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 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
--sync word1 64-- (from tx_ofdm example), 6x0., 13x(0.,scaled_rand), 6x0.
[0., 0., 0., 0., 0., 0., 0., 1.41421356, 0., -1.41421356, 0., 1.41421356, 0.,
-1.41421356, 0., -1.41421356, 0., -1.41421356, 0., 1.41421356, 0., -1.41421356,
0., 1.41421356, 0., -1.41421356, 0., -1.41421356, 0., -1.41421356, 0.,
-1.41421356,
0., 1.41421356, 0., -1.41421356, 0., 1.41421356, 0., 1.41421356, 0.,
1.41421356, 0., -1.41421356, 0., 1.41421356, 0., 1.41421356, 0., 1.41421356,
0., -1.41421356, 0., 1.41421356, 0., 1.41421356, 0., 1.41421356, 0., 0., 0.,
0., 0., 0.]
--sync word2-- (from tx_ofdm example), 64 6x0, 26x(rand+0j), 1x0, 26xrand, 5x0
[0j, 0j, 0j, 0j, 0j, 0j, (-1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j), (1+0j),
(-1+0j), (-1+0j), (-1+0j), (1+0j), (-1+0j), (1+0j), (1+0j), (1 +0j), (1+0j),
(1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j), (-1+0j), (-1+0j),
(1+0j), (-1+0j), 0j, (1+0j), (-1+0j), (1+0j), (1+0j), (1+0j), (-1+0j), (1+0j),
(1+0j), (1+0j), (-1+0j), (1+0j), (1+0j), (1+0j), (1+0j), (-1+0j), (1+0j),
(-1+0j), (-1+0j), (-1+0j), (1+0j), (-1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j),
(-1+0j), 0j, 0j, 0j, 0j, 0j]
--sync word1 128-- recreated from sync64, 12x0, 26x(0.+scaled_rand), 12x0
[0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.,
0., 1.41421356, 0., 1.41421356, 0., -1.41421356, 0., 1.41421356, 0.,
-1.41421356, 0., -1.41421356, 0., -1.41421356, 0., 1.41421356,
0., -1.41421356, 0., 1.41421356, 0., -1.41421356, 0., -1.41421356, 0.,
-1.41421356, 0., -1.41421356, 0., -1.41421356, 0., 1.41421356,
0., -1.41421356, 0., -1.41421356, 0., -1.41421356, 0., 1.41421356, 0.,
-1.41421356, 0., 1.41421356, 0., -1.41421356, 0., -1.41421356,
0., -1.41421356, 0., -1.41421356, 0., 1.41421356, 0., -1.41421356, 0.,
1.41421356, 0., 1.41421356, 0., 1.41421356, 0., -1.41421356,
0., 1.41421356, 0., 1.41421356, 0., 1.41421356, 0., -1.41421356, 0.,
1.41421356, 0., 1.41421356, 0., 1.41421356, 0., -1.41421356,
0., 1.41421356, 0., 1.41421356, 0., 1.41421356, 0., -1.41421356, 0.,
1.41421356, 0., 1.41421356, 0., 1.41421356, 0., -1.41421356,
0., 1.41421356, 0., 1.41421356, 0., 1.41421356, 0., 1.41421356,
0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.]
--sync word2 128-- recreated from sync64, 12x0, 52x(rand+0j), 1x0, 52xrand, 11x0
[0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j,
(-1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j), (1+0j),
(-1+0j), (-1+0j), (-1+0j), (1+0j), (-1+0j), (-1+0j), (1+0j), (1+0j),
(-1+0j), (-1+0j), (-1+0j), (1+0j), (-1+0j), (1+0j), (1+0j), (1 +0j),
(1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j), (1+0j), (1 +0j),
(1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j),
(-1+0j), (-1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j),
(-1+0j), (-1+0j), (1+0j), (-1+0j), 0j, (1+0j), (-1+0j), (1+0j), (1+0j),
(1+0j), (-1+0j), (1+0j), (1+0j), (1+0j), (-1+0j), (1+0j), (1+0j),
(1+0j), (-1+0j), (1+0j), (1+0j), (1+0j), (-1+0j), (1+0j), (1+0j),
(1+0j), (1+0j), (-1+0j), (1+0j), (1+0j), (-1+0j), (1+0j), (1+0j),
(1+0j), (1+0j), (-1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j),
(-1+0j), (1+0j), (-1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j),
(-1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j), (-1+0j),
0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j, 0j]
--sync word1 256-- recreated from sync64, 24x0, 52x(0., scaled_rand), 24x0
[0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.,
0., 0., 0., 0., 0.,
0., 1.41421356, 0., -1.41421356, 0., -1.41421356, 0., -1.41421356,
0., -1.41421356, 0., -1.41421356, 0., 1.41421356, 0., -1.41421356, 0.,
1.41421356, 0., -1.41421356, 0., -1.41421356, 0., 1.41421356,
0., -1.41421356, 0., 1.41421356, 0., -1.41421356, 0., -1.41421356, 0.,
-1.41421356, 0., 1.41421356, 0., -1.41421356, 0., 1.41421356,
0., -1.41421356, 0., 1.41421356, 0., 1.41421356, 0., -1.41421356, 0.,
-1.41421356, 0., 1.41421356, 0., -1.41421356, 0., 1.41421356,
