[Discuss-gnuradio] OFDM Training Sequence

[Mateusz]

Hey, I do my Bachelor Thesis on OFDM using GnuRadio.

I am using the joint system created from tx_ofdm and rx_ofdm examples. 
In simulation I try to use a bigger fft. So far I have managed to send 
and receive for fft_len=128 and fft_len=256, BPSK modulation. I ask to 
help me understand the creation of sync_words for bigger fft.

I see the influence of the training sequences which I use on the quality 
of transmission. Of course I have read that the synchronization is based 
on "PN Sequence Correlation" and "Maximal Likelihood" papers. I suppose 
that sync_word1 and sync_word2 are based on those algorithms 
respectively. However I don't see "two identical parts of PN sequence" 
like it was described in the Schmidl&Cox paper.

I tried to use the sequences containing 0's where needed, and random 
-1's and 1's elsewhere, but then the timing synchronization error 
(missing trigger signal in sync_sc) occurs more often, than when I use 
the replicas of original sync_words from the OFDM example.

I attach the file with the training sequences which I have used.

Regards,
Mateusz Loch

gnuradio sync words.txt
Description: Text document