Pulse code modulation

Matlab program for Pulse code modulation.

Matlab code

clc; close all; clear all;

A=1;

fm=input('Enter the frequency of Message signal = ');

fc=input('Enter the frequency of Carrier signal (Pulse-train) = ');

N=0.0001;

t = 0:N:1/fm;

Sm=A+A*sin(2*pi*fm*t); % Message signal

Ssqw=square(2*pi*fc*t); % Square Wave

% CONVERSION OF SQUARE WAVE TO PULSE TRAIN (Sp = Carrier signal)

for i=1:length(Ssqw)

    if (Ssqw(i)<=0)

        Sp(i)=0;

    else

        Sp(i)=1;

    end

end

Spam=Sp.*Sm; % Pulse Amplitude Modulated Signal

% QUANTIZATION OF PAM SIGNAL (LEVEL ASSIGNMENT)

m1=[];

tc=0:N:1/fc; % tc = Time period of one Pulse train

for j=1:length(tc)-1:length(Spam)-1

     p=Spam(j:j+length(tc)-2);

     m2=max(p);

     if m2<=0.25

         m3=1;

     elseif  m2<=0.5;

         m3=2;

     elseif m2<=0.75;

         m3=3;

     elseif m2<=1;

         m3=4;

     elseif m2<=1.25;

         m3=5;

     elseif m2<=1.5;

         m3=6;  

     elseif m2<=1.75;

         m3=7;   

     elseif m2<=2;

         m3=8;  

     end;

     m1=[m1 m3];

end;

m1

% CONVERSION OF QUANTIZED VALUE TO DIGITAL CODE (CODE ASSIGNMENT)

Sq=[];

for i=1:length(m1)

    if m1(i)==1

        n1=[0,0,0];

    elseif m1(i)==2

        n1=[0,0,1];

    elseif m1(i)==3

        n1=[0,1,0];

    elseif m1(i)==4

        n1=[0,1,1];

    elseif m1(i)==5

        n1=[1,0,0];

    elseif m1(i)==6

        n1=[1,0,1];

    elseif m1(i)==7

        n1=[1,1,0];

    elseif m1(i)==8

        n1=[1,1,1];   

    end;

Sq=[Sq n1];

end;

Sq

% GENERATING PCM SIGNAL (BIT STREAM)

Spcm=[];

t1=[];

t2=0;

tpb=(1/fc)/3;% tpb = Time per 3 bits(3 bits are sent per 1 Time period of pulse train)

for i=1:length(Sq)

    if Sq(i)==0

        t3=t2:0.0001:t2+tpb;

        Bs=zeros(1,length(t3));

    else

         t3=t2:0.0001:t2+tpb;

        Bs=ones(1,length(t3));

    end;

    t1=[t1 t3];

    Spcm=[Spcm Bs];

    t2=t2+tpb;

end;

   

subplot(4,1,1);

plot(t,Sm);

xlabel('Time-->');

ylabel('Amplitude-->');

title('Message Signal');

subplot(4,1,2);

plot(t,Sp);

xlabel('Time-->');

ylabel('Amplitude-->');

title('Carrier signal (Pulse-train)');

axis([0 1/fm -A-1 A+1]);

subplot(4,1,3);

plot(t,Spam);

grid;

xlabel('Time-->');

ylabel('Amplitude-->');

title('Pulse Amplitude Modulated Signal (PAM)');

subplot(4,1,4);

plot(t1,Spcm);

xlabel('Time-->');

ylabel('Amplitude-->');

title('Pulse Code Modulated Signal (PCM)');

axis([0 1/fm -1 2]);

Command window

Enter the frequency of Message signal = 2

Enter the frequency of Carrier signal (Pulse-train) = 20

m1 =

     6     8     8     8     7     5     2     1     1     3

Sq =

  Columns 1 through 17

     1     0     1     1     1     1     1     1     1     1     1     1     1     1     0     1     0

  Columns 18 through 30

     0     0     0     1     0     0     0     0     0     0     0     1     0

Figure window