On Wed, Feb 10, 2010 at 11:40 AM, bin zan [email protected] wrote:
Can you help me answer the following questions?
1. Does that mean, the data has not be divided into sync’d
segments until ofdm_sampler.cc?
I’m not sure what “that” is you are talking about (please reply inline
and don’t top post when responding), but I think I get what you are
asking. Yes, the sampler separates the stream into vectors that are
fft_length in size.
2. Why d_timeout_max=1000? Pre-defined preambles only appear
every 1000 FFT length of data?
1000 was just an arbitrary number. We wanted to make sure that it
would stop sampling after a while if no new packets are seen. It just
has to be long enough to make sure the timeout/reset doesn’t happen
during the reception of one full packet.
3. Only data after state_frame will go through FFT process, others
will be dropped (including CP)?
Yes, the sampler removes the CP. It’s purpose is served so it is no
4. According to your powerpoint OFDM implementation in GNU radio,
FFT happens before preamble correlation, which file actually do the preamble
This correlation is done in the ofdm_frame_acq (part of
ofdm_receiver). We use the preamble in the frequency domain to figure
out the subcarrier offset (how many bins away from DC the signal is)
and then create the equalizer from it. The output of this block is
just the occupied tones post equalizer.