SSB_HighSpeed_Modem/hsmodem/symboltracker.cpp

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2020-11-14 19:32:47 -05:00
#include "hsmodem.h"
SYMTRACK km_symtrack;
SYMTRACK* q = &km_symtrack;
// create km_symtrack object with basic parameters
// _ftype : filter type (e.g. LIQUID_FIRFILT_RRC)
// _k : samples per symbol
// _m : filter delay (symbols)
// _beta : filter excess bandwidth
// _ms : modulation scheme (e.g. LIQUID_MODEM_QPSK)
void km_symtrack_cccf_create(int _ftype,
unsigned int _k,
unsigned int _m,
float _beta,
int _ms)
{
// validate input
if (_k < 2)
printf((char *)"symtrack_cccf_create(), filter samples/symbol must be at least 2\n");
if (_m == 0)
printf((char*)"symtrack_cccf_create(), filter delay must be greater than zero\n");
if (_beta <= 0.0f || _beta > 1.0f)
printf((char*)"symtrack_cccf_create(), filter excess bandwidth must be in [0,1]\n");
if (_ms == LIQUID_MODEM_UNKNOWN || _ms >= LIQUID_MODEM_NUM_SCHEMES)
printf((char*)"symtrack_cccf_create(), invalid modulation scheme\n");
// set input parameters
q->filter_type = _ftype;
q->k = _k;
q->m = _m;
q->beta = _beta;
q->mod_scheme = _ms == LIQUID_MODEM_UNKNOWN ? LIQUID_MODEM_BPSK : _ms;
// create automatic gain control
q->agc = agc_crcf_create();
// create symbol synchronizer (output rate: 2 samples per symbol)
if (q->filter_type == LIQUID_FIRFILT_UNKNOWN)
q->symsync = symsync_crcf_create_kaiser(q->k, q->m, 0.9f, 16);
else
q->symsync = symsync_crcf_create_rnyquist(q->filter_type, q->k, q->m, q->beta, 16);
symsync_crcf_set_output_rate(q->symsync, 2);
// create equalizer as default low-pass filter with integer symbol delay (2 samples/symbol)
q->eq_len = 2 * 4 + 1;
q->eq = eqlms_cccf_create_lowpass(q->eq_len, 0.45f);
q->eq_strategy = q->SYMTRACK_EQ_DD;
// nco and phase-locked loop
q->nco = nco_crcf_create(LIQUID_VCO);
// demodulator
q->demod = modem_create((modulation_scheme)q->mod_scheme);
// set default bandwidth
km_symtrack_cccf_set_bandwidth(0.9f);
// reset and return main object
km_symtrack_cccf_reset(0xff);
}
void km_symtrack_cccf_reset(int mode)
{
// reset objects
if (mode & 1) agc_crcf_reset(q->agc);
if (mode & 2) symsync_crcf_reset(q->symsync);
if (mode & 4) eqlms_cccf_reset(q->eq);
if (mode & 8) nco_crcf_reset(q->nco);
if (mode & 0x10) modem_reset(q->demod);
// reset internal counters
q->symsync_index = 0;
q->num_syms_rx = 0;
}
void km_symtrack_cccf_set_bandwidth(float _bw)
{
// validate input
if (_bw < 0)
printf("symtrack_set_bandwidth(), bandwidth must be in [0,1]\n");
// set bandwidths accordingly
float agc_bandwidth = 0.02f * _bw;
float symsync_bandwidth = 0.001f * _bw;
float eq_bandwidth = 0.02f * _bw;
float pll_bandwidth = 0.001f * _bw;
// automatic gain control
agc_crcf_set_bandwidth(q->agc, agc_bandwidth);
// symbol timing recovery
symsync_crcf_set_lf_bw(q->symsync, symsync_bandwidth);
// equalizer
eqlms_cccf_set_bw(q->eq, eq_bandwidth);
// phase-locked loop
nco_crcf_pll_set_bandwidth(q->nco, pll_bandwidth);
}
#define MX 10
// execute synchronizer on single input sample
// _q : synchronizer object
// _x : input data sample
// _y : output data array
// _ny : number of samples written to output buffer
void km_symtrack_execute(liquid_float_complex _x, liquid_float_complex* _y, unsigned int* _ny, unsigned int *psym_out)
{
liquid_float_complex v; // output sample
unsigned int i;
unsigned int num_outputs = 0;
// run sample through automatic gain control
agc_crcf_execute(q->agc, _x, &v);
// symbol synchronizer
unsigned int nw = 0;
symsync_crcf_execute(q->symsync, &v, 1, q->symsync_buf, &nw);
// process each output sample
for (i = 0; i < nw; i++) {
// update phase-locked loop
nco_crcf_step(q->nco);
nco_crcf_mix_down(q->nco, q->symsync_buf[i], &v);
// equalizer/decimator
eqlms_cccf_push(q->eq, v);
// decimate result, noting that symsync outputs at exactly 2 samples/symbol
q->symsync_index++;
if (!(q->symsync_index % 2))
continue;
// increment number of symbols received
q->num_syms_rx++;
// compute equalizer filter output; updating coefficients is dependent upon strategy
liquid_float_complex d_hat;
eqlms_cccf_execute(q->eq, &d_hat);
// demodulate result, apply phase correction
unsigned int sym_out;
modem_demodulate(q->demod, d_hat, &sym_out);
*psym_out = sym_out;
float phase_error = modem_get_demodulator_phase_error(q->demod);
// update pll
nco_crcf_pll_step(q->nco, phase_error);
// update equalizer independent of the signal: estimate error
// assuming constant modulus signal
// TODO: check lock conditions of previous object to determine when to run equalizer
liquid_float_complex d_prime;
d_prime.real = d_prime.imag = 0;
if (q->num_syms_rx > 200)
{
modem_get_demodulator_sample(q->demod, &d_prime);
eqlms_cccf_step(q->eq, d_prime, d_hat);
}
// save result to output
_y[num_outputs++] = d_hat;
}
/*float fr = nco_crcf_get_frequency(q->nco);
float ph = nco_crcf_get_phase(q->nco);
printf("%10.6f %10.6f %10.6f %10.6f\n", fr, ph, _x.real, _x.imag);*/
* _ny = num_outputs;
}