说明：  采用重要性采样的方法来代替蒙特卡罗仿真方法，确定数字通信系统的BER。重要性采样方法可以简单的增加信道噪声的方差，等效于使系统工作在一个较低的信噪比的环境下。
(Using importance sampling method to replace the Monte Carlo simulation method to determine the digital communication system BER. Importance sampling method can be a simple increase in the variance of channel noise, is equivalent to make the system work in a lower signal to noise ratio environments.)