Re: [Discuss-gnuradio] OFDM GRC block attempt

[Josh Blum]

Its not quite that. I should explain. The packet modulator block in blks 
is weird for another reason, it takes another gnuradio block (a 
modulator) as an argument in the constructor. The problem being that 
this does not fit into GRC too well.

My "old" solution was to feed the constructor a dummy block (just to 
forward data). And then, to connect the actual modulator block to the 
output of the packet modulator. Something like: gr data stream -> 
message sink -> packet modulator w/ dummy (byte out) -> dpsk_mod 
(complex out) -> data sink

However, the "new" blks2 packet modulator has an io signature that 
requires a byte input and a complex output. The io signature will not 
allow a dummy block (one that just forwards data) because the data types 
will not match. I think it is best to just make my own packet modulator 
block that uses the code from the blks2.

This implementation of the packet modulator will take a data stream (of 
any type), read data from a message sink, packetize, write data to a 
message source. Then, a modulator (like dpsk) could be connected to the 
output of this packet modulator using top_block.connect.

...Similar story for the packet demodulator.

Maybe it would be useful to have a packet modulator/demodulator that 
fits into the typical gnuradio block model? Also, I was under the 
impression that the mblocks will eventually implement this kind of 
functionality (packets, error encoding, recovery..).

Thoughts?

-Josh

address@hidden wrote:
> The conversion of all the example code and blks code on the trunk to the new 
> 3.1 flow graph code is nearly complete.
>
> This is being done in the jcorgan/t162 developer branch if you want to take a 
> look.
>
> Once this is merged into the trunk, you'll be able to restore GRC functionality.
>
> Sent via BlackBerry by AT&T
>
> -----Original Message-----
> From: Josh Blum <address@hidden>
>
> Date: Fri, 14 Sep 2007 20:34:40 
> To:Dev Ramudit <address@hidden>
> Cc:address@hidden
> Subject: Re: [Discuss-gnuradio] OFDM GRC block attempt
>
>
> In short, the GRC code for the packet modulator was no good after the 
> "incompatible trunk check in". So, I just deleted the packet mod/demod 
> code in GRC.
>
> To restore the functionality of the packet mod/demod (in grc), i would 
> have to cannibalize the current blks.pkt code. I will be glad to do 
> this, especially if someone is using the blocks.
>
> The only thing about the packet mod/demod blocks is that they are 
> implemented poorly. For example, to implement a packet modulation block, 
> you have to sample the gnuradio stream with a message sink and a thread, 
> the error coding/packetizing is done in python with packet utils, and 
> then the data is pushed back into the gnuradio stream with a message 
> source. Not too efficient. Any suggestions before I go ahead with the 
> message source/sink idea?
>
> Anyway, it would be great to get ofdm working with GRC.
>
> -Josh
>
>
>
> Dev Ramudit wrote:
> > Hello all,
> >
> >         I'm trying to write an OFDM mod/demod for the gnuradio companion and
> > I'm running into a problem. I'm following the (now deprecated?) packet
> > modulator code that was in GRC very closely. I have an OFDMDemod block
> > which creates the following class when its used:
> >
> > ---
> >
> > class OFDMDemodHelper(gr.hier_block2):
> >         """Forward data from ofdm demod to the gr data stream."""
> >         def __init__(self, item_size, options):
> >                 #create hier block
> >                 gr.hier_block2.__init__(
> >                         self, 'ofdm_demod',
> >                         gr.io_signature(1, 1, Complex().get_num_bytes()),
> >                         gr.io_signature(1, 1, item_size)
> >                 )
> >                 #the message source (handles the output data stream)
> >                 msg_source = gr.message_source(item_size, DEFAULT_QUEUE_LIMIT)
> >                 msgq = msg_source.msgq()
> >                 def callback(ok, payload):
> >                         if ok: msgq.insert_tail(gr.message_from_string(payload, 
> > 0, item_size,
> > len(payload)/item_size))
> >                 ofdm_demod = blks.ofdm_demod(
> >                         fg=self,
> >                         options=options,
> >                         callback=callback,
> >                 )
> >                 #connections
> >                 self.connect(msg_source, self)
> >                 self.connect(self, ofdm_demod.head)
> >
> > ---
> >
> > This is basically the same as the old packet demod code, with a few
> > small changes for OFDM. Unfortunately, I get the following error:
> >
> > ---
> >
> >  File "/home/dramudit/work/gnuradio/grc/src/SignalBlockDefs/Packet.py",
> > line 337, in __init__
> >     callback=callback,
> >   File
> > "/usr/local/lib/python2.4/site-packages/gnuradio/blksimpl/ofdm.py", line
> > 218, in __init__
> >     options.log)
> >   File
> > "/usr/local/lib/python2.4/site-packages/gnuradio/blksimpl/ofdm_receiver.py",
> > line 56, in __init__
> >     self.fg.connect(self.chan_filt, self.ofdm_sync)
> >   File
> > "/usr/local/lib/python2.4/site-packages/gnuradio/gr/hier_block2.py",
> > line 46, in connect
> >     self._connect(points[i-1], points[i])
> >   File
> > "/usr/local/lib/python2.4/site-packages/gnuradio/gr/hier_block2.py",
> > line 50, in _connect
> >     (dst_block, dst_port) = self._coerce_endpoint(dst)
> >   File
> > "/usr/local/lib/python2.4/site-packages/gnuradio/gr/hier_block2.py",
> > line 61, in _coerce_endpoint
> >     raise ValueError("unable to coerce endpoint")
> > ValueError: unable to coerce endpoint
> >
> > ---
> >
> > Any suggestions as far as fixing this error, or another approach?
> >
> > Thanks,
> > Dev
> >
> >
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>
>
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