Re: anyone successful in running tx_ofdm and rx_ofdm grc files?

Martin,

I think my question would have been clearer if i had said that when I
talk of symbol rate I do not define a symbol to be the OFDM symbol of
length
fft_length+CP_length, but its fft_length+CP_length components.

So for me symbol rate is

symbol_rate = (fft_length+CP_length) x OFDM_symbol_rate

The grc examples are defining this as the sample_rate, which
implies that they use one sample for each symbol (my definition).

In any case, from your answer I understand that the S&C operates on
ONE sample per symbol (my definition).


I still have trouble getting anything out of the S&C synchronizer:
The frequency offset output responds as expected when i introduce a
freq error but the “detect” output does not give anything out
even with noiseless input…

I have uploaded the follwoing grc files

http://web.eecs.umich.edu/~anastas/gnuradio/tx_ofdm2.grc
http://web.eecs.umich.edu/~anastas/gnuradio/rx_ofdm2.grc

which, illustrate my point. Any thoughts?

thanks for the help,
Achilleas

On Sun, May 19, 2013 at 11:45:42PM -0400, Achilleas A.
wrote:

I am having trouble setting some parameters and getting anything out of it…

In particular

in ofdm_rx

  1. is the processing done on an 1 sample per symbol basis at the Scmidl&Cox ?

I don’t understand the question. The correlator has no info about OFDM
symbol boundaries.

In that case the input sample rate has to be set to the symbol rate?
(what is called samp_rate in ofdm_tx)

This is the input sample rate. The bit rate depends on the number of
carriers used, the length of the CP and the modulation type on the
payload. The OFDM symbol rate is the sample rate / (fft_len + cp_len).

On Tue, May 21, 2013 at 01:55:57PM -0400, Achilleas A.
wrote:

Martin,

I think my question would have been clearer if i had said that when I
talk of symbol rate I do not define a symbol to be the OFDM symbol of
length
fft_length+CP_length, but its fft_length+CP_length components.

OK, that works.


I still have trouble getting anything out of the S&C synchronizer:
The frequency offset output responds as expected when i introduce a
freq error but the “detect” output does not give anything out
even with noiseless input…

The synchronizer works fine, at least it does here. Try writing the
output into a file, and then view it with gr_plot_char (or whatever you
use). You will see a train of spikes at the distance of the length of
the packets.

The flow graph itself randomly stalls, though. I’m currently working on
the reason, but it has to do with the large abuse of the scheduler.

MB


Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin B.
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT – University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association