The gnuradio ofdm receiver

GNU Radio
1

Hi,

1.Any one can tell me in gnuradio OFDM, after ofdm_sync block, what are
the
data looks like?

  1. Does the output go through FFT operation already?
    If not, when does the FFT actually actually come ? Does it after the
    ofdm_sampler block?
    If yes, how can I actually get these data? And, how can I match the data
    to
    the sub-carriers.

Thanks,
Bin

2

On Tue, Feb 9, 2010 at 9:04 PM, bin zan [email protected] wrote:

Hi,

1.Any one can tell me in gnuradio OFDM, after ofdm_sync block, what are the
data looks like?

The output of this block is a “voltage” level used to control and NCO
as well as a timing signal. The NCO control signal is a stream of
floats that is proportional to the frequency offset of the
subcarriers. The timing signal is a stream of characters where a 1
indicates a preamble has been found at this sample position.

  1. Does the output go through FFT operation already?
    If not, when does the FFT actually actually come ? Does it after the
    ofdm_sampler block?
    If yes, how can I actually get these data? And, how can I match the data to
    the sub-carriers.

Thanks,
Bin

Yes, the FFT is done right after the ofdm_sampler.

If you use --log when running the benchmark_ofdm.py script, you will
get a bunch of data files, including ofdm_receiver-fft_out_c.dat,
which is the data you are asking for. You can view it (if you have
scipy and matplotlib installed) with gr_plot_ofdm.py. In the current
git master, though, there’s a small bug in this script because we
changed the names of one of the output files. Just edit the script to
use the right name (look at the error message and it should be
obvious). This will show you a lot of what you are probably looking
for.

Tom

3

Dear Tom,

On 02/10/2010 11:48 AM, Tom R. wrote:

What is the unit of these floats? Is it angle in the range of -\pi…\pi?
In our testbed, we saw values such as 0.8, 0.3, etc.

Thanks
Tianji