OFDM mod/demod test code

GNU Radio
1

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
OFDM
yet, I’ve decided to dig into the OFDM receiver implementation. I want
to
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
works.

I found that there is a test file for OFDM mod and demod, named
ofdm_mod_demod_test.py, without invoking OFDM synchronization, FFT,
preamble
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 However, that code is outdated and not applicable for the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
mod
and demod but there seems to be no straight-forward way. It used to be
that
we can hook the ofdm_mapper straight into an ofdm_frame_sink. It’s no
long
the case as the frame_sink now requires a 2nd input, which is a stream
of
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
x_x.

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

Thanks a lot,

Johnny

2

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,

Johnny

Johnny,
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
timing
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
you
are looking at doing.

Tom

3

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