void ampmodem_modulate(ampmodem _q,
float _x,
float complex *_y)
{
float complex x_hat = 0.0f;
float complex y_hat;
if (_q->type == LIQUID_AMPMODEM_DSB) {
x_hat = _x;
} else {
// push through Hilbert transform
// LIQUID_AMPMODEM_USB:
// LIQUID_AMPMODEM_LSB: conjugate Hilbert transform output
firhilbf_r2c_execute(_q->hilbert, _x, &x_hat);
if (_q->type == LIQUID_AMPMODEM_LSB)
x_hat = conjf(x_hat);
}
if (_q->suppressed_carrier)
y_hat = x_hat;
else
y_hat = 0.5f*(x_hat + 1.0f);
// mix up
nco_crcf_mix_up(_q->oscillator, y_hat, _y);
nco_crcf_step(_q->oscillator);
}
int main()
{
// spectral periodogram options
unsigned int nfft = 1200; // spectral periodogram FFT size
unsigned int num_samples = 64000; // number of samples
float fc = 0.20f; // carrier (relative to sampling rate)
// create objects
iirfilt_crcf filter_tx = iirfilt_crcf_create_lowpass(15, 0.05);
nco_crcf mixer_tx = nco_crcf_create(LIQUID_VCO);
nco_crcf mixer_rx = nco_crcf_create(LIQUID_VCO);
iirfilt_crcf filter_rx = iirfilt_crcf_create_lowpass(7, 0.2);
// set carrier frequencies
nco_crcf_set_frequency(mixer_tx, fc * 2*M_PI);
nco_crcf_set_frequency(mixer_rx, fc * 2*M_PI);
// create objects for measuring power spectral density
spgramcf spgram_tx = spgramcf_create_default(nfft);
spgramf spgram_dac = spgramf_create_default(nfft);
spgramcf spgram_rx = spgramcf_create_default(nfft);
// run through loop one step at a time
unsigned int i;
for (i=0; i<num_samples; i++) {
// STEP 1: generate input signal (filtered noise with offset tone)
float complex v1 = (randnf() + randnf()*_Complex_I) + 3.0f*cexpf(-_Complex_I*0.2f*i);
iirfilt_crcf_execute(filter_tx, v1, &v1);
// save spectrum
spgramcf_push(spgram_tx, v1);
// STEP 2: mix signal up and save real part (DAC output)
nco_crcf_mix_up(mixer_tx, v1, &v1);
float v2 = crealf(v1);
nco_crcf_step(mixer_tx);
// save spectrum
spgramf_push(spgram_dac, v2);
// STEP 3: mix signal down and filter off image
float complex v3;
nco_crcf_mix_down(mixer_rx, v2, &v3);
iirfilt_crcf_execute(filter_rx, v3, &v3);
nco_crcf_step(mixer_rx);
// save spectrum
spgramcf_push(spgram_rx, v3);
}
// compute power spectral density output
float psd_tx [nfft];
float psd_dac [nfft];
float psd_rx [nfft];
spgramcf_get_psd(spgram_tx, psd_tx);
spgramf_get_psd( spgram_dac, psd_dac);
spgramcf_get_psd(spgram_rx, psd_rx);
// destroy objects
spgramcf_destroy(spgram_tx);
spgramf_destroy(spgram_dac);
spgramcf_destroy(spgram_rx);
iirfilt_crcf_destroy(filter_tx);
nco_crcf_destroy(mixer_tx);
nco_crcf_destroy(mixer_rx);
iirfilt_crcf_destroy(filter_rx);
//
// 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\n");
fprintf(fid,"nfft = %u;\n", nfft);
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"psd_tx = zeros(1,nfft);\n");
fprintf(fid,"psd_dac= zeros(1,nfft);\n");
fprintf(fid,"psd_rx = zeros(1,nfft);\n");
for (i=0; i<nfft; i++) {
fprintf(fid,"psd_tx (%6u) = %12.4e;\n", i+1, psd_tx [i]);
fprintf(fid,"psd_dac(%6u) = %12.4e;\n", i+1, psd_dac[i]);
fprintf(fid,"psd_rx (%6u) = %12.4e;\n", i+1, psd_rx [i]);
}
fprintf(fid,"figure;\n");
fprintf(fid,"hold on;\n");
fprintf(fid," plot(f, psd_tx, '-', 'LineWidth',1.5,'Color',[0.7 0.7 0.7]);\n");
fprintf(fid," plot(f, psd_dac, '-', 'LineWidth',1.5,'Color',[0.0 0.5 0.3]);\n");
fprintf(fid," plot(f, psd_rx, '-', 'LineWidth',1.5,'Color',[0.0 0.3 0.5]);\n");
fprintf(fid,"hold off;\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('Power Spectral Density [dB]');\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"axis([-0.5 0.5 -100 60]);\n");
fprintf(fid,"legend('transmit (complex)','DAC output (real)','receive (complex)','location','northeast');\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
int main(int argc, char*argv[]) {
srand( time(NULL) );
// parameters
float phase_offset = M_PI/10;
float frequency_offset = 0.001f;
float SNRdB = 30.0f;
float pll_bandwidth = 0.02f;
modulation_scheme ms = LIQUID_MODEM_QPSK;
unsigned int n=256; // number of iterations
int dopt;
while ((dopt = getopt(argc,argv,"uhs:b:n:P:F:m:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 's': SNRdB = atof(optarg); break;
