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

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

[KALYAN ACHARJYA]

share the complete code, if you can?

[yang-En Hsiao]

i change the s.*H+w to s.*abs(H)+w,and i think it works