%Problem3.31;
%flat fading effect (BProb. 3.31); ffdb;

clear all; close all;
t=[0:1999]/1000; %time scale;
S=exp(-16*((t-1).^2)); %real envelope;
Sbp=real(S.*exp(i*2*pi*25*t)); %bandpass signal;
subplot(311); plot(t,Sbp); ylim([-1.2 1.2]); xlabel('t/T'); ylabel('signal'); grid; %plotting signal;
Fi=(unidrnd(10,1,10)-1)*pi/5; %uniform initial phases;
SRbp=exp(i*Fi)'*S; %10 realizations of the signal complex envelope with random phases;
Sres=sum(SRbp); %resulting signal complex envelope;
Sbpres=real(Sres.*exp(i*2*pi*25*t)); %resultant bandpass signal;
subplot(312); plot(t,Sbpres); ylim([-6 6]); xlabel('t/T'); ylabel('res. signal'); grid; %plotting resulting bandpass signal;
subplot(313); plot(t,abs(Sres)); ylim([-0.5 6]); xlabel('t/T'); ylabel('res. envelope'); grid; %plotting resulting signal envelope;