void gmskframesync_execute_detectframe(gmskframesync _q,
float complex _x)
{
// push sample into pre-demod p/n sequence buffer
windowcf_push(_q->buffer, _x);
// push through pre-demod synchronizer
int detected = detector_cccf_correlate(_q->frame_detector,
_x,
&_q->tau_hat,
&_q->dphi_hat,
&_q->gamma_hat);
// check if frame has been detected
if (detected) {
//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));
// push buffered samples through synchronizer
// NOTE: state will be updated to STATE_RXPREAMBLE internally
gmskframesync_pushpn(_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 sample into pre-demod p/n sequence buffer
windowcf_push(_q->buffer, _x);
// push through pre-demod synchronizer
int detected = detector_cccf_correlate(_q->frame_detector,
_x,
&_q->tau_hat,
&_q->dphi_hat,
&_q->gamma_hat);
// check if frame has been detected
if (detected) {
//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));
// push buffered samples through synchronizer
// NOTE: this will set internal state appropriately
// to STATE_DETECTFRAME
flexframesync_pushpn(_q);
}
}
// autotest helper function
// _n : sequence length
// _dt : fractional sample offset
// _dphi : carrier frequency offset
void detector_cccf_runtest(unsigned int _n,
float _dt,
float _dphi)
{
// TODO: validate input
unsigned int i;
// fixed values
float noise_floor = -80.0f; // noise floor [dB]
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
unsigned int m = 11; // resampling filter semi-length
float threshold = 0.3f; // detection threshold
// derived values
unsigned int num_samples = _n + 2*m + 1;
float nstd = powf(10.0f, noise_floor/20.0f);
float gamma = powf(10.0f, (SNRdB + noise_floor)/20.0f);
float delay = (float)(_n + m) + _dt; // expected delay
// arrays
float complex s[_n]; // synchronization pattern (samples)
float complex x[num_samples]; // resampled signal with noise and offsets
// generate synchronization pattern (two samples per symbol)
unsigned int n2 = (_n - (_n%2)) / 2; // n2 = floor(n/2)
unsigned int mm = liquid_nextpow2(n2); // mm = ceil( log2(n2) )
msequence ms = msequence_create_default(mm);
float complex v = 0.0f;
for (i=0; i<_n; i++) {
if ( (i%2)==0 )
v = msequence_advance(ms) ? 1.0f : -1.0f;
s[i] = v;
}
msequence_destroy(ms);
// create fractional sample interpolator
firfilt_crcf finterp = firfilt_crcf_create_kaiser(2*m+1, 0.45f, 40.0f, _dt);
// generate sequence
for (i=0; i<num_samples; i++) {
// add fractional sample timing offset
if (i < _n) firfilt_crcf_push(finterp, s[i]);
else firfilt_crcf_push(finterp, 0.0f);
// compute output
firfilt_crcf_execute(finterp, &x[i]);
// add channel gain
x[i] *= gamma;
// add carrier offset
x[i] *= cexpf(_Complex_I*_dphi*i);
// add noise
x[i] += nstd * ( randnf() + _Complex_I*randnf() ) * M_SQRT1_2;
}
// destroy fractional sample interpolator
firfilt_crcf_destroy(finterp);
// create detector
detector_cccf sync = detector_cccf_create(s, _n, threshold, 2*_dphi);
// push signal through detector
float tau_hat = 0.0f; // fractional sample offset estimate
float dphi_hat = 0.0f; // carrier offset estimate
float gamma_hat = 1.0f; // signal level estimate (linear)
float delay_hat = 0.0f; // total delay offset estimate
int signal_detected = 0; // signal detected flag
for (i=0; i<num_samples; i++) {
// correlate
int detected = detector_cccf_correlate(sync, x[i], &tau_hat, &dphi_hat, &gamma_hat);
if (detected) {
signal_detected = 1;
delay_hat = (float)i + (float)tau_hat;
if (liquid_autotest_verbose) {
printf("****** preamble found, tau_hat=%8.6f, dphi_hat=%8.6f, gamma_hat=%8.6f\n",
tau_hat, dphi_hat, gamma_hat);
}
}
}
// destroy objects
detector_cccf_destroy(sync);
//
// run tests
//
// convert to dB
gamma = 20*log10f(gamma);
gamma_hat = 20*log10f(gamma_hat);
if (liquid_autotest_verbose) {
printf("detector autotest [%3u]: signal detected? %s\n", _n, signal_detected ? "yes" : "no");
printf(" dphi : estimate = %12.6f (expected %12.6f)\n", dphi_hat, _dphi);
printf(" delay : estimate = %12.6f (expected %12.6f)\n", delay_hat, delay);
printf(" gamma : estimate = %12.6f (expected %12.6f)\n", gamma_hat, gamma);
}
// ensure signal was detected
CONTEND_EXPRESSION( signal_detected );
// check carrier offset estimate
CONTEND_DELTA( dphi_hat, _dphi, 0.01f );
// check delay estimate
CONTEND_DELTA( delay_hat, delay, 0.2f );
// check signal level estimate
CONTEND_DELTA( gamma_hat, gamma, 2.0f );
}
