Using benchmark_ofdm.py & gr_plot_ofdm.py

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1

Hi,

I was taking a look at the ofdm files by using first the benchmark
with log enabled and then the plot.

First I copied ofdm_frame_sink_c.dat to ofdm_frame_acq_c.dat because
this last file was missing.

I would like to have some comments about the resulting plot I had :
http://www.skelton.eu.org/Image%201.png

What I mainly don’t understand is why the red and the blue parts are
not the same. According to the python file, it should be the same as
acq_data and derot_data seem to be processed in parallel with the same
set of functions and are actually from the same data file.

Secondly, I would like to know exactly what is the meaning of the
Symbol number on top of the picture. In my mind, a symbol should be
one element from the constellation.

Then, why is the time scale going to at least 200s as I only ran the
simulation for a few secondes ?

Finally, how can I generate correctly the ofdm_frame_acq_c.dat file ?

Thanks,
Jérémy

2

What I mainly don’t understand is why the red and the blue parts are
not the same. According to the python file, it should be the same as
acq_data and derot_data seem to be processed in parallel with the
same set of functions and are actually from the same data file.

OK, for this part I realized that the blue part of Constellation and
Equalized Angle graphs is a former processing I made with bpsk that I
copied to ofdm_frame_acq_c.dat thought that everything else comes from
the next processing with qpsk.

Any idea for the other questions ?

3

On Wed, Feb 04, 2009 at 07:26:33PM +0100, Jérémy Skelton wrote:

Hi,

I would like to have some comments about the resulting plot I had :
http://www.skelton.eu.org/Image%201.png

Secondly, I would like to know exactly what is the meaning of the Symbol
number on top of the picture. In my mind, a symbol should be one element
from the constellation.

That would be the case something like QAM, but with OFDM, there’s a
constellation point for each bin of the FFT. The symbols are quite
long.

Then, why is the time scale going to at least 200s as I only ran the
simulation for a few secondes ?

Not sure. Have you looked at the code to see what it’s actually
plotting?

Eric