Question

Given: a 315MHz binary message is being ASK modulated with a carrier frequency of 38KHz.

Write a MatLab program to demodulate the signal, and graph the output.

Answer 1

MATLAB CODE

clc;
clear all;
close all;
x=input('Enter the sequence : '); % Binary Information
bp=1/(315e6); %Bp=1/Fm % bit period
disp(' Binary information at Trans mitter :');
disp(x);
%XX representation of transmitting binary information as digital signal XXX
bit=[];
for n=1:1:length(x)
if x(n)==1;
se=ones(1,100);
else x(n)==0;
se=zeros(1,100);
end
bit=[bit se];
end
t1=bp/100:bp/100:100*length(x)*(bp/100);
subplot(3,1,1);
plot(t1,bit,'lineWidth',2.5);grid on;
axis([ 0 bp*length(x) -.5 1.5]);
ylabel('amplitude(volt)');
xlabel(' time(sec)');
title('transmitting information as digital signal');
A1=input('Enter the Amplitude of carrier signal for information 1 : ');
A2=input('Enter the Amplitude of carrier signal for information 0 : ');
br=1/bp; % bit rate
f=br*10; % carrier frequency
t2=bp/99:bp/99:bp;   
ss=length(t2);
m=[];
for (i=1:1:length(x))
if (x(i)==1)
y=A1*cos(2*pi*f*t2);
else
y=A2*cos(2*pi*f*t2);
end
m=[m y];
end
t3=bp/99:bp/99:bp*length(x);
subplot(3,1,2);
plot(t3,m);
xlabel('time(sec)');
ylabel('amplitude(volt)');
title('waveform for binary ASK modulation coresponding binary information');
%XXXXXXXXXXXXXXXXXXXX Binary ASK demodulation XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
mn=[];
for n=ss:ss:length(m)
t=bp/99:bp/99:bp;
y=cos(2*pi*f*t); % carrier siignal
mm=y.*m((n-(ss-1)):n);
t4=bp/99:bp/99:bp;
z=trapz(t4,mm) % intregation
zz=round((2*z/bp))   
if(zz>7.5) % logic level = (A1+A2)/2=7.5
a=1;
else
a=0;
end
mn=[mn a];
end
disp(' Binary information at Reciver :');
disp(mn);
%XXXXX Representation of binary information as digital signal which achived
%after ASK demodulation XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
bit=[];
for n=1:length(mn);
if mn(n)==1;
se=ones(1,100);
else mn(n)==0;
se=zeros(1,100);
end
bit=[bit se];
end
t4=bp/100:bp/100:100*length(mn)*(bp/100);
subplot(3,1,3)
plot(t4,bit,'LineWidth',2.5);grid on;
axis([ 0 bp*length(mn) -.5 1.5]);
ylabel('amplitude(volt)');
xlabel(' time(sec)');
title('recived information as digital signal after binary ASK demodulation');

Results