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ofdm matlab with fft/ifft implementation

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neotech

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hi all,

what is the proper way of implementing the ifft in an ofdm using qpsk?

i have this qpsk modulation code using Gray coding but when i insert the ifft before the command of adding the noise, and an fft before demodulation, the BER is rising to ~ 0.5.
 

Hi

random data> qpsk> zero pad> serila to parallel> IFFT> parallel to serial > noise


serial to parallel> FFT> parallel to serial > remove zero pad> qpsk demod> received data
 

thanks aya, i didnt implement the zero pad before the serial to parallel..

how can i implement it?

as well as, the zero pad removal..

and is x=ifft(parallel_data); enough as a command for the IFFT block..

parallel_data is the modulated data converted to parallel..


thank you.
 

neotech said:
thanks aya, i didnt implement the zero pad before the serial to parallel..

how can i implement it?

as well as, the zero pad removal..

and is x=ifft(parallel_data); enough as a command for the IFFT block..

parallel_data is the modulated data converted to parallel..


thank you.
Click to expand...


yes,

the zero pad which means adding zeros to your input data (in the middle of the input data) to make your number of data bits equals 2^N where N is the length of your FFT/IFFT block.

at the receiver you must remove these zeros.

Yes, the command x=ifft(parallel_data); enough as a command for the IFFT block.

regards
 

Hi Aya,

How are you?

Aya, I'm a master degree student in telecommunication field, my interest is related to the equalization, channel estimation issues.

My master thesis related to the OFDM, I want to ask about the zero padding, did you mean that this zero padding will be the in-active subcarriers?

Further I have a big trouble in the turbo erqualization, if you have any knoweldge in that would you help me please?

Best Regards, and Thank you very much in advance.

Added after 11 minutes:

Aya,

you mentioned that you have to add the noise after the ifft process, but I don't think that this is correct, the noise addition must be in the time domain, then the IFFT operation is applied.


Best Regards.
 

mankeer said:
you mentioned that you have to add the noise after the ifft process, but I don't think that this is correct, the noise addition must be in the time domain, then the IFFT operation is applied.


Best Regards.
Click to expand...

IFFT convert from frequency domain to time domain so i added the noise in the time domain. :)
 

hi every one

i would like to ask about how to use rs coding in the ofdm system if any one could help me it is very ergent...
thanks and with my best wishes ...
 

to add zeros, you have to add them as shown in this link:
**broken link removed**

it is message number 52

note that the output zero is at the center i mean the zero frequency is at the center.

check out it, it is very useful.
 

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