Thanks Tom, your information completely answered my question. In my case, the subcarriers start from 1, I guess that's why there will be 1 number difference.
Thanks for your time, Bin On Thu, Feb 18, 2010 at 11:11 AM, Tom Rondeau <trondeau1...@gmail.com>wrote: > On Wed, Feb 17, 2010 at 4:48 PM, bin zan <zanbin2...@gmail.com> wrote: > > 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 > > DC offset. There's a large amount of energy that gets built up in the > DC carrier, so we drop it. Otherwise, it completely messes up the > symbol in that bin. Since we often use even numbers of bins, we don't > really have a "DC subcarrier," and to make it easier for the examples, > I just dropped the center two, knowing that at least one of them would > be hit by this effect. In fact, Matt and I in our work last week ended > up dropping the center 4 so that this large amount of energy didn't > bleed into the next subcarrier, too. > > Even though the center two subcarriers are dropped, we still use all > occupied_tones number of carriers, so this is going to take an extra > one on either side. So it should use carriers (15 - 30) and (33 - 48). > Also, the center two subcarriers that are dropped should be 31 and 32 > and I mostly see the DC peak happen in the right-most bin (in this > case, 32). Are your numbers coming from starting the counting of > subcarriers at 0? > > Tom >
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