// modulate block of samples
// _q : ampmodem object
// _m : message signal m(t), [size: _n x 1]
// _n : number of input, output samples
// _s : complex baseband signal s(t) [size: _n x 1]
void ampmodem_modulate_block(ampmodem _q,
float * _m,
unsigned int _n,
float complex * _s)
{
// TODO: implement more efficient method
unsigned int i;
for (i=0; i<_n; i++)
ampmodem_modulate(_q, _m[i], &_s[i]);
}
int main(int argc, char*argv[])
{
// options
float mod_index = 0.1f; // modulation index (bandwidth)
float fc = 0.10f; // AM carrier
liquid_ampmodem_type type = LIQUID_AMPMODEM_DSB;
int suppressed_carrier = 0; // suppress the carrier?
unsigned int num_samples = 201; // number of samples
float SNRdB = 60.0f; // signal-to-noise ratio [dB]
// derived values
unsigned int nfft = 1024;
// create mod/demod objects
ampmodem mod = ampmodem_create(mod_index, fc, type, suppressed_carrier);
ampmodem demod = ampmodem_create(mod_index, fc, type, suppressed_carrier);
ampmodem_print(mod);
unsigned int i;
float x[num_samples];
float complex y[num_samples];
float z[num_samples];
#if 0
// generate input data: windowed sinusoid
float f_audio = 0.04179f; // input sine frequency
for (i=0; i<num_samples; i++) {
x[i] = sinf(2*M_PI*i*f_audio) + 0.5f*sinf(2*M_PI*i*f_audio*1.8f);
x[i] *= 0.7f*hamming(i,num_samples);
}
#else
// generate un-modulated input signal (filtered noise)
float fc_audio = 0.07f;
float f0_audio = 0.10f;
iirfilt_rrrf f = iirfilt_rrrf_create_prototype(LIQUID_IIRDES_BUTTER,
LIQUID_IIRDES_BANDPASS,
LIQUID_IIRDES_SOS,
6, fc_audio, f0_audio, 1.0f, 1.0f);
// push noise through filter
for (i=0; i<100; i++)
iirfilt_rrrf_execute(f, 1.5f*randnf(), &x[0]);
// generate filtered/windowed output
for (i=0; i<num_samples; i++) {
iirfilt_rrrf_execute(f, 1.5f*randnf(), &x[i]);
x[i] *= hamming(i,num_samples);
}
iirfilt_rrrf_destroy(f);
#endif
// modulate signal
for (i=0; i<num_samples; i++)
ampmodem_modulate(mod, x[i], &y[i]);
// add noise
float nstd = powf(10.0f,-SNRdB/20.0f);
for (i=0; i<num_samples; i++)
cawgn(&y[i], nstd);
// demodulate signal
for (i=0; i<num_samples; i++)
ampmodem_demodulate(demod, y[i], &z[i]);
// destroy objects
ampmodem_destroy(mod);
ampmodem_destroy(demod);
// compute power spectral density
float complex Y[nfft];
liquid_doc_psdwindow wtype = LIQUID_DOC_PSDWINDOW_HANN;
int normalize = 1;
liquid_doc_compute_psdcf(y, num_samples, Y, nfft, wtype, normalize);
//
// export output files
//
FILE * fid;
// time-domain plot
fid = fopen(OUTPUT_FILENAME_TIME,"w");
if (!fid) {
fprintf(stderr,"error: %s, could not open '%s' for writing\n", argv[0], OUTPUT_FILENAME_TIME);
exit(1);
}
fprintf(fid,"# %s: auto-generated file\n\n", OUTPUT_FILENAME_TIME);
fprintf(fid,"reset\n");
fprintf(fid,"set terminal postscript eps enhanced color solid rounded\n");
fprintf(fid,"set xrange [0:%u];\n",num_samples-1);
fprintf(fid,"set yrange [-1.2:1.2]\n");
fprintf(fid,"set size ratio 0.3\n");
fprintf(fid,"set xlabel 'Sample Index'\n");
fprintf(fid,"set key top right nobox\n");
fprintf(fid,"set ytics -5,0.5,5\n");
