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//
// cpfskmodem_example.c
//
// This example demonstrates the continuous phase frequency-shift keying
// (CP-FSK) modem in liquid. A message signal is modulated and the
// resulting signal is recovered using a demodulator object.
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "cpfskmodem_example.m"
// print usage/help message
void usage()
{
printf("cpfskmodem_example -- continuous-phase frequency-shift keying example\n");
printf("options:\n");
printf(" -h : print help\n");
printf(" -t <type> : filter type: [square], rcos-full, rcos-half, gmsk\n");
printf(" -p <b/s> : bits/symbol, default: 1\n");
printf(" -H <index> : modulation index, default: 0.5\n");
printf(" -k <s/sym> : samples/symbol, default: 8\n");
printf(" -m <delay> : filter delay (symbols), default: 3\n");
printf(" -b <rolloff> : filter roll-off, default: 0.35\n");
printf(" -n <num> : number of data symbols, default: 80\n");
printf(" -s <snr> : SNR [dB], default: 40\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 = 4; // filter samples/symbol
unsigned int m = 3; // filter delay (symbols)
float beta = 0.35f; // GMSK bandwidth-time factor
unsigned int num_symbols = 20; // number of data symbols
float SNRdB = 40.0f; // signal-to-noise ratio [dB]
int filter_type = LIQUID_CPFSK_SQUARE;
int dopt;
while ((dopt = getopt(argc,argv,"ht:p:H:k:m:b:n:s:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 't':
if (strcmp(optarg,"square")==0) {
filter_type = LIQUID_CPFSK_SQUARE;
} else if (strcmp(optarg,"rcos-full")==0) {
filter_type = LIQUID_CPFSK_RCOS_FULL;
} else if (strcmp(optarg,"rcos-half")==0) {
filter_type = LIQUID_CPFSK_RCOS_PARTIAL;
} else if (strcmp(optarg,"gmsk")==0) {
filter_type = LIQUID_CPFSK_GMSK;
} else {
fprintf(stderr,"error: %s, unknown filter type '%s'\n", argv[0], optarg);
exit(1);
}
break;
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;
case 's': SNRdB = atof(optarg); break;
default:
exit(1);
}
}
unsigned int i;
// derived values
unsigned int num_samples = k*num_symbols;
unsigned int M = 1 << bps;
float nstd = powf(10.0f, -SNRdB/20.0f);
// arrays
unsigned int sym_in [num_symbols]; // input symbols
float complex x [num_samples]; // transmitted signal
float complex y [num_samples]; // received signal
unsigned int sym_out[num_symbols]; // output symbols
// create modem objects
cpfskmod mod = cpfskmod_create(bps, h, k, m, beta, filter_type);
cpfskdem dem = cpfskdem_create(bps, h, k, m, beta, filter_type);
// print modulator
cpfskmod_print(mod);
cpfskdem_print(dem);
// get full symbol delay
unsigned int delay = cpfskmod_get_delay(mod) + cpfskdem_get_delay(dem);
printf("delay: %u samples\n", delay);
// generate message signal
for (i=0; i<num_symbols; i++)
sym_in[i] = rand() % M;
// modulate signal
for (i=0; i<num_symbols; i++)
cpfskmod_modulate(mod, sym_in[i], &x[k*i]);
// push through channel (add noise)
for (i=0; i<num_samples; i++)
y[i] = x[i] + nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// demodulate signal
for (i=0; i<num_symbols; i++)
sym_out[i] = cpfskdem_demodulate(dem, &y[i*k]);
// print/count errors
unsigned int num_errors = 0;
for (i=delay; i<num_symbols; i++) {
int is_err = (sym_in[i-delay] == sym_out[i]) ? 0 : 1;
printf(" %3u : %2u %2u %s\n", i, sym_in[i-delay], sym_out[i], is_err ? "*" : "");
num_errors += is_err;
}
printf("symbol errors: %u / %u\n", num_errors, num_symbols-delay);
// destroy modem objects
cpfskmod_destroy(mod);
cpfskdem_destroy(dem);
// compute power spectral density of transmitted signal
unsigned int nfft = 1024;
float psd[nfft];
spgramcf_estimate_psd(nfft, x, num_samples, psd);
//
// 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,"h = %f;\n", h);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"delay = %u; %% receive filter delay\n", m);
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++) {
fprintf(fid,"x(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
}
// save power spectral density
fprintf(fid,"psd = zeros(1,nfft);\n");
for (i=0; i<nfft; i++)
fprintf(fid,"psd(%4u) = %12.8f;\n", i+1, psd[i]);
fprintf(fid,"t=[0:(num_samples-1)]/k;\n");
fprintf(fid,"i = 1:k:num_samples;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,4,1:3);\n");
fprintf(fid," plot(t,real(x),'-', t(i),real(x(i)),'ob',...\n");
fprintf(fid," t,imag(x),'-', t(i),imag(x(i)),'og');\n");
fprintf(fid," axis([0 num_symbols -1.2 1.2]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('x(t)');\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,4,5:7);\n");
fprintf(fid," plot(t,real(y),'-', t(i),real(y(i)),'ob',...\n");
fprintf(fid," t,imag(y),'-', t(i),imag(y(i)),'og');\n");
fprintf(fid," axis([0 num_symbols -1.2 1.2]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('y(t)');\n");
fprintf(fid," grid on;\n");
// plot I/Q constellations
fprintf(fid,"subplot(3,4,4);\n");
fprintf(fid," plot(real(x),imag(x),'-',real(x(i)),imag(x(i)),'rs','MarkerSize',4);\n");
fprintf(fid," xlabel('I');\n");
fprintf(fid," ylabel('Q');\n");
fprintf(fid," axis([-1 1 -1 1]*1.2);\n");
fprintf(fid," axis square;\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,4,8);\n");
fprintf(fid," plot(real(y),imag(y),'-',real(y(i)),imag(y(i)),'rs','MarkerSize',4);\n");
fprintf(fid," xlabel('I');\n");
fprintf(fid," ylabel('Q');\n");
fprintf(fid," axis([-1 1 -1 1]*1.2);\n");
fprintf(fid," axis square;\n");
fprintf(fid," grid on;\n");
// plot PSD
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"subplot(3,4,9:12);\n");
fprintf(fid," plot(f,psd,'LineWidth',1.5);\n");
fprintf(fid," axis([-0.5 0.5 -60 20]);\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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