// execute synchronizer, receiving header
// _q : frame synchronizer object
// _x : input sample
// _sym : demodulated symbol
void flexframesync_execute_rxheader(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) {
// save payload symbols (modem input/output)
_q->header_sym[_q->symbol_counter] = mf_out;
// increment counter
_q->symbol_counter++;
if (_q->symbol_counter == _q->header_sym_len) {
// decode header
flexframesync_decode_header(_q);
if (_q->header_valid) {
// continue on to decoding payload
_q->symbol_counter = 0;
_q->state = FLEXFRAMESYNC_STATE_RXPAYLOAD;
return;
}
// update statistics
_q->framedatastats.num_frames_detected++;
// header invalid: invoke callback
if (_q->callback != NULL) {
// set framestats internals
_q->framesyncstats.evm = 0.0f; //20*log10f(sqrtf(_q->framesyncstats.evm / 600));
_q->framesyncstats.rssi = 20*log10f(_q->gamma_hat);
_q->framesyncstats.cfo = nco_crcf_get_frequency(_q->mixer);
_q->framesyncstats.framesyms = NULL;
_q->framesyncstats.num_framesyms = 0;
_q->framesyncstats.mod_scheme = LIQUID_MODEM_UNKNOWN;
_q->framesyncstats.mod_bps = 0;
_q->framesyncstats.check = LIQUID_CRC_UNKNOWN;
_q->framesyncstats.fec0 = LIQUID_FEC_UNKNOWN;
_q->framesyncstats.fec1 = LIQUID_FEC_UNKNOWN;
// invoke callback method
_q->callback(_q->header_dec,
_q->header_valid,
NULL, // payload
0, // payload length
0, // payload valid,
_q->framesyncstats,
_q->userdata);
}
// reset frame synchronizer
flexframesync_reset(_q);
return;
}
}
}
// 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;
}
}
}
// create flexframesync object
// _callback : callback function invoked when frame is received
// _userdata : user-defined data object passed to callback
flexframesync flexframesync_create(framesync_callback _callback,
void * _userdata)
{
flexframesync q = (flexframesync) malloc(sizeof(struct flexframesync_s));
q->callback = _callback;
q->userdata = _userdata;
unsigned int i;
// generate p/n sequence
msequence ms = msequence_create(6, 0x005b, 1);
for (i=0; i<64; i++)
q->preamble_pn[i] = (msequence_advance(ms)) ? 1.0f : -1.0f;
msequence_destroy(ms);
// interpolate p/n sequence with matched filter
q->k = 2; // samples/symbol
q->m = 7; // filter delay (symbols)
q->beta = 0.25f; // excess bandwidth factor
float complex seq[q->k*64];
firinterp_crcf interp = firinterp_crcf_create_rnyquist(LIQUID_FIRFILT_ARKAISER,q->k,q->m,q->beta,0);
for (i=0; i<64+q->m; i++) {
// compensate for filter delay
if (i < q->m) firinterp_crcf_execute(interp, q->preamble_pn[i], &seq[0]);
else firinterp_crcf_execute(interp, q->preamble_pn[i%64], &seq[q->k*(i-q->m)]);
}
firinterp_crcf_destroy(interp);
// create frame detector
float threshold = 0.4f; // detection threshold
float dphi_max = 0.05f; // maximum carrier offset allowable
q->frame_detector = detector_cccf_create(seq, q->k*64, threshold, dphi_max);
q->buffer = windowcf_create(q->k*(64+q->m));
// create symbol timing recovery filters
q->npfb = 32; // number of filters in the bank
q->mf = firpfb_crcf_create_rnyquist(LIQUID_FIRFILT_ARKAISER, q->npfb,q->k,q->m,q->beta);
q->dmf = firpfb_crcf_create_drnyquist(LIQUID_FIRFILT_ARKAISER,q->npfb,q->k,q->m,q->beta);
// create down-coverters for carrier phase tracking
q->nco_coarse = nco_crcf_create(LIQUID_NCO);
q->nco_fine = nco_crcf_create(LIQUID_VCO);
nco_crcf_pll_set_bandwidth(q->nco_fine, 0.05f);
// create header objects
q->demod_header = modem_create(LIQUID_MODEM_BPSK);
q->p_header = packetizer_create(FLEXFRAME_H_DEC,
FLEXFRAME_H_CRC,
FLEXFRAME_H_FEC0,
FLEXFRAME_H_FEC1);
assert(packetizer_get_enc_msg_len(q->p_header)==FLEXFRAME_H_ENC);
// frame properties (default values to be overwritten when frame
// header is received and properly decoded)
q->ms_payload = LIQUID_MODEM_QPSK;
q->bps_payload = 2;
q->payload_dec_len = 1;
q->check = LIQUID_CRC_NONE;
q->fec0 = LIQUID_FEC_NONE;
q->fec1 = LIQUID_FEC_NONE;
// create payload objects (overridden by received properties)
q->demod_payload = modem_create(LIQUID_MODEM_QPSK);
q->p_payload = packetizer_create(q->payload_dec_len, q->check, q->fec0, q->fec1);
