// Design root-Nyquist harris-Moerder filter using Parks-McClellan
// algorithm
//
// _k : filter over-sampling rate (samples/symbol)
// _m : filter delay (symbols)
// _beta : filter excess bandwidth factor (0,1)
// _dt : filter fractional sample delay
// _h : resulting filter [size: 2*_k*_m+1]
void liquid_firdes_hM3(unsigned int _k,
unsigned int _m,
float _beta,
float _dt,
float * _h)
{
if ( _k < 2 ) {
fprintf(stderr,"error: liquid_firdes_hM3(): k must be greater than 1\n");
exit(1);
} else if ( _m < 1 ) {
fprintf(stderr,"error: liquid_firdes_hM3(): m must be greater than 0\n");
exit(1);
} else if ( (_beta < 0.0f) || (_beta > 1.0f) ) {
fprintf(stderr,"error: liquid_firdes_hM3(): beta must be in [0,1]\n");
exit(1);
} else;
unsigned int n=2*_k*_m+1; // filter length
//
float fc = 1.0 / (float)(2*_k); // filter cutoff
float fp = fc*(1.0 - _beta); // pass-band
float fs = fc*(1.0 + _beta); // stop-band
// root nyquist
unsigned int num_bands = 3;
float bands[6] = {0.0f, fp, fc, fc, fs, 0.5f};
float des[3] = {1.0f, 1.0f/sqrtf(2.0f), 0.0f};
float weights[3] = {1.0f, 1.0f, 1.0f};
liquid_firdespm_btype btype = LIQUID_FIRDESPM_BANDPASS;
liquid_firdespm_wtype wtype[3] = {LIQUID_FIRDESPM_FLATWEIGHT,
LIQUID_FIRDESPM_FLATWEIGHT,
LIQUID_FIRDESPM_EXPWEIGHT};
//unsigned int i;
float h[n];
firdespm_run(n,num_bands,bands,des,weights,wtype,btype,h);
// copy results
memmove(_h, h, n*sizeof(float));
float isi_max;
float isi_rms;
liquid_filter_isi(h,_k,_m,&isi_rms,&isi_max);
// iterate...
float isi_rms_min = isi_rms;
unsigned int p, pmax=100;
for (p=0; p<pmax; p++) {
// increase pass-band edge
fp = fc*(1.0 - _beta * p / (float)(pmax) );
bands[1] = fp;
// execute filter design
firdespm_run(n,num_bands,bands,des,weights,wtype,btype,h);
// compute inter-symbol interference (MSE, max)
liquid_filter_isi(h,_k,_m,&isi_rms,&isi_max);
#if DEBUG_hM3
printf(" isi mse : %20.8e (min: %20.8e)\n", isi_rms, isi_rms_min);
#endif
if (isi_rms > isi_rms_min) {
// search complete
break;
} else {
isi_rms_min = isi_rms;
// copy results
memmove(_h, h, n*sizeof(float));
}
};
// normalize
float e2 = 0.0f;
unsigned int i;
for (i=0; i<n; i++) e2 += _h[i]*_h[i];
for (i=0; i<n; i++) _h[i] *= sqrtf(_k/e2);
}
// Design (root-)Nyquist filter from prototype
// _type : filter type (e.g. LIQUID_FIRFILT_RRRC)
// _k : samples/symbol
// _m : symbol delay
// _beta : excess bandwidth factor, _beta in [0,1]
// _dt : fractional sample delay
// _h : output coefficient buffer (length: 2*k*m+1)
void liquid_firdes_prototype(liquid_firfilt_type _type,
unsigned int _k,
unsigned int _m,
float _beta,
float _dt,
float * _h)
{
// compute filter parameters
unsigned int h_len = 2*_k*_m + 1; // length
float fc = 0.5f / (float)_k; // cut-off frequency
float df = _beta / (float)_k; // transition bandwidth
float As = estimate_req_filter_As(df,h_len); // stop-band attenuation
// Parks-McClellan algorithm parameters
float bands[6] = { 0.0f, fc-0.5f*df,
fc, fc,
fc+0.5f*df, 0.5f};
float des[3] = { (float)_k, 0.5f*_k, 0.0f };
float weights[3] = {1.0f, 1.0f, 1.0f};
liquid_firdespm_wtype wtype[3] = { LIQUID_FIRDESPM_FLATWEIGHT,
LIQUID_FIRDESPM_FLATWEIGHT,
LIQUID_FIRDESPM_FLATWEIGHT};
switch (_type) {
// Nyquist filter prototypes
case LIQUID_FIRFILT_KAISER:
liquid_firdes_kaiser(h_len, fc, As, _dt, _h);
break;
case LIQUID_FIRFILT_PM:
// WARNING: input timing offset is ignored here
firdespm_run(h_len, 3, bands, des, weights, wtype, LIQUID_FIRDESPM_BANDPASS, _h);
break;
case LIQUID_FIRFILT_RCOS:
liquid_firdes_rcos(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_FEXP:
liquid_firdes_fexp(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_FSECH:
liquid_firdes_fsech(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_FARCSECH:
liquid_firdes_farcsech(_k, _m, _beta, _dt, _h);
break;
// root-Nyquist filter prototypes
case LIQUID_FIRFILT_ARKAISER:
liquid_firdes_arkaiser(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_RKAISER:
liquid_firdes_rkaiser(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_RRC:
liquid_firdes_rrcos(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_hM3:
liquid_firdes_hM3(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_GMSKTX:
liquid_firdes_gmsktx(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_GMSKRX:
liquid_firdes_gmskrx(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_RFEXP:
liquid_firdes_rfexp(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_RFSECH:
liquid_firdes_rfsech(_k, _m, _beta, _dt, _h);
break;
case LIQUID_FIRFILT_RFARCSECH:
liquid_firdes_rfarcsech(_k, _m, _beta, _dt, _h);
break;
default:
fprintf(stderr,"error: liquid_firdes_prototype(), invalid root-Nyquist filter type '%d'\n", _type);
exit(1);
}
}
