Re: question about the receiver sensitivity

GNU Radio
1

----- Original Message ----
From: Matt E. [email protected]
To: Bill S. [email protected]
Cc: [email protected]
Sent: Sunday, September 21, 2008 10:26:32 PM
Subject: Re: [Discuss-gnuradio] question about the receiver sensitivity

Bill S. wrote:

Hello, all

I am using USRP1 board with RFX Transceivers and I want to know the
receiver sensitivity of the daugterboards. For example, for BER less
than 1e-5 and data rate 54Mbps, the 802.11a standard specifies the
receiver sensitivity to be at least -65dbm. Once the receiver
sensitivity is known, the transmission range will be determined, so i
want to know the sensitivity for the RFX boards. Could anyone tell me?
Thank you!

Sensitivity is a very hard parameter to define, since it depends on many
factors including the modulation system in use. The best way to spec a
general radio is with the noise figure. The RFX boards all have a noise
figure in the 6-10 dB range. If you need one lower than that you can
use an LNA in front of it.

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!!!

Bill

2

On Tue, Sep 23, 2008 at 7:20 PM, Bill S.
[email protected] wrote:

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