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I have a Dell Latitude E6410, which uses an Intel Ultimate N-6300 Wireless card. iwconfig does not show the Noise level of the wireless interface , wlan0. Does anyone know the reason for that?

precise@ubuntu:~/Desktop/Work/transmitter$ iwconfig  
lo no wireless extensions.

mon0 IEEE 802.11abgn Mode:Monitor Tx-Power=15 dBm
Retry long limit:7 RTS thr:off Fragment thr:off Power Management:off

wlan0 IEEE 802.11abgn ESSID:"AirPennNet"
Mode:Managed Frequency:2.412 GHz Access Point: D8:C7:C8:D7:A6:C1
Bit Rate=130 Mb/s Tx-Power=15 dBm
Retry long limit:7 RTS thr:off Fragment thr:off Power Management:on Link Quality=65/70 Signal level=-45 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:800 Invalid misc:540 Missed beacon:0

eth0 no wireless extensions.

I tried to use cat /proc/net/wireless and got these results:

Inter-| sta-| Quality | Discarded packets | Missed | WE face | tus | link level noise | nwid crypt frag retry misc | beacon | 22 wlan0: 0000 64. -46. -256 0 0 0 818 566 0

Is -256 the noise level? How do I interpret this in dBm?

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2 Answers 2

up vote 1 down vote accepted

The reason is that typically the LQI (Link Quality Indicator) and RSSI (Received Signal Strength Indication) are used as relative measurements of the quality and strength.

Look at this line:

Retry long limit:7 RTS thr:off Fragment thr:off Power Management:on Link Quality=65/70 Signal level=-45 dBm

In particular the end of it:

Link Quality=65/70 Signal level=-45 dBm

There is the link quality and signal level, which should give an indication of how well the connection is. The link I gave above details how to interpret them, you'll want to use these instead of the noise.


As for the noise value, you've got that right:

Inter-| sta- | Quality          | Discarded packets          | Missed | WE
 face | tus  | link level noise | nwid crypt frag retry misc | beacon | 22
 wlan0: 0000    64.  -46. -256      0    0     0   818   566    0

Note the -46 which is your signal level (in dBm), the -256 is indeed the noise level (in dBm).

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Was not the question how to read noise value? –  akostadinov Sep 20 '13 at 12:20
    
@akostadinov: Answer updated with more information. –  Tom Wijsman Sep 20 '13 at 13:20
    
@akostadinov: Answer updated with more information. –  Tom Wijsman Sep 20 '13 at 13:20

There is another way: wavemon. It can be found in many distros. A nice curses based wireless information visualization program.

btw the -256 noise level seems to say that no value is returned by driver.

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