MATLAB Program for Pulse Code Modulation m file

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps.

MATLAB Program: 

a=4;

fm=2;

fs=100*fm;

t=0:1/fs:1;%for sampling

x=a*sin(2*pi*fm*t);%let us take one simple sin signla for Pulse code modulation

subplot(5,1,1);

plot(t,x,'r');

xlabel('time');

ylabel('amplitude');

title('Original message signal');

subplot(5,1,2);

stem(t,x,'r');

xlabel('time');

ylabel('amplitude');

title('Sampled message signal');

enc=[];

for(i=1:length(x))

 if (x(i)>0 && x(i)<=1)

 e=[1 0 0];

 xq(i)=0.5;

 elseif (x(i)>1 && x(i)<=2)

 e=[1 0 1];

 xq(i)=1.5;

 elseif (x(i)>2 && x(i)<=3)

 e=[1 1 0];

 xq(i)=2.5;

 elseif (x(i)>3 && x(i)<=4)

 e=[1 1 1];

 xq(i)=3.5;

 elseif (x(i)>-4 && x(i)<=-3)

 e=[0 0 0];

 xq(i)=-3.5;

 elseif (x(i)>-3 && x(i)<=-2)

 e=[0 0 1];

 xq(i)=-2.5;

 elseif (x(i)>-2 && x(i)<=-1)

 e=[0 1 0];

 xq(i)=-1.5;

 else (x(i)>-1 && x(i)<=0)

 e=[0 1 1];

 xq(i)=-0.5;

 end

 enc=[enc e];

 end

 subplot(5,1,3);

 plot(t,xq,'b');

 title('Quantised signla');

% decoding(Receiver section)

 X_Q=[];

 for i=1:3:length(enc)-2

 if(enc(i)==0 && enc(i+1)==0 && enc(i+2)==0)

 x_q=-3.5;

 elseif(enc(i)==0 && enc(i+1)==0 && enc(i+2)==1)

 x_q=-2.5;

 elseif(enc(i)==0 && enc(i+1)==1 && enc(i+2)==0)

 x_q=-1.5;

 elseif(enc(i)==0 && enc(i+1)==1 && enc(i+2)==1)

 x_q=-0.5;

 elseif(enc(i)==1 && enc(i+1)==0 && enc(i+2)==0)

 x_q=0.5;

 elseif(enc(i)==1 && enc(i+1)==0 && enc(i+2)==1)

 x_q=1.5;

 elseif(enc(i)==1 && enc(i+1)==1 && enc(i+2)==0)

 x_q=2.5;

 elseif(enc(i)==1 && enc(i+1)==1 && enc(i+2)==1)

 x_q=3.5;

 end

 X_Q=[X_Q x_q];

 end

 subplot(5,1,4);

 plot(t,X_Q);

 title('Decoded signal');

 [num,den]=butter(6,4*fm/fs);

 recon=filter(num,den,X_Q);

 subplot(5,1,5);

 plot(t,recon);

 title('Reconstructed signal in the receiver');

Output: