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//
// cpfsk_psd_example.c
//
// This example demonstrates the differences in power spectral
// density (PSD) for different continuous-phase frequency-shift
// keying (CP-FSK) modems in liquid. Identical bit streams are fed
// into modulators with different pulse-shaping filters and the
// resulting PSDs are computed and logged to a file.
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "cpfsk_psd_example.m"
// print usage/help message
void usage()
{
printf("cpfsk_psd_example -- continuous-phase frequency-shift keying example\n");
printf("options:\n");
printf(" h : print help\n");
printf(" p : bits/symbol, default: 1\n");
printf(" H : modulation index, default: 0.5\n");
printf(" k : samples/symbol, default: 8\n");
printf(" m : filter delay (symbols), default: 3\n");
printf(" b : filter roll-off, default: 0.35\n");
printf(" n : number of data symbols, default: 80\n");
}
int main(int argc, char*argv[])
{
// options
unsigned int bps = 1; // number of bits/symbol
float h = 0.5f; // modulation index (h=1/2 for MSK)
unsigned int k = 8; // filter samples/symbol
unsigned int m = 7; // filter delay (symbols)
float beta = 0.35f; // GMSK bandwidth-time factor
unsigned int num_symbols = 48000; // number of data symbols
unsigned int nfft = 2400; // spectral periodogram FFT size
int dopt;
while ((dopt = getopt(argc,argv,"hp:H:k:m:b:n:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'p': bps = atoi(optarg); break;
case 'H': h = atof(optarg); break;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'n': num_symbols = atoi(optarg); break;
default:
exit(1);
}
}
unsigned int i;
// derived values
unsigned int M = 1 << bps; // constellation size
// create modulators
cpfskmod mod_0 = cpfskmod_create(bps, h, k, m, beta, LIQUID_CPFSK_SQUARE);
cpfskmod mod_1 = cpfskmod_create(bps, h, k, m, beta, LIQUID_CPFSK_RCOS_FULL);
cpfskmod mod_2 = cpfskmod_create(bps, h, k, m, beta, LIQUID_CPFSK_RCOS_PARTIAL);
cpfskmod mod_3 = cpfskmod_create(bps, h, k, m, beta, LIQUID_CPFSK_GMSK);
// buffers
float complex buf_0[k];
float complex buf_1[k];
float complex buf_2[k];
float complex buf_3[k];
// create PSD estimators
// spectral periodogram options
// create spectral periodogram
spgramcf spgram_0 = spgramcf_create_default(nfft);
spgramcf spgram_1 = spgramcf_create_default(nfft);
spgramcf spgram_2 = spgramcf_create_default(nfft);
spgramcf spgram_3 = spgramcf_create_default(nfft);
// estimate PSD for each symbol
for (i=0; i<num_symbols; i++) {
// generate random symbol
unsigned int sym = rand() % M;
// modulate
cpfskmod_modulate(mod_0, sym, buf_0);
cpfskmod_modulate(mod_1, sym, buf_1);
cpfskmod_modulate(mod_2, sym, buf_2);
cpfskmod_modulate(mod_3, sym, buf_3);
// estimate PSD
spgramcf_write(spgram_0, buf_0, k);
spgramcf_write(spgram_1, buf_1, k);
spgramcf_write(spgram_2, buf_2, k);
spgramcf_write(spgram_3, buf_3, k);
}
// compute power spectral density estimate output
float psd_0[nfft]; spgramcf_get_psd(spgram_0, psd_0);
float psd_1[nfft]; spgramcf_get_psd(spgram_1, psd_1);
float psd_2[nfft]; spgramcf_get_psd(spgram_2, psd_2);
float psd_3[nfft]; spgramcf_get_psd(spgram_3, psd_3);
// destroy modulators
cpfskmod_destroy(mod_0);
cpfskmod_destroy(mod_1);
cpfskmod_destroy(mod_2);
cpfskmod_destroy(mod_3);
// destroy spgram objects
spgramcf_destroy(spgram_0);
spgramcf_destroy(spgram_1);
spgramcf_destroy(spgram_2);
spgramcf_destroy(spgram_3);
//
// export results
//
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,"k = %u;\n", k);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"nfft = %u;\n", nfft);
// save power spectral density
fprintf(fid,"psd_0 = zeros(1,nfft);\n");
fprintf(fid,"psd_1 = zeros(1,nfft);\n");
fprintf(fid,"psd_2 = zeros(1,nfft);\n");
fprintf(fid,"psd_3 = zeros(1,nfft);\n");
for (i=0; i<nfft; i++) {
fprintf(fid,"psd_0(%4u) = %12.8f;\n", i+1, psd_0[i] - 10*log10(k));
fprintf(fid,"psd_1(%4u) = %12.8f;\n", i+1, psd_1[i] - 10*log10(k));
fprintf(fid,"psd_2(%4u) = %12.8f;\n", i+1, psd_2[i] - 10*log10(k));
fprintf(fid,"psd_3(%4u) = %12.8f;\n", i+1, psd_3[i] - 10*log10(k));
}
// plot PSD
fprintf(fid,"figure;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"hold on;\n");
fprintf(fid," plot(f,psd_0,'LineWidth',1.5,'Color',[0.0 0.5 0.2]);\n");
fprintf(fid," plot(f,psd_1,'LineWidth',1.5,'Color',[0.0 0.2 0.5]);\n");
fprintf(fid," plot(f,psd_2,'LineWidth',1.5,'Color',[0.5 0.0 0.0]);\n");
fprintf(fid," plot(f,psd_3,'LineWidth',1.5,'Color',[0.5 0.5 0.0]);\n");
fprintf(fid,"hold off;\n");
fprintf(fid,"legend('square','rcos (full)','rcos (partial)','GMSK, BT=%.2f');\n", beta);
fprintf(fid,"axis([-0.5 0.5 -80 10]);\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
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