Header_payload_demux

GNU Radio
1

Hi:
Thank you in advance.
I have two simple question:
1.In the grc,i see a block: header_payload_demux
It has 3 input:in,trigger,header_data.But i see the
header_payload_demux_impl.cc:iosignature::make2(1,2,…,…).But it has 3
input,why?
Thank you.
2.fft:I see the shift:yes.
I want to save the symbol to file sink and analyse by matlab.But
now i don’t know it’s shift earlier or fft earlier?
Thank you.
Best regards,
xianda

2

On 05/29/2014 08:07 PM, xianda wrote:

Hi:
Thank you in advance.
I have two simple question:
1.In the grc,i see a block: header_payload_demux
It has 3 input:in,trigger,header_data.But i see
the header_payload_demux_impl.cc:iosignature::make2(1,2,…,…).But it
has 3 input,why?

Why 3 inputs or how come only 2 are in the io signature?
header_data is a message port, I guess that’s what you’re after.

 Thank you.
 2.fft:I see the shift:yes.
  I want to save the symbol to file sink and analyse by matlab.But

now i don’t know it’s shift earlier or fft earlier?

Can you rephrase that question?

M

3

Hi
Thanks for your kindly reply.
1.The second question
is:I see the fft block,it has one option:shift,and you set yes.

And in the transmit part,we should do the ifft.And in the receive
part,we should do the fft.
They all set the shift:yes.

And now I want to save the data to file and analyse the data by
matlab.
In the transmit maybe ifft(fftshift(symbol)),but in the
receive what command?
2.I see maybe you don’t use the pilot in
the receive part.Am I right?
3.I see maybe the cyclic prefix is
dropped in the header_payload_demux block.Am I right?
Thank
you.Can you explain it?Thank you.
Best regards

4

On 30.05.2014 03:28, xianda wrote:

explain it?Thank you.
Best regards At 2014-05-30 05:05:54,
Xianda,

sorry, I still have troubles understanding your question. It depends on
where in the flow graph you’re actually saving the file. If shift is set
to yes, the output is shifted, or the input is regarded as shifted.

M

5

The second question is:I see the fft block,it has one option:shift,and
you set yes.
The FFT block is able to shift the left half of your vector to the end.
It’s basically identical to the fftshift function in Matlab: With shift,
f=0 is the middle bin (and not the first one) .

And now I want to save the data to file and analyse the data by matlab.
In the transmit maybe ifft(fftshift(symbol))

ifft(Ifftshift()), iff you want to have the pre-fft data.

but in the receive what command?
What receiver?
You don’t really tell us how and under what aspect you want to analyze
the data; this seems to more of an communications engineering/design
question, than GNU Radio-related?

I see maybe you don’t use the pilot in the receive part. Am I right?

Sorry, I did not understand. Receive part of what? So long, we have only
been talking about header_payload_demux, which does exactly that:
demuxing packet header and payload.

I think that generally you are on a good way of analyzing what the
individual blocks do!
I think it would be easier for us to understand you, if you asked only
one or two questions in the same mail and explained more exactly what
you are considering.

Greetings,
Marcus