Re: [Discuss-gnuradio] trellis encoder and OFDM modulator

[Friederike Maier]

Hi

I was also looking around the OFDM Modulation recently. Found this nice
project here: http://people.csail.mit.edu/szym/rawofdm/README.html
where ofdm mod and channel est are done separately. I didn't had the
time to follow ths more...perhaps it helps.

best, friederike

On 01/20/2012 02:38 PM, vanITA1082 wrote:
> 
> Did you solve it?
> 
> I am trying to add FEC in the OFDM chain but I didn't figure out how to do
> this, yet.
> 
> Any advice or do you know if someone did it and the code is public?
> 
> Thanks
> 
> Veljko Pejovic wrote:
>>
>> Hi,
>>
>> 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?
>>
>>
>> Thanks,
>>
>>
>> Veljko
>>
>>
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>