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Frequent Contributor I
Posts: 71
Registered: ‎10-08-2011

Noise Floor - "non-802.11" noise?

A previous poster has prompted me to ask:-

 

When Aruba kit reports a high noise floor, say -80dBm, it's talking about non-wi-fi radiation...BUT, does it class other Wi-Fi traffic which it cannot translate (because of to high rate encoding) as noise?

 

Consider:-

 

3 AP's sitting on channel 1 (say).

AP 1 transmits a signal encoded at MCS 31.

AP 2 is a few meters away and hears this as Wi-Fi, and decodes it

AP 3 is significantly further away and hears it at a signal strength of (say) -80dBm , and cannot translate it.

 

Would this AP report this as a noise floor of -80dBm?

 

TIA.

Contributor II
Posts: 40
Registered: ‎01-21-2011

Re: Noise Floor - "non-802.11" noise?

AFAIK the answer is no, because each 802.11 frame starts with preable which is transmitted over slowest speed so everyone could understand.

However I've heard that doesn't apply for historic 802.11 (not to be mistaken with 802.11 b/g) which would than appear as noise floor, but it is up to Aruba TAC to confirm.

 

What is background of your question?
I have a customer issue in with warehouse deployment with this symptoms:

-AP's periodically report noise floors 65-70dB , a while later -90dB

-it goes in cycles circa 20sec high noise floor, 40 sec normal noise floor and that repeats forever

-onsite inspection didn't find any obvious interference source

-support case with spectrum analysis didn't identify any interfence source

Frequent Contributor I
Posts: 71
Registered: ‎10-08-2011

Re: Noise Floor - "non-802.11" noise?


v.dvorak wrote:

AFAIK the answer is no, because each 802.11 frame starts with preable which is transmitted over slowest speed so everyone could understand.

However I've heard that doesn't apply for historic 802.11 (not to be mistaken with 802.11 b/g) which would than appear as noise floor, but it is up to Aruba TAC to confirm.

 

 


Interesting, I've managed to go a good few years working with Wi-Fi without actually processing this point!

 

(Having just looked it up in the CWAP book i'm going to have to rebuild my mental picture of how 802.11 works a bit...eg In principle, the preamble from our really fast transmissions @ MCS 31 (HT-mixed) will still be visible a long way away ...how will this effect other devices on the same channel)

 

So, yeah, the AP's should not be reporting these transmissions as noise. Which really does make me wonder what they are reporting. Go-Go gadget spectrum-analyser.

 

 

 

 

 

 

 

Frequent Contributor I
Posts: 71
Registered: ‎10-08-2011

Re: Noise Floor - "non-802.11" noise?

Regarding background, just a general query to clarify how this stuff works. Mainly for the purpose of quality control and site survey in high density deployments. 

 

If nothing was picked up by a spectrum analyser on the channel I'd suggest a software bug might be causing the perceved high noise floor. I'd have thought a regular pulse as you've suggested should show up quite clearly.

New Contributor
Posts: 4
Registered: ‎12-06-2012

Re: Noise Floor - "non-802.11" noise?

Any revelations here? Did you find some interfering hardware? Firmware bug?

 

I've got a very similar issue with one IAP-93. There are 11 others on site and none of them report any noise. The problematic one, though, shows regular "spikes" in noise. It will peak around -44dBm, then go back down to about -85dBm. Average is -65dBm. This happens even during the middle of the night, when nobody is on the network.

 

I have searched the room and nearby rooms for interfering devices, but found nothing obvious.

Contributor II
Posts: 40
Registered: ‎01-21-2011

Re: Noise Floor - "non-802.11" noise?

I found this last week in 6.2 realease note:

Bug 58361

Symptom: The noise floor reported right after an 802.11n AP reset was much higher than normal
noise floor values, which sometimes resulted in client connectivity issues. This issue has been
resolved.
Scenario: This issue occurred when ARM scanning was enabled

 

This doesn't sound directly like my or your problem, but maybye it's worth retesting. Unfortunately I can't retest this in my case.

MVP
Posts: 1,110
Registered: ‎10-11-2011

Re: Noise Floor - "non-802.11" noise?

I've struggled with this as well.  My issue ended up being that I disabled 40MHz channels for 802.11n in the WLAN HT SSID profile, however I did not disable 40MHz channels in the ARM profile.  After setting the ARM profile correctly the noise floor raised by about -5 dB for many of the APs.

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