Re: [Discuss-gnuradio] question about the receiver sensitivity

[Brian Padalino]

On Tue, Sep 23, 2008 at 7:20 PM, Bill Stevenson
<address@hidden> wrote:
> Matt
>
> Thank you Matt!
>
> What did u mean that RFX boards have a noise figure in 6-10dB range? Could u
> tell me the sensitivity for the USRP receiver boards with respect to
> different data rate, say from 100Kbps to 1Mbps with a step of 100Kbps? One
> thing confusing me is that the receiver sensitivity under different data
> rate specified in 802.11a is measured by lots of testing or it is decided by
> some certain organizations? If it were the later case, I would not care
> about the receiver sensitivity cuz I can also specify it by myself. Does
> anyone know this? Any help will be highly appreciated!
>
> The reason I wanna know the receiver boards' sensitivity is I am trying to
> find out the transmission range with regard to some data rate, say 100Kbps,
> 200Kbps,etc. Is there any other way to work this out without knowing the
> receiver boards' sensitivity? Thanks!!!

First, I recommend reading and trying to understand this page:

    http://sss-mag.com/ebn0.html

Second, take away the fact that the noise floor is determined by the
bandwidth of your system as well as the temperature.  Remember the
number -174 dBm/Hz as this is the noise floor at room temperature.

Now (assuming AWGN), if you had a modulation scheme which could
perform adequately at 0dB SNR with a bandwidth of 1MHz with the noise
figure of the board at 10dB, you can calculate the absolute
sensitivity of your system:

  Sensitivity = -174 dBm + 10*log10(1.0e6) + 10 dB
  Sensitivity = -104 dBm

Given enough gain in the front end, if your signal is below -104dBm,
you won't reach the performance you want.  Otherwise, you should have
enough signal to demodulate properly.

This is just my understanding of things, which could be completely
wrong or over simplified.

Hope this was helpful.

Brian