www.pudn.com > QPSK_System_BER_Simulation.rar > PAMSignalSpectrumCalculation.m

% Calculation of PAM Signal Spectrum 
echo on 
T=1;                        % symbol duration 
delta_T=T/200;              % sampling interval 
alpha=0.5;                  % roll-off factor 
fc=40/T;                    % carrier frequency 
A_m=1;                      % amplitude 
t=-5*T+delta_T:delta_T:5*T; % time axis 
N=length(t);                % number of samples 
for i=1:N,                  % calculation of raised cosine pulse 
    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(t,g_T); 
figure(3) 
plot(f,fftshift(U_m)); 
figure(4); 
plot(t,u_m);