void ampmodem_demodulate(ampmodem _q,
float complex _y,
float *_x)
{
#if DEBUG_AMPMODEM
windowcf_push(_q->debug_x, _y);
#endif
if (_q->suppressed_carrier) {
// single side-band suppressed carrier
if (_q->type != LIQUID_AMPMODEM_DSB) {
*_x = crealf(_y);
return;
}
// coherent demodulation
// mix signal down
float complex y_hat;
nco_crcf_mix_down(_q->oscillator, _y, &y_hat);
// compute phase error
float phase_error = tanhf( crealf(y_hat) * cimagf(y_hat) );
#if DEBUG_AMPMODEM
// compute frequency error
float nco_freq = nco_crcf_get_frequency(_q->oscillator);
float freq_error = nco_freq/(2*M_PI) - _q->fc/(2*M_PI);
// retain phase and frequency errors
windowf_push(_q->debug_phase_error, phase_error);
windowf_push(_q->debug_freq_error, freq_error);
#endif
// adjust nco, pll objects
nco_crcf_pll_step(_q->oscillator, phase_error);
// step NCO
nco_crcf_step(_q->oscillator);
// set output
*_x = crealf(y_hat);
} else {
// non-coherent demodulation (peak detector)
float t = cabsf(_y);
// remove DC bias
_q->ssb_q_hat = ( _q->ssb_alpha)*t +
(1 - _q->ssb_alpha)*_q->ssb_q_hat;
*_x = 2.0f*(t - _q->ssb_q_hat);
}
}
//
// test phase-locked loop
// _type : NCO type (e.g. LIQUID_NCO)
// _phase_offset : initial phase offset
// _freq_offset : initial frequency offset
// _pll_bandwidth : bandwidth of phase-locked loop
// _num_iterations : number of iterations to run
// _tol : error tolerance
void nco_crcf_pll_test(int _type,
float _phase_offset,
float _freq_offset,
float _pll_bandwidth,
unsigned int _num_iterations,
float _tol)
{
// objects
nco_crcf nco_tx = nco_crcf_create(_type);
nco_crcf nco_rx = nco_crcf_create(_type);
// initialize objects
nco_crcf_set_phase(nco_tx, _phase_offset);
nco_crcf_set_frequency(nco_tx, _freq_offset);
nco_crcf_pll_set_bandwidth(nco_rx, _pll_bandwidth);
// run loop
unsigned int i;
float phase_error;
float complex r, v;
for (i=0; i<_num_iterations; i++) {
// received complex signal
nco_crcf_cexpf(nco_tx,&r);
nco_crcf_cexpf(nco_rx,&v);
// error estimation
phase_error = cargf(r*conjf(v));
// update pll
nco_crcf_pll_step(nco_rx, phase_error);
// update nco objects
nco_crcf_step(nco_tx);
nco_crcf_step(nco_rx);
}
// ensure phase of oscillators is locked
float nco_tx_phase = nco_crcf_get_phase(nco_tx);
float nco_rx_phase = nco_crcf_get_phase(nco_rx);
CONTEND_DELTA(nco_tx_phase, nco_rx_phase, _tol);
// ensure frequency of oscillators is locked
float nco_tx_freq = nco_crcf_get_frequency(nco_tx);
float nco_rx_freq = nco_crcf_get_frequency(nco_rx);
CONTEND_DELTA(nco_tx_freq, nco_rx_freq, _tol);
// clean it up
nco_crcf_destroy(nco_tx);
nco_crcf_destroy(nco_rx);
}
// once p/n symbols are buffered, estimate residual carrier
// frequency and phase offsets, push through fine-tuned NCO
void flexframesync_syncpn(flexframesync _q)
{
unsigned int i;
// estimate residual carrier frequency offset from p/n symbols
float complex dphi_metric = 0.0f;
float complex r0 = 0.0f;
float complex r1 = 0.0f;
for (i=0; i<64; i++) {
r0 = r1;
r1 = _q->preamble_rx[i]*_q->preamble_pn[i];
dphi_metric += r1 * conjf(r0);
}
float dphi_hat = cargf(dphi_metric);
// estimate carrier phase offset from p/n symbols
