# Is there any dependency between SNR and Link Speed for WiFi AP?

Today we use RSSI as indicator of AP quality. However even if you have rssi=-45dm it's not enough to say that AP WiFi guarantees you good BW. Because if many clients connected to the same AP and some of them have the same channel the RSSI still will be good but actually we get low BW (throughput).

For that reason I try to fetch SNR or Noise from AP. The problem is - for mobiles like Android and iOS we can't get nor SNR neither Noise. I have only RSSI and AP Link speed.

For that reason I try to find any correlation between SNR and Link Speed.

Any suggestions, documents?

Generally for radio receivers there is the following "rule of thumb" formula that describes the minimum received antenna power needed to operate at a low bit error rate: -

Receive power (dBm) = -154 dBm + 10log$_{10}$(data rate)

So if you have a 1Mbps data stream, you need to ensure the received signal is: -

-154 dBm + 60 dBm = -94 dBm.

I call it a rule of thumb because there is so much variability in radio but the actual formula is derived mathematically and I can recommend the document I use: -

"Essentials of radio wave propagation" by Christopher Haslett. I got mine by googling but it is getting difficult to find this way (without paying money of course)

OK try here and look on page 14: -

• It's very interesting, I'm going to read it. Sounds like it's what I'm looking for. – Maxim Shoustin Jun 26 '14 at 15:09