# OFDM and FEC combined

**URL:** <https://www.ruby-forum.com/t/ofdm-and-fec-combined/242958>\
**Category:** GNU Radio\
**Created:** [August 11, 2015, 3:51am UTC](https://www.ruby-forum.com/t/ofdm-and-fec-combined/242958 "2015-08-11T03:51:05Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Sadaf\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@Sadaf\_N](https://www.ruby-forum.com/u/Sadaf_N)\
**Post date:** [August 11, 2015, 3:51am UTC](https://www.ruby-forum.com/t/ofdm-and-fec-combined/242958/1 "2015-08-11T03:51:05Z")

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I am working with the OFDM and FEC blocks combined in the same  
flowgraph,  
but this configuration led to some issues and I am not being able to  
sort  
this out.

I am using the OFDM Transmitter and Receiver Hier Blocks and FEC Encoder  
and Decoder, but I already used “FEC Extended Decoder/Encoder” with  
convolutional and dummy variables. With the following parameters:

OFDM:

- FFT Length: 64
- CP Lenght: 16
- Packet Length: 96

FEC (Repetition)

- Frame Bits: 2048
- Repetitions: 2
- a prior prob: 500m

I have made individual tests using this configuration and each block  
works  
perfectly fine. But apparently there is a bug with their integration

Then, I created file sinks in the flowgraph for debugging: One just  
after  
the encoder, to show me how the repetition encoder works and if it’s  
working properly; other after the receiver, to look into the packet  
after  
all OFDM process.

The file after reception lost part of the packets, thus, I believe it  
means  
that they are being dropped somewhere between transmission and  
reception.

For example:

If I am transmitting: “A B C\nD E F\nG H I\n”  
I am receiving: “A B C\nG H I\nD E F\nG H I\nA B C\n”, i.e. one packet  
with  
“D E F\n” and other with “A B C\n” were dropped or lost along the way.

After searching for this type of problem, I found something about  
“Header/Payload  
Demuxer”.

Best Regards,

Davi