// 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 GMSK frame synchronizer // _callback : callback function // _userdata : user data pointer passed to callback function gmskframesync gmskframesync_create(framesync_callback _callback, void * _userdata) { gmskframesync q = (gmskframesync) malloc(sizeof(struct gmskframesync_s)); q->callback = _callback; q->userdata = _userdata; q->k = 2; // samples/symbol q->m = 3; // filter delay (symbols) q->BT = 0.5f; // filter bandwidth-time product #if GMSKFRAMESYNC_PREFILTER // create default low-pass Butterworth filter q->prefilter = iirfilt_crcf_create_lowpass(3, 0.5f*(1 + q->BT) / (float)(q->k)); #endif unsigned int i; // frame detector q->preamble_len = 63; q->preamble_pn = (float*)malloc(q->preamble_len*sizeof(float)); q->preamble_rx = (float*)malloc(q->preamble_len*sizeof(float)); float complex preamble_samples[q->preamble_len*q->k]; msequence ms = msequence_create(6, 0x6d, 1); gmskmod mod = gmskmod_create(q->k, q->m, q->BT); for (i=0; i<q->preamble_len + q->m; i++) { unsigned char bit = msequence_advance(ms); // save p/n sequence if (i < q->preamble_len) q->preamble_pn[i] = bit ? 1.0f : -1.0f; // modulate/interpolate if (i < q->m) gmskmod_modulate(mod, bit, &preamble_samples[0]); else gmskmod_modulate(mod, bit, &preamble_samples[(i-q->m)*q->k]); } gmskmod_destroy(mod); msequence_destroy(ms); #if 0 // print sequence for (i=0; i<q->preamble_len*q->k; i++) printf("preamble(%3u) = %12.8f + j*%12.8f;\n", i+1, crealf(preamble_samples[i]), cimagf(preamble_samples[i])); #endif // create frame detector float threshold = 0.5f; // detection threshold float dphi_max = 0.05f; // maximum carrier offset allowable q->frame_detector = detector_cccf_create(preamble_samples, q->preamble_len*q->k, threshold, dphi_max); q->buffer = windowcf_create(q->k*(q->preamble_len+q->m)); // create symbol timing recovery filters q->npfb = 32; // number of filters in the bank q->mf = firpfb_rrrf_create_rnyquist( LIQUID_FIRFILT_GMSKRX,q->npfb,q->k,q->m,q->BT); q->dmf = firpfb_rrrf_create_drnyquist(LIQUID_FIRFILT_GMSKRX,q->npfb,q->k,q->m,q->BT); // create down-coverters for carrier phase tracking q->nco_coarse = nco_crcf_create(LIQUID_NCO); // create/allocate header objects/arrays q->header_mod = (unsigned char*)malloc(GMSKFRAME_H_SYM*sizeof(unsigned char)); q->header_enc = (unsigned char*)malloc(GMSKFRAME_H_ENC*sizeof(unsigned char)); q->header_dec = (unsigned char*)malloc(GMSKFRAME_H_DEC*sizeof(unsigned char)); q->p_header = packetizer_create(GMSKFRAME_H_DEC, GMSKFRAME_H_CRC, GMSKFRAME_H_FEC, LIQUID_FEC_NONE); // create/allocate payload objects/arrays q->payload_dec_len = 1; q->check = LIQUID_CRC_32; q->fec0 = LIQUID_FEC_NONE; q->fec1 = LIQUID_FEC_NONE; 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_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char)); q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char)); #if DEBUG_GMSKFRAMESYNC // debugging structures q->debug_enabled = 0; q->debug_objects_created = 0; q->debug_x = NULL; q->debug_fi = NULL; q->debug_mf = NULL; q->debug_framesyms = NULL; #endif // reset synchronizer gmskframesync_reset(q); // return synchronizer object return 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 ); }