ASK USING MATLAB

Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. Like AM, ASK is also linear and sensitive to atmospheric noise, distortions, propagation conditions on different routes in PSTN, etc. Both ASK modulation and demodulation processes are relatively inexpensive. The ASK technique is also commonly used to transmit digital data over optical fiber. For LED transmitters, binary 1 is represented by a short pulse of light and binary 0 by the absence of light.

There are two ways in which we can do ASK using MATLAB:

1. ASK by square pulses: here we will the carrier frequency and frequency of square wave. From that we will generate a square function & carrier signal which is a sine wave and perform ASK.
2.  ASK by BIT stream: here we will give different bits i.e. ‘1’ or ‘0’ from that we will generate a signal and then perform the ASK.

ASK BY SQUARE PULSES - MATLAB CODE

clear all;
clc;
close all;
F1=input('Enter the frequency of carrier=');
F2=input('Enter the frequency of pulse=');
A=3;       %Amplitude
t=0:0.001:1;
x=A.*sin(2*pi*F1*t);    %Carrier Sine wave
u=A/2.*square(2*pi*F2*t)+(A/2);       %Square wave
v =x.*u;
subplot(3,1,1);
plot(t,x);
xlabel('Time');
ylabel('Amplitude');
title('Carrier');
subplot(3,1,2);
plot(t,u);
xlabel('Time');
ylabel('Amplitude');
title('Square Pulses');
subplot(3,1,3);
plot(t,v);
xlabel('Time');
ylabel('Amplitude');
title('ASK Signal');

             

I  INPUT 1:

              Enter the frequency of carrier=100

              Enter the frequency of pulse=10

  

  OUTPUT GRAPH

  Fig 2: ASK modulated and demodulated signals for carrier frequency 100 Hz and square pulse frequency 10 Hz.

    

     INPUT 2:

Enter the frequency of carrier=70

Enter the frequency of pulse=5

    OUTPUT

 Fig 2: ASK modulated and demodulated signals for carrier frequency 70 Hz and square pulse frequency 5 Hz.

    ASK BY BIT STREAM - MATLAB CODE

clc;

clear all;

close all;

%carrier frequency and amplitude

f=5;

a=1;

n = input('ENTER THE BIT STREAM:')

l=length(n);

if n(l)==1

   n(l+1)=1

  else

  n(l+1)=0

end

l1=length(n)

tn=0:l1-1;

 %plot message signal

subplot(4,1,1);

stairs(tn,n);

title('MESSAGE SIGNAL');

xlabel('TIME');

ylabel('AMPLITUDE');

 %plot carrier signal

 t=0:0.01:l;

y1=a*sin(2*pi*f*t);

subplot(4,1,2);

plot(t,y1);

title('CARRIER SIGNAL');

xlabel('TIME');

ylabel('AMPLITUDE');

 %modulation process

for i=1:l

   for j=(i-1)*100:i*100

      if(n(i)==1)

          s(j+1)=y1(j+1);

         else

          s(j+1)=0;

       end

   end

end

 %plot ASK signal

subplot(4,1,3);

plot(t,s);

title('ASK MODULATED SIGNAL');

xlabel('TIME');

ylabel('AMPLITUDE');

%Demodulation process

for i=1:l

  for j=(i-1)*100:i*100

   if(s(j+1)==y1(j+1))

      x(j+1)=1;

      else

       x(j+1)=0;

    end

  end

end

%plot demodulated signal

subplot(4,1,4);

plot(t,x);

title('ASK DEMODULATED SIGNAL');

xlabel('TIME');

ylabel('AMPLITUDE');

    INPUT 3:

              ENTER THE BIT STREAM:[1 0 0 1 1 1 1 0 0 0]

    OUTPUT GRAPH:

               Fig 3: ASK modulated and demodulated signal for [1 0 0 1 1 1 1 0 0 0] bit stream.

    INPUT 4:

              ENTER THE BIT STREAM:[1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 1]

    OUTPUT GRAPH:

             Fig 4: ASK modulated and demodulated signal for [1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 1] bit stream.