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.

[Sushilkumar]

% Define the analog signal

t = 0:0.001:1; % Time vector from 0 to 1 second

Analog_Signal = sin(2*pi*5*t); % Example analog signal (sine wave)

% PCM parameters

bit_depth = 8; % Number of bits for quantization

quantization_levels = 2^bit_depth; % Total quantization levels

% Quantization

Quantized_Signal = round((Analog_Signal + 1) * (quantization_levels - 1) / 2);

% Demodulation

Demodulated_Signal = (2 * Quantized_Signal) / (quantization_levels - 1) - 1;

% Encoding PCM

Encoded_PCM = de2bi(Quantized_Signal, bit_depth, 'left-msb');

% Plotting

subplot(4,1,1);

plot(t, Analog_Signal);

title('Analog Signal');

xlabel('Time');

ylabel('Amplitude');

subplot(4,1,2);

stairs(t, Quantized_Signal);

title('Quantized Signal');

xlabel('Time');

ylabel('Amplitude');

subplot(4,1,3);

plot(t, Demodulated_Signal);

title('Demodulated Signal');

xlabel('Time');

ylabel('Amplitude');

subplot(4,1,4);

plot(t, Encoded_PCM);

title('Encoded PCM');

xlabel('Time');

ylabel('Bit');

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:');

Error using input
Support for user input is required, which is not available on this platform.

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 :  ');

Error using input
Support for user input is required, which is not available on this platform.

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--->');