// 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); } }
int main() { // options unsigned int num_channels=64; // must be even number unsigned int num_symbols=16; // number of symbols unsigned int m=3; // filter delay (symbols) float beta = 0.9f; // filter excess bandwidth factor float phi = 0.0f; // carrier phase offset; float dphi = 0.04f; // carrier frequency offset // number of frames (compensate for filter delay) unsigned int num_frames = num_symbols + 2*m; unsigned int num_samples = num_channels * num_frames; unsigned int i; unsigned int j; // create filter prototype unsigned int h_len = 2*num_channels*m + 1; float h[h_len]; float complex hc[h_len]; float complex gc[h_len]; liquid_firdes_rkaiser(num_channels, m, beta, 0.0f, h); unsigned int g_len = 2*num_channels*m; for (i=0; i<g_len; i++) { hc[i] = h[i]; gc[i] = h[g_len-i-1] * cexpf(_Complex_I*dphi*i); } // data arrays float complex s[num_channels]; // input symbols float complex y[num_samples]; // time-domain samples float complex Y0[num_frames][num_channels]; // channelized output float complex Y1[num_frames][num_channels]; // channelized output // create ofdm/oqam generator object and generate data ofdmoqam qs = ofdmoqam_create(num_channels, m, beta, 0.0f, LIQUID_SYNTHESIZER, 0); for (i=0; i<num_frames; i++) { for (j=0; j<num_channels; j++) { if (i<num_symbols) { #if 0 // QPSK on all subcarriers s[j] = (rand() % 2 ? 1.0f : -1.0f) + (rand() % 2 ? 1.0f : -1.0f) * _Complex_I; s[j] *= 1.0f / sqrtf(2.0f); #else // BPSK on even subcarriers s[j] = rand() % 2 ? 1.0f : -1.0f; s[j] *= (j%2)==0 ? 1.0f : 0.0f; #endif } else { s[j] = 0.0f; } } // run synthesizer ofdmoqam_execute(qs, s, &y[i*num_channels]); } ofdmoqam_destroy(qs); // channel for (i=0; i<num_samples; i++) y[i] *= cexpf(_Complex_I*(phi + dphi*i)); // // analysis filterbank (receiver) // // create filterbank manually dotprod_cccf dp[num_channels]; // vector dot products windowcf w[num_channels]; // window buffers #if DEBUG // print coefficients printf("h_prototype:\n"); for (i=0; i<h_len; i++) printf(" h[%3u] = %12.8f\n", i, h[i]); #endif // create objects unsigned int gc_sub_len = 2*m; float complex gc_sub[gc_sub_len]; for (i=0; i<num_channels; i++) { // sub-sample prototype filter, loading coefficients in // reverse order #if 0 for (j=0; j<gc_sub_len; j++) gc_sub[j] = h[j*num_channels+i]; #else for (j=0; j<gc_sub_len; j++) gc_sub[gc_sub_len-j-1] = gc[j*num_channels+i]; #endif // create window buffer and dotprod objects dp[i] = dotprod_cccf_create(gc_sub, gc_sub_len); w[i] = windowcf_create(gc_sub_len); #if DEBUG printf("gc_sub[%u] : \n", i); for (j=0; j<gc_sub_len; j++) printf(" g[%3u] = %12.8f + %12.8f\n", j, crealf(gc_sub[j]), cimagf(gc_sub[j])); #endif } // generate DFT object float complex x[num_channels]; // time-domain buffer float complex X[num_channels]; // freq-domain buffer #if 0 fftplan fft = fft_create_plan(num_channels, X, x, FFT_REVERSE, 0); #else fftplan fft = fft_create_plan(num_channels, X, x, FFT_FORWARD, 0); #endif // // run analysis filter bank // #if 0 unsigned int filter_index = 0; #else unsigned int filter_index = num_channels-1; #endif float complex y_hat; // input sample float complex * r; // read pointer for (i=0; i<num_frames; i++) { // load buffers for (j=0; j<num_channels; j++) { // grab sample y_hat = y[i*num_channels + j]; // push sample into buffer at filter index windowcf_push(w[filter_index], y_hat); // decrement filter index filter_index = (filter_index + num_channels - 1) % num_channels; //filter_index = (filter_index + 1) % num_channels; } // execute filter outputs, reversing order of output (not // sure why this is necessary) for (j=0; j<num_channels; j++) { windowcf_read(w[j], &r); dotprod_cccf_execute(dp[j], r, &X[num_channels-j-1]); } #if 1 // compensate for carrier frequency offset (before transform) for (j=0; j<num_channels; j++) { X[j] *= cexpf(-_Complex_I*(dphi*i*num_channels)); } #endif // execute DFT, store result in buffer 'x' fft_execute(fft); #if 0 // compensate for carrier frequency offset (after transform) for (j=0; j<num_channels; j++) { x[j] *= cexpf(-_Complex_I*(dphi*i*num_channels)); } #endif // move to output array for (j=0; j<num_channels; j++) Y0[i][j] = x[j]; } // destroy objects for (i=0; i<num_channels; i++) { dotprod_cccf_destroy(dp[i]); windowcf_destroy(w[i]); } fft_destroy_plan(fft); #if 0 // print filterbank channelizer printf("\n"); printf("filterbank channelizer:\n"); for (i=0; i<num_symbols; i++) { printf("%3u: ", i); for (j=0; j<num_channels; j++) { printf(" %8.5f+j%8.5f, ", crealf(Y0[i][j]), cimagf(Y0[i][j])); } printf("\n"); } #endif // // export data // FILE*fid = fopen(OUTPUT_FILENAME,"w"); fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME); fprintf(fid,"clear all;\nclose all;\n\n"); fprintf(fid,"num_channels=%u;\n", num_channels); fprintf(fid,"num_symbols=%u;\n", num_symbols); fprintf(fid,"num_frames = %u;\n", num_frames); fprintf(fid,"num_samples = num_frames*num_channels;\n"); fprintf(fid,"y = zeros(1,%u);\n", num_samples); fprintf(fid,"Y0 = zeros(%u,%u);\n", num_frames, num_channels); fprintf(fid,"Y1 = zeros(%u,%u);\n", num_frames, num_channels); for (i=0; i<num_frames; i++) { for (j=0; j<num_channels; j++) { fprintf(fid,"Y0(%4u,%4u) = %12.4e + j*%12.4e;\n", i+1, j+1, crealf(Y0[i][j]), cimagf(Y0[i][j])); fprintf(fid,"Y1(%4u,%4u) = %12.4e + j*%12.4e;\n", i+1, j+1, crealf(Y1[i][j]), cimagf(Y1[i][j])); } } // plot BPSK results fprintf(fid,"figure;\n"); fprintf(fid,"plot(Y0(:,1:2:end),'x');\n"); fprintf(fid,"axis([-1 1 -1 1]*1.2*sqrt(num_channels));\n"); fprintf(fid,"axis square;\n"); fprintf(fid,"grid on;\n"); fclose(fid); printf("results written to '%s'\n", OUTPUT_FILENAME); printf("done.\n"); return 0; }
// 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; }