float complex theta_metric = 0.0f;
for (i=0; i<64; i++)
theta_metric += _q->preamble_rx[i]*liquid_cexpjf(-dphi_hat*i)*_q->preamble_pn[i];
float theta_hat = cargf(theta_metric);
// TODO: compute gain correction factor
// initialize fine-tuned nco
nco_crcf_set_frequency(_q->nco_fine, dphi_hat);
nco_crcf_set_phase( _q->nco_fine, theta_hat);
// correct for carrier offset, pushing through phase-locked loop
for (i=0; i<64; i++) {
// mix signal down
nco_crcf_mix_down(_q->nco_fine, _q->preamble_rx[i], &_q->preamble_rx[i]);
// push through phase-locked loop
float phase_error = cimagf(_q->preamble_rx[i]*_q->preamble_pn[i]);
nco_crcf_pll_step(_q->nco_fine, phase_error);
#if DEBUG_FLEXFRAMESYNC
//_q->debug_nco_phase[i] = nco_crcf_get_phase(_q->nco_fine);
#endif
// update nco phase
nco_crcf_step(_q->nco_fine);
}
}
// execute synchronizer, receiving payload
// _q : frame synchronizer object
// _x : input sample
// _sym : demodulated symbol
void flexframesync_execute_rxpayload(flexframesync _q,
float complex _x)
{
// mix signal down
float complex y;
nco_crcf_mix_down(_q->nco_coarse, _x*0.5f/_q->gamma_hat, &y);
nco_crcf_step(_q->nco_coarse);
// update symbol synchronizer
float complex mf_out = 0.0f;
int sample_available = flexframesync_update_symsync(_q, y, &mf_out);
// compute output if timeout
if (sample_available) {
// push through fine-tuned nco
nco_crcf_mix_down(_q->nco_fine, mf_out, &mf_out);
// save payload symbols for callback (up to 256 values)
if (_q->payload_counter < 256)
_q->payload_sym[_q->payload_counter] = mf_out;
// demodulate
unsigned int sym_out = 0;
modem_demodulate(_q->demod_payload, mf_out, &sym_out);
_q->payload_mod[_q->payload_counter] = (unsigned char)sym_out;
// update phase-locked loop and fine-tuned NCO
float phase_error = modem_get_demodulator_phase_error(_q->demod_payload);
nco_crcf_pll_step(_q->nco_fine, phase_error);
nco_crcf_step(_q->nco_fine);
// increment counter
_q->payload_counter++;
if (_q->payload_counter == _q->payload_mod_len) {
// decode payload and invoke callback
flexframesync_decode_payload(_q);
// invoke callback
if (_q->callback != NULL) {
// set framestats internals
_q->framestats.evm = 20*log10f(sqrtf(_q->framestats.evm / FLEXFRAME_H_SYM));
_q->framestats.rssi = 20*log10f(_q->gamma_hat);
_q->framestats.cfo = nco_crcf_get_frequency(_q->nco_coarse) +
nco_crcf_get_frequency(_q->nco_fine) / 2.0f; //(float)(_q->k);
_q->framestats.framesyms = _q->payload_sym;
_q->framestats.num_framesyms = _q->payload_mod_len > 256 ? 256 : _q->payload_mod_len;
_q->framestats.mod_scheme = _q->ms_payload;
_q->framestats.mod_bps = _q->bps_payload;
_q->framestats.check = _q->check;
_q->framestats.fec0 = _q->fec0;
_q->framestats.fec1 = _q->fec1;
// invoke callback method
_q->callback(_q->header,
_q->header_valid,
_q->payload_dec,
_q->payload_dec_len,
_q->payload_valid,
_q->framestats,
_q->userdata);
}
// reset frame synchronizer
flexframesync_reset(_q);
return;
}
}
}
// execute synchronizer, receiving header
// _q : frame synchronizer object
// _x : input sample
void flexframesync_execute_rxheader(flexframesync _q,
float complex _x)
{
// mix signal down
float complex y;
