Hi Mohamed,
I can not really point you to more reference than your basic (discrete)
signal theory textbook[1].
Basically, when processing sampled signals, time stops mattering, since
samples are but numbers. Thus, "sample" is no unit.
the notion that a digital signal has a frequency is only that it has
periodic properties every N samples --- that doesn't automatically match
to any "real world" frequency in Hz.
Thus, *every single line* of signal processing in GNU radio is based on
this concept, and there is no explicit code related to this.
But for example, take a look at the signal source: Computational, it
does not even *care* what you enter as frequency and sampling rate. It
just computes values, as fast as it can and as often as it's asked.
These samples, on the other hand, contain values with complex values on
the unit circle (|x| == 1). The rate at which the argument of each
sample increases in comparison to the last sample is the qoutient of
sample rate and desired signal frequency,
$\frac{f_\text{signal}}{f_\text{sample}}$. So if you set
$f_\text{signal} = \num{200}$ and $f_\text{sample} = \num{1000}$, you
will get the very same samples as when you set $f_\text{signal} =
\num{2e5}, f_\text{sample} = \num{1e6}$. GNU Radio doesn't care about
these numbers at all. All GNU Radio itself does is shuffle samples
around. Some blocks use frequencies to calculate what should happen for
one sample. Thus, sample is the unit (if you want to call it like that
at all).
This is the basic Software Radio concept most beginners find hard to
understand. When I started dealing with digital signals, it helped me a
lot to really do the sampling in my head --
to try to be always aware of the fact that I'm now working with a series
of numbers with indices rather than with a function of time. I don't
know if this really helps you...
Greetings,
Marcus
[1] GNU Radio's website has a page of recommended readings:
http://gnuradio.org/redmine/projects/gnuradio/wiki/SuggestedReading
Pick a book from the "Digital Signal Processing" list.
On 24.05.2014 21:34, mohamedx wrote:
> Hi Martin,
>
> I'm not sure that (what I've understood) was the opposite of what Martin
> said, but anyway, I really appreciate your answer.
> Could you please tell me where I can find more about this question ? and
> where I can find the source code related to that "sample" unit ? so I can
> see closely how the things were done.
>
> Regards,
> Mohamed
>
>
>
>
> On Sat, May 24, 2014 at 12:44 PM, Marcus Müller-3 [via GnuRadio] <
> ml-node+s4n48473...@n7.nabble.com> wrote:
>
>> Hi Mohamed,
>>
>>> I was sure that is just related to what my machine can process
>> that's the opposite of what Martin said.
>> GNU Radio does not care the slightest about how high your sampling rate
>> is. Some blocks need this information to calculate relative frequence
>> (ie. frequencies related to the unit "sample"), but there is absolutely
>> no restriction that links your theoretical sampling rate to your
>> processing speed. If you start using hardware, then, of course, you'll
>> have to make sure that a) your sampling rate matches your application
>> and your hardware and b) your computer is able to process the samples
>> fast enough to keep everything running in real time.
>>
>> Greetings,
>> Marcus
>>
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