q->payload_enc_len = packetizer_get_enc_msg_len(q->p_payload);
q->payload_mod_len = 4 * q->payload_enc_len;
q->payload_mod = (unsigned char*) malloc(q->payload_mod_len*sizeof(unsigned char));
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
q->payload_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
#if DEBUG_FLEXFRAMESYNC
// set debugging flags, objects to NULL
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_x = NULL;
#endif
// reset state
flexframesync_reset(q);
return q;
}
// 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;
}
}
}
// create flexframesync object
// _callback : callback function invoked when frame is received
// _userdata : user-defined data object passed to callback
flexframesync flexframesync_create(framesync_callback _callback,
void * _userdata)
{
flexframesync q = (flexframesync) malloc(sizeof(struct flexframesync_s));
q->callback = _callback;
q->userdata = _userdata;
q->m = 7; // filter delay (symbols)
q->beta = 0.3f; // excess bandwidth factor
unsigned int i;
// generate p/n sequence
q->preamble_pn = (float complex*) malloc(64*sizeof(float complex));
q->preamble_rx = (float complex*) malloc(64*sizeof(float complex));
msequence ms = msequence_create(7, 0x0089, 1);
for (i=0; i<64; i++) {
q->preamble_pn[i] = (msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2) +
(msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2)*_Complex_I;
}
msequence_destroy(ms);
// create frame detector
unsigned int k = 2; // samples/symbol
q->detector = qdetector_cccf_create_linear(q->preamble_pn, 64, LIQUID_FIRFILT_ARKAISER, k, q->m, q->beta);
qdetector_cccf_set_threshold(q->detector, 0.5f);
// create symbol timing recovery filters
q->npfb = 32; // number of filters in the bank
q->mf = firpfb_crcf_create_rnyquist(LIQUID_FIRFILT_ARKAISER, q->npfb,k,q->m,q->beta);
#if FLEXFRAMESYNC_ENABLE_EQ
// create equalizer
unsigned int p = 3;
q->equalizer = eqlms_cccf_create_lowpass(2*k*p+1, 0.4f);
eqlms_cccf_set_bw(q->equalizer, 0.05f);
#endif
// create down-coverters for carrier phase tracking
q->mixer = nco_crcf_create(LIQUID_NCO);
q->pll = nco_crcf_create(LIQUID_NCO);
nco_crcf_pll_set_bandwidth(q->pll, 1e-4f); // very low bandwidth
// header demodulator/decoder
q->header_dec = (unsigned char *) malloc(FLEXFRAME_H_DEC*sizeof(unsigned char));
q->header_decoder = qpacketmodem_create();
qpacketmodem_configure(q->header_decoder,
FLEXFRAME_H_DEC,
FLEXFRAME_H_CRC,
FLEXFRAME_H_FEC0,
FLEXFRAME_H_FEC1,
LIQUID_MODEM_QPSK);
q->header_mod_len = qpacketmodem_get_frame_len(q->header_decoder);
q->header_mod = (float complex*) malloc(q->header_mod_len*sizeof(float complex));
// header pilot synchronizer
q->header_pilotsync = qpilotsync_create(q->header_mod_len, 16);
q->header_sym_len = qpilotsync_get_frame_len(q->header_pilotsync);
q->header_sym = (float complex*) malloc(q->header_sym_len*sizeof(float complex));
// payload demodulator for phase recovery
q->payload_demod = modem_create(LIQUID_MODEM_QPSK);
// create payload demodulator/decoder object
q->payload_dec_len = 64;
int check = LIQUID_CRC_24;
int fec0 = LIQUID_FEC_NONE;
int fec1 = LIQUID_FEC_GOLAY2412;
int mod_scheme = LIQUID_MODEM_QPSK;
q->payload_decoder = qpacketmodem_create();
qpacketmodem_configure(q->payload_decoder, q->payload_dec_len, check, fec0, fec1, mod_scheme);
//qpacketmodem_print(q->payload_decoder);
//assert( qpacketmodem_get_frame_len(q->payload_decoder)==600 );
q->payload_sym_len = qpacketmodem_get_frame_len(q->payload_decoder);
// allocate memory for payload symbols and recovered data bytes
q->payload_sym = (float complex*) malloc(q->payload_sym_len*sizeof(float complex));
q->payload_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
// reset global data counters
flexframesync_reset_framedatastats(q);
#if DEBUG_FLEXFRAMESYNC
// set debugging flags, objects to NULL
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_qdetector_flush = 0;
q->debug_x = NULL;
#endif
// reset state and return
flexframesync_reset(q);
return q;
}
