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[renluop]

This comes from the many moans one sees on forums about router performance.

I was thinking could the sensitivity of the target the router is transmitting to have a bearing on some problems folk have, but prefer not to consider?

[burakkucat]

A good question.

Consider a simplex data link. There are three variables to consider when configuring it for the reliable transmission of information. The output power at the transmitting end. The losses incurred whilst in transit via the transmission medium. The sensitivity (grain) at the receiving end. All three are significant.

We know that the transmitter power output is variable. We also know that the quality of the transmission medium varies. I wonder if the receiver gain is variable? 

[JGO]

" The sensitivity (grain) at the receiving end."

I take it that "grain" should be gain ?!
It is a bit more complex than just gain, as the modem generates quantisation noise in it's ADC as well as that produced in its front end amplifier. Also there is a need for a minimum signal level needed to hold sync.
The gain is a compromise between avoiding overload on a strong signal and holding sync on to a weak one. The AR7 chip AIRI wasn't too good on weak signals, but perhaps it needed an adaptive gain control to maximise it's usable signal range and some modem designers didn't bother ? Also, my modem will hang on to sync down to 0dB S/N margin and below; I doubt if the error rate is usable there but loosing sync and taking 30 sec to re-acquire it isn't a good response to a single noise spike so it "works" below the "usable"  S/N.

So in response to the orriginal query yes the modem design can have a lot of influence and it is complex.
 
 for a deeper discussion see :=
http://www.eetimes.com/electronics-news/4138114/Taking-the-Noise-Out-of-ADSL-Modem-Designs

[burakkucat]

" The sensitivity (grain) at the receiving end."

I take it that "grain" should be gain ?!

  b*cat's excuse is that he was thinking about a single malt whiskey at the time and the grain just 'slipped out'. 

As for holding onto sync, my Huawei HG612 can cope at a SNRM of -1.9 dB and only 'lets go' at -2.0 dB.