信号频谱分析方法一级使用非参数方法直接使用信号进行功率谱估计，以周期图法为例，提供了周期图法和welch法估计信号功率谱(The signal spectrum analysis method uses the nonparametric method to directly use the signal to estimate the power spectrum. The periodogram method is used as an example to provide the periodogram and the Welch method to estimate the signal power spectrum)