iwconfig does not show Noise Level for wireless

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?

Solution 1:

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).