Ofdm

GNU Radio
1

I’m pretty new to gnu radio and I want to transmit an OFDM signal using
different modulation types (BPSK, QPSK, and 64-QAM). The concept is
pretty simple: read data, map it to a specified constellation map, and
then send it through an IFFT. I don’t know if this code already exists
but I could use some help.

Nick

2

[email protected] wrote:

I’m pretty new to gnu radio and I want to transmit an OFDM signal
using different modulation types (BPSK, QPSK, and 64-QAM). The
concept is pretty simple: read data, map it to a specified
constellation map, and then send it through an IFFT. I don’t know if
this code already exists but I could use some help.

There is work underway in this area to create a parameterized OFDM
modulator/demodulator pair, but it is incomplete and not yet merged into
the trunk. You can see the code in:

http://gnuradio.org/trac/browser/gnuradio/branches/developers/n4hy/ofdm2/gnuradio-examples/python/ofdm

These examples depend on C++ elsewhere in the tree in this developer
branch so they won’t run as-is. You can, however, see how the transmit
path is put together.

By the way, you’re right–the modulator is the easy part. It’s the
receiver synchronization that always turns out to be the black magic
part. (Why is this always glossed over? :slight_smile:

Johnathan C.
Corgan Enterprises LLC
http://corganenterprises.com

3

Johnathan C. wrote:

There is work underway in this area to create a parameterized OFDM
receiver synchronization that always turns out to be the black magic
part. (Why is this always glossed over? :slight_smile:

Johnathan C.
Corgan Enterprises LLC
http://corganenterprises.com

As Johnathan said, we’ve pretty much got the modulator and demodulator
done. A few of us will be working next week on pulling it all together
and finishing the synchronization. With any luck and the alignment of
the Zodiac (or whatever astrological/mythological concept you want to
wish on), we’ll get this merged into the trunk by the end of next week.

From there, hack away and make improvements.

Tom

4

The OFDM work has begun under my (n4hy) branch. Next week it will
continue as I travel to Virginia Tech to work with Tom, Matt, and others
on this and other work.

When we have an OFDM transceiver and can drive one of the Flexible
boards from Matt on the air, we will move it into the trunk so we can
add FEC, interleaving, etc. easily and learn how Achilleas work needs
to be optimized (if at all) to be used with this code.

Bob
(ARS N4HY)

[email protected] wrote:

–
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
“Taking fun as simply fun and earnestness in earnest shows
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