Discussion:
[Discuss-gnuradio] OFDM cyclic prefixer
Yuri P.M
2014-05-14 01:06:34 UTC
Permalink
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.
Ron Economos
2014-05-14 02:36:41 UTC
Permalink
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
Post by Yuri P.M
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.
Martin Braun
2014-05-14 08:28:31 UTC
Permalink
Post by Ron Economos
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.
Post by Ron Economos
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
Post by Ron Economos
Ron
Post by Yuri P.M
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.
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Discuss-gnuradio mailing list
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Yuri P.M
2014-05-14 20:50:19 UTC
Permalink
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.
Post by Martin Braun
Post by Ron Economos
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)
Post by Ron Economos
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
Post by Ron Economos
Ron
Post by Yuri P.M
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.
_______________________________________________
Discuss-gnuradio mailing list
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
_______________________________________________
Discuss-gnuradio mailing list
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Ron Economos
2014-05-15 00:12:04 UTC
Permalink
If you haven't already, you may want to take a look
at this GnuRadio DVB-T implementation.

https://github.com/BogdanDIA/gr-dvbt

Ron
Post by Yuri P.M
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.
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
Ron
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.
Yuri P.M
2014-05-15 12:27:50 UTC
Permalink
Thank you very much, for your help Mr. Economos,

For sure I will take a look at this project,

Yuri.
Post by Ron Economos
If you haven't already, you may want to take a look
at this GnuRadio DVB-T implementation.
https://github.com/BogdanDIA/gr-dvbt
Ron
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.
Post by Martin Braun
Post by Ron Economos
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)
Post by Ron Economos
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
Post by Ron Economos
Ron
Post by Yuri P.M
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.
_______________________________________________
Discuss-gnuradio mailing list
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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