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   Code Snippets

Unipolar NRZ

Senthilkumar ● March 24, 2011 ● Coded in Scilab 
//Nonreturn-to-zero unipolar format: Discrete PAM Signals Generation
//Unipolar NRZ 
clear;
close;
clc;
x = [0 1 0 0 0 1 0 0 1 1];
binary_zero = [0 0 0 0 0 0 0 0 0 0];
binary_one = [1 1 1 1 1 1 1 1 1 1];
L = length(x);
L1 = length(binary_zero);
total_duration = L*L;
//plotting
a =gca();
a.data_bounds =[0 -2;L*L1 2];
for i =1:L
  if(x(i)==0)
    plot([i*L-L+1:i*L],binary_zero);
    poly1= a.children(1).children(1);
    poly1.thickness =3;
  else
    plot([i*L-L+1:i*L],binary_one);
    poly1= a.children(1).children(1);
    poly1.thickness =3;
  end
end
xgrid(1)
title('Unipolar NRZ')

A-Law Compression - non uniform Quantization

Senthilkumar ● March 24, 2011●1 comment ● Coded in Scilab 
function [Cx,Xmax] =  Alaw(x,A)
  //Non-linear Quantization
  //A-law: A-law nonlinear quantization
  //x = input vector
  //Cx = A-law compressor output
  //Xmax = maximum of input vector x
  Xmax  = max(abs(x));
  for i = 1:length(x)
    if(x(i)/Xmax < = 1/A)
       Cx(i) = A*abs(x(i)/Xmax)./(1+log(A));
    elseif(x(i)/Xmax > 1/A)
      Cx(i) = (1+log(A*abs(x(i)/Xmax)))./(1+log(A));
    end
  end
  Cx = Cx/Xmax; //normalization of output vector
  Cx = Cx';
endfunction

u -Law and Inverse u-Law

Senthilkumar ● March 24, 2011 ● Coded in Scilab 
function [Cx,Xmax] =  mulaw(x,mu)
  //Non-linear Quantization
  //mulaw: mulaw nonlinear quantization
  //x = input vector
  //Cx = mulaw compressor output
  //Xmax = maximum of input vector x
  Xmax  = max(abs(x));
  if(log(1+mu)~=0)
    Cx = (log(1+mu*abs(x/Xmax))./log(1+mu));
  else
    Cx = x/Xmax;
  end
  
  Cx = Cx/Xmax; //normalization of output vector
endfunction

////////////////////////////////////////////////////
function x =  invmulaw(y,mu)
  //Non-linear Quantization
  //invmulaw: inverse mulaw nonlinear quantization
  //x = output vector 
  //y = input vector (using mulaw nonlinear comression)
  x = (((1+mu).^(abs(y))-1)./mu)  
endfunction

Uniform Quantization - PCM

Senthilkumar ● March 24, 2011 ● Coded in Scilab 
function [SQNR,xq,en_code] = uniform_pcm(x,L)
  //x = input sequence
  //L = number of qunatization levels 
 xmax = max(abs(x));
xq = x/xmax;
en_code = xq;
d = 2/L;
q = d*[0:L-1];
q = q-((L-1)/2)*d;
for i = 1:L
    xq(find(((q(i)-d/2)<= xq)&(xq<=(q(i)+d/2))))=...     
    q(i).*ones(1,length(find(((q(i)-d/2)<=xq)&(xq<=(q(i)+d/2)))));
    en_code(find(xq == q(i)))= (i-1).*ones(1,length(find(xq == q(i))));
end
  xq = xq*xmax;
  SQNR = 20*log10(norm(x)/norm(x-xq));
endfunction

PCM Encoding-Converting Quantized decimal sample values in to binary

Senthilkumar ● March 24, 2011 ● Coded in Scilab 
function [c] = PCM_Encoding(x,L,en_code)
  //Encoding: Converting Quantized decimal sample values in to binary
   //x = input sequence
   //L = number of qunatization levels 
   //en_code = normalized input sequence
n = log2(L);
c = zeros(length(x),n);
for i = 1:length(x)
  for j = n:-1:0
    if(fix(en_code(i)/(2^j))==1)
      c(i,(n-j)) =1;
      en_code(i) = en_code(i)-2^j;
    end
  end
end
disp(c)