fprintf(fid,"set grid xtics ytics\n");
fprintf(fid,"set pointsize 0.6\n");
fprintf(fid,"set grid linetype 1 linecolor rgb '%s' lw 1\n", LIQUID_DOC_COLOR_GRID);
fprintf(fid,"set multiplot layout 2,1 scale 1.0,1.0\n");
fprintf(fid,"# input/demodulated signals\n");
fprintf(fid,"set ylabel 'input/output signal'\n");
fprintf(fid,"plot '-' using 1:2 with lines linetype 1 linewidth 2 linecolor rgb '%s' title 'input',\\\n",LIQUID_DOC_COLOR_RED);
fprintf(fid," '-' using 1:2 with lines linetype 1 linecolor rgb '%s' title 'demodulated'\n",LIQUID_DOC_COLOR_GRAY);
for (i=0; i<num_samples; i++)
fprintf(fid,"%12u %12.4e\n", i, x[i]);
fprintf(fid,"e\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"%12u %12.4e\n", i, z[i]);
fprintf(fid,"e\n");
fprintf(fid,"# demodulated signals\n");
fprintf(fid,"set ylabel 'modulated signal'\n");
fprintf(fid,"plot '-' using 1:2 with lines linetype 1 linewidth 1 linecolor rgb '%s' title 'real',\\\n",LIQUID_DOC_COLOR_BLUE);
fprintf(fid," '-' using 1:2 with lines linetype 1 linewidth 1 linecolor rgb '%s' title 'imag',\\\n",LIQUID_DOC_COLOR_GREEN);
fprintf(fid," '-' using 1:2 with lines linetype 0 linewidth 2 linecolor rgb '#222222' notitle,\\\n");
fprintf(fid," '-' using 1:2 with lines linetype 0 linewidth 2 linecolor rgb '#222222' notitle\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"%12u %12.4e\n", i, crealf(y[i]));
fprintf(fid,"e\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"%12u %12.4e\n", i, cimagf(y[i]));
fprintf(fid,"e\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"%12u %12.4e\n", i, cabsf(y[i]));
fprintf(fid,"e\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"%12u %12.4e\n", i, -cabsf(y[i]));
fprintf(fid,"e\n");
fclose(fid);
printf("results written to '%s\n", OUTPUT_FILENAME_TIME);
// frequency-domain plot
fid = fopen(OUTPUT_FILENAME_FREQ,"w");
if (!fid) {
fprintf(stderr,"error: %s, could not open '%s' for writing\n", argv[0], OUTPUT_FILENAME_FREQ);
exit(1);
}
fprintf(fid,"# %s: auto-generated file\n\n", OUTPUT_FILENAME_FREQ);
fprintf(fid,"reset\n");
fprintf(fid,"set terminal postscript eps enhanced color solid rounded\n");
fprintf(fid,"set xrange [-0.5:0.5];\n");
fprintf(fid,"set yrange [-100:10]\n");
fprintf(fid,"set size ratio 0.6\n");
fprintf(fid,"set xlabel 'Normalized Frequency'\n");
fprintf(fid,"set ylabel 'Power Spectral Density [dB]'\n");
fprintf(fid,"set nokey\n");
fprintf(fid,"set xtics -0.5,0.1,0.5\n");
fprintf(fid,"set ytics -200,20,200\n");
fprintf(fid,"set grid xtics ytics\n");
fprintf(fid,"set grid linetype 1 linecolor rgb '%s' lw 1\n", LIQUID_DOC_COLOR_GRID);
fprintf(fid,"# spectrum\n");
fprintf(fid,"set style fill solid 0.1\n");
fprintf(fid,"plot '-' using 1:2 with filledcurves above y1=-200 linetype 1 linewidth 3 linecolor rgb '%s' title 'input'\n",LIQUID_DOC_COLOR_PURPLE);
for (i=0; i<nfft; i++)
fprintf(fid,"%12.8f %12.4e\n", (float)i/(float)nfft - 0.5f, 20*log10f(cabsf(Y[(i+nfft/2)%nfft])));
fprintf(fid,"e\n");
fclose(fid);
printf("results written to '%s\n", OUTPUT_FILENAME_FREQ);
return 0;
}