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// This example demonstrates the iirinterp object (IIR interpolator)
// interface.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <getopt.h>
#include "liquid.h"
#define OUTPUT_FILENAME "iirinterp_crcf_example.m"
// print usage/help message
void usage()
{
printf("iirinterp_crcf_example:\n");
printf(" h : print help\n");
printf(" k : samples/symbol (interp factor), k > 1, default: 4\n");
printf(" n : number of input samples, default: 64\n");
}
int main(int argc, char*argv[]) {
// options
unsigned int k = 4; // interpolation factor
unsigned int num_samples = 64; // number of input samples
int dopt;
while ((dopt = getopt(argc,argv,"uhk:n:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'k': k = atoi(optarg); break;
case 'n': num_samples = atoi(optarg); break;
default:
exit(1);
}
}
// validate options
if (k < 2) {
fprintf(stderr,"error: %s, interp factor must be greater than 1\n", argv[0]);
exit(1);
} else if (num_samples < 1) {
fprintf(stderr,"error: %s, must have at least one data symbol\n", argv[0]);
usage();
return 1;
}
// create interpolator from prototype
unsigned int order = 8;
iirinterp_crcf q = iirinterp_crcf_create_default(k,order);
// derived values
float delay = iirinterp_crcf_groupdelay(q,0.0f);
// generate input signal and interpolate
float complex x[ num_samples]; // input samples
float complex y[k*num_samples]; // output samples
unsigned int i;
for (i=0; i<num_samples; i++) {
// input signal (sinusoidal chirp)
x[i] = cexpf(_Complex_I*(-0.17f*i + 0.9*i*i/(float)num_samples));
// apply window
x[i] *= (i < num_samples-5) ? liquid_hamming(i,num_samples) : 0.0f;
// push through interpolator
iirinterp_crcf_execute(q, x[i], &y[k*i]);
}
// destroy interpolator object
iirinterp_crcf_destroy(q);
// 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,"delay = %f;\n", delay);
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"x = zeros(1, num_samples);\n");
fprintf(fid,"y = zeros(1,k*num_samples);\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
for (i=0; i<k*num_samples; i++)
fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"\n\n");
fprintf(fid,"tx = [0:( num_samples-1)];\n");
fprintf(fid,"ty = [0:(k*num_samples-1)]/k - delay;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," plot(tx,real(x),'-s','MarkerSize',3,ty,real(y),'-s','MarkerSize',1);\n");
fprintf(fid," legend('input','interp','location','northeast');\n");
fprintf(fid," axis([0 num_samples -1.2 1.2]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('real');\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," plot(tx,imag(x),'-s','MarkerSize',3,ty,imag(y),'-s','MarkerSize',1);\n");
fprintf(fid," legend('input','interp','location','northeast');\n");
fprintf(fid," axis([0 num_samples -1.2 1.2]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('imag');\n");
fprintf(fid," grid on;\n");
// power spectral density
fprintf(fid,"nfft = 1024;\n");
fprintf(fid,"fx = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"fy = k*fx;\n");
fprintf(fid,"X = 20*log10(abs(fftshift(fft(x ,nfft))));\n");
fprintf(fid,"Y = 20*log10(abs(fftshift(fft(y/k,nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(fx,X,'LineWidth',2, fy,Y,'LineWidth',1);\n");
fprintf(fid,"legend('input','interp','location','northeast');\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('Power Spectral Density [dB]');\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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