QPSK利用载波的四种不同相位来表征数字信息。由于每一种载波相位代表两个比特信息，因此，对于输入的二进制数字序列应该先进行分组，将每两个比特编为一组，然后用四种不同的载波相位来表征。我们把组成双比特码元的前一信息比特用a代表，后一信息比特用b代表。双比特码元中两个信息比特ab通常是按格雷码排列的，它与载波相位的关系如表1-1所示，矢量关系如图1-1所示。图1-1（a）表示A方式时QPSK信号矢量图，图1-1（b）表示B方式时QPSK信号的矢量图。

-should first group, will each make up two bit of a group, and then used four different carrier phase to represent. We ShuangBi of this information before the yuan with a representative, a bit after information with b is for. This ShuangBi two yuan information ab usually is arranged according to gray yards, it and the relationship between the carrier phase shown in table 1-1, vector relation as shown in figure 1-1 below. Figure 1-1 (a) said a way QPSK signal when the column picture, figure 1-1 (b) b way QPSK signal when said the vector diagram