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//
// firdecim_crcf_example.c
//
// This example demonstrates the interface to the firdecim (finite
// impulse response decimator) family of objects.
//
// SEE ALSO: firinterp_crcf_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <getopt.h>
#include "liquid.h"
#define OUTPUT_FILENAME "firdecim_crcf_example.m"
// print usage/help message
void usage()
{
printf("firdecim_crcf_example:\n");
printf(" -h : print usage/help\n");
printf(" -M <decim> : decimation factor, M > 1 default: 2\n");
printf(" -m <delay> : filter delay (symbols), m > 0, default: 2\n");
printf(" -s <atten> : filter stop-band attenuation [dB], default: 60\n");
printf(" -n <num> : number of samples (after decim), default: 8\n");
}
int main(int argc, char*argv[]) {
// options
unsigned int M = 6; // decimation factor
unsigned int m = 8; // filter delay
float As = 60.0f; // filter stop-band attenuation
unsigned int num_samples = 120; // number of samples (after decim)
int dopt;
while ((dopt = getopt(argc,argv,"hM:m:s:n:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'M': M = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 's': As = atof(optarg); break;
case 'n': num_samples = atoi(optarg); break;
default:
usage();
return 1;
}
}
// validate options
if (M < 2) {
fprintf(stderr,"error: %s, decim factor must be greater than 1\n", argv[0]);
return 1;
} else if (m < 1) {
fprintf(stderr,"error: %s, filter delay must be greater than 0\n", argv[0]);
return 1;
} else if (As <= 0.0) {
fprintf(stderr,"error: %s, stop-band attenuation must be greater than zero\n", argv[0]);
return 1;
} else if (num_samples < 1) {
fprintf(stderr,"error: %s, must have at least one sample\n", argv[0]);
return 1;
}
// data arrays
float complex x[M*num_samples]; // number of samples before decimation
float complex y[ num_samples]; // number of samples after decimation
// initialize input array
unsigned int i;
unsigned int w_len = (unsigned int)(0.9*M*num_samples);
float f0 = 0.017f;
float f1 = 0.021f;
for (i=0; i<M*num_samples; i++) {
x[i] = 0.6f*cexpf(_Complex_I*2*M_PI*f0*i);
x[i] += 0.4f*cexpf(_Complex_I*2*M_PI*f1*i);
x[i] *= (i < w_len) ? liquid_hamming(i,w_len) : 0;
}
// create decimator object and set scale
firdecim_crcf decim = firdecim_crcf_create_kaiser(M, m, As);
firdecim_crcf_set_scale(decim, 1.0f/(float)M);
// execute decimator
firdecim_crcf_execute_block(decim, x, num_samples, y);
// destroy decimator object
firdecim_crcf_destroy(decim);
//
// export results to file
//
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"M = %u;\n", M);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"num_samples=%u;\n", num_samples);
// inputs
for (i=0; i<M*num_samples; i++)
fprintf(fid,"x(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
// outputs
for (i=0; i<num_samples; i++)
fprintf(fid,"y(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
// plot results
fprintf(fid,"figure('position',[100 100 600 800]);\n");
fprintf(fid,"tx = [0:(M*num_samples-1)];\n");
fprintf(fid,"ty = [0:( num_samples-1)]*M - M*m;\n");
fprintf(fid,"nfft=3*2^nextpow2(M*num_samples);\n");
fprintf(fid,"fx = [0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid,"fy = fx/M;\n");
fprintf(fid,"X=20*log10(abs(fftshift(fft( x,nfft))));\n");
fprintf(fid,"Y=20*log10(abs(fftshift(fft(M*y,nfft))));\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," plot(tx,real(x),'-',ty,real(y),'s');\n");
fprintf(fid," grid on;\n");
fprintf(fid," axis([-M*m M*num_samples -1.2 1.2]);\n");
fprintf(fid," xlabel('Input sample index');\n");
fprintf(fid," ylabel('Real');\n");
fprintf(fid," legend('original','decimated','location','northeast');");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," plot(tx,imag(x),'-',ty,imag(y),'s');\n");
fprintf(fid," grid on;\n");
fprintf(fid," axis([-M*m M*num_samples -1.2 1.2]);\n");
fprintf(fid," xlabel('Input sample index');\n");
fprintf(fid," ylabel('Imag');\n");
fprintf(fid," legend('original','decimated','location','northeast');");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," plot(fx,X,'Color',[0.5 0.5 0.5],fy,Y,'LineWidth',2);\n");
fprintf(fid," grid on;\n");
fprintf(fid," axis([-0.5 0.5 -40 60]);\n");
fprintf(fid," xlabel('normalized frequency');\n");
fprintf(fid," ylabel('PSD [dB]');\n");
fprintf(fid," legend('original/real','transformed/decimated','location','northeast');");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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