fftshift implementation in Simulink

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Hamza
Hamza 2025-1-23
评论： Paul 2025-1-24
I need to generate IPs for HDL implementation of an algorithm. I need to do fftshift in simulink but there is no fftshift block avaiable. Is there any way we can do fftshift of the output data from FFT block from DSP HDL toolbox? I am attaching FFT model for reference.

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Walter Roberson
Walter Roberson 2025-1-23
Fork the fft output. Use https://www.mathworks.com/help/dsp/ref/variableselector.html variable selector block on each of the branches, with Fixed selector. In one of the branches select 1:floor(signal_length)/2 and in the other branch select floor(signal_length)/2+1:signal_length . Now concatenate those two together in reverse order.
This potentially requires hard-coding the signal length.
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Walter Roberson
Walter Roberson 2025-1-24
Ran in:
@Paul
good point
x = 1:9;
signal_length = numel(x);
fftshift(x)
ans = 1×9
6 7 8 9 1 2 3 4 5
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[x(ceil(signal_length/2)+1:signal_length), x(1:ceil(signal_length/2))]
ans = 1×9
6 7 8 9 1 2 3 4 5
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Paul
Paul 2025-1-24
I just realized that this block requires the FFT length to be a power of 2, so the ceil() isn't necessary for this particular use case.

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Paul
Paul 2025-1-23
编辑：Paul 2025-1-23
fftshift is extended to code generation. Assuming the data output from the FFT block is in linear order, you can call fftshift from inside a MatlabFunction block.

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