what is shift keying modulation ?

Amplitude shift keying (ASK modulation)

Amplitude shift keying is a modulation technique in digital communication. It is a form of amplitude modulation that represents the digital data in discrete amplitude levels.

For a binary data, there are two levels 1s and 0s. In ASK modulation for binary symbol 1, a fixed-amplitude carrier wave is transmitted with constant frequency and phase. And the for symbol 0 no signal will be transmitted.

An ASK system is similar to an ON and OFF switching of sinusoidal transmission for the state of 1 and 0 respectively.

ASK output waveform

amplitude shift keying, Amplitude-shift-keying-modulation, ASK-MATLAB-waveform,ASK-output

Amplitude shift keying MATLAB code
 clear all
close all
clc
g=[0 0 1 0 1 0 1 1];
f=50;
n=1;
while n <= length (g)
if g(n) == 0
t1 = (n-1) * 0.1:0.1/100:n*0.1
s1 = (0)*cos(2 *pi*f*t1)
plot(t1,s1)
grid on
hold on
else
t =(n-1)*0.1:0.1/100:n*0.1;
s=(5)*cos(2*pi*f*t);
plot(t,s);
grid on;
hold on;
end
n=n+1;
end
title('ASK')
xlabel('Time')
ylabel('Amplitude')

Phase shift keying (PSK modulation)

Phase shift keying (PSK) is a digital communication method in which the phase of a transmitted signal is varied to represent digital states.

For the binary form of PSK called binary phase-shift keying (BPSK), uses signal phase difference of  0 and 180 degrees to represent the two binary states.

PSK output waveform

Phase shift keying,Phase-shift-keying-modulation,PSK-circuit-diagram,PSK-MATLAB-output-waveform

Phase shift keying MATLAB code
clear all
close all
clc
g=[1 0 1 0 1 0 ];
f=10;
n=1;
while n <= length (g)
t = (n-1) * 0.1:0.1/100:n*0.1;
if g(n) == 0
p = cos(2 *pi*f*t+0);
plot(t,p);
grid on;
hold on;
else
p1=cos(2*pi*f*t+(pi));
plot(t,p1);
grid on;
hold on;
end
n=n+1;
end
title('PSK')
xlabel('Time')
ylabel('Amplitude')

Frequency shift keying (FSK modulation)

Frequency shift keying (FSK) is a frequency modulation technique in digital communication. FSK transmits through discrete frequency changes of a carrier signal at a constant amplitude and phase.

In Binary frequency shift keying (BFSK), the two binary symbols 0 and 1, are each represented by using a specific frequency for logic 0 and another frequency value for logic 1. Mostly a lower frequency (space frequency) representative for state 0 and a higher frequency (mark frequency) for state 1.

 

FSK output waveform

Frequency shift keying,Frequency-shift-keying-modulation,FSK-matlab-output-waveform
Frequency shift keying MATLAB code
clear all
close all
clc
g=[1 0 1 0 1 0];
f=10;
n=1;
while n <= length (g)
t = (n-1) * 0.1:0.001:n*0.1;
if g(n) == 0
p = cos(2 *pi*f*t);
plot(t,p);
grid on;
hold on;
else
p1=cos(2*pi*f*10*t);
plot(t,p1);
grid on;
hold on;
end
n=n+1;
end
title('FSK')
xlabel('Time')
ylabel('Amplitude')
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