OFDM Blocks

GNU Radio
1

Hello,

I’m working with USRP OFDM blocks. I’m confused about how to use
built-in
OFDM Transmitter and OFDM Receiver blocks.

  1. How to set the fields- occupied carriers, pilot carriers, sync word
    and
    pilot symbols?

  2. I’m using N200 board. I transmitted signal using OFDM Mod block UHD
    Sink
    block. It seems it transmits properly. But when I receive the
    signal
    using OFDM Demod and UHD Source block then it looks the signal is not
    received properly. The received signal shows a quite different pattern
    than
    the transmit one. It looks it receives something different signal, not
    the
    transmitted one. Note: I’m using same USRP board to transmit and receive
    signal simultaneously.

  3. Again, I need to control the frequency offset of the subcarriers. How
    can I do that using the built-in blocks?

  4. And is there any way to control the transmit signal power?

  5. Well, does the OFDM Mod2 block works? If it is then how to use that
    one?

I already asked a lot of questions. Thanks for your patience.

Regads
Nashid Anjum
Graduate Student
South Dakota School of Mines and Technology

2

On 07/25/2014 01:18 AM, Md. Anjum wrote:

Hello,

I’m working with USRP OFDM blocks. I’m confused about how to use
built-in OFDM Transmitter and OFDM Receiver blocks.

  1. How to set the fields- occupied carriers, pilot carriers, sync word
    and pilot symbols?

Before I go into this, did you read the manual page? If yes, what
specifically is unclear? Also, did you go through the examples in
gr-diigtal/examples/ofdm?

  1. I’m using N200 board. I transmitted signal using OFDM Mod block UHD
    Sink block. It seems it transmits properly. But when I receive the
    signal using OFDM Demod and UHD Source block then it looks the signal
    is not received properly. The received signal shows a quite different
    pattern than the transmit one. It looks it receives something different
    signal, not the transmitted one. Note: I’m using same USRP board to
    transmit and receive signal simultaneously.

I recommend sticking to the OFDM Transmitter and -Receiver blocks.

  1. Again, I need to control the frequency offset of the subcarriers. How
    can I do that using the built-in blocks?

Do you mean the sub-carrier spacing? If so, of course you can control
that.

  1. And is there any way to control the transmit signal power?

There are many ways to control the transmit power. You can vary the
signal amplitude digitally, you can increase the tx gain… just make
sure you don’t distort your signal.

  1. Well, does the OFDM Mod2 block works? If it is then how to use that one?

No, it doesn’t. That’s actually spurious XML.

M

3

Before you are going to do work with USRPs, first you go through some
fundamental concepts on digital communications and test the examples
given in “gr-diigtal/examples”. All your doubts will be cleared on your
own. Still, if you will get any doubts, you can post without any
hesitation.

4

Nashid,

please stick to the mailing list.

There’s lots of tutorials out there to get the OFDM blocks running with
the default settings. Once you have that going, work your way from
there.

M