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amr_yassin
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Registered: ‎04-06-2009

OFDM system

Hi everyone
I  implementing a simple OFDM system using modules from core generator.So i started with the fft v.5 but i cant understand a lot of thing about this IP core i mean why is there a real input and an imaginary input in matlab the fft just takes a vector as an input and what is scale_sch i couldnt quite understand the descreption from the fft documentation so if someone can elaborate it
i know these questions might sound stupid but i am not very familiar with dsp
and if someone knows a working examplein order to test   the core

 

amralaa87@hotmail.com

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chenhongyi123
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Registered: ‎01-05-2009

  implementing a simple OFDM system using modules from core generator.So i started with the fft v.5 but i cant understand a lot of thing about this IP core i mean why is there a real input and an imaginary input in matlab the fft just takes a vector as an input and what is scale_sch i couldnt quite understand the descreption from the fft documentation so if someone can elaborate it
i know these questions might sound stupid but i am not very familiar with dsp
and if someone knows a working examplein order to test   the core

 

in fact no complex signal, in your OFDM system, at the IFFT , realpart=your input signal, imagpart =0.  After FFT, realpart=your  signal, imagpart =0.

scale_sch :

1/N
[10 10... 10] for Radix-4 or Pipelined architecture when N is a
power of 4.  for example , a Radix-4, 256 points ,   scale_sch  <= "10101010" at the IFFT, at the FFT set  scale_sch  <= "00000000"
[01 10... 10] for Radix-4 or Pipelined architecture when N is not
a power of 4.  for example , a Radix-4, 512 points ,   scale_sch  <= "0110101010" at the IFFT, at the FFT set  scale_sch  <= "0000000000"

[01 01... 01] for Radix-2 or Radix-2-Lite   scale_sch  is always 010101...01

 

 

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amr_yassin
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Registered: ‎04-06-2009

Thank you vey much that was very helpful i have another question do i have to put a serial to parallel block before the FFt or the FFT core does that internaly and the input is in 2's complement so do i have to design a block to change the output from my QAM mapper to 2's complement
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