nco_crcf_mix_down(_q->nco_coarse, _x*0.5f/_q->gamma_hat, &y);
nco_crcf_step(_q->nco_coarse);
// update symbol synchronizer
float complex mf_out = 0.0f;
int sample_available = flexframesync_update_symsync(_q, y, &mf_out);
// compute output if timeout
if (sample_available) {
// push through fine-tuned nco
nco_crcf_mix_down(_q->nco_fine, mf_out, &mf_out);
#if DEBUG_FLEXFRAMESYNC
if (_q->debug_enabled)
_q->header_sym[_q->header_counter] = mf_out;
#endif
// demodulate
unsigned int sym_out = 0;
#if DEMOD_HEADER_SOFT
unsigned char bpsk_soft_bit = 0;
modem_demodulate_soft(_q->demod_header, mf_out, &sym_out, &bpsk_soft_bit);
_q->header_mod[_q->header_counter] = bpsk_soft_bit;
#else
modem_demodulate(_q->demod_header, mf_out, &sym_out);
_q->header_mod[_q->header_counter] = (unsigned char)sym_out;
#endif
// update phase-locked loop and fine-tuned NCO
float phase_error = modem_get_demodulator_phase_error(_q->demod_header);
nco_crcf_pll_step(_q->nco_fine, phase_error);
nco_crcf_step(_q->nco_fine);
// update error vector magnitude
float evm = modem_get_demodulator_evm(_q->demod_header);
_q->framestats.evm += evm*evm;
// increment counter
_q->header_counter++;
if (_q->header_counter == FLEXFRAME_H_SYM) {
// decode header and invoke callback
flexframesync_decode_header(_q);
// invoke callback if header is invalid
if (!_q->header_valid && _q->callback != NULL) {
// set framestats internals
_q->framestats.evm = 20*log10f(sqrtf(_q->framestats.evm / FLEXFRAME_H_SYM));
_q->framestats.rssi = 20*log10f(_q->gamma_hat);
_q->framestats.cfo = nco_crcf_get_frequency(_q->nco_coarse) +
nco_crcf_get_frequency(_q->nco_fine) / 2.0f; //(float)(_q->k);
_q->framestats.framesyms = NULL;
_q->framestats.num_framesyms = 0;
_q->framestats.mod_scheme = LIQUID_MODEM_UNKNOWN;
_q->framestats.mod_bps = 0;
_q->framestats.check = LIQUID_CRC_UNKNOWN;
_q->framestats.fec0 = LIQUID_FEC_UNKNOWN;
_q->framestats.fec1 = LIQUID_FEC_UNKNOWN;
// invoke callback method
_q->callback(_q->header,
_q->header_valid,
NULL,
0,
0,
_q->framestats,
_q->userdata);
}
if (!_q->header_valid) {
flexframesync_reset(_q);
return;
}
// update state
_q->state = STATE_RXPAYLOAD;
}
}
}
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;
}
// execute synchronizer, receiving payload
// _q : frame synchronizer object
// _x : input sample
// _sym : demodulated symbol
void flexframesync_execute_rxpayload(flexframesync _q,
float complex _x)
{
// step synchronizer
float complex mf_out = 0.0f;
int sample_available = flexframesync_step(_q, _x, &mf_out);
// compute output if timeout
if (sample_available) {
// TODO: clean this up
// mix down with fine-tuned oscillator
nco_crcf_mix_down(_q->pll, mf_out, &mf_out);
// track phase, accumulate error-vector magnitude
unsigned int sym;
modem_demodulate(_q->payload_demod, mf_out, &sym);
float phase_error = modem_get_demodulator_phase_error(_q->payload_demod);
float evm = modem_get_demodulator_evm (_q->payload_demod);
nco_crcf_pll_step(_q->pll, phase_error);
nco_crcf_step(_q->pll);
_q->framesyncstats.evm += evm*evm;
// save payload symbols (modem input/output)
_q->payload_sym[_q->symbol_counter] = mf_out;
