gusucode.com > 现代通信系统——使用MATLAB(+全部程序) > 现代通信系统——使用MATLAB(+全部程序)/现代通信系统——使用MATLAB(+全部程序)/Matlab 程序/Chapter7/ip_07_01.m
% MATLAB script for Illustrated Problem 7.1. echo on T=1; delta_T=T/200; % sampling interval alpha=0.5; % rolloff factor fc=40/T; % carrier frequency A_m=1; % amplitude t=-5*T+delta_T:delta_T:5*T; % time axis N=length(t); for i=1:N, if (abs(t(i))~=T/(2*alpha)), g_T(i) = sinc(t(i)/T)*(cos(pi*alpha*t(i)/T)/(1-4*alpha^2*t(i)^2/T^2)); else g_T(i) = 0; % The value of g_T is 0 at t=T/(2*alpha) end; % and at t=-T/(2*alpha). echo off ; end; echo on; G_T=abs(fft(g_T)); % spectrum of g_T u_m=A_m*g_T.*cos(2*pi*fc*t); % the modulated signal U_m=abs(fft(u_m)); % spectrum of the modulated signal % actual frequency scale f=-0.5/delta_T:1/(delta_T*(N-1)):0.5/delta_T; % Plotting commands follow. figure(1); plot(f,fftshift(G_T)); axis([-1/T 1/T 0 max(G_T)]); figure(2); plot(f,fftshift(U_m));