Re: WiFi AP selection



I completely agree. However, I think most WiFi radios don't report S/N ratios so you have to draw the line somewhere without that data. There maybe a way of interpreting the number of bad packets received as a surrogate.

I Microsoft considers -100dBm to be 'no' signal and Linux -110dBm. There probably is a noise floor that the radio has when it is simply sitting in a laptop at the North Pole (thermal noise, shot noise, Johnson noise, and always 1/f noise -- it is a long while since I studied noise). Not to mention the E coli in the human guts nearby but their little motors probably don't radiate much at 2.4GHz.

On 11/9/19 1:45 PM, Bill Riemers wrote:

I will bite.  How can a signal be too small to be considered a no signal?  You need a certain minimum to receive data over the background noise.  Anything smaller than that you want to consider no signal.


On Sat, Nov 9, 2019 at 3:55 PM Clive McCarthy via networkmanager-list <networkmanager-list gnome org> wrote:
I haven't given up in the hope that NM will make a better WiFi AP selection.

From what you have told me, a "supplicant", requests the NM to open a network connection. The NM manager then selects something from the various WiFi APs or wired connections. From what you have said so far, the NM manager prioritizes potential data bandwidth over signal strength. As a consequence, a 5GHz signal at -100dBm wins out over a -40dBm 2.4GHz signal, despite the fact that the 5GHz signal one millionth the power of the 2.4GHz signal.

So I began to research how much power -100dBm represents. My first thought was to compare the power to an ant. Not a good choice since an ant can put out 50mW, according to some people. A more useful comparison turns out to be a bacterial flagellar motor (E. coli has them, for example). They crank out 10⁻¹² mW which is  -120dBm. So for -100dBm you need 100 E. coli.

So the point of this? -100dBm is way too small to be considered no signal. The edge of an acceptable signal is around the power output 100,000 E. coli.





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Bill C Riemers, PhD, CSM, CSD, SALESFORCE CPD I

Senior Software Engineer

Red Hat Canada Ltd

Enterprise Sales + Services (ESSA)






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