Pulse Code Modulation and Demodulation

I have written a code to do Pulse Code Modulation but I am unable to retrieve the message signal back. Can someone please help me write demodulation code.

Here is what I have written for modulation

time = 0:0.0001:20;
const = input('Enter Bit Depth of PCM Coding:');
part = -1:0.1:1;
codebook = -1:0.1:1.1;
msg = sin(time);
[indx,quants] = quantiz(msg,part,codebook);
subplot(3,1,1);
plot(time,msg);
title('Message Signal');
subplot(3,1,2);
plot(time,quants);
title('Quantized Signal');
y = uencode(quants,const);
ybin = dec2bin(y,const);
subplot(3,1,3);
plot(time,y);
title('PCM PLOT');

How can I convert back the modulated signal to original.

Answer 1

[Darel]

If the bit depth is reasonably large (say const = 8), then you can get back the uencoded signal with udecode:

newquants = udecode(y, const)
max(abs(quants(:) - newquants(:)))

One other thing about this code is that the quantiz function could be configured better. The "codebook" entry for quantiz provides the values assigned to represent input numbers that fall within each quantization bin. So you probably want to select values that represent the center of the bins, not the endpoints. Note also that the first and last entries represent values that fall outside the total range. So a better setting for "codebook" would be

codebook = [-10, -.95:0.1:.95, 10];

Answer 2

[Asmita Jangam]

c=input('Enter Bit Depth Of PCM Coding:');

Answer 3

[Avinash]

PCM Modulation and Demodulation using Trainer Kit and MATLAB

Answer 4

[mohan]

time = 0:0.0001:20;

const = input('Enter Bit Depth of PCM Coding:');

part = -1:0.1:1;

codebook = -1:0.1:1.1;

msg = sin(time);

[indx,quants] = quantiz(msg,part,codebook);

subplot(3,1,1);

plot(time,msg);

title('Message Signal');

subplot(3,1,2);

plot(time,quants);

title('Quantized Signal');

y = uencode(quants,const);

ybin = dec2bin(y,const);

subplot(3,1,3);

plot(time,y);

title('PCM PLOT');

Answer 5

[Sudarshan]

clc;

close all;

clear all;

n=input('Enter n value for n-bit PCM system : ');

n1=input('Enter number of samples in a period : ');

L=2^n;

% % Signal Generation

% x=0:1/100:4*pi;

% y=8*sin(x); % Amplitude Of signal is 8v

% subplot(2,2,1);

% plot(x,y);grid on;

% Sampling Operation

x=0:2*pi/n1:4*pi; % n1 nuber of samples have tobe selected

s=8*sin(x);

subplot(3,1,1);

plot(s);

title('Analog Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

subplot(3,1,2);

stem(s);grid on; title('Sampled Sinal'); ylabel('Amplitude--->'); xlabel('Time--->');

% Quantization Process

vmax=8;

vmin=-vmax;

del=(vmax-vmin)/L;

part=vmin:del:vmax; % level are between vmin and vmax with difference of del

code=vmin-(del/2):del:vmax+(del/2); % Contaion Quantized valuses

[ind,q]=quantiz(s,part,code); % Quantization process

% ind contain index number and q contain quantized values

l1=length(ind);

l2=length(q);

for i=1:l1

if(ind(i)~=0) % To make index as binary decimal so started from 0 to N

ind(i)=ind(i)-1;

end

i=i+1;

end

for i=1:l2

if(q(i)==vmin-(del/2)) % To make quantize value inbetween the levels

q(i)=vmin+(del/2);

end

end

subplot(3,1,3);

stem(q);grid on; % Display the Quantize values

title('Quantized Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

% Encoding Process

figure

code=de2bi(ind,'left-msb'); % Cnvert the decimal to binary

k=1;

for i=1:l1

for j=1:n

coded(k)=code(i,j); % convert code matrix to a coded row vector

j=j+1;

k=k+1;

end

i=i+1;

end

subplot(2,1,1); grid on;

stairs(coded); % Display the encoded signal

axis([0 100 -2 3]); title('Encoded Signal');

ylabel('Amplitude--->');

% Demodulation Of PCM signal

qunt=reshape(coded,n,length(coded)/n);

index=bi2de(qunt','left-msb'); % Getback the index in decimal form

q=del*index+vmin+(del/2); % getback Quantized values

subplot(2,1,2); grid on;

plot(q);

% Plot Demodulated signal

title('Demodulated Signal');

ylabel('Amplitude--->');

xlabel('Time--->');