int main() { // spectral periodogram options unsigned int nfft = 1200; // spectral periodogram FFT size unsigned int num_samples = 64000; // number of samples float fc = 0.20f; // carrier (relative to sampling rate) // create objects iirfilt_crcf filter_tx = iirfilt_crcf_create_lowpass(15, 0.05); nco_crcf mixer_tx = nco_crcf_create(LIQUID_VCO); nco_crcf mixer_rx = nco_crcf_create(LIQUID_VCO); iirfilt_crcf filter_rx = iirfilt_crcf_create_lowpass(7, 0.2); // set carrier frequencies nco_crcf_set_frequency(mixer_tx, fc * 2*M_PI); nco_crcf_set_frequency(mixer_rx, fc * 2*M_PI); // create objects for measuring power spectral density spgramcf spgram_tx = spgramcf_create_default(nfft); spgramf spgram_dac = spgramf_create_default(nfft); spgramcf spgram_rx = spgramcf_create_default(nfft); // run through loop one step at a time unsigned int i; for (i=0; i<num_samples; i++) { // STEP 1: generate input signal (filtered noise with offset tone) float complex v1 = (randnf() + randnf()*_Complex_I) + 3.0f*cexpf(-_Complex_I*0.2f*i); iirfilt_crcf_execute(filter_tx, v1, &v1); // save spectrum spgramcf_push(spgram_tx, v1); // STEP 2: mix signal up and save real part (DAC output) nco_crcf_mix_up(mixer_tx, v1, &v1); float v2 = crealf(v1); nco_crcf_step(mixer_tx); // save spectrum spgramf_push(spgram_dac, v2); // STEP 3: mix signal down and filter off image float complex v3; nco_crcf_mix_down(mixer_rx, v2, &v3); iirfilt_crcf_execute(filter_rx, v3, &v3); nco_crcf_step(mixer_rx); // save spectrum spgramcf_push(spgram_rx, v3); } // compute power spectral density output float psd_tx [nfft]; float psd_dac [nfft]; float psd_rx [nfft]; spgramcf_get_psd(spgram_tx, psd_tx); spgramf_get_psd( spgram_dac, psd_dac); spgramcf_get_psd(spgram_rx, psd_rx); // destroy objects spgramcf_destroy(spgram_tx); spgramf_destroy(spgram_dac); spgramcf_destroy(spgram_rx); iirfilt_crcf_destroy(filter_tx); nco_crcf_destroy(mixer_tx); nco_crcf_destroy(mixer_rx); iirfilt_crcf_destroy(filter_rx); // // export output file // FILE * fid = fopen(OUTPUT_FILENAME,"w"); fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME); fprintf(fid,"clear all;\n"); fprintf(fid,"close all;\n\n"); fprintf(fid,"nfft = %u;\n", nfft); fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n"); fprintf(fid,"psd_tx = zeros(1,nfft);\n"); fprintf(fid,"psd_dac= zeros(1,nfft);\n"); fprintf(fid,"psd_rx = zeros(1,nfft);\n"); for (i=0; i<nfft; i++) { fprintf(fid,"psd_tx (%6u) = %12.4e;\n", i+1, psd_tx [i]); fprintf(fid,"psd_dac(%6u) = %12.4e;\n", i+1, psd_dac[i]); fprintf(fid,"psd_rx (%6u) = %12.4e;\n", i+1, psd_rx [i]); } fprintf(fid,"figure;\n"); fprintf(fid,"hold on;\n"); fprintf(fid," plot(f, psd_tx, '-', 'LineWidth',1.5,'Color',[0.7 0.7 0.7]);\n"); fprintf(fid," plot(f, psd_dac, '-', 'LineWidth',1.5,'Color',[0.0 0.5 0.3]);\n"); fprintf(fid," plot(f, psd_rx, '-', 'LineWidth',1.5,'Color',[0.0 0.3 0.5]);\n"); fprintf(fid,"hold off;\n"); fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n"); fprintf(fid,"ylabel('Power Spectral Density [dB]');\n"); fprintf(fid,"grid on;\n"); fprintf(fid,"axis([-0.5 0.5 -100 60]);\n"); fprintf(fid,"legend('transmit (complex)','DAC output (real)','receive (complex)','location','northeast');\n"); fclose(fid); printf("results written to %s.\n", OUTPUT_FILENAME); printf("done.\n"); return 0; }
int main() { // spectral periodogram options unsigned int nfft = 1024; // spectral periodogram FFT size unsigned int num_samples = 4000; // number of samples float beta = 10.0f; // Kaiser-Bessel window parameter float noise_floor = -60.0f; // noise floor [dB] float alpha = 0.1f; // PSD estimate bandwidth unsigned int i; // derived values float nstd = powf(10.0f, noise_floor/20.0f); // create spectral periodogram unsigned int window_size = nfft/2; // spgramf window size spgramf q = spgramf