Re: [Discuss-gnuradio] ASK Modulation

[Brian Padalino]

2009/3/17 William Harding <address@hidden>:
> I am trying to write an ASK Modulation block to transmit streams of 0's and
> 1's.  In order to match the "symbol timing" of the protocol that I am trying
> to implement, would I keep an instance variable in the block that, in
> effect, keeps track of how many samples have been processed by the block so
> far?  In other words, using the known sampling frequency and how many
> samples have been processed in the block so far, to know whether to go to
> the next bit to be sent or not.
>
> Also, what is the best way to define what bit sequence I would like to
> send?  Would it be file_source?
>
> Any other better ways that this can be done?  I am brand-new to gnuradio,
> but I have gone through most of the GnuRadio tutorial and the "How to write
> a block" tutorial.

I have never written a block for GNU Radio before, but I think you're
missing a fundamental concept here.

For the transmitter, you are given N bits and generate M*N output
samples of the appropriate amplitude.

Why do you feel there is a need to keep track of "symbol timing" in
the transmit path?

On the RX side, you should take a look at the source code.  There are
plenty of blocks which have instance variables associated with them
that can keep track of how many samples you've processed as well as
looking back in your history in case you need more information.  Try
here:

    
http://www.gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/lib/general

Easy examples are the linear feedback shift registers, and there are
plenty of more complicated examples in the same directory.

I hope this has been helpful to you.

Good luck.

Brian