RE: [Discuss-gnuradio] OFDM - on air?

[Dominik Auras]

Hi!

So there is no obvious fault, e.g. that I set the wrong
decimation/interpolation rate? (the samplerate should be 400kS/s?)

I just compared "tx_ofdm.dat", recorded in your simulation, to my
recorded file. Therefore I modified usrp_fft.py. In tx_ofdm.dat, it
shows a large frequency band in use, as expected. Unfortunately, my file
does not show the same behavior :-( It looks like gaussian noise with a
small carrier in the middle. Maybe I did not setup correctly the
transmit path.

The first few seconds while recording, there were no signal
transmission. This stage can be recognized in a waterfall diagram. It
seems to me that "the gaussian noise" I saw could be the transmitted
OFDM signal.

> If you want to start playing around with it, benchmark_ofdm.py does a
> loopback simulation with optional AWGN and multipath channels between the Tx
> and Rx blocks. We're hoping to inject some quiet time into this simulation
> to test the signal acquisition capabilities. That is, we know that under
> steady-state conditions we synchronize pretty well, but we don't know the
> transient behavior when we first get s signal into the receiver.
Good work! I studied the simulation for some hours, before I started to
port the sim to use the usrp.

> Yes, we've injected a lot of debug information here, but I thought the code
> checked in had that output turned off. Are you using the newest code (and
> yes, I did just check a few new things in that we didn't do before Matt
> left).
The debug information appear because I turned it on. I am working on the
latest copy.

> Thanks! It's a bit premature still, but I'm sure we'll all be glad for more
> feedback as it comes together.
If you like, I can give you further feedback from time to time.

Dominik