Methods for implementing a dynamic frequency selection (DFS) feature for WLAN devices

• US 20040151137A1
• Filed: 04/02/2003
• Published: 08/05/2004
• Est. Priority Date: 01/30/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: McFarland, William J., Green, Michael R.
• Granted Patent: US 7,606,193 B2
• Time in Patent Office: Days
• US Class Current: 370/329
• CPC Class Codes: G01S 7/021 Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals
• CPC Class Codes: H04L 1/22 using redundant apparatus to increase reliability
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26
• CPC Class Codes: H04L 63/162 at the data link layer
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 24/04 Arrangements for maintaining operational condition
• CPC Class Codes: H04W 36/06 Reselecting a communication resource in the serving access point
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

Various regulatory domains promulgate standards to define how wireless devices should operate in certain frequency bands. The 5 GHz spectrum is of particular importance to certain regulatory domains because of radar systems also operating in this spectrum. To avoid interference with such radar systems, wireless devices operating in this spectrum should be able to detect radar and quickly vacate any channels currently used by the radar systems. Techniques are provided for performing startup scans for radar, identifying backup channels for a possible channel switch, and efficiently changing channels in the event of radar detection in the operating channel. These techniques advantageously meet current regulatory standards governing DFS while minimizing network startup delays and disruption to users during a radar event.

Claims

1. A method of populating a backup channel list for a wireless local area network (WLAN) device operable in a spectrum, the method comprising:

weighting the channels based on actual and potential use of allowed sub-bands in the spectrum; and

selecting channels from the allowed sub-bands to achieve mandatory channel spreading requirements.

2. A method of populating a radar-free channel list for a wireless local area network (WLAN) device operable in a 5 GHz spectrum, the spectrum being divided into a first sub-band of 5150-5250 MHz, a second sub-band of 5250-5350 MHz, and a third sub-band of 5470-5725 MHz, the method comprising:

populating an allowed channel list with channels allowed by a regulatory domain for that spectrum;

populating a BSS-free channel list with the allowed channels having acceptable levels of current WLAN transmission thereon;

if the allowed channel list includes channels from the first, second, and third sub-bands, then determining whether the BSS-free channel list has less than two channels,

if so, then choosing three channels from the allowed channel list, wherein a first channel is chosen from the first sub-band, a second channel is chosen from the second sub-band, and a third channel is chosen from the third sub-band,

if not, then choosing three channels from the BSS-free channel list, wherein a first channel is chosen from the first sub-band, a second channel is chosen from the second sub-band, and a third channel is chosen from the third sub-band,;

if the allowed channel list includes channels from the first and second sub-bands, then determining whether the BSS-free channel list has less than two channels,

if so, then choosing three channels from the allowed channel list, wherein a first channel is chosen from the first sub-band, a second channel is chosen from the first sub-band, and a third channel is chosen from the second sub-band,

if not, then choosing three channels from the BSS-free channel list, wherein a first channel is chosen from the first sub-band, a second channel is chosen from the first sub-band, and a third channel is chosen from the second sub-band; and

if the allowed channel list includes channels from only the first sub-band, then determining whether the BSS-free channel list has less than two channels,

if so, then choosing two channels from the allowed channel list in the first sub-band,

if not, then choosing two channels from the BSS-free channel list in the first sub-band.

3. A method of populating a radar-free channel list for a wireless local area network (WLAN) device operable in a 5 GHz spectrum, the spectrum being divided into a first sub-band of 5150-5250 MHz, a second sub-band of 5250-5350 MHz, and a third sub-band of 5470-5725 MHz, the method comprising:

populating an allowed channel list with channels allowed by a regulatory domain for that spectrum;

populating a BSS-free channel list with the allowed channels having acceptable levels of current WLAN transmission thereon;

if the allowed channel list includes channels from all the sub-bands, then determining whether the BSS-free channel list has less than two channels,

if so, then choosing three channels from the allowed channel list,

if not, then choosing three channels from the BSS-free channel list;

if the allowed channel list includes channels from only two sub-bands, then determining whether the BSS-free channel list has less than two channels,

if so, then choosing three channels from the allowed channel list,

if not, then choosing three channels from the BSS-free channel list; and

if the allowed channel list includes channels from only one sub-band, then determining whether the BSS-free channel list has less than two channels,

if so, then choosing two channels from the allowed channel list,

if not, then choosing two channels from the BSS-free channel list.

4. The method of claim 3, wherein if the allowed channel list includes channels from all sub-bands, then choosing the three channels includes a pseudo-random selection that increases a likelihood of choosing a channel unused by other basic service sets (BSSs) and free of radar signals.

5. The method of claim 3, wherein if the allowed channel list includes channels from all sub-bands, then choosing the three channels includes a pseudo-random selection that increases frequency spreading.

6. The method of claim 3, wherein if the allowed channel list includes channels from all sub-bands, then choosing three channels includes a pseudo-random selection that increases a likelihood of most stations associated with the access point being operable in the three channels.

7. The method of claim 3, wherein if the allowed channel list only includes channels from only two sub-bands, then of the three channels, two channels are selected from the first sub-band and one channel is selected from the second sub-band.

8. The method of claim 3, wherein if the allowed channel list includes channels from only two sub-bands, then using a weighting function to select more channels from the first sub-band than from the second sub-band.

