Re: [Discuss-gnuradio] question about gr_ofdm_sampler.cc

[bin zan]

Hi Tom,
          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?
          2. Why d_timeout_max=1000? Pre-defined preambles only  appear every 1000 FFT length of data?      
          3. Only data after state_frame will go through FFT process, others will be dropped (including CP)? 
          4. According to your powerpoint OFDM implementation in GNU radio,  FFT happens before preamble correlation, which file actually do the preamble correlation?


Thanks,
Bin

On Wed, Feb 10, 2010 at 12:36 PM, Tom Rondeau <address@hidden> wrote:

On Wed, Feb 10, 2010 at 8:10 AM, bin zan <address@hidden> wrote:
> Hi,
>       I just wonder why in gr_ofdm_sampler.cc, the  consume_each for
> STATE_NO_SIG and STATE_PREAMBLE are different.
> consume_each(index - d_fft_length + 1);
> consume_each(index-d_fft_length);
>
> Both suppose to  leave one  fft length, right?
> Can any one explain it?
>
> Thanks,
> Bi

It's just like the comments say, in STATE_NO_SIG, we consume 1 less
because we need to leave behind a full fft_length of items to test for
the preamble. When we have the preamble in STATE_PREAMBLE, we consume
everything including that one so that the next input block is the
start of the packets.

FYI: Matt and I are working on the OFDM stuff this week. We're seeing
some issues that we need to work out, so things we thought were right
could be wrong and will hopefully be fixed.

Tom