case 'b': pll_bandwidth = atof(optarg); break;
case 'n': n = atoi(optarg); break;
case 'P': phase_offset = atof(optarg); break;
case 'F': frequency_offset= atof(optarg); 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);
}
}
unsigned int d=n/32; // print every "d" lines
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid, "%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid, "clear all;\n");
fprintf(fid, "phi=zeros(1,%u);\n",n);
fprintf(fid, "r=zeros(1,%u);\n",n);
// objects
nco_crcf nco_tx = nco_crcf_create(LIQUID_VCO);
nco_crcf nco_rx = nco_crcf_create(LIQUID_VCO);
modem mod = modem_create(ms);
modem demod = modem_create(ms);
unsigned int bps = modem_get_bps(mod);
// initialize objects
nco_crcf_set_phase(nco_tx, phase_offset);
nco_crcf_set_frequency(nco_tx, frequency_offset);
nco_crcf_pll_set_bandwidth(nco_rx, pll_bandwidth);
float noise_power = powf(10.0f, -SNRdB/20.0f);
// print parameters
printf("PLL example :\n");
printf("modem : %u-%s\n", 1<<bps, modulation_types[ms].name);
printf("frequency offset: %6.3f, phase offset: %6.3f, SNR: %6.2fdB, pll b/w: %6.3f\n",
frequency_offset, phase_offset, SNRdB, pll_bandwidth);
// run loop
unsigned int i, M=1<<bps, sym_in, sym_out, num_errors=0;
float phase_error;
float complex x, r, v, noise;
for (i=0; i<n; i++) {
// generate random symbol
sym_in = rand() % M;
// modulate
modem_modulate(mod, sym_in, &x);
// channel
//r = nco_crcf_cexpf(nco_tx);
nco_crcf_mix_up(nco_tx, x, &r);
// add complex white noise
crandnf(&noise);
r += noise * noise_power;
//
//v = nco_crcf_cexpf(nco_rx);
nco_crcf_mix_down(nco_rx, r, &v);
// demodulate
modem_demodulate(demod, v, &sym_out);
num_errors += count_bit_errors(sym_in, sym_out);
// error estimation
//phase_error = cargf(r*conjf(v));
phase_error = modem_get_demodulator_phase_error(demod);
// perfect error estimation
//phase_error = nco_tx->theta - nco_rx->theta;
// print every line in a format that octave can read
fprintf(fid, "phi(%u) = %10.6E;\n", i+1, phase_error);
fprintf(fid, "r(%u) = %10.6E + j*%10.6E;\n",
i+1, crealf(v), cimagf(v));
if ((i+1)%d == 0 || i==n-1) {
printf(" %4u: e_hat : %6.3f, phase error : %6.3f, freq error : %6.3f\n",
i+1, // iteration
phase_error, // estimated phase error
nco_crcf_get_phase(nco_tx) - nco_crcf_get_phase(nco_rx),// true phase error
nco_crcf_get_frequency(nco_tx) - nco_crcf_get_frequency(nco_rx)// true frequency error
);
}
// update tx nco object
nco_crcf_step(nco_tx);
// update pll
nco_crcf_pll_step(nco_rx, phase_error);
// update rx nco object
nco_crcf_step(nco_rx);
}
fprintf(fid, "figure;\n");
fprintf(fid, "plot(1:length(phi),phi,'LineWidth',2,'Color',[0 0.25 0.5]);\n");
fprintf(fid, "xlabel('Symbol Index');\n");
fprintf(fid, "ylabel('Phase Error [radians]');\n");
fprintf(fid, "grid on;\n");
fprintf(fid, "t0 = round(0.25*length(r));\n");
fprintf(fid, "figure;\n");
fprintf(fid, "plot(r(1:t0),'x','Color',[0.6 0.6 0.6],r(t0:end),'x','Color',[0 0.25 0.5]);\n");
fprintf(fid, "grid on;\n");
fprintf(fid, "axis([-1.5 1.5 -1.5 1.5]);\n");
fprintf(fid, "axis('square');\n");
fprintf(fid, "xlabel('In-Phase');\n");
fprintf(fid, "ylabel('Quadrature');\n");
fprintf(fid, "legend(['first 25%%'],['last 75%%'],1);\n");
fclose(fid);
printf("results written to %s.\n",OUTPUT_FILENAME);
nco_crcf_destroy(nco_tx);
nco_crcf_destroy(nco_rx);
modem_destroy(mod);
modem_destroy(demod);
printf("bit errors: %u / %u\n", num_errors, bps*n);
printf("done.\n");
return 0;
}
int main(int argc, char*argv[])
{
srand(time(NULL));
// options
unsigned int M = 64; // number of subcarriers
unsigned int cp_len = 16; // cyclic prefix length
unsigned int taper_len = 4; // taper length
unsigned int payload_len = 120; // length of payload (bytes)
modulation_scheme ms = LIQUID_MODEM_QPSK;
fec_scheme fec0 = LIQUID_FEC_NONE;
fec_scheme fec1 = LIQUID_FEC_HAMMING128;
crc_scheme check = LIQUID_CRC_32;
float noise_floor = -30.0f; // noise floor [dB]
float SNRdB = 20.0f; // signal-to-noise ratio [dB]
float dphi = 0.02f; // carrier frequency offset
int debug_enabled = 0; // enable debugging?
