Re: [Discuss-gnuradio] preamble and simple framer and correlator

On Fri, Jun 24, 2011 at 2:49 AM, Songsong Gee <gee.songsong@gmail.com> wrote:

Continueing with http://www.ruby-forum.com/topic/1983866, and http://www.ruby-forum.com/topic/1991680

I am trying to append preamble to a signal so that RX can recognize it and see a start position of data exactly.

I roughly draw what I thought.

(http://dl.dropbox.com/u/11382666/for_gnuradio_mailinglist/desired_signal.jpg)

I learned that there is gr_simple_framer and gr_simple_correlator in gnuradio.

I guess that gr_simple_framer appends sync field and other files, and gr_simple_correlator removes additional fields by gr_simple_framer

To verify this guess, I make a flow graph and run it.

(http://dl.dropbox.com/u/11382666/for_gnuradio_mailinglist/framer_correlator_test.png)

As a flow graph runs, file size of framer_sink goes large, but that of correlator_sink remains 0 forever.

I have tried to figure out how I can use these blocks from doxygen (http://gnuradio.org/doc/doxygen/)

But I cannot figure out it easily.

Does anyone know what value should be in Payload Byte Size for framer and correlator

and where I can find some examples of these two blocks?

--
Seokseong Jeon (aka Songsong Gee)

Look at the digital examples in gnuradio-examples/python/digital/benchmark_rx.py. They are a bit complicated to follow when you first look at them, but you'll find a lot of the digital stuff in gnuradio-core/src/python/gnuradio/ and (same path)/blks2impl includeing packet_utils.py, pkt.py, and the modulators/demodulators (dbpsk[2].py, dqpsk[2].py, gmsk.py, etc.). The receiver chain that uses all of these pieces uses a preamble to detect the packet and do the decoding. They should help you understand the blocks you are interested in.

Tom