2.　　关于无线信道的多普勒谱，请回答以下问题：

(1)　　在某些无线信道中，多普勒频移会引起无线信道输出信号的混叠。请描述产生混叠的各种原因；

(2)　　无线信道中的多普勒谱有一种经典谱(classic spectrum)，请解释产生这种谱形状的机理；

(3)　　请用Simulink工具编写代码(S-Function方式)，产生一单径瑞利信道，其多普勒谱为经典谱，其中移动速率为120km/h。并请回答：证明自己用计算机产生的经典谱是正确的可能方法。

-On the wireless channel of the Doppler spectrum, please answer the following questions: (1) In some radio channels, the Doppler frequency shift will cause the output signal of the wireless channel aliasing. Please describe the aliasing produced a variety of reasons　(2) wireless channel in the Doppler spectrum has a classical spectrum (classic spectrum), please explain the mechanism of produce such spectral shape　(3), please use the Simulink tool to write code ( S-Function mode), resulting in a single-path Rayleigh channel, the Doppler spectrum for the classical spectrum, including mobile rate of 120km/h. And requested the answer: that they used computer-generated classical spectrum is the right possible way.