// 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; }