说明：  QPSK在加性高斯白噪声环境下，信噪比与误码率的仿真。 先产生一个四组符号的序列，，再将该序列映射到对应的相位上。用相应的函数产生均值为零、方差为δ2的加性高斯噪声。
(QPSK in additive white Gaussian noise environment, the signal to noise ratio and bit error rate simulation. First produce a sequence of four sets of symbols, then the sequence is mapped to the corresponding phase. The corresponding function with zero mean, variance δ2 additive Gaussian noise.)