DFS channels unavailble due to RADAR interferance, best way to use NON DFS channels

[Rod_Robertson2]

We have an extreme wireless configuration (5210 controller and ap 3805 ) and had been using the additional DFS channels.
These Ap's are giving us alarms about RADAR.. Ok we are near an local Airport so I can understand this . So my question is , now we do not have the 4 additional channels , what is the best way to use the 4 available non DFS Channels, small cells ? still using the auto channel selection with low power ?

We have just checked the internet and can see that Weather Radar works between 4 -8GHz.. working with our 5Ghz for Wireless..

Any comments and advice , would be apprecieted

[Rod_Robertson2]

I found this link useful;
http://wifinigel.blogspot.co.uk/2012/09/wifi-channels-on-5ghz-in-uk.html

[Rod_Robertson2]

MAny thanks for your excellent responses.

This is what I have sent to my collegues for discussion.

Wow what a subject..



Basically what happens , if the AP configured to use DFS channels sees a Weather Radar or other military type frequencies it automatically moves to a none DFS channel , which then basically messes up the wireless cell structure as then you could have 2 or more AP’s in the same location of the same frequency , causing cell interference and general rubbish wifi performance.



There is also another issue with using DFS and that is, does the “end user equipment”( Phones/Mac/Tablets ) support these upper channels , again the only way to see this would be to somehow monitor the connections per AP .. those on the higher channels , have less /same / more connections than your average none DFS AP .



Looking at the Weather Radar, we discussed a few options:



We could be more selective in how we allocate 5Ghz channels allowing the external accessible AP’s ie those that would “see” the weather radar scans to be configured as NON DFS , and as we are aware 5Ghz does not penetrate too far into the building through walls , use DFS channels on these AP’s.



From what I have read “weather radar “ uses channels 116-132 , therefore these should be removed from our configuration ..



Another option is to give the DFS configured AP’s a predetermined NON DFS channel to switch to in the event of a weather radar scan, though again here we are basically going back to static configuration of AP’s and also knowing the surrounding allocated channels.





So there you go , the start of an interesting discussion.

[Ostrovsky__Yury]

Some time ago I made a small video regarding DFS and how we can prepare our network to carefully use it . If you have time please take a look here https://youtu.be/9DG0Q1CRHeQ . Any comment appreciated.

[Ondrej_Lepa]

Hi Rod,

First thing is - do you need 40 / 80 MHz wide channels or is it more about having more separate channels to be used?

Second - DFS is based on country regulations so take a look where / if there is a gap where DFS is not required.

Third - DFS is not related to AP coverage cells or radio Tx power. Once AP senses RADAR signal, it just have to act.

See below part of CWAP study guide

When a radar blast is detected, all stations must leave the affected frequency. This capability is a part of Dynamic Frequency Selection (DFS). In countries where compliance with 802.11h is implemented, stations operating on UNII-2 and UNII-2 extended bands must also comply with transmit power regulations. This is called Transmit Power Control (TPC).

I would recommend to tweak supported channel plan to use rather non-required channels (based on country code) if possible. Otherwise I am afraid you'll need to accept the DFS at your location.

Let me know if you have any further questions.

Regards,
Ondrej