// increment counter
_q->symbol_counter++;
if (_q->symbol_counter == _q->payload_sym_len) {
// decode payload
_q->payload_valid = qpacketmodem_decode(_q->payload_decoder,
_q->payload_sym,
_q->payload_dec);
// update statistics
_q->framedatastats.num_frames_detected++;
_q->framedatastats.num_headers_valid++;
_q->framedatastats.num_payloads_valid += _q->payload_valid;
_q->framedatastats.num_bytes_received += _q->payload_dec_len;
// invoke callback
if (_q->callback != NULL) {
// set framestats internals
int ms = qpacketmodem_get_modscheme(_q->payload_decoder);
_q->framesyncstats.evm = 10*log10f(_q->framesyncstats.evm / (float)_q->payload_sym_len);
_q->framesyncstats.rssi = 20*log10f(_q->gamma_hat);
_q->framesyncstats.cfo = nco_crcf_get_frequency(_q->mixer);
_q->framesyncstats.framesyms = _q->payload_sym;
_q->framesyncstats.num_framesyms = _q->payload_sym_len;
_q->framesyncstats.mod_scheme = ms;
_q->framesyncstats.mod_bps = modulation_types[ms].bps;
_q->framesyncstats.check = qpacketmodem_get_crc(_q->payload_decoder);
_q->framesyncstats.fec0 = qpacketmodem_get_fec0(_q->payload_decoder);
_q->framesyncstats.fec1 = qpacketmodem_get_fec1(_q->payload_decoder);
// invoke callback method
_q->callback(_q->header_dec,
_q->header_valid,
_q->payload_dec,
_q->payload_dec_len,
_q->payload_valid,
_q->framesyncstats,
_q->userdata);
}
// reset frame synchronizer
flexframesync_reset(_q);
return;
}
}
}
void ModemFMStereo::demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut) {
ModemKitFMStereo *fmkit = (ModemKitFMStereo *)kit;
size_t bufSize = input->data.size();
liquid_float_complex u, v, w, x, y;
double audio_resample_ratio = fmkit->audioResampleRatio;
if (demodOutputData.size() != bufSize) {
if (demodOutputData.capacity() < bufSize) {
demodOutputData.reserve(bufSize);
}
demodOutputData.resize(bufSize);
}
size_t audio_out_size = (size_t)ceil((double) (bufSize) * audio_resample_ratio) + 512;
freqdem_demodulate_block(demodFM, &input->data[0], bufSize, &demodOutputData[0]);
if (resampledOutputData.size() != audio_out_size) {
if (resampledOutputData.capacity() < audio_out_size) {
resampledOutputData.reserve(audio_out_size);
}
resampledOutputData.resize(audio_out_size);
}
unsigned int numAudioWritten;
msresamp_rrrf_execute(fmkit->audioResampler, &demodOutputData[0], bufSize, &resampledOutputData[0], &numAudioWritten);
if (demodStereoData.size() != bufSize) {
if (demodStereoData.capacity() < bufSize) {
demodStereoData.reserve(bufSize);
}
demodStereoData.resize(bufSize);
}
float phase_error = 0;
for (size_t i = 0; i < bufSize; i++) {
// real -> complex
firhilbf_r2c_execute(fmkit->firStereoR2C, demodOutputData[i], &x);
// 19khz pilot band-pass
iirfilt_crcf_execute(fmkit->iirStereoPilot, x, &v);
nco_crcf_cexpf(fmkit->stereoPilot, &w);
w.imag = -w.imag; // conjf(w)
// multiply u = v * conjf(w)
u.real = v.real * w.real - v.imag * w.imag;
u.imag = v.real * w.imag + v.imag * w.real;
// cargf(u)
phase_error = atan2f(u.imag,u.real);
// step pll
nco_crcf_pll_step(fmkit->stereoPilot, phase_error);
nco_crcf_step(fmkit->stereoPilot);
// 38khz down-mix
nco_crcf_mix_down(fmkit->stereoPilot, x, &y);
