# SNR vs Signal Strength for digital throughput

I'm trying to compare two antennas, A and B for WiFi.

A is showing: Signal Strength of -77dBm, but SNR of 9dB.

B is showing: Signal Strength of -85dBm, but SNR of 24dB.

My understanding is as follows - but I'm no expert on the matter: Better signal means I'll be able to receive data further away from the source, but better SNR means that signal will have a higher throughput (because less packets are being corrupted).

Does this make sense? And is there some equation to use both of these measures to form a single comparable number for digital throughput?

## 2 Answers

"Signal Strength": I believe you are referring to the RSSI value, which is the Received Signal Strength Indicator this value is typically shown as a negative dBm value. RSSI is the measurement of power in an RF signal, the more power in an RF signal the better the connection quality is. It’s typically best practice to have the SNR value 20 to 25 dB’s away from the RSSI value. Please see the figure below, where it's also taken into account the Noise Level (-50 - (-96) = +46):

After a bunch of searching, the value I'm looking for is apparently called the SINR (Signal-to-interference-plus-noise ratio) - http://en.wikipedia.org/wiki/SINR

• This doesn't answer the 'does this make sense' question. – RJR Aug 12 '14 at 3:17
• Not sure why not. I'm trying to find a way to evaluate a connection on a single metric, and RSSI/SNR didn't seem to provide a single axis I could evaluate along. It turns out that the appropriate metric is the SINR. – Jono Aug 24 '14 at 19:51
• Sorry, that I meant was that although the link you provided might make sense, but you don't explain why it answers your question. Do you mean that in order to compare antennas for both noise and power, you have to compare the SINR values (assuming those are given)? I'd think that noise power isn't an antenna characteristic at all. – RJR Aug 25 '14 at 1:19
• Since WiFi uses OFDM or Spread Spectrum modulation, other WiFi sources nearby will only appear as broadband noise, not as a clearly recognizable interferer. For this reason, the SINR measured by your WiFi receiver is likely to be almost exactly the same as the SNR, and doesn't tell you any additional information. Then consider that the signal strength isn't particularly important, so long as the received SNR is good. Also consider what the other terminal thinks of your return transmissions, i.e. the SNR at the other end of the link. – Mark Ch Nov 30 '15 at 8:05