# OFDM Blocks **URL:** \ **Category:** GNU Radio\ **Created:** [July 25, 2014, 1:19am UTC](https://www.ruby-forum.com/t/ofdm-blocks/231173 "2014-07-25T01:19:19Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [July 25, 2014, 1:19am UTC](https://www.ruby-forum.com/t/ofdm-blocks/231173/1 "2014-07-25T01:19:19Z")
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 ---
**Author:** ![MdSAnjum](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/f07891/32.png) [@MdSAnjum](https://www.ruby-forum.com/u/MdSAnjum)\ **Post date:** [July 25, 2014, 11:08am UTC](https://www.ruby-forum.com/t/ofdm-blocks/231173/2 "2014-07-25T11:08:18Z")
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 ---
**Author:** ![MdSAnjum](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/f07891/32.png) [@MdSAnjum](https://www.ruby-forum.com/u/MdSAnjum)\ **Post date:** [July 28, 2014, 6:21am UTC](https://www.ruby-forum.com/t/ofdm-blocks/231173/3 "2014-07-28T06:21:49Z")
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. ---
**Author:** ![MdSAnjum](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/f07891/32.png) [@MdSAnjum](https://www.ruby-forum.com/u/MdSAnjum)\ **Post date:** [August 5, 2014, 3:55am UTC](https://www.ruby-forum.com/t/ofdm-blocks/231173/4 "2014-08-05T03:55:30Z")
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