// get options
int dopt;
while((dopt = getopt(argc,argv,"uhds:F:M:C:n:m:v:c:k:")) != EOF){
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'd': debug_enabled = 1; break;
case 's': SNRdB = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 'M': M = atoi(optarg); break;
case 'C': cp_len = atoi(optarg); break;
case 'n': payload_len = atol(optarg); break;
case 'm':
ms = liquid_getopt_str2mod(optarg);
if (ms == LIQUID_MODEM_UNKNOWN) {
fprintf(stderr,"error: %s, unknown/unsupported mod. scheme: %s\n", argv[0], optarg);
exit(-1);
}
break;
case 'v':
// data integrity check
check = liquid_getopt_str2crc(optarg);
if (check == LIQUID_CRC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported CRC scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
case 'c':
// inner FEC scheme
fec0 = liquid_getopt_str2fec(optarg);
if (fec0 == LIQUID_FEC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported inner FEC scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
case 'k':
// outer FEC scheme
fec1 = liquid_getopt_str2fec(optarg);
if (fec1 == LIQUID_FEC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported outer FEC scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
default:
exit(-1);
}
}
unsigned int i;
// TODO : validate options
// derived values
unsigned int frame_len = M + cp_len;
float complex buffer[frame_len]; // time-domain buffer
float nstd = powf(10.0f, noise_floor/20.0f);
float gamma = powf(10.0f, (SNRdB + noise_floor)/20.0f);
// allocate memory for header, payload
unsigned char header[8];
unsigned char payload[payload_len];
// initialize subcarrier allocation
unsigned char p[M];
ofdmframe_init_default_sctype(M, p);
// create frame generator
ofdmflexframegenprops_s fgprops;
ofdmflexframegenprops_init_default(&fgprops);
fgprops.check = check;
fgprops.fec0 = fec0;
fgprops.fec1 = fec1;
fgprops.mod_scheme = ms;
ofdmflexframegen fg = ofdmflexframegen_create(M, cp_len, taper_len, p, &fgprops);
// create frame synchronizer
ofdmflexframesync fs = ofdmflexframesync_create(M, cp_len, taper_len, p, callback, (void*)payload);
if (debug_enabled)
ofdmflexframesync_debug_enable(fs);
// initialize header/payload and assemble frame
for (i=0; i<8; i++)
header[i] = i & 0xff;
for (i=0; i<payload_len; i++)
payload[i] = rand() & 0xff;
ofdmflexframegen_assemble(fg, header, payload, payload_len);
ofdmflexframegen_print(fg);
ofdmflexframesync_print(fs);
// initialize frame synchronizer with noise
for (i=0; i<1000; i++) {
float complex noise = nstd*( randnf() + _Complex_I*randnf())*M_SQRT1_2;
ofdmflexframesync_execute(fs, &noise, 1);
}
// generate frame, push through channel
int last_symbol=0;
nco_crcf nco = nco_crcf_create(LIQUID_VCO);
nco_crcf_set_frequency(nco, dphi);
while (!last_symbol) {
// generate symbol
last_symbol = ofdmflexframegen_writesymbol(fg, buffer);
// apply channel
for (i=0; i<frame_len; i++) {
float complex noise = nstd*( randnf() + _Complex_I*randnf())*M_SQRT1_2;
buffer[i] *= gamma;
buffer[i] += noise;
nco_crcf_mix_up(nco, buffer[i], &buffer[i]);
nco_crcf_step(nco);
}
// receive symbol
ofdmflexframesync_execute(fs, buffer, frame_len);
}
nco_crcf_destroy(nco);
// export debugging file
if (debug_enabled)
ofdmflexframesync_debug_print(fs, "ofdmflexframesync_debug.m");
// destroy objects
ofdmflexframegen_destroy(fg);
ofdmflexframesync_destroy(fs);
printf("done.\n");
return 0;
}
