I can't say for sure, but the numbers appear to be in dBm. If you tune to an idle channel (or connect a dummy load) and decrease bandwidth to a half, the noise level drops by 3 dB.
The number that really matters is the E<sub>b</sub>N<sub>0</sub>, the ratio of the energy per data bit to the noise spectral density. This is the same as the SNR only when the modulation is one bit per second per hertz. 802.11 has a huge list of modulation methods to choose from, some more and some less than 1 bps/Hz, and it usually picks one based on the current quality of the link. So you can't always tell how reliable your link is from just the SNR, but along with the bandwidth it will usually tell you the data rate you're likely to get.
Here the perl module that has that info: http://bloodhound.aredn.org/products/AREDN/browser/aredn_ar71xx/files/ww...
Look at the get_wifi_signal function. It is using the iwinfo command from openWRT: http://wiki.openwrt.org/doc/howto/wireless.utilities
The signal and noise information comes from this low-level information provided by the driver. Ratio is the difference between signal and noise.
Thanks, Michael - I'll play with that when I get home tonight.
Orv
I can't say for sure, but the numbers appear to be in dBm. If you tune to an idle channel (or connect a dummy load) and decrease bandwidth to a half, the noise level drops by 3 dB.
The number that really matters is the E<sub>b</sub>N<sub>0</sub>, the ratio of the energy per data bit to the noise spectral density. This is the same as the SNR only when the modulation is one bit per second per hertz. 802.11 has a huge list of modulation methods to choose from, some more and some less than 1 bps/Hz, and it usually picks one based on the current quality of the link. So you can't always tell how reliable your link is from just the SNR, but along with the bandwidth it will usually tell you the data rate you're likely to get.