PseudoNoise Sequence Generator

Senthilkumar ● March 24, 2011●4 comments ● Coded in Scilab 
//PN sequence generation
//Maximum-length sequence generator
//Program to generate Maximum Length Pseudo Noise Sequence
clc;
//Assign Initial value for PN generator
x0= 1;
x1= 0;
x2 =0;
x3 =0;
N = input('Enter the period of the signal')
for i =1:N
  x3 =x2;
  x2 =x1;
  x1 = x0;
  x0 =xor(x1,x3);
  disp(i,'The PN sequence at step')
  x = [x1 x2 x3];
  disp(x,'x=')
end
m = [7,8,9,10,11,12,13,17,19];
N = 2^m-1;
disp('Table Range of PN Sequence lengths')
disp('_________________________________________________________')
disp('Length of shift register (m)')
disp(m)
disp('PN sequence Length (N)')
disp(N)
disp('_________________________________________________________')

Logical XOR - not available inh scilab 5.2

Senthilkumar ● March 24, 2011●1 comment ● Coded in Scilab 
function [value] = xor(A,B)
  if(A==B)
    value = 0;
  else
    value = 1;
  end
endfunction

Hamming Weight and Hamming Distance

Senthilkumar ● March 24, 2011●1 comment ● Coded in Scilab 
// Hamming Weight and Hamming Distance
//H(7,4)
//Code Word Length = 7, Message Word length = 4, Parity bits =3
close;
clc;
//Getting Code Words
code1 = input('Enter the first code word');
code2 =  input('Enter the second code word');
Hamming_Distance = 0;
for i = 1:length(code1)
  Hamming_Distance =Hamming_Distance+xor(code1(i),code2(i));
end
disp(Hamming_Distance,'Hamming Distance')
//Result
//Enter the first code word [0,1,1,1,0,0,1]
//Enter the second code word[1,1,0,0,1,0,1]
//Hamming Distance       4.

Convolutional Encoding

Senthilkumar ● March 24, 2011 ● Coded in Scilab 
//Caption:Convolutional Code Generation
//Time Domain Approach
close;
clc;
g1 = input('Enter the input Top Adder Sequence:=')
g2 = input('Enter the input Bottom Adder Sequence:=')
m = input('Enter the message sequence:=')
x1 = round(convol(g1,m));
x2 = round(convol(g2,m));
x1 = modulo(x1,2);
x2 = modulo(x2,2);
N = length(x1);
for i =1:length(x1)
  x(i,:) =[x1(N-i+1),x2(N-i+1)];
end
x = string(x)
//Result
//Enter the input Top Adder Sequence:=[1,1,1]
//Enter the input Bottom Adder Sequence:=[1,0,1]
//Enter the message sequence:=[1,1,0,0,1]
//x =
//!1  1  !
//!      !
//!1  0  !
//!      !
//!1  1  !
//!      !
//!1  1  !
//!      !
//!0  1  !
//!      !
//!0  1  !
//!      !
//!1  1  !

Hamming Code(7,4)

Senthilkumar ● March 24, 2011 ● Coded in Scilab 
//Hamming Encoding
//H(7,4)
//Code Word Length = 7, Message Word length = 4, Parity bits =3
//clear;
close;
clc;
//Getting Message Word
m3 = input('Enter the 1 bit(MSb) of message word');
m2 = input('Enter the 2 bit of message word');
m1 = input('Enter the 3 bit of message word');
m0 = input('Enter the 4 bit(LSb) of message word');
//Generating Parity bits
for i = 1:(2^4)
  b2(i) = xor(m0(i),xor(m3(i),m1(i)));
  b1(i) = xor(m1(i),xor(m2(i),m3(i)));
  b0(i) = xor(m0(i),xor(m1(i),m2(i)));
  m(i,:) = [m3(i) m2(i) m1(i) m0(i)];
  b(i,:) = [b2(i) b1(i) b0(i)];
end
C = [b m];
disp('___________________________________________________________')
for i = 1:2^4
  disp(i)
  disp(m(i,:),'Message Word')
  disp(b(i,:),'Parity Bits')
  disp(C(i,:),'CodeWord')
  disp("   ");
  disp("   ");
end
disp('___________________________________________________________')
//disp(m b C)
//Result
//Enter the 1 bit(MSb) of message word [0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1];
//Enter the 2 bit of message word [0,0,0,0,1,1,1,1,0,0,0,0,1,1,1,1];
//Enter the 3 bit of message word [0,0,1,1,0,0,1,1,0,0,1,1,0,0,1,1];
//Enter the 4 bit(LSb) of message word [0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1];