linear_fft.m

本程序仿真一个从卫星到区域数据中心的下行链路（由一组6个载波构成）

% File: linear_fft.m
function [fftx,freq] = linear_fft(x,n,ts)
% This function takes n (must be even) time domain samples (real or
% complex) and finds the PSD by taking (fft/n)^2. The two sided
% spectrum is produced by shifting the PSD. The array freq provides
% the appropriate frequency values for plotting purposes.
y = zeros(1,n);
for k=1:n
   freq(k) =(k-1-(n/2))/(n*ts);
   y(k) = x(k)*((-1.0)^(k+1));
end;
fftx = fft(y)/n;
% End of function file.