# Noise Floor in Wifi

I notify that my AP records a noise floor data in wifi, which state -82 dBm. What does it tell and is the value acceptable or not ?

Tks
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Commented:
If your quoting Signal to Noise Ratio then -86 dBm must be subtracted from the signal strength to give a positive value.
The higher the positive value the better the Signal to Noise Ratio

If your quoting Noise Level then -86 dBm is very low (The closer the value to 0, the greater the noise level)

http://www.watchguard.com/help/docs/wsm/xtm_11/en-US/index.html#cshid=en-US/wireless/ap_wireless_signalstrength_c.html

Also see:
http://help.netspotapp.com/what-is-the-signal-to-noise/
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Author Commented:
do, how can I check snd reduce the noise issue
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Commented:
A noise floor of -82dBm indicates interference of some sort.  Can the AP see other APs on overlapping channels?
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How do you know you have noise?  Noise does not manifest itself in Wi-Fi except through packet retransmissions. You signal strength is very low. That is probably your problem.
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Commented:
@John - noise is identified in many ways in Wifi.  If the noise floor is at -82dBm that means there is something the AP is seeing.  You can use the SNR value to determine whether you have noise, too.
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Let me say this another way. If your signal is adequate (greater than about -30dBm or so) noise is normally not an issue. Never has been for me in over a decade.
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Commented:
Well, a signal of -30dBm would usually indicate that you're sat right on the AP.  A usual signal will yield a signal of no more than around -45dBm given the fact that APs are (in 90% of installations) mounted at least 10ft from the client.

In any case, you could have a signal of -45dBm (for argument's sake) and it be mostly noise.  What's generally important is the SNR (signal-to-noise ratio).  If that's less than 20dB you should expect issues.

You could have a signal of -70dBm with a SNR of 35dB and the link be perfect, whereas if you had a -45dBm signal with SNR 2 that would be unusable.
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Author Commented:
Get some confusion...

"If your quoting Noise Level then -86 dBm is very low (The closer the value to 0, the greater the noise level)"

For this value, does it has a low or high interference ?  suppose the RSSI is -75db. What can I make use of this two set of data ?

Below is an extraction from H3C description :
"The Noise Floor item in the table indicates various random electromagnetic waves during the wireless
communication. For the environment with a high noise floor, you can improve the signal-to-noise ration
(SNR) by increasing the transmit power or reducing the noise floor."

Tks again.
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Commented:
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Commented:
Really??

You need to understand the difference between RSSI (signal strength), SNR (signal-to-noise ratio) and the noise floor...

RSSI is measured in dBm and is always a negative value.

The noise floor is also measured in dBm and is always a negative value.

SNR is a positive value and is the RSSI minus the noise floor.  It isn't actually a ratio, but rather a calculation of the RSSI minus the noise floor.  Technically the SNR could be a negative value, but the client would disconnect and never establish a link, so it's unlikely you'll ever see that in a WLAN system.

Let's say your client has a signal of -65dBm and a SNR of 30dB.  That means you would have a noise floor of -95dBm.  That's good.

If you had a signal of -60dBm and a noise floor of -70dBm that would be bad.  Your SNR would be 10dB and would probably give you a poor link.

When you describe the noise floor you also need to tell us what the signal reading (or RSSI) is.  That will help us to tell you whether it's likely to be a good link or not.

Now, when I say you must have some interference as your noise floor is -86dBm, that is because the AP is saying that.  It's not reporting the client stats, so it's just what's in the air but isn't part of the WLAN.  If you connect a client and the report is -86dBm that could be good and it could be bad.  If the client's RSSI was -82dBm the SNR would be 4dB.  That would give a virtually pointless link, whereas a client whose RSSI is -48dBm would yield a SNR of 38dB, so that would be a great link.
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Author Commented:
Tks
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