经典的二阶矩四阶矩信噪比估计，有不经过上采样、成型滤波和经过上采样、成型滤波的两种版本。加噪方式也分别用了matlab自带函数和自写两种版本。望大家参考。-Second Moment classic SNR estimation fourth moment, there is not through the sampling, the shaping filter and sampled, two versions of shaping filter. Plus noise mode were