构造一组输入为白噪声加三个频率非常接近的正弦波，其信噪比为10dB，观测长度为256。试分别用普通AR谱估计和采用功率噪声抵消算法的AR谱估计估计这组信号的频率，并比较结果。-constructed a group of white noise input plus three very close to the frequency sine wave, the signal-to-noise ratio of 10dB. Observing length of 256. Were used t