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//
// nco_example.c
//
// This example demonstrates the most basic functionality of the
// numerically-controlled oscillator (NCO) object.
//
// SEE ALSO: nco_pll_example.c
// nco_pll_modem_example.c
//
#include <stdio.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "nco_example.m"
int main()
{
// options
int type = LIQUID_NCO; // nco type
float fc = 0.1f*M_SQRT1_2; // nco tone frequency
unsigned int num_samples = 240000; // number of samples to run
unsigned int nfft = 4000; // spectral periodogram FFT size
// create the NCO object
nco_crcf q = nco_crcf_create(type);
nco_crcf_set_frequency(q, 2*M_PI*fc);
nco_crcf_print(q);
// create spectral periodogram
spgramcf periodogram = spgramcf_create_default(nfft);
spgramcf_print(periodogram);
unsigned int i;
for (i=0; i<num_samples; i++) {
float complex y;
nco_crcf_cexpf(q, &y);
nco_crcf_step(q);
// push resulting sample through periodogram
spgramcf_push(periodogram, y);
}
// compute power spectral density output
float psd[nfft];
spgramcf_get_psd(periodogram, psd);
// destroy objects
spgramcf_destroy(periodogram);
nco_crcf_destroy(q);
// export output 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\n");
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"psd = zeros(1,nfft);\n");
for (i=0; i<nfft; i++)
fprintf(fid,"psd(%6u) = %12.4e;\n", i+1, psd[i]);
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f, psd, '-', 'LineWidth',1.5);\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('Power Spectral Density [dB]');\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"axis([-0.5 0.5 -60 40]);\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
return 0;
}
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