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// This example demonstrates the functionality of the arbitrary
// modem, a digital modulator/demodulator object with signal
// constellation points chosen arbitrarily. A simple bit-error
// rate simulation is then run to test the performance of the
// modem. The results are written to a file.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <getopt.h>
#include "liquid.h"
#define OUTPUT_FILENAME "modem_arb_example.m"
// print usage/help message
void usage()
{
printf("modem_arb_example [options]\n");
printf(" u/h : print usage\n");
printf(" p : modulation depth (default 4 bits/symbol)\n");
}
int main(int argc, char*argv[])
{
// options
unsigned int bps=6; // bits per symbol
unsigned int n=1024; // number of data points to evaluate
int dopt;
while ((dopt = getopt(argc,argv,"uhp:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'p': bps = atoi(optarg); break;
default:
exit(1);
}
}
// validate input
if (bps == 0) {
fprintf(stderr,"error: %s, bits/symbol must be greater than zero\n", argv[0]);
exit(1);
}
// derived values
unsigned int i;
unsigned int M = 1<<bps; // constellation size
// initialize constellation table
float complex constellation[M];
// initialize constellation (spiral)
for (i=0; i<M; i++) {
float r = (float)i / logf((float)M) + 4.0f;
float phi = (float)i / logf((float)M);
constellation[i] = r * cexpf(_Complex_I*phi);
}
// create mod/demod objects
modemcf mod = modemcf_create_arbitrary(constellation, M);
modemcf demod = modemcf_create_arbitrary(constellation, M);
modemcf_print(mod);
// run simulation
float complex x[n];
unsigned int num_errors = 0;
// run simple BER simulation
num_errors = 0;
unsigned int sym_in;
unsigned int sym_out;
for (i=0; i<n; i++) {
// generate and modulate random symbol
sym_in = modemcf_gen_rand_sym(mod);
modemcf_modulate(mod, sym_in, &x[i]);
// add noise
x[i] += 0.05 * randnf() * cexpf(_Complex_I*M_PI*randf());
// demodulate
modemcf_demodulate(demod, x[i], &sym_out);
// accumulate errors
num_errors += count_bit_errors(sym_in,sym_out);
}
printf("num bit errors: %4u / %4u\n", num_errors, bps*n);
// destroy modem objects
modemcf_destroy(mod);
modemcf_destroy(demod);
//
// 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");
fprintf(fid,"bps = %u;\n", bps);
fprintf(fid,"M = %u;\n", M);
for (i=0; i<n; i++) {
fprintf(fid,"x(%3u) = %12.4e + j*%12.4e;\n", i+1,
crealf(x[i]),
cimagf(x[i]));
}
// plot results
fprintf(fid,"figure;\n");
fprintf(fid,"plot(x,'x','MarkerSize',1);\n");
fprintf(fid,"xlabel('in-phase');\n");
fprintf(fid,"ylabel('quadrature phase');\n");
fprintf(fid,"title(['Arbitrary ' num2str(M) '-QAM']);\n");
fprintf(fid,"axis([-1 1 -1 1]*1.9);\n");
fprintf(fid,"axis square;\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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