// 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);
}
}
// create FIR polyphase filterbank channelizer object with
// prototype root-Nyquist filter
// _type : channelizer type (LIQUID_ANALYZER | LIQUID_SYNTHESIZER)
// _M : number of channels
// _m : filter delay (symbols)
// _beta : filter excess bandwidth factor, in [0,1]
// _ftype : filter prototype (rrcos, rkaiser, etc.)
FIRPFBCH() FIRPFBCH(_create_rnyquist)(int _type,
unsigned int _M,
unsigned int _m,
float _beta,
int _ftype)
{
// validate input
if (_type != LIQUID_ANALYZER && _type != LIQUID_SYNTHESIZER) {
fprintf(stderr,"error: firpfbch_%s_create_rnyquist(), invalid type %d\n", EXTENSION_FULL, _type);
exit(1);
} else if (_M == 0) {
fprintf(stderr,"error: firpfbch_%s_create_rnyquist(), number of channels must be greater than 0\n", EXTENSION_FULL);
exit(1);
} else if (_m == 0) {
fprintf(stderr,"error: firpfbch_%s_create_rnyquist(), invalid filter size (must be greater than 0)\n", EXTENSION_FULL);
exit(1);
}
// design filter
unsigned int h_len = 2*_M*_m + 1;
float h[h_len];
// TODO : actually design based on requested filter prototype
switch (_ftype) {
case LIQUID_FIRFILT_ARKAISER:
// root-Nyquist Kaiser (approximate optimum)
liquid_firdes_arkaiser(_M, _m, _beta, 0.0f, h);
break;
case LIQUID_FIRFILT_RKAISER:
// root-Nyquist Kaiser (true optimum)
liquid_firdes_rkaiser(_M, _m, _beta, 0.0f, h);
break;
case LIQUID_FIRFILT_RRC:
// root raised-cosine
liquid_firdes_rrcos(_M, _m, _beta, 0.0f, h);
break;
case LIQUID_FIRFILT_hM3:
// harris-Moerder-3 filter
liquid_firdes_hM3(_M, _m, _beta, 0.0f, h);
break;
default:
fprintf(stderr,"error: firpfbch_%s_create_rnyquist(), unknown/invalid prototype (%d)\n", EXTENSION_FULL, _ftype);
exit(1);
}
// copy coefficients to type-specfic array, reversing order if
// channelizer is an analyzer, matched filter: g(-t)
unsigned int g_len = 2*_M*_m;
TC gc[g_len];
unsigned int i;
if (_type == LIQUID_SYNTHESIZER) {
for (i=0; i<g_len; i++)
gc[i] = h[i];
} else {
for (i=0; i<g_len; i++)
gc[i] = h[g_len-i-1];
}
// create filterbank object
unsigned int p = 2*_m;
FIRPFBCH() q = FIRPFBCH(_create)(_type, _M, p, gc);
// return filterbank object
return q;
}