Re: [Discuss-gnuradio] appending preamble with different power

[Nick Foster]

On Fri, 2011-06-24 at 01:17 +0900, Songsong Gee wrote:
> Continueing with http://www.ruby-forum.com/topic/1983866,
> 
> 
> I have planned to append a preamble before an actual signal and turn
> RX on earlier than TX.
> 
> 
> Then RX will receive a signal like below:
>         |---RX turn on------|---TX turn
>         on-----------------------------
>         (---trash signal---)(---preamble---)(---actual signal---)
>         
>         
> And this signal is demodulated and stored into a sink file.
> After that, I run a program that extracts an actual data only and
> compare it to the original.
> 
> 
> My concern is that this preamble should be assumed to be perfect i.e.
> no errors
> Of course, there isn't no error. However if I set an amplitude to
> maximum value, it can be said to be no error.

I don't understand what you mean here. You can find an "imperfect"
preamble sequence using a correlator.

> I have a pre-defined preamble sequence with length n (n = around
> 100-200, can be changed)
> 
> 
> Thus, I am trying to change amplitude of modulated signal for preamble
> and actual signal
> But I have problem with some quadrature modulation. Flow graphs are in
> below:
>         http://dl.dropbox.com/u/11382666/for_gnuradio_mailinglist/M-DPSK.png
>         http://dl.dropbox.com/u/11382666/for_gnuradio_mailinglist/M-FSK.png
>         
>         
> My question is that, how many samples after DPSK mod or frequency mod
> block corresponds to each sample from file source?

It's right there in the block, where it says "samples/symbol".

> I have to solve this problem in order to figure out how many samples
> are generated from preamble with length n.
> If I know that information, I can set a duration for Multiply const
> block having large value for preamble and normal value for actual
> signal

Why would you set the amplitude of the preamble differently than the
actual data?

--n

> 
> 
> And second question is that, although I know that information, I don't
> know how I can control value.
> For example, preamble with length 200, then I want to set large value
> for duration 200 * x (number of samples generated after DPSK,
> Frequency mod), and after that I want to set normal value for
> remaining duration.
> 
> 
> Is it too complex for gnuradio-companion flow graph to make? And is
> python hard coding possible?
> 
> 
> -- 
> Seokseong Jeon (aka Songsong Gee)
> 
> 
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