// create nco/vco object
NCO() NCO(_create)(liquid_ncotype _type)
{
NCO() q = (NCO()) malloc(sizeof(struct NCO(_s)));
q->type = _type;
// initialize sine table
unsigned int i;
for (i=0; i<1024; i++)
q->sintab[i] = SIN(2.0f*M_PI*(float)(i)/1024.0f);
// set default pll bandwidth
NCO(_pll_set_bandwidth)(q, NCO_PLL_BANDWIDTH_DEFAULT);
// reset object and return
NCO(_reset)(q);
return q;
}
// create 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)
SYMTRACK() SYMTRACK(_create)(int _ftype,
unsigned int _k,
unsigned int _m,
float _beta,
int _ms)
{
// validate input
if (_k < 2) {
fprintf(stderr,"error: symtrack_%s_create(), filter samples/symbol must be at least 2\n", EXTENSION_FULL);
exit(1);
} else if (_m == 0) {
fprintf(stderr,"error: symtrack_%s_create(), filter delay must be greater than zero\n", EXTENSION_FULL);
exit(1);
} else if (_beta <= 0.0f || _beta > 1.0f) {
fprintf(stderr,"error: symtrack_%s_create(), filter excess bandwidth must be in (0,1]\n", EXTENSION_FULL);
exit(1);
} else if (_ms == LIQUID_MODEM_UNKNOWN || _ms >= LIQUID_MODEM_NUM_SCHEMES) {
fprintf(stderr,"error: symtrack_%s_create(), invalid modulation scheme\n", EXTENSION_FULL);
exit(1);
}
// allocate memory for main object
SYMTRACK() q = (SYMTRACK()) malloc( sizeof(struct SYMTRACK(_s)) );
// 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(_create)();
// create symbol synchronizer (output rate: 2 samples per symbol)
if (q->filter_type == LIQUID_FIRFILT_UNKNOWN)
q->symsync = SYMSYNC(_create_kaiser)(q->k, q->m, 0.9f, 16);
else
q->symsync = SYMSYNC(_create_rnyquist)(q->filter_type, q->k, q->m, q->beta, 16);
SYMSYNC(_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(_create_lowpass)(q->eq_len,0.45f);
// nco and phase-locked loop
q->nco = NCO(_create)(LIQUID_VCO);
// demodulator
q->demod = MODEM(_create)(q->mod_scheme);
// set default bandwidth
SYMTRACK(_set_bandwidth)(q, 0.9f);
// reset and return main object
SYMTRACK(_reset)(q);
return q;
}
struct NCO(_s) {
liquid_ncotype type; // NCO type (e.g. LIQUID_VCO)
T sintab[1024]; // sine look-up table
uint32_t theta; // 32-bit phase [radians]
uint32_t d_theta; // 32-bit frequency [radians/sample]
// phase-locked loop
T alpha; // frequency proportion
T beta; // phase proportion
};
// constrain phase (or frequency) and convert to fixed-point
uint32_t NCO(_constrain)(float _theta);
// compute index for sine look-up table
unsigned int NCO(_index)(NCO() _q);
// create nco/vco object
NCO() NCO(_create)(liquid_ncotype _type)
{
NCO() q = (NCO()) malloc(sizeof(struct NCO(_s)));
q->type = _type;
// initialize sine table
unsigned int i;
for (i=0; i<1024; i++)
q->sintab[i] = SIN(2.0f*M_PI*(float)(i)/1024.0f);
// set default pll bandwidth
NCO(_pll_set_bandwidth)(q, NCO_PLL_BANDWIDTH_DEFAULT);
// create dds object
// _num_stages : number of halfband stages
// _fc : input carrier
// _bw : input signal bandwidth
// _As : stop-band attenuation
DDS() DDS(_create)(unsigned int _num_stages,
float _fc,
float _bw,
float _As)
{
// create object
DDS() q = (DDS()) malloc(sizeof(struct DDS(_s)));
q->num_stages = _num_stages;
q->rate = 1<<(q->num_stages);
q->fc0 = _fc;
q->bw0 = _bw;
q->As0 = _As;
// error checking
if (q->fc0 > 0.5f || q->fc0 < -0.5f) {
fprintf(stderr,"error: dds_xxxf_create(), frequency %12.4e is out of range [-0.5,0.5]\n", q->fc0);
exit(1);
}
// allocate memory for filter properties
q->fc = (float*) malloc((q->num_stages)*sizeof(float));
q->ft = (float*) malloc((q->num_stages)*sizeof(float));
q->As = (float*) malloc((q->num_stages)*sizeof(float));
q->h_len = (unsigned int*) malloc((q->num_stages)*sizeof(unsigned int));
unsigned int i;
float fc, bw;
fc = 0.5*(1<<q->num_stages)*q->fc0; // filter center frequency
bw = q->bw0; // signal bandwidth
// TODO : compute/set filter bandwidths, lengths appropriately
for (i=0; i<q->num_stages; i++) {
q->fc[i] = fc;
while (q->fc[i] > 0.5f) q->fc[i] -= 1.0f;
while (q->fc[i] < -0.5f) q->fc[i] += 1.0f;
// compute transition bandwidth
q->ft[i] = 0.5f*(1.0f - bw);
if (q->ft[i] > 0.45) q->ft[i] = 0.45f; // set maximum bandwidth
q->As[i] = q->As0;
// compute (estimate) required filter length
//q->h_len[i] = i==0 ? 37 : q->h_len[i-1]*0.7;
q->h_len[i] = estimate_req_filter_len(q->ft[i], q->As[i]);
if ((q->h_len[i] % 2) == 0) q->h_len[i]++;
// ensure h_len[i] is of form 4*m+1
unsigned int m = (q->h_len[i]-1)/4;
if (m < 1) m = 1;
q->h_len[i] = 4*m+1;
// update carrier, bandwidth parameters
fc *= 0.5f;
bw *= 0.5f;
}
// allocate memory for buffering
q->buffer_len = q->rate;
q->buffer0 = (T*) malloc((q->buffer_len)*sizeof(T));
q->buffer1 = (T*) malloc((q->buffer_len)*sizeof(T));
// allocate memory for resampler pointers and create objects
q->halfband_resamp = (RESAMP2()*) malloc((q->num_stages)*sizeof(RESAMP()*));
for (i=0; i<q->num_stages; i++) {
q->halfband_resamp[i] = RESAMP2(_create)(q->h_len[i],
q->fc[i],
q->As[i]);
}
// set down-converter scaling factor
q->zeta = 1.0f / ((float)(q->rate));
// create NCO and set frequency
q->ncox = NCO(_create)(LIQUID_VCO);
// TODO : ensure range is in [-pi,pi]
NCO(_set_frequency)(q->ncox, 2*M_PI*(q->rate)*(q->fc0));
return q;
}
