A problem in MATLAB, I don't know what went wrong, the input and output are different, please help me to answer it. The code is as follows:

Problems arise when the sender performs QPSK modulation.

The initial procedure is:

ich 1=ich。 * kmod

qch 1=qch。 * kmod

x = ich 1+qch 1 * sqrt(- 1)； ? Using this program, you will find that the generated constellation points are not standard constellation points.

The constellation points are as follows:

The reason is that when performing QPSK modulation, there should be alternate sign inversion. In the program, the original sequence is converted into bipolar, that is, this code.

ich0=ich。 *2- 1;

qch0=qch。 *2- 1; But it is not used. The way to correct it is to use bipolar code for modulation, that is, to change it to

ich 1=ich0。 * kmod

qch 1=qch0。 * After KMOD correction, the constellation points are normal, so there will be no problem in demodulation.