nco_crcf_mix_down(fmkit->stereoPilot, y, &x);
// complex -> real
firhilbf_c2r_execute(fmkit->firStereoC2R, x, &demodStereoData[i]);
}
// std::cout << "[PLL] phase error: " << phase_error;
// std::cout << " freq:" << (((nco_crcf_get_frequency(stereoPilot) / (2.0 * M_PI)) * inp->sampleRate)) << std::endl;
if (audio_out_size != resampledStereoData.size()) {
if (resampledStereoData.capacity() < audio_out_size) {
resampledStereoData.reserve(audio_out_size);
}
resampledStereoData.resize(audio_out_size);
}
msresamp_rrrf_execute(fmkit->stereoResampler, &demodStereoData[0], bufSize, &resampledStereoData[0], &numAudioWritten);
audioOut->channels = 2;
if (audioOut->data.capacity() < (numAudioWritten * 2)) {
audioOut->data.reserve(numAudioWritten * 2);
}
audioOut->data.resize(numAudioWritten * 2);
for (size_t i = 0; i < numAudioWritten; i++) {
float l, r;
float ld, rd;
if (fmkit->demph) {
iirfilt_rrrf_execute(fmkit->iirDemphL, 0.568f * (resampledOutputData[i] - (resampledStereoData[i])), &ld);
iirfilt_rrrf_execute(fmkit->iirDemphR, 0.568f * (resampledOutputData[i] + (resampledStereoData[i])), &rd);
firfilt_rrrf_push(fmkit->firStereoLeft, ld);
firfilt_rrrf_execute(fmkit->firStereoLeft, &l);
firfilt_rrrf_push(fmkit->firStereoRight, rd);
firfilt_rrrf_execute(fmkit->firStereoRight, &r);
} else {
firfilt_rrrf_push(fmkit->firStereoLeft, 0.568f * (resampledOutputData[i] - (resampledStereoData[i])));
firfilt_rrrf_execute(fmkit->firStereoLeft, &l);
firfilt_rrrf_push(fmkit->firStereoRight, 0.568f * (resampledOutputData[i] + (resampledStereoData[i])));
firfilt_rrrf_execute(fmkit->firStereoRight, &r);
}
audioOut->data[i * 2] = l;
audioOut->data[i * 2 + 1] = r;
}
}
int main(int argc, char*argv[])
{
//srand(time(NULL));
// options
unsigned int num_symbols=800; // number of symbols to observe
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
float fc = 0.002f; // carrier offset
unsigned int hc_len=5; // channel filter length
unsigned int k=2; // matched filter samples/symbol
unsigned int m=3; // matched filter delay (symbols)
float beta=0.3f; // matched filter excess bandwidth factor
unsigned int p=3; // equalizer length (symbols, hp_len = 2*k*p+1)
float mu = 0.08f; // equalizer learning rate
// modulation type/depth
modulation_scheme ms = LIQUID_MODEM_QPSK;
int dopt;
while ((dopt = getopt(argc,argv,"hn:s:c:k:m:b:p:u:M:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'n': num_symbols = atoi(optarg); break;
case 's': SNRdB = atof(optarg); break;
case 'c': hc_len = atoi(optarg); break;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'p': p = atoi(optarg); break;
case 'u': mu = 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);
}
}
// validate input
if (num_symbols == 0) {
fprintf(stderr,"error: %s, number of symbols must be greater than zero\n", argv[0]);
exit(1);
} else if (hc_len == 0) {
fprintf(stderr,"error: %s, channel must have at least 1 tap\n", argv[0]);
exit(1);
} else if (k < 2) {
fprintf(stderr,"error: %s, samples/symbol must be at least 2\n", argv[0]);
exit(1);
} else if (m == 0) {
fprintf(stderr,"error: %s, filter semi-length must be at least 1 symbol\n", argv[0]);
exit(1);
