// 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;
}
// 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;
}
