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[Discuss-gnuradio] trellis encoder and OFDM modulator

From: Veljko Pejovic
Subject: [Discuss-gnuradio] trellis encoder and OFDM modulator
Date: Fri, 5 Mar 2010 20:04:24 -0800


I tried to use trellis_encoder from trellis package to perform
convolution coding before sending the message to the OFDM modulator.
However, ofdm_mod has zero input signature, and relies on send_pkt()
which calls ofdm_packet_utils.make_packet() and then puts the message
in the queue at gr.ofdm_mapper_bcv. Since the chain basically starts
with ofdm_mod I don't see the way to connect the trellis_encoder
before the signal is already modulated. In ftw80211 project they
modify ofdm_packet_utils and write their own convolution coding
method, I could do the same, but then I would miss all the benefits of
this nice trellis package.

Interestingly, the other modulation blocks such as dbpsk or d8psk have
different input signatures, and I would put the trellis_encoder
between the gr.message_source and modulator in pkt.py. Is there a way
to seamlessly introduce trellis_encoder in the flow graph with an OFDM
modulator? Am I missing something here?



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