Adaptive Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 263

// Adaptc.c - Adaptation using LMS WITHOUT TI compiler

#include <stdio.h>
#include <math.h>
#define beta 0.01 //convergence rate
#define N 21 //order of filter
#define NS 40 //number of samples
#define Fs 8000 //sampling frequency
#define pi 3.1415926
#define DESIRED 2*cos(2*pi*T*1000/Fs) //desired signal
#define NOISE sin(2*pi*T*1000/Fs) //noise signal

main()
{
long I, T;
double D, Y, E;
double W[N+1] = {0.0};
double X[N+1] = {0.0};
FILE *desired, *Y_out, *error;
desired = fopen ("DESIRED", "w++"); //file for desired samples
Y_out = fopen ("Y_OUT", "w++"); //file for output samples
error = fopen ("ERROR", "w++"); //file for error samples
for (T = 0; T < NS; T++) //start adaptive algorithm
{
X[0] = NOISE; //new noise sample
D = DESIRED; //desired signal
Y = 0; //filter'output set to zero
for (I = 0; I <= N; I++)
Y += (W[I] * X[I]); //calculate filter output
E = D - Y; //calculate error signal
for (I = N; I >= 0; I--)
{
W[I] = W[I] + (beta*E*X[I]); //update filter coefficients
if (I != 0)
X[I] = X[I-1]; //update data sample
}
fprintf (desired, "\n%10g %10f", (float) T/Fs, D);
fprintf (Y_out, "\n%10g %10f", (float) T/Fs, Y);
fprintf (error, "\n%10g %10f", (float) T/Fs, E);
}
fclose (desired);
fclose (Y_out);
fclose (error);
}

FIGURE 7.11. Adaptive filter program compiled with Borland C/C++ ( adaptc.c ).

. The executable file is
also on the CD. It uses a desired cosine signal with an amplitude of 1 and a filter
order of 31. Execute this program, enter a

panying CD as adaptive.c , compiled with Borland C/C ++

value of 0.01, and verify the results in
Figure 7.13. Note that the output converges to the desired cosine signal. Press F2
to execute this program again with a different beta value.

b