OFDM cyclic prefixer

GNU Radio
1

Hello,

My name is Yuri.
​ I very new to GNU Radio, and I’m using GRC 3.7.1.​

I am doing a research, and I need to modulate specific signal in OFDM. I
would like to insert cyclic prefix (or guard interval in my project, the
same thing with a different name).

I looked at the examples
​under gr-digital
​/examples/ofdm, and I’ve also read some papers about OFDM technics.

My doubt is: what is the parameter “Length Tag Key”? I’ve seen it
working
in the examples located in the folder above, I’ve tried to do the same
in
my project, but it states a message that this parameter is missing.

By chance, does this cyclic prefixer block only works with other blocks
of
the same category? I mean, do I need to use OFDM carrier allocator
before
it, or something like that?

Thank you for your attention,

Yuri.

2

If you’re sending packets, then Length Tag Key should be
set to the packet length you’re using. If you’re sending
a stream (like DVB-T), then this field is not used (and
left blank).

The OFDM cyclic prefixer is used after the (reverse)
FFT block. The FFT Length in the OFDM Cyclic Prefixer
block should match the FFT Size in the FFT block.

Ron

3

On 14.05.2014 04:36, Ron E. wrote:

If you’re sending packets, then Length Tag Key should be
set to the packet length you’re using. If you’re sending
a stream (like DVB-T), then this field is not used (and
left blank).

It needs an empty string, in this case.

The OFDM cyclic prefixer is used after the (reverse)
FFT block. The FFT Length in the OFDM Cyclic Prefixer
block should match the FFT Size in the FFT block.

That’s right. The block doesn’t check if the input is actually OFDM.

Martin

4

Hi,

Thanks Mr. Economos and Mr. Braun,

I left this parameter in blank (I guess this is the same as an empty
string), it seems that it is working now.

Actually I am trying to modulate ISDB-T data stream. I am working with
vectors, instead of data stream.

Thanks again.

2014-05-14 5:28 GMT-03:00 Martin B. [email protected]:

5

Thank you very much, for your help Mr. Economos,

For sure I will take a look at this project,

Yuri.

2014-05-14 21:12 GMT-03:00 Ron E. [email protected]:

6

If you haven’t already, you may want to take a look
at this GnuRadio DVB-T implementation.

Ron