说明：  信号时正弦波加正态零均值白噪声，信噪比10db，信号频率2kHZ，采样频率100kHZ，数据长度N=256。 (1). 用周期图法进行谱估计。
(Sine wave signal plus zero-mean normal white noise, SNR 10db, frequency 2kHZ, sampling frequency 100kHZ, data length N = 256. (1) with the periodogram spectral estimation.)