AWR1642: Why TI calculate doppler fft for every range FFT instead of the first half of range FFT?

Hi

    As we know, the Image band of range FFT(index from rangeBin/2 to rangeBin) contains useless information.

    But why TI's demo in MmwDemo_interFrameProcessing() function actually calculate doppler FFT for every range FFT in 2-D FFT calculation,? Only calculate the first half(0 to rangeBin/2) may be enough.

    Where did I go wrong? Thank you !