Re: [Discuss-gnuradio] OFDM GRC block attempt

[Josh Blum]

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
>
>
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