# Re: \[trellis - ofdm\] **URL:** \ **Category:** GNU Radio\ **Created:** [May 31, 2015, 5:00pm UTC](https://www.ruby-forum.com/t/re-trellis-ofdm/242147 "2015-05-31T17:00:49Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [May 31, 2015, 5:00pm UTC](https://www.ruby-forum.com/t/re-trellis-ofdm/242147/1 "2015-05-31T17:00:49Z")
Hello Rita’s pcf I’m trying to use the trellis encoder with the ofdm mod and the ofdm demod too. Could you please tell me why it can’t be used just by connecting the trellis encoder’s output with the ofdm mod’s input. Did you find a way to do this? Please forgive me for my english – View this message in context: [http://gnuradio.4.n7.nabble.com/trellis-ofdm-tp29324p53950.html](http://gnuradio.4.n7.nabble.com/trellis-ofdm-tp29324p53950.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [May 31, 2015, 5:17pm UTC](https://www.ruby-forum.com/t/re-trellis-ofdm/242147/2 "2015-05-31T17:17:11Z")
Hi DCardona, you should be able to do that – could you explain what _doesn’t work_? Your problem description is too vague to help you. By the way, your English is excellent; don’t worry. but: who is Rita, and what’s her pcf? Best regards, Marcus ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [May 31, 2015, 6:23pm UTC](https://www.ruby-forum.com/t/re-trellis-ofdm/242147/3 "2015-05-31T18:23:46Z")
Hi Marcus Thank you for your quick response. I think it works. I mean, i’m using an Error Rate block to compare the Trellis Enoder’s output and the Viterbi Combos’ output (I’m also doing this with the PCCC Encoder and the PCCC Decoder Combo blocks) and the results is 0 (like it should be). But i’m not sure if i’m missing something because the Viterbi Combo block (and the PCCC Decoder Combo) uses a constellation parameter, doesnt that mean that it decodes and demodulates at the same time? The OFDM Mod block makes a digital modulation, and the OFDM Demod block demodulates it. So, am I demodulating twice? I am new at this and i don’t know if I am wrong. I’m sending you my flowgraph, if you could see it, i would be really gratefull. Thank you very much. Pd: I though Rita’s pcf was a user and I was answering a post. Sorry if I was wrong. Like I said, I’m new at this. FUNCIONA\_\_INTENTOCOMPLETO\_PCC\_OFDMMOD\_OFDMDEMOD\_ErrorRate\_VECTOR.grc [http://gnuradio.4.n7.nabble.com/file/n53953/FUNCIONA\_\_INTENTOCOMPLETO\_PCC\_OFDMMOD\_OFDMDEMOD\_ErrorRate\_VECTOR.grc](http://gnuradio.4.n7.nabble.com/file/n53953/FUNCIONA__INTENTOCOMPLETO_PCC_OFDMMOD_OFDMDEMOD_ErrorRate_VECTOR.grc) – View this message in context: [http://gnuradio.4.n7.nabble.com/trellis-ofdm-tp29324p53953.html](http://gnuradio.4.n7.nabble.com/trellis-ofdm-tp29324p53953.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).