说明：  数字调制是通过改变正弦载波的相位和幅度特性而进行的。另外，我们已经知道对于QAM调制，原始的比特流会被分拆成组，每组包含log2(M)比特。最后，我们知道，每对极坐标是如何转换成现实世界中的实际信号的
(Digital modulation is carried out by changing the phase and amplitude characteristics of sinusoidal carrier. In addition, we have known that for QAM modulation, the original bit stream will be divided into groups, each containing log2 (m) bits. Finally, we know how each pair of polar coordinates is converted into actual signals in the real world)