4.4

代码说明：

  主要用途是对抗多径衰落。由于多径衰落的存在，使得同一个帧由于路径不同，到达用户端的时延有先有后。在相关的频域上的会造成子载波之间的相互干扰，影响 性能。另外，由于有了循环前缀，使得IFFT FFT操作把原来的线性卷积变成循环卷积，大大简化了相应的信号处理复杂度(The main purpose is to fight against multipath fading. Due to the presence of multipath fading, the first after they have the same frame different paths to reach the client delay. Would cause mutual interference between sub-carriers in the frequency domain, affecting performance. In addition, thanks to the cyclic prefix, so IFFT FFT operation to the linear convolution of the original into a circular convolution, greatly simplifying the corresponding signal processing complexity)