} else if (beta < 0.0f || beta > 1.0f) {
fprintf(stderr,"error: %s, filter excess bandwidth must be in [0,1]\n", argv[0]);
exit(1);
} else if (p == 0) {
fprintf(stderr,"error: %s, equalizer semi-length must be at least 1 symbol\n", argv[0]);
exit(1);
} else if (mu < 0.0f || mu > 1.0f) {
fprintf(stderr,"error: %s, equalizer learning rate must be in [0,1]\n", argv[0]);
exit(1);
}
// derived values
unsigned int hm_len = 2*k*m+1; // matched filter length
unsigned int hp_len = 2*k*p+1; // equalizer filter length
unsigned int num_samples = k*num_symbols;
// bookkeeping variables
float complex syms_tx[num_symbols]; // transmitted data symbols
float complex x[num_samples]; // interpolated time series
float complex y[num_samples]; // channel output
float complex z[num_samples]; // equalized output
float complex syms_rx[num_symbols]; // received data symbols
float hm[hm_len]; // matched filter response
float complex hc[hc_len]; // channel filter coefficients
float complex hp[hp_len]; // equalizer filter coefficients
unsigned int i;
// generate matched filter response
liquid_firdes_rnyquist(LIQUID_FIRFILT_RRC, k, m, beta, 0.0f, hm);
firinterp_crcf interp = firinterp_crcf_create(k, hm, hm_len);
// create the modem objects
modem mod = modem_create(ms);
modem demod = modem_create(ms);
unsigned int M = 1 << modem_get_bps(mod);
// generate channel impulse response, filter
hc[0] = 1.0f;
for (i=1; i<hc_len; i++)
hc[i] = 0.09f*(randnf() + randnf()*_Complex_I);
firfilt_cccf fchannel = firfilt_cccf_create(hc, hc_len);
// generate random symbols
for (i=0; i<num_symbols; i++)
modem_modulate(mod, rand()%M, &syms_tx[i]);
// interpolate
for (i=0; i<num_symbols; i++)
firinterp_crcf_execute(interp, syms_tx[i], &x[i*k]);
// push through channel
float nstd = powf(10.0f, -SNRdB/20.0f);
for (i=0; i<num_samples; i++) {
firfilt_cccf_push(fchannel, x[i]);
firfilt_cccf_execute(fchannel, &y[i]);
// add carrier offset and noise
y[i] *= cexpf(_Complex_I*2*M_PI*fc*i);
y[i] += nstd*(randnf() + randnf()*_Complex_I)*M_SQRT1_2;
}
// push through equalizer
// create equalizer, intialized with square-root Nyquist filter
eqlms_cccf eq = eqlms_cccf_create_rnyquist(LIQUID_FIRFILT_RRC, k, p, beta, 0.0f);
eqlms_cccf_set_bw(eq, mu);
// get initialized weights
eqlms_cccf_get_weights(eq, hp);
// filtered error vector magnitude (emperical RMS error)
float evm_hat = 0.03f;
// nco/pll for phase recovery
nco_crcf nco = nco_crcf_create(LIQUID_VCO);
nco_crcf_pll_set_bandwidth(nco, 0.02f);
float complex d_hat = 0.0f;
unsigned int num_symbols_rx = 0;
for (i=0; i<num_samples; i++) {
// print filtered evm (emperical rms error)
if ( ((i+1)%50)==0 )
printf("%4u : rms error = %12.8f dB\n", i+1, 10*log10(evm_hat));
eqlms_cccf_push(eq, y[i]);
eqlms_cccf_execute(eq, &d_hat);
// store output
z[i] = d_hat;
// decimate by k
if ( (i%k) != 0 ) continue;
// update equalizer independent of the signal: estimate error
// assuming constant modulus signal
eqlms_cccf_step(eq, d_hat/cabsf(d_hat), d_hat);
// apply carrier recovery
float complex v;
nco_crcf_mix_down(nco, d_hat, &v);
// save resulting data symbol
if (num_symbols_rx < num_symbols)
syms_rx[num_symbols_rx++] = v;
