// Helper function to keep code base small
void qdetector_cccf_bench(struct rusage * _start,
struct rusage * _finish,
unsigned long int * _num_iterations,
unsigned int _n)
{
// adjust number of iterations
*_num_iterations *= 4;
*_num_iterations /= _n;
// generate sequence (random)
float complex h[_n];
unsigned long int i;
for (i=0; i<_n; i++) {
h[i] = (rand() % 2 ? 1.0f : -1.0f) +
(rand() % 2 ? 1.0f : -1.0f)*_Complex_I;
}
// generate synchronizer
int ftype = LIQUID_FIRFILT_ARKAISER;
unsigned int k = 2; // samples/symbol
unsigned int m = 7; // filter delay [symbols]
float beta = 0.3f; // excess bandwidth factor
float threshold = 0.5f; // threshold for detection
float range = 0.05f; // carrier offset search range [radians/sample]
qdetector_cccf q = qdetector_cccf_create_linear(h, _n, ftype, k, m, beta);
qdetector_cccf_set_threshold(q,threshold);
qdetector_cccf_set_range (q, range);
// input sequence (random)
float complex x[7];
for (i=0; i<7; i++) {
x[i] = (rand() % 2 ? 1.0f : -1.0f) +
(rand() % 2 ? 1.0f : -1.0f)*_Complex_I;
}
// start trials
getrusage(RUSAGE_SELF, _start);
int detected = 0;
for (i=0; i<(*_num_iterations); i++) {
// push input sequence through synchronizer
detected ^= qdetector_cccf_execute(q, x[0]) != NULL;
detected ^= qdetector_cccf_execute(q, x[1]) != NULL;
detected ^= qdetector_cccf_execute(q, x[2]) != NULL;
detected ^= qdetector_cccf_execute(q, x[3]) != NULL;
detected ^= qdetector_cccf_execute(q, x[4]) != NULL;
detected ^= qdetector_cccf_execute(q, x[5]) != NULL;
detected ^= qdetector_cccf_execute(q, x[6]) != NULL;
}
getrusage(RUSAGE_SELF, _finish);
*_num_iterations *= 7;
// clean up allocated objects
qdetector_cccf_destroy(q);
}
// execute synchronizer, seeking p/n sequence
// _q : frame synchronizer object
// _x : input sample
// _sym : demodulated symbol
void flexframesync_execute_seekpn(flexframesync _q,
float complex _x)
{
// push through pre-demod synchronizer
float complex * v = qdetector_cccf_execute(_q->detector, _x);
// check if frame has been detected
if (v != NULL) {
// get estimates
_q->tau_hat = qdetector_cccf_get_tau (_q->detector);
_q->gamma_hat = qdetector_cccf_get_gamma(_q->detector);
_q->dphi_hat = qdetector_cccf_get_dphi (_q->detector);
_q->phi_hat = qdetector_cccf_get_phi (_q->detector);
#if DEBUG_FLEXFRAMESYNC_PRINT
printf("***** frame detected! tau-hat:%8.4f, dphi-hat:%8.4f, gamma:%8.2f dB\n",
_q->tau_hat, _q->dphi_hat, 20*log10f(_q->gamma_hat));
#endif
// set appropriate filterbank index
if (_q->tau_hat > 0) {
_q->pfb_index = (unsigned int)( _q->tau_hat * _q->npfb) % _q->npfb;
_q->mf_counter = 0;
} else {
_q->pfb_index = (unsigned int)((1.0f+_q->tau_hat) * _q->npfb) % _q->npfb;
_q->mf_counter = 1;
}
// output filter scale (gain estimate, scaled by 1/2 for k=2 samples/symbol)
firpfb_crcf_set_scale(_q->mf, 0.5f / _q->gamma_hat);
// set frequency/phase of mixer
nco_crcf_set_frequency(_q->mixer, _q->dphi_hat);
nco_crcf_set_phase (_q->mixer, _q->phi_hat );
// update state
_q->state = FLEXFRAMESYNC_STATE_RXPREAMBLE;
#if DEBUG_FLEXFRAMESYNC
// the debug_qdetector_flush prevents samples from being written twice
_q->debug_qdetector_flush = 1;
#endif
// run buffered samples through synchronizer
unsigned int buf_len = qdetector_cccf_get_buf_len(_q->detector);
flexframesync_execute(_q, v, buf_len);
#if DEBUG_FLEXFRAMESYNC
_q->debug_qdetector_flush = 0;
#endif
}
}
int main(int argc, char*argv[])
{
// options
unsigned int sequence_len = 80; // number of sync symbols
unsigned int k = 2; // samples/symbol
unsigned int m = 7; // filter delay [symbols]
float beta = 0.3f; // excess bandwidth factor
int ftype = LIQUID_FIRFILT_ARKAISER;
float gamma = 10.0f; // channel gain
float tau = -0.3f; // fractional sample timing offset
float dphi = -0.01f; // carrier frequency offset
float phi = 0.5f; // carrier phase offset
float SNRdB = 20.0f; // signal-to-noise ratio [dB]
float threshold = 0.5f; // detection threshold
int dopt;
while ((dopt = getopt(argc,argv,"hn:k:m:b:F:T:S:t:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'n': sequence_len = atoi(optarg); break;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 'T': tau = atof(optarg); break;
case 'S': SNRdB = atof(optarg); break;
case 't': threshold = atof(optarg); break;
default:
exit(1);
}
}
unsigned int i;
// validate input
if (tau < -0.5f || tau > 0.5f) {
