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[Discuss-gnuradio] OFDM Training Sequence

From: Mateusz
Subject: [Discuss-gnuradio] OFDM Training Sequence
Date: Thu, 17 Mar 2016 12:47:19 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

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.

Mateusz Loch

Attachment: gnuradio sync words.txt
Description: Text document

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