To generate the waveform of Amplitude Shift Keying (ASK) signal using MATLAB.

Objective:

To generate the waveform of Amplitude Shift Keying (ASK) signal using MATLAB.

Software required:

1. MATLAB
2. Computer installed with Windows XP or higher Version

Theory

Generation of ASK:Amplitude shift keying - ASK - is a modulation process, which imparts to a sinusoid two or more discrete amplitude levels. These are related to the number of levels adopted by the digital message. For a binary message sequence there are two levels, one of which is typically zero. The data rate is a sub-multiple of the carrier frequency. Thus the modulated waveform consists of bursts of a sinusoid. The disadvantage of ASK, compared with FSK and PSK, is that it has not a constant envelope. This makes its processing (eg. power amplification) more difficult, since linearity becomes an important factor. However, it does make for ease of demodulation with an envelope detector.

ASK modulation:

1. Generate carrier signal.
2. Start for loop
3. Generate binary data and message signal (on-off form)
4. Generate ASK modulated signal.
5. Plot message signal and ASK modulated signal.
6. End for loop
7. Plot the binary data and carrier.

Program:

%ASK Modulation

clc;

clear all;

close all;

%Generate Carrier Signal

Tb=1; fc=10;

t=0:Tb/100:1;

c=sqrt(2/Tb)*sin(2*pi*fc*t);

%Generate Message Signal

N=8;

m=rand(1,N);

t1=0;t2=Tb

for i=1:N t=[t1:.01:t2]

if m(i)>0.5

m(i)=1;

m_s=ones(1,length(t));

m_s=zeros(1,length(t));

end

message(i,:)=m_s;

%product of carrier and message

ask_sig(i,:)=c.*m_s;

t1=t1+(Tb+.01);

t2=t2+(Tb+.01);

% Plot the message and ASK signal

subplot(5,1,2);

axis([0 N -2 2]);

plot(t,message(i,:),'r');

title('message signal');

xlabel('t--->');

ylabel('m(t)');

grid on

hold on

subplot(5,1,4);

title('ASK signal');

xlabel('t--->');

ylabel('s(t)');

grid on

hold on

end

hold off

%Plot the carrier signal and input binary data

subplot(5,1,3);

plot(t,c);

title('carrier signal');

xlabel('t--->');

ylabel('c(t)');

grid on

subplot(5,1,1);

stem(m);

title('binary data bits');

xlabel('n--->');

ylabel('b(n)');

grid on

Observation:The desired ASK waveforms i.e. binary data, message signal, carrier signal and output waveforms are shown in figure 6.1.

Conclusion:The program for ASK modulation has been simulated in MATLAB and observed the desired waveforms.

Questions:

1. What is ASK?
2. Write a MATLAB program to generate sync function
3. Differentiate plot and subplot commands in MATLAB.