fprintf(stderr,"error: %s, fractional sample offset must be in [-0.5,0.5]\n", argv[0]);
exit(1);
}
// generate synchronization sequence (QPSK symbols)
float complex sequence[sequence_len];
for (i=0; i<sequence_len; i++) {
sequence[i] = (rand() % 2 ? 1.0f : -1.0f) * M_SQRT1_2 +
(rand() % 2 ? 1.0f : -1.0f) * M_SQRT1_2 * _Complex_I;
}
//
float tau_hat = 0.0f;
float gamma_hat = 0.0f;
float dphi_hat = 0.0f;
float phi_hat = 0.0f;
int frame_detected = 0;
// create detector
qdetector_cccf q = qdetector_cccf_create_linear(sequence, sequence_len, ftype, k, m, beta);
qdetector_cccf_set_threshold(q, threshold);
qdetector_cccf_print(q);
//
unsigned int seq_len = qdetector_cccf_get_seq_len(q);
unsigned int buf_len = qdetector_cccf_get_buf_len(q);
unsigned int num_samples = 2*buf_len; // double buffer length to ensure detection
unsigned int num_symbols = buf_len;
// arrays
float complex y[num_samples]; // received signal
float complex syms_rx[num_symbols]; // recovered symbols
// get pointer to sequence and generate full sequence
float complex * v = (float complex*) qdetector_cccf_get_sequence(q);
unsigned int filter_delay = 15;
firfilt_crcf filter = firfilt_crcf_create_kaiser(2*filter_delay+1, 0.4f, 60.0f, -tau);
float nstd = 0.1f;
for (i=0; i<num_samples; i++) {
// add delay
firfilt_crcf_push(filter, i < seq_len ? v[i] : 0);
firfilt_crcf_execute(filter, &y[i]);
// channel gain
y[i] *= gamma;
// carrier offset
y[i] *= cexpf(_Complex_I*(dphi*i + phi));
// noise
y[i] += nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
}
firfilt_crcf_destroy(filter);
// run detection on sequence
for (i=0; i<num_samples; i++) {
v = qdetector_cccf_execute(q,y[i]);
if (v != NULL) {
printf("\nframe detected!\n");
frame_detected = 1;
// get statistics
tau_hat = qdetector_cccf_get_tau(q);
gamma_hat = qdetector_cccf_get_gamma(q);
dphi_hat = qdetector_cccf_get_dphi(q);
phi_hat = qdetector_cccf_get_phi(q);
break;
}
}
unsigned int num_syms_rx = 0; // output symbol counter
unsigned int counter = 0; // decimation counter
if (frame_detected) {
// recover symbols
firfilt_crcf mf = firfilt_crcf_create_rnyquist(ftype, k, m, beta, tau_hat);
firfilt_crcf_set_scale(mf, 1.0f / (float)(k*gamma_hat));
nco_crcf nco = nco_crcf_create(LIQUID_VCO);
nco_crcf_set_frequency(nco, dphi_hat);
nco_crcf_set_phase (nco, phi_hat);
for (i=0; i<buf_len; i++) {
//
float complex sample;
nco_crcf_mix_down(nco, v[i], &sample);
nco_crcf_step(nco);
// apply decimator
firfilt_crcf_push(mf, sample);
counter++;
if (counter == k-1)
firfilt_crcf_execute(mf, &syms_rx[num_syms_rx++]);
counter %= k;
}
nco_crcf_destroy(nco);
firfilt_crcf_destroy(mf);
}
// destroy objects
qdetector_cccf_destroy(q);
// print results
printf("\n");
printf("frame detected : %s\n", frame_detected ? "yes" : "no");
printf(" gamma hat : %8.3f, actual=%8.3f (error=%8.3f)\n", gamma_hat, gamma, gamma_hat - gamma);
printf(" tau hat : %8.3f, actual=%8.3f (error=%8.3f) samples\n", tau_hat, tau, tau_hat - tau );
printf(" dphi hat : %8.5f, actual=%8.5f (error=%8.5f) rad/sample\n", dphi_hat, dphi, dphi_hat - dphi );
printf(" phi hat : %8.5f, actual=%8.5f (error=%8.5f) radians\n", phi_hat, phi, phi_hat - phi );
printf(" symbols rx : %u\n", num_syms_rx);
printf("\n");
//
// export results
//
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,"sequence_len= %u;\n", sequence_len);
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"y = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++)
fprintf(fid,"y(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"num_syms_rx = %u;\n", num_syms_rx);
fprintf(fid,"syms_rx = zeros(1,num_syms_rx);\n");
for (i=0; i<num_syms_rx; i++)
fprintf(fid,"syms_rx(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(syms_rx[i]), cimagf(syms_rx[i]));
fprintf(fid,"t=[0:(num_samples-1)];\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(4,1,1);\n");
fprintf(fid," plot(t,real(y), t,imag(y));\n");
fprintf(fid," grid on;\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('received signal');\n");
fprintf(fid,"subplot(4,1,2:4);\n");
fprintf(fid," plot(real(syms_rx), imag(syms_rx), 'x');\n");
fprintf(fid," axis([-1 1 -1 1]*1.5);\n");
fprintf(fid," axis square;\n");
fprintf(fid," grid on;\n");
fprintf(fid," xlabel('real');\n");
fprintf(fid," ylabel('imag');\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
