looking for general ideal signal strength goals

[Genaro]

Hey guys,
Could someone point me to somewhere where I can get info on "ideal signal strength"? Basically, I am going to be running a small site survey shortly and I am trying to get an idea as to the numbers I need to achieve for the various activities that will be done by the users.

An example of what I would be looking for: I had read in a cisco press book that to run VoWiFi I would need -67dBm or better with an SNR no worse than 20 - 25dBm.

Is there a page or thread where I might find info like this for acivities such as basic surfing, streaming audio, video, etc?

thanks!!

 

[stevech]

It's not so much signal strength as air link bit rate achieved, esp. on the to-router link direction.

The bit rate on the air link is chosen dynamically, and you see reported a snapshot or average.

The hardware vendors of worth publish their receiver sensitivity versus bit rate, e.g, xxx dBm = 54Mbps in 802.11g, and so on.

Reality is that there is competition for air time among nearby WiFi systems within 3 channels of one another, so it depends on how busy other SSIDs are at any day and time.

In terms of simple received signal strength, with line of sight, you should see something on the order of
10 ft: -30 to -40dBm = highest bit rate for 11g or 11n 20MHz, double if using 11n 40MHz mode (yuck)
50 ft: -40 to -60dBm a speed or two down from the ideal
etc
-90 too weak

Allow 10 dB excess for fading

One double-drywall layer wall costs about 4dB. Much more for masonry or thick wood floors.


VoIP on WiFi is not about signal strength- the data rate is low. It's about latency - from competition for air time and routing to the VoIP server.

 

[Genaro]

thank you for the reply. I had been planning on setting the AP in location A and then finding a few other locations to set down my metageeks RF sniffer (5 or so mins at each) for strength testing and RF interference. I have taken into account the radio output (in dBm) of both the AP and one of the clients in the "fleet" - as well as the deviation (or difference) between their outputs. I have been hoping the dBm ratings would work well. I seem to be having difficulty finding dBm > Mbps ratings on the devises though. Ultimately, I am just trying to correlate a particular dBm reading with an acceptable maximum throughput capability.

I'll keep messing around with this stuff.

cheers.

 

[thiggins]

I seem to be having difficulty finding dBm > Mbps ratings on the devises though. Ultimately, I am just trying to correlate a particular dBm reading with an acceptable maximum throughput capability.

No offense intended, but you are on a fool's errand. dBm ratings are not consistent from device to device and in many cases not calibrated to an absolute level. And even if they were, differences in radios, antennas, firmware and operating systems make your attempted correlation very difficult, if not impossible.