Re: [Discuss-gnuradio] "Give me a ping, Vasili. One ping only, please."

[Fons Adriaensen]

On Fri, Aug 10, 2018 at 02:57:34PM +0200, Markus Heller wrote:

> I wonder how I could generate one single shortest possible pulse on my
> USRP2 with GNURadio. 
> 
> Normally all the blocks would always generate an entire sequence, a
> continuous signal. 
> 
> I want to generate (and analyze) the shortest possible signal. 
> 
> Any ideas?

Seems you need the impulse response (IR) of whatever system
or channel you want to measure.

I'm by no means a GNURadio expert, but the same problem arises
in other domains, e.g. audio, and that I know well.

The shortest signal you can generate is just a single sample.
Whatever comes back is (by definition) the impulse response.

Problem with this is that your signal has very low energy,
and in a noisy channel you may not get back anything useful.

There are several solutions to this. All of them mean you use
some longer signal which will have more energy and hence a
better S/N ratio, and on reception apply a filter that in
the ideal case (a perfect channel) would reduce that signal
to a single impulse. 

Possible signals that can be used are pseudo-random binary
sequences and sweeps. The latter are known in radar/sonar
as 'chirp' signals. How to do this GNURadio I don't know,
but these are the sort of signals you'll need.

Ciao,

-- 
FA