We can use four variations of a signal and let each phase shift represent two bits (4-PSK). Then we can transmit data two times as fast using 4-PSK as 2-PSK.

• 我们还可以采用四种信号相位变化方式，让每一种变化代表两个比特(4-PSK)。此时我们可以用两倍于2-PSK的速率传输数据。