说明：  本代码为matlab编写，编程实现信号经过QPSK调制后，再经过AWGN信道下，得到的误码率性能曲线，并且与理论上的误码率进行对比。
(The matlab code is written in programming through the QPSK modulation signal, and then through the AWGN channel, the resulting bit error rate performance curve, and with the theoretical bit error rates were compared)