9. The method of claim 3, wherein if the allowed channel list includes channels from only one sub-band, then randomly choosing two channels in the first sub-band.

10. A method of performing a startup operation for an access point in a regulatory domain, the regulatory domain having a frequency spreading requirement, the access point being allowed to communicate using allowed channels in a spectrum, the method comprising:

(i) populating an allowed channel list with the allowed channels;

(ii) populating a BSS-free channel list with allowed channels having acceptable levels of current WLAN transmission thereon;

(iii) populating a radar-free channel list using the BSS-free channel list and the allowed channel list;

(iv) performing a radar scan on each channel in the radar-free channel list;

(v) deleting any channel with radar in the radar-free channel list;

(vi) repeating steps (i)-(v) until a predetermined number of channels remain in the radar-free channel list;

(vii) choosing a first channel in the radar-free channel list for operation; and

(viii) beginning operation with the first channel.

11. The method of claim 10, wherein choosing a first channel includes deleting the first channel from the radar-free channel.

12. The method of claim 11, further including setting a time to re-scan any channels in the radar-free channel list.

13. The method of claim 10, wherein populating the radar-free channel list includes:

weighting the channels based on actual and potential use of allowed sub-bands in the spectrum; and

selecting at least one channel from each allowed sub-band.

14. A method of performing a startup operation for an access point in a regulatory domain, the regulatory domain having a frequency spreading requirement, the access point being allowed to communicate using allowed channels in a spectrum, the method comprising:

(i) populating an allowed channel list with the allowed channels;

(ii) populating a BSS-free channel list with allowed channels having acceptable levels of current WLAN transmission thereon;

(iii) populating a radar-free channel list using the BSS-free channel list, if possible, and otherwise the allowed channel list;

(iv) performing a radar scan on each channel in the radar-free channel list;

(v) deleting any channel with radar in the radar-free channel list;

(vi) repeating steps (i)-(v) until a predetermined number of channels remain in the radar-free channel list;

(vii) choosing a first channel in the radar-free channel list for operation; and

(viii) beginning operation with the first channel.

15. A method of switching channels for an access point operating in a 5 GHz spectrum, wherein the 5 GHz spectrum is divided into a first sub-band of 5150-5250 MHz, a second sub-band of 5250-5350 MHz, and a third sub-band of 5470-5725 MHz, the method comprising:

accessing a radar-free channel list; and

setting the new channel to one of a most distant channel, a lowest channel, and a highest channel in the radar-free channel list.

16. The method of claim 15, wherein if the access point is operating in the first sub-band, then setting the new channel to the most distant channel.

17. The method of claim 15, wherein if the access point is operating in the second sub-band and at least one channel in the radar-free channel is in the first sub-band, then setting the new channel to the lowest channel.

18. The method of claim 15, wherein if the access point is operating in the second sub-band and no channel in the radar-free channel is in the first sub-band, then setting the new channel to the highest channel.

19. The method of claim 15, wherein if the access point is operating in the third sub-band, then setting the new channel to the lowest channel.

20. A method of switching channels for an access point operating in a spectrum, the method comprising:

accessing a radar-free channel list; and

setting the new channel to one of a most distant channel, a lowest channel, and a highest channel in the radar-free channel list.

21. A method of designating backup channels for a radar-free channel list usable by an access point operable in a spectrum, the method comprising:

determining candidate backup channels for the radar-free channel list;

performing a radar scan on each candidate backup channel until a radar-free channel is found and deleting any candidate backup channel from the radar-free channel list found with radar during the step of performing;

choosing the radar-free channel as a current channel and deleting the radar-free channel from the radar-free channel list;

sending beacons using the current channel;

allowing stations to authenticate and associate with the access point;

scanning other candidate backup channels in the radar-free channel using any associated stations that are willing to scan, or else the access point;

designating candidate backup channels as backup channels and deleting candidate backup channels with radar from the radar-free channel list during the step of scanning.

22. The method of claim 21, wherein each associated station willing to scan performs a scan on only one candidate backup channel.

23. A method of performing a startup operation for an access point in a regulatory domain, the regulatory domain having a frequency spreading requirement, the access point being allowed to communicate using allowed channels in a spectrum, the method comprising:

(i) populating an allowed channel list with the allowed channels;

(ii) populating a BSS-free channel list with allowed channels having acceptable levels of current WLAN transmission thereon;

(iii) populating a radar-free channel list using the BSS-free channel list and the allowed channel list;

(iv) randomly selecting a first channel from the radar-free channel list;

(v) if the first channel is in a first sub-band and the regulatory domain exempts scanning in the first sub-band, then designating the first channel as a current channel, selecting a backup channel from the radar-free channel list in the first sub-band without scanning, and proceeding directly to (xi);

(vi) if the first channel is not in the first sub-band and the regulatory domain exempts scanning in the first sub-band, then performing a radar scan on each channel in the radar-free channel list, except any channel in the first sub-band;

(vii) if the first channel is in the first sub-band and the regulatory domain requires scanning in the first sub-band, then performing a radar scan on each channel in the radar-free channel list;

(viii) for steps (vi) and (vii), deleting any channel with radar in the radar-free channel list;

(ix) repeating steps (i)-(viii) until a predetermined number of channels remain in the radar-free channel list;

(x) after step (ix), choosing a first channel in the radar-free channel list for operation; and

(xi) beginning operation with the first channel.