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// This example demonstrates the digital modulator/demodulator
// (modem) object. Data symbols are modulated into complex
// samples which are then demodulated without noise or phase
// offsets. The user may select the modulation scheme via
// the command-line interface.
#include <stdlib.h>
#include <stdio.h>
#include <getopt.h>
#include "liquid.h"
#define OUTPUT_FILENAME "modem_example.m"
// print usage/help message
void usage()
{
printf("modem_example [options]\n");
printf(" h : print help\n");
printf(" v/q : verbose/quiet\n");
printf(" m : modulation scheme (qam16 default)\n");
liquid_print_modulation_schemes();
}
int main(int argc, char*argv[])
{
// create mod/demod objects
modulation_scheme ms = LIQUID_MODEM_QAM16;
int verbose = 1;
int dopt;
while ((dopt = getopt(argc,argv,"hvqm:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'v': verbose = 1; break;
case 'q': verbose = 0; break;
case 'm':
ms = liquid_getopt_str2mod(optarg);
if (ms == LIQUID_MODEM_UNKNOWN) {
fprintf(stderr,"error: %s, unknown/unsupported modulation scheme '%s'\n", argv[0], optarg);
return 1;
}
break;
default:
exit(1);
}
}
// create the modem objects
modemcf mod = modemcf_create(ms);
modemcf demod = modemcf_create(ms);
// ensure bits/symbol matches modem description (only
// applicable to certain specific modems)
unsigned int bps = modemcf_get_bps(mod);
modemcf_print(mod);
// open 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,"m = %u;\n", bps);
fprintf(fid,"M = %u;\n", 1<<bps);
fprintf(fid,"c = zeros(1,M);\n");
fprintf(fid,"i_str = cell(1,M);\n");
unsigned int i; // modulated symbol
unsigned int s; // demodulated symbol
unsigned int num_symbols = 1<<bps;
float complex x;
unsigned int num_sym_errors = 0;
unsigned int num_bit_errors = 0;
for (i=0; i<num_symbols; i++) {
modemcf_modulate(mod, i, &x);
modemcf_demodulate(demod, x, &s);
if (verbose)
printf("%4u : %12.8f + j*%12.8f\n", i, crealf(x), cimagf(x));
num_sym_errors += i == s ? 0 : 1;
num_bit_errors += count_bit_errors(i,s);
// write symbol to output file
fprintf(fid,"c(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(x), cimagf(x));
fprintf(fid,"i_str{%3u} = [num2str(%3u)];\n", i+1, i);
}
printf("num sym errors: %4u / %4u\n", num_sym_errors, num_symbols);
printf("num bit errors: %4u / %4u\n", num_bit_errors, num_symbols*bps);
// plot results
fprintf(fid,"\n\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(c,'o','MarkerSize',2);\n");
fprintf(fid,"hold on;\n");
fprintf(fid,"text(real(c)+0.02, imag(c)+0.02, i_str);\n");
fprintf(fid,"hold off;\n");
fprintf(fid,"axis([-1 1 -1 1]*1.6);\n");
fprintf(fid,"axis square;\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"xlabel('in phase');\n");
fprintf(fid,"ylabel('quadrature phase');\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
modemcf_destroy(mod);
modemcf_destroy(demod);
return 0;
}
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