Saturday, January 14, 2017

OFDM Preamble Ripple Structure in Frequency Domain



After performing a time and frequency tuning of a signal, and plotting the result in frequency domain(abs value), the following ripple structure can be witnessed.


enter image description here


The extracted bits are LFSR sequence(row wise bellow).


0 0 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 0 1 1 1 0 1 0 0 0 1 1 0 1 0 1 1 1 0 0 1 0 1 1 1 0 1 0 1 1 0 1 1 1 1 1 0 1 1 1 1 0 1 0 1 0 1 1 1 1 1 1 0 1 1 1 0 1 0 1 0 1 0 0 0 0 0 1 0 0 0 1 0 0 1 1 0 0 0 1 1 0 1 1 0 1 0 0 1 1 1 1 0 1 0 0 0 1 1 1 1 1 1 0 1 1 0 0 0 0 0 0 0 0 1 0 1 1 0 0 1 1 0 0 1 0 0 0 0 1 1 1 1 0 0 0 1 1 0 0 0 0 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 1 0 0 0 0 1 1 1 0 1 0 1 1 0 0 1 0 1 0 0 0 1 0 1 1 0 1 1 1 0 0 1 0 0 0 0 1 0 1 0 0 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 0 1 1 0 0 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 1 0 0 1 1 1 1 0 0 0 0 0 1 1 1 1 1 1 0 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 1 0 1 1 1 0 0 0 1 0 1 0 0 0 0 0 1 1 0 1 1 1 0 0 1 1 0 1 0 0 0 0 0 1 1 1 1 0 1 1 0 0 1 1 1 1 1 1 0 1 0 0 1 0 1 0 1 0 1 1 1 0 0 0 1 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 0 0 1 1 1 1 1 0 0 0 1 1 0 1 0 1 0 1 1 0 0 0 0 1 0 0 0 1 0 1 1 0 0 1 0 0 1 1 1 0 1 0 0 1 0 0 1 0 1 0 0 0 1



BPSK modulation is used. Total number of SCs used in Preamble - 432.


enter image description here


Seems that this structure is intended by design. Wondered what may be the reason for such preamble design.


Thanks in Advance.




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