中文说明：
论述了多种时频分析方法,其中包括短时傅里叶变换、Cohen类时频分布、Hilbert-Huang变换、引入小波包分解的改进型Hilbert-Huang变换。
English Description：
Several time-frequency analysis methods are discussed, including short-time Fourier transform, Cohen class time-frequency distribution, Hilbert Huang transform and improved Hilbert Huang transform with wavelet packet decomposition.