// demodulate
unsigned int sym_out; // output symbol
float complex d_prime; // estimated input sample
modem_demodulate(demod, v, &sym_out);
modem_get_demodulator_sample(demod, &d_prime);
float phase_error = modem_get_demodulator_phase_error(demod);
// update pll
nco_crcf_pll_step(nco, phase_error);
// update rx nco object
nco_crcf_step(nco);
// update filtered evm estimate
float evm = crealf( (d_prime-v)*conjf(d_prime-v) );
evm_hat = 0.98f*evm_hat + 0.02f*evm;
}
// get equalizer weights
eqlms_cccf_get_weights(eq, hp);
// destroy objects
eqlms_cccf_destroy(eq);
nco_crcf_destroy(nco);
firinterp_crcf_destroy(interp);
firfilt_cccf_destroy(fchannel);
modem_destroy(mod);
modem_destroy(demod);
//
// export output
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all\n");
fprintf(fid,"close all\n");
fprintf(fid,"k = %u;\n", k);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = num_symbols*k;\n");
// save transmit matched-filter response
fprintf(fid,"hm_len = 2*k*m+1;\n");
fprintf(fid,"hm = zeros(1,hm_len);\n");
for (i=0; i<hm_len; i++)
fprintf(fid,"hm(%4u) = %12.4e;\n", i+1, hm[i]);
// save channel impulse response
fprintf(fid,"hc_len = %u;\n", hc_len);
fprintf(fid,"hc = zeros(1,hc_len);\n");
for (i=0; i<hc_len; i++)
fprintf(fid,"hc(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(hc[i]), cimagf(hc[i]));
// save equalizer response
fprintf(fid,"hp_len = %u;\n", hp_len);
fprintf(fid,"hp = zeros(1,hp_len);\n");
for (i=0; i<hp_len; i++)
fprintf(fid,"hp(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(hp[i]), cimagf(hp[i]));
// save sample sets
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
fprintf(fid,"z = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++) {
fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"z(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(z[i]), cimagf(z[i]));
}
fprintf(fid,"syms_rx = zeros(1,num_symbols);\n");
for (i=0; i<num_symbols; i++) {
fprintf(fid,"syms_rx(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(syms_rx[i]), cimagf(syms_rx[i]));
}
// plot time response
fprintf(fid,"t = 0:(num_samples-1);\n");
fprintf(fid,"tsym = 1:k:num_samples;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(t,real(z),...\n");
fprintf(fid," t(tsym),real(z(tsym)),'x');\n");
// plot constellation
fprintf(fid,"syms_rx_0 = syms_rx(1:(length(syms_rx)/2));\n");
fprintf(fid,"syms_rx_1 = syms_rx((length(syms_rx)/2):end);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(real(syms_rx_0),imag(syms_rx_0),'x','Color',[1 1 1]*0.7,...\n");
fprintf(fid," real(syms_rx_1),imag(syms_rx_1),'x','Color',[1 1 1]*0.0);\n");
fprintf(fid,"xlabel('In-Phase');\n");
fprintf(fid,"ylabel('Quadrature');\n");
fprintf(fid,"axis([-1 1 -1 1]*1.5);\n");
fprintf(fid,"axis square;\n");
fprintf(fid,"grid on;\n");
// compute composite response
fprintf(fid,"g = real(conv(conv(hm,hc),hp));\n");
// plot responses
fprintf(fid,"nfft = 1024;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"Hm = 20*log10(abs(fftshift(fft(hm/k,nfft))));\n");
fprintf(fid,"Hc = 20*log10(abs(fftshift(fft(hc, nfft))));\n");
fprintf(fid,"Hp = 20*log10(abs(fftshift(fft(hp, nfft))));\n");
