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Re: [Discuss-gnuradio] Packet handling blocks

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Packet handling blocks
Date: Sun, 21 Nov 2010 23:14:39 -0500

On Sun, Nov 21, 2010 at 12:19 PM, Ben Reynwar <address@hidden> wrote:
> I just found simple_framer and simple_correlator which were what I was 
> missing.
> Cheers,
> Ben
> On Fri, Nov 19, 2010 at 10:47 PM, Ben Reynwar <address@hidden> wrote:
>> Hi all,
>> I'm playing with gnuradio and am trying to create a simple example
>> where I take some data, do a virtual transmission, and then check I
>> have the same data at the receiving end.
>> I've got it successfully working with the following string of blocks:
>> vector_source_b, dbpsk_mod, channel_model, dpsk_demod, vector_sink_b
>> It works but I have to do some messing round in python beforehand and
>> afterwards adding on access codes and headers and putting some buffers
>> before and after the packet.  I expect that blocks already exist to do
>> most of this stuff but I haven't managed to find them.
>> I don't have any background in this kind of stuff so I might be going
>> about this in completely the wrong way.  I also don't have a good idea
>> of what exactly gnuradio's scope is and what I should expect it to be
>> able to do.
>> The following is the list of the steps I would like my simple example
>> to do, and what I have or have not been able to find in gnuradio.
>> 1) Start of with some raw data.
>>   There are lots of source blocks to choose from, no problem here.
>> 2) Parcel it into packets.
>>   gr_message_sink? (puts it into a message queue, all in one message)
>> 3) Add access codes and headers to packets.
>>   I couldn't find anything to do this.  Seems surprising.
>> 4) Combine packets into a stream to be transmitted.
>>   Can't find anything.
>> 5) Modulation.
>>   Plenty of options.
>> 6) Transmit stream.
>>   gr_channel_model (because I don't have anything real)
>> 7) Demodulation.
>>   Plenty of options.
>> 8) Receive stream, split out packets and remove access codes and headers.
>>   gr_correlate_access_code_bb/gr_framer_sink_1 (to queue)
>>   OR
>>   gr_packet_sink (to queue)
>> 9) Combine packets to get original raw data.
>>   Can't find anything.
>> If anyone could tell me of any blocks I've overlooked, or how I should be 
>> going
>> about it differently I'd appreciate it.
>> Cheers,
>> Ben

The other place to look is gnuradio-examples/python/digital. The main
program you will probably want to look at is benchmark_loopback.py. If
you have qtgui installed, I recommend, benchmark_qt_loopback2.py,
instead. This will show you how to handle the input/output issues.
It's a bit tricky to find your way through the code, I admit, but if
you can follow it, it should answer most of your questions. (we will
hopefully be able to clean this up at some point.)


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