[Discuss-gnuradio] question about ofdm subcarrier-mapping

[bin zan]

Hi,
    For a fft-length 64, occupied-tones 32 ofdm mapping will actually use subcarrier (16-30) and (33-47) according to the code. However, when I plot the results from ofdm_receiver-fft_out_c.dat, I find it will have a peak at subcarrier 33 always, and the occupied tone seems start from 16 and end at 49. Can any one give me some explanation on that? 

Thank you,
Bin