fprintf(fid,"G = 20*log10(abs(fftshift(fft(g/k, nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f,Hm, f,Hc, f,Hp, f,G,'-k','LineWidth',2, [-0.5/k 0.5/k],[-6.026 -6.026],'or');\n");
fprintf(fid,"xlabel('Normalized Frequency');\n");
fprintf(fid,"ylabel('Power Spectral Density');\n");
fprintf(fid,"legend('transmit','channel','equalizer','composite','half-power points','location','northeast');\n");
fprintf(fid,"axis([-0.5 0.5 -12 8]);\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
int main(int argc, char*argv[])
{
// set random seed
srand( time(NULL) );
// parameters
float phase_offset = 0.0f; // initial phase offset
float frequency_offset = 0.40f; // initial frequency offset
float pll_bandwidth = 0.003f; // phase-locked loop bandwidth
unsigned int n = 512; // number of iterations
int dopt;
while ((dopt = getopt(argc,argv,"uhb:n:p:f:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
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;
default:
exit(1);
}
}
// objects
nco_crcf nco_tx = nco_crcf_create(LIQUID_VCO);
nco_crcf nco_rx = nco_crcf_create(LIQUID_VCO);
// 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);
// generate input
float complex x[n];
float complex y[n];
float phase_error[n];
unsigned int i;
for (i=0; i<n; i++) {
// generate complex sinusoid
nco_crcf_cexpf(nco_tx, &x[i]);
// update nco
nco_crcf_step(nco_tx);
}
// run loop
for (i=0; i<n; i++) {
#if 0
// test resetting bandwidth in middle of acquisition
if (i == 100) nco_pll_set_bandwidth(nco_rx, pll_bandwidth*0.2f);
#endif
// generate input
nco_crcf_cexpf(nco_rx, &y[i]);
// update rx nco object
nco_crcf_step(nco_rx);
// compute phase error
phase_error[i] = cargf(x[i]*conjf(y[i]));
// update pll
nco_crcf_pll_step(nco_rx, phase_error[i]);
// print phase error
if ( (i+1)%50 == 0 || i==n-1 || i==0)
printf("%4u : phase error = %12.8f\n", i+1, phase_error[i]);
}
nco_crcf_destroy(nco_tx);
nco_crcf_destroy(nco_rx);
// write 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,"n = %u;\n", n);
fprintf(fid,"x = zeros(1,n);\n");
fprintf(fid,"y = zeros(1,n);\n");
for (i=0; i<n; i++) {
fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"e(%4u) = %12.4e;\n", i+1, phase_error[i]);
}
fprintf(fid,"t=0:(n-1);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(t,real(x),'Color',[1 1 1]*0.8);\n");
fprintf(fid," plot(t,real(y),'Color',[0 0.2 0.5]);\n");
fprintf(fid," hold off;\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('real');\n");
fprintf(fid," axis([0 n -1.2 1.2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," hold on;\n");
fprintf(fid," plot(t,imag(x),'Color',[1 1 1]*0.8);\n");
fprintf(fid," plot(t,imag(y),'Color',[0 0.5 0.2]);\n");
fprintf(fid," hold off;\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('imag');\n");
fprintf(fid," axis([0 n -1.2 1.2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," plot(t,e,'Color',[0.5 0 0]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('phase error');\n");
fprintf(fid," axis([0 n -pi pi]);\n");
fprintf(fid," grid on;\n");
fclose(fid);
printf("results written to %s.\n",OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
