explain zero padding in OFDM

[Communications_Engineer]

ifft zero padding dvb-t 1705 2048

Hi communication_engineer,

we are working in the frequency domain not in the time domain so leave the casual and non casual aside.

Yes but we put the cyclic prefix in time domain and not the frequency domain to deal with 1) Avoid losing info in Multi-path and 2) Make sure that we have cyclic convolution in time domain so that in frequency domain we can use simple multiplication, now my point is that both these operations are in time domain and if we copy something from the end (future) to the beginning (present) requires future knowledge of what would be the signal at the end.

I know this works somehow, I mean thats why we have successful implementations so .... how does it happen or more precisely how can it happen

It is possible in code time to do the copy and paste for the end to paste it in the begining of the signal.

I hope my answere is cleare.

What is code time, do we buffer our signal till the end and afterwards copy the end at the beginning?

 

[Aya2002]

ifft zero padding 2048

code time: i mean in the matlab code design time.

now, we wait the signal to be generated by the IFFT block and then we did what we need. so it is no need to deal as a casual or not a casual.

hope it is cleare

 

[rramya]

zero padding in frequency domain matlab

communication_engineer wrote:
we wait the signal to be generated by the IFFT block and then we did what we need. so it is no need to deal as a casual or not a casual.

It is not possible to generate Non-causal signal.

communication_engineer wrote:
"if we copy something from the end (future) to the beginning (present) requires future knowledge of what would be the signal at the end. "


the signal thet comes at the end is the delayed signal not the future valued signal.
Also, there is always the processing time delay in LTI system. as we know IFFT block(parallel block) is linear processing.(we will using buffer) defintely there will be group and phase delay.

In MATLAB we use array processing. where we compute the whole signal values and only then we do cyclic prefix.

Happy learning.

 

[Communications_Engineer]

dft and padded data in ofdm

Thanks rramya, always good to know someone who can help

 

[rramya]

make correct zero padding

Hi communication engineer,
I like to add some more point reg use of non-causal signals.

Causality property is not used in applications , in which the indepent variable is not time .

It is often used where procesisng data that are recorded already, especially speech, meteorological , stock market analysis. Here are by no means constrained
to causal processing


Happy Learning

 

[mena2009]

zero padding in ofdm fft

hi friends,

thank you very much,

I want to start in the digital communicatios. Can i have an advise?

thanks

 

[rramya]

cours zero padding ofdm

start learning from the book digital communication by bernaud sklar. which is the best book of all


Happy learning

 

[mena2009]

elementary period in ofdm concept

Hi rramya,

can you tell me more.

Thank you

 

[Aya2002]

zero padding end beginning

Communication Systems
With Solutions Manual supported by Matlab Code
4th Eddition
-------------------------------------------------------------
Modern Analoge And Digital Communications_Systems
by: B. P. Lathi
-------------------------------------------------------

there are many others. Just decide your direction at first !