OFDM mod/demod test code

A lot of people seem to have problem with the OFDM receiver in gnuradio.
Since there’s no confirmation of a working 2-way communication using
yet, I’ve decided to dig into the OFDM receiver implementation. I want
test the performance of the OFDM synchronization block. To do that,
first I
want to isolate the ofdm_sync block and make sure the rest of the chain

I found that there is a test file for OFDM mod and demod, named
ofdm_mod_demod_test.py, without invoking OFDM synchronization, FFT,
and cyclic. However, that code is outdated and not applicable for the
current implementation.

I’m trying to generate similar test code for the current version of OFDM
and demod but there seems to be no straight-forward way. It used to be
we can hook the ofdm_mapper straight into an ofdm_frame_sink. It’s no
the case as the frame_sink now requires a 2nd input, which is a stream
bytes signaling the beginning of a symbol. This input is provided by
ofdm_frame_acquisition, which in turn requires the signaling from the
ofdm_sampler. The ofdm_sampler gets the signaling from the ofdm_sync

Long story short, I haven’t found a way to test the system while
the ofdm_sync block yet. Can anyone give me some suggestion?

Thanks a lot,


On Wed, Feb 23, 2011 at 5:41 PM, Tuan (Johnny) Ta
[email protected]wrote:

current implementation.
the ofdm_sync block yet. Can anyone give me some suggestion?

Thanks a lot,


Try using the “fixed” version of the ofdm_sync block found on line 96 of
ofdm_receiver.py. This takes information about what you expect the
and frequency offset to be and does nothing but use that to trigger the
follow-on components. It was made for doing exactly the kind of things
are looking at doing.


Sounds great. I’ll give it a shot and report the result later.

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