// step receiver mixer, matched filter, decimator
// _q : frame synchronizer
// _x : input sample
// _y : output symbol
int flexframesync_step(flexframesync _q,
float complex _x,
float complex * _y)
{
// mix sample down
float complex v;
nco_crcf_mix_down(_q->mixer, _x, &v);
nco_crcf_step (_q->mixer);
// push sample into filterbank
firpfb_crcf_push (_q->mf, v);
firpfb_crcf_execute(_q->mf, _q->pfb_index, &v);
#if FLEXFRAMESYNC_ENABLE_EQ
// push sample through equalizer
eqlms_cccf_push(_q->equalizer, v);
#endif
// increment counter to determine if sample is available
_q->mf_counter++;
int sample_available = (_q->mf_counter >= 1) ? 1 : 0;
// set output sample if available
if (sample_available) {
#if FLEXFRAMESYNC_ENABLE_EQ
// compute equalizer output
eqlms_cccf_execute(_q->equalizer, &v);
#endif
// set output
*_y = v;
// decrement counter by k=2 samples/symbol
_q->mf_counter -= 2;
}
// return flag
return sample_available;
}
// update symbol synchronizer internal state (filtered error, index, etc.)
// _q : frame synchronizer
// _x : input sample
// _y : output symbol
int flexframesync_update_symsync(flexframesync _q,
float complex _x,
float complex * _y)
{
// push sample into filterbanks
firpfb_crcf_push(_q->mf, _x);
firpfb_crcf_push(_q->dmf, _x);
//
float complex mf_out = 0.0f; // matched-filter output
float complex dmf_out = 0.0f; // derivatived matched-filter output
int sample_available = 0;
// compute output if timeout
if (_q->pfb_timer <= 0) {
sample_available = 1;
// reset timer
_q->pfb_timer = 2; // k samples/symbol
firpfb_crcf_execute(_q->mf, _q->pfb_index, &mf_out);
firpfb_crcf_execute(_q->dmf, _q->pfb_index, &dmf_out);
// update filtered timing error
// hi bandwidth parameters: {0.92, 1.20}, about 100 symbols settling time
// med bandwidth parameters: {0.98, 0.20}, about 200 symbols settling time
// lo bandwidth parameters: {0.99, 0.05}, about 500 symbols settling time
_q->pfb_q = 0.99f*_q->pfb_q + 0.05f*crealf( conjf(mf_out)*dmf_out );
// accumulate error into soft filterbank value
_q->pfb_soft += _q->pfb_q;
// compute actual filterbank index
_q->pfb_index = roundf(_q->pfb_soft);
// contrain index to be in [0, npfb-1]
while (_q->pfb_index < 0) {
_q->pfb_index += _q->npfb;
_q->pfb_soft += _q->npfb;
// adjust pfb output timer
_q->pfb_timer--;
}
while (_q->pfb_index > _q->npfb-1) {
_q->pfb_index -= _q->npfb;
_q->pfb_soft -= _q->npfb;
// adjust pfb output timer
_q->pfb_timer++;
}
}
// decrement symbol timer
_q->pfb_timer--;
// set output and return
*_y = mf_out;
return sample_available;
}