Scicos Block
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Gaussian White Noise Generator block

Contents

• Gaussian White Noise Generator block
  • Palette
  • Description
  • Dialog box
  • Default properties
  • Interfacing function
  • Computational function (type 4)
  • See also
  • Authors

Palette

• Sources.cosf - Sources palette

Description

In communication system simulator, a Gaussian noise generator is generally computed using the box Muller law. This method allows noising both amplitude and phase a given complex value. It is defined with these two equations:

$$\tilde{I}\,=\,\sigma\sqrt{-\log(\tilde{p})\:\cos(2\pi\tilde{q})}$$

$$\tilde{Q}\,=\,\sigma\sqrt{-\log(\tilde{p})\:\sin(2\pi\tilde{q})}$$

where $\tilde{p}$ and $\tilde{q}$ are two uniform random variables, $\sigma$ the variance of the noise source and $\tilde{I}$ $\tilde{Q}$ the real and imaginary part of the noisy complex sample.

Dialog box

• Size of outputs :
  Type 'vec' of size 1. integer. The size of the regular output port
• sigma :
  Type 'vec' of size -1. vector of real. The variance of the noise generator.
• mean :
  Type 'vec' of size -1. vector of real. The mean of the noise generator.
• seed :
  Type 'vec' of size 1. scalar. The seed of the noise generator.
• Type :
  Type 'vec' of size 1. integer. The seed of the noise generator.
  • 0 :
    for a cosine output
  • 1 :
    for a sine output
  • 2 :
    for both cosine and sine output (two regular outputs)

Default properties

• always active: no
• direct-feedthrough: no
• zero-crossing: no
• mode: no
• number/sizes of inputs: 0 /
• number/sizes of outputs: 1 / 64
• number/sizes of activation inputs: 1 / 1
• number/sizes of activation outputs: 0 /
• continuous-time state: no
• discrete-time state: no
• name of computational function: noiseblk

Interfacing function

NOISEBLK_f.sci

Computational function (type 4)

/* noiseblk Scicos Gaussian random generator block
 * Type 4 simulation function ver 1.0 - scilab-3.0
 * 22 décembre 2004 - IRCOM GROUP - Author : A.Layec
 */
 
/* REVISION HISTORY :
 * $Log$
 */
 
#include "scicos_block.h"
#include <math.h>
#include <stdlib.h>  /*pour RAND_MAX*/
#define M_PI		3.14159265358979323846

/* noiseblkv_c routine de calcul d'échantillons bruités par la méthode "Box Muller Law"
 *
 * Entrées :
 * n    : taille des vecteurs
 * typ  : type de sortie (0:cos/1:sin)
 * sig  : vecteurs des variances
 * mean : vecteurs des moyennes
 * Sorties :
 * y    : vecteur des sorties
 * 
 * dépendances
 * math.h
 */
void noiseblkv_c(int *n,int *typ,double *sig,double *mean,double *y_i,double *y_q)
{
 /*déclaration des variables*/
 int i;
 double rand1, rand2;
 double rand_m;
 double ampl, phase;
  
 /*récupération de la valeur de RAND_MAX*/
 rand_m=RAND_MAX;
 
 for(i=0;i<(*n);i++)
 {
  /*calcul rand1*/
  rand1=rand()/rand_m;
  /*test rand1*/
  while((rand1<=0)||(rand1>=1)) rand1=rand()/rand_m;
       
  /*calcul rand2*/
  rand2=rand()/rand_m;
  /*test rand2*/
  while((rand2<=0)||(rand2>=1)) rand2=rand()/rand_m;

  /*Calcul amplitude et phase*/
  ampl=sig[i]*sqrt(-log(rand1));
  phase=2*M_PI*rand2;

  /*Calcul y*/
  switch(*typ)
  {
   case 0 :
   {
    y_i[i]=mean[i]+ampl*cos(phase);
    break;
   }
   
   case 1 :
   {
    y_q[i]=mean[i]+ampl*sin(phase);
    break;
   }
   
   case 2 :
   {
    y_i[i]=mean[i]+ampl*cos(phase);
    y_q[i]=mean[i]+ampl*sin(phase);
    break;
   }
  }
 }
 return;
}

void noiseblk(scicos_block *block,int flag)
{
  /*Déclaration des variables*/
  double *y1,*y2;
  int ny,typ;
  
  /*récupération de l'adresses des ports réguliers*/
  y1=(double *)block->outptr[0];
  
  /*récupère taille de sortie*/
  ny=block->outsz[0];
  
  /*récupère le type de générateur*/
  typ=block->ipar[1];

  if(flag==6)  
  {
   srand(block->ipar[0]);
  }
  
  else if(flag==1)
  {
   switch(typ)
   {
    case 0 :
    {
     /*Appel noiseblk_c*/
     noiseblkv_c(&ny,&typ,&block->rpar[0],&block->rpar[ny],&y1[0],y2);
     break;
    }
    
    case 1 :
    {
     /*Appel noiseblk_c*/
     noiseblkv_c(&ny,&typ,&block->rpar[0],&block->rpar[ny],y2,&y1[0]);
     break;
    }
    
    case 2 :
    {
     /*récupération de l'adresse de sortie*/
     y2=(double *)block->outptr[1];
     /*Appel noiseblk_c*/
     noiseblkv_c(&ny,&typ,&block->rpar[0],&block->rpar[ny],&y1[0],&y2[0]);
     break;
    }
   }
  }
}

See also

• noiseblk_c - white gaussian noise generator computational routine (Low level routine)

Authors

IRCOM Group Alan Layec