; and

providing the number of stations as the measure of channel activity.

13. A method as in claim 1, wherein the measure of channel activity is obtained by:

overhearing in the channel frames that are not addressed to the mobile station;

extracting from each overheard frame an associated access category;

for each access category, accumulating time durations of the frames associated with that access category; and

providing the accumulated time as the measure of channel activity for the access category.

14. The method of claim 1, wherein each channel is examined for a time period between a minimum time value and a maximum time value, the minimum time value.

15. An apparatus for selecting an access point in a wireless local area network (WLAN), comprising:

BSS load request means for obtaining load information according to access categories from a plurality of access points associated with a plurality of channels and for obtaining from frames transmitted within each channel heard load information according to access categories;

Calculation and storage means calculating a load metric based on the load information;

Access point selection means that selects the access point from the calculated load metric; and

Judgment means for controlling the operations of the load request means, the calculation and storage means, and the access point selection means according to an access point selection method.

16. An apparatus as in claim 15, wherein the calculation and storage means further performs (i) recording the load information obtained from the access points, (ii) recording the heard load information obtained from each channel;

and (iii) calculating for each channel a hidden terminal effect based on the load information, the heard load information and a bandwidth requirement by the mobile station; and

wherein the access point selection means take into consideration the calculated hidden terminal effects.

17. An apparatus as in claim 15, wherein the load information is derived from beacon frames received at the mobile station operating under a passive scanning mode.

18. An apparatus as in claim 15, wherein the load information is derived from probe-request transactions conducted between the mobile station and the access point according to an active scanning mode.

19. An apparatus as in claim 15, wherein the load information is derived from administrative frames exchanged between the mobile station and the access point according to an administrative function.

20. An apparatus as in claim 15, wherein the load information comprises the numbers of mobile stations associated with the access point by access categories.

21. An apparatus as in claim 15, wherein the load information comprises channel utilization measures by access categories.

22. An apparatus as in claim 15, wherein the load information is provided as a combination of:

a bitmask indicating the access categories represented, and (ii) a listing of the load information according to access categories.

23. An apparatus as in claim 15, wherein the load information is provided as a combination of (i) load information pertaining to a specified category, and (ii) load information pertaining to access categories other than the specified category.

24. An apparatus as in claim 15, wherein the calculation and storage means provide a data rate based on the measured signal strength received in a transmission from the access point.

25. An apparatus as in claim 15, wherein the calculation and storage means takes into consideration load information pertaining only to access categories that has an equal or higher priority than an access category associated with the mobile terminal.

26. An apparatus as in claim 15, wherein the heard load information is obtained by:

overhearing in the channel frames that are not addressed to the mobile station;

extracting from each overheard frame an identity of a sending station and an associated access category;

for each access category, accumulating a number of stations based on the identities extracted; and

providing the number of stations as the heard load information for the access category.

27. An apparatus as in claim 15, wherein the heard load information is obtained by:

overhearing in the channel frames that are not addressed to the mobile station;

extracting from each overheard frame an associated access category;

for each access category, accumulating time durations of the frames associated with that access category; and

providing the accumulated time as the heard load information for the access category.

28. The apparatus of claim 15, wherein each channel is examined for a time period between a minimum time value and a maximum time value, the minimum time value.

29. A system for allowing an efficient access point selection in a wireless computer network, comprising:

a plurality of access points of the wireless computer network having overlapping coverage areas operating on a plurality channels, each access point being configured to provide load information regarding its channel by access categories; and

a mobile station configured to (i) receive at the overlapping coverage areas the load information by access categories from the access point;

(ii) calculate a load metric for each channel based on the load information from the access points; and

(iii) select one of the access point based on the calculated load metrics.

30. A system as in claim 29, wherein the mobile station is further configured to (i) listen to other mobile stations in each channel to obtain heard load information of each channel by access categories;

(ii) calculate a hidden terminal effect metric for each channel based on the load information from the access points and the heard load information from the other mobile terminals; and

(iii) when selecting one of the access point, take into consideration the calculated hidden terminal effect metrics.

31. A system as in claim 29, wherein the load information is derived from beacon frames received at the mobile station operating under a passive scanning mode.

32. A system as in claim 29, wherein the load information is derived from probe-request transactions conducted between the mobile station and the access point according to an active scanning mode.

33. An system as in claim 29, wherein the load information is derived from roaming management frames exchanged between the mobile station and the access point according to a roaming function.

34. A system as in claim 29, wherein the load information comprises the numbers of mobile stations associated with the access point by access categories.