Preamble and simple framer and correlator

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.
[image: desired_signal.jpg]
(
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.
[image: framer_correlator_test.png]
(
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?

On Fri, Jun 24, 2011 at 2:49 AM, Songsong G.
[email protected]wrote:


Seokseong Jeon (aka Songsong G.)

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