The bit error rate is wrong when adding the channel,where am i wrong?

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yang-En Hsiao 2018-8-27

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https://ww2.mathworks.cn/matlabcentral/answers/416377-the-bit-error-rate-is-wrong-when-adding-the-channel-where-am-i-wrong

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The first picture is using MAP rule but no channel,that is receive signal= signal + noise ,to find the QPSK error probability

Now i want to add the fading channel , CN~(0,1), that is receive signal = (signal*channel) + noise.Here is the code that i add the channel,however,the simulation is wrong,like the second picture below,does anyone know where am i wrong?

    vComplexNoise = sqrt(1/2) * (randn(1,intput_data) + (1i * randn(1,intput_data))); %complex AWGN
    H = fft(vComplexNoise);  %fourier the channel from time domain to frequency domain   
    r = s.*H+w; %receive signal = (signal*channel) + noise