5 Ghz radio resource management - why would power be lowered?

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Apr 16th, 2014
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Under what circumstances will a controller lower the power level on a 5 Ghz radio?  In some areas I am seeing RRM controlled power levels as low as 5.

 

I thought because of the greater number of available channels, the potential for co-channel interference would be reduced to the point where decreasing power would seldom be necessary.  The channel width is 20Mhz, and the ap's are in the US.

 

It seems to be happening more frequently with the higher version of code, i.e. 7.5 and 7.6 on 5508's and wism2's.  It doesn't seem to happen on older 4402 controllers running 7.0 code.

 

So why would a controller lower the power of a 5Ghz radio, and is there a difference in the RRM configuration in 7.0 and 7.5/7.6 version code?

 

Please ask questions if  more information is needed to respond.

 

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Rasika Nayanajith Wed, 04/16/2014 - 13:43
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Hi Will,

"is there a difference in the RRM configuration in 7.0 and 7.5/7.6 version code?"

Yes, there are differences in RRM  in WLC version 7.0 to the later codes (7.2.x onwards). Here is the detail explanation how RRM works in these code (page 14 shows a summary table of version compatibility) . It talks about upto 7.4 & I think there are no RRM behaviour changes in 7.5/7.6 compare to 7.4.

http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-4/RRM_DG_74.pdf

 

CH126 of the below configuration guide (v7.6) explain configuration steps of RRM.

http://www.cisco.com/c/dam/en/us/td/docs/wireless/controller/7-6/configuration/guide/b_cg76.pdf

 

HTH

Rasika

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willsmith1701 Thu, 04/17/2014 - 04:01
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Thank you for the TPM docs.  I am still reviewing them and trying to understand them.

 

But do you know what might cause interference in the 5Ghz band?  Can there really be co-channel interference with so many available channels?  What other devices operate in the same frequency band that can cause interference with 5Ghz wifi?

 

 

 

 

 

ericgarnel Thu, 04/17/2014 - 06:41
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Poor design can lead to CCI in 5 GHz.

Keep in mind (depending on regulatory body) some channels are not enabled by default and not recommended for various reasons - DFS, etc.

in the US, FCC area.  8 channels, UNII-1 and UNII-3 are available, as well as UNII-2 and UNII-2e, but 2, and 2e are DFS and are not commonly used.

Thus, you have only 8 channels available.

If you use 40 MHz/Wide Channel/Bonded on 5 GHz, you now have reduced your channel re-use by half.

I see many installs with 5 GHz cranked up too high with 3 dBi or less delta between APs on the same channels.

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