what is amplitude, frequency & phase shift keying modulations ?

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 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 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 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')