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Newbie
Newbie
2,913 Views
Registered: ‎06-22-2013

Problem with result of fft core v.8 when using cyclic prefix

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Hi, why does the output of the IFFT core is totally out of order when using the option of cyclic prefix insertion?

 

I tried running the testbench (available with the core) and the order of the outputs (by comparing them with the outputs of the core without using cyclic prefix option, and also by comparing the results with the matlab) = 1,2,0,7,6,5,4,3,2,1. 

 

I am using 8-point IFFT, pipelined/streaming, input width = 13 bits. 

 

Thanks in advance

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Xilinx Employee
Xilinx Employee
2,901 Views
Registered: ‎08-01-2008

Re: Problem with result of fft core v.8 when using cyclic prefix

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I think this is expected output. If cyclic prefix insertion is used, the cyclic prefix is unloaded first and XK_INDEX counts from (point_size) - (cyclic prefix length) up to (point size) -1. After the cyclic prefix has been unloaded, or if the cyclic prefix length is zero, the whole frame of output data is unloaded. XK_INDEX counts from 0 up to (point size) -1 as before. Cyclic Prefix Insertion is only possible with natural order outputs. For detail refer DS808 Xk_index section
Thanks and Regards
Balkrishan
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Xilinx Employee
Xilinx Employee
2,902 Views
Registered: ‎08-01-2008

Re: Problem with result of fft core v.8 when using cyclic prefix

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I think this is expected output. If cyclic prefix insertion is used, the cyclic prefix is unloaded first and XK_INDEX counts from (point_size) - (cyclic prefix length) up to (point size) -1. After the cyclic prefix has been unloaded, or if the cyclic prefix length is zero, the whole frame of output data is unloaded. XK_INDEX counts from 0 up to (point size) -1 as before. Cyclic Prefix Insertion is only possible with natural order outputs. For detail refer DS808 Xk_index section
Thanks and Regards
Balkrishan
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