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//
// nyquist_filter_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "nyquist_filter_example.m"
// print usage/help message
void usage()
{
printf("nyquist_filter_example options:\n");
printf(" u/h : print usage/help\n");
printf(" t : filter type: [kaiser], pm, rcos, fexp, fsech, farcsech\n");
printf(" k : filter samples/symbol, k >= 2, default: 2\n");
printf(" m : filter delay (symbols), m >= 1, default: 4\n");
printf(" b : filter excess bandwidth factor, 0 < b < 1, default: 0.33\n");
}
int main(int argc, char*argv[]) {
// options
unsigned int k=2; // samples/symbol
unsigned int m=4; // symbol delay
float beta=0.33f; // excess bandwidth factor
int ftype = LIQUID_FIRFILT_RCOS;
int dopt;
while ((dopt = getopt(argc,argv,"uht:k:m:b:")) != EOF) {
switch (dopt) {
case 'u':
case 'h':
usage();
return 0;
case 't':
if (strcmp(optarg,"kaiser")==0) {
ftype = LIQUID_FIRFILT_KAISER;
} else if (strcmp(optarg,"pm")==0) {
ftype = LIQUID_FIRFILT_PM;
} else if (strcmp(optarg,"rcos")==0) {
ftype = LIQUID_FIRFILT_RCOS;
} else if (strcmp(optarg,"fexp")==0) {
ftype = LIQUID_FIRFILT_FEXP;
} else if (strcmp(optarg,"fsech")==0) {
ftype = LIQUID_FIRFILT_FSECH;
} else if (strcmp(optarg,"farcsech")==0) {
ftype = LIQUID_FIRFILT_FARCSECH;
} else {
fprintf(stderr,"error: %s, unknown filter type '%s'\n", argv[0], optarg);
exit(1);
}
break;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
default:
exit(1);
}
}
if (k < 2) {
fprintf(stderr,"error: %s, k must be at least 2\n", argv[0]);
exit(1);
} else if (m < 1) {
fprintf(stderr,"error: %s, m must be at least 1\n", argv[0]);
exit(1);
} else if (beta <= 0.0f || beta >= 1.0f) {
fprintf(stderr,"error: %s, beta must be in (0,1)\n", argv[0]);
exit(1);
}
// initialize objects
unsigned int h_len = 2*k*m+1;
float h[h_len];
// design the filter
liquid_firdes_prototype(ftype,k,m,beta,0,h);
// print the coefficients to the screen
unsigned int i;
for (i=0; i<h_len; i++)
printf("h(%3u) = %12.8f\n", i+1, h[i]);
//
// export output file
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"k = %u;\n", k);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"beta = %12.8f;\n", beta);
fprintf(fid,"h_len = 2*k*m+1;\n");
fprintf(fid,"h = zeros(1,h_len);\n");
for (i=0; i<h_len; i++)
fprintf(fid,"h(%3u) = %20.8e;\n", i+1, h[i]);
fprintf(fid,"nfft=1024;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"H = 20*log10(abs(fftshift(fft(h/k,nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f,H,'-','LineWidth',2,...\n");
fprintf(fid," [0.5/k],[-20*log10(2)],'or',...\n");
fprintf(fid," [0.5/k*(1-beta) 0.5/k*(1-beta)],[-100 10],'-r',...\n");
fprintf(fid," [0.5/k*(1+beta) 0.5/k*(1+beta)],[-100 10],'-r');\n");
fprintf(fid,"xlabel('normalized frequency');\n");
fprintf(fid,"ylabel('PSD');\n");
fprintf(fid,"axis([-0.5 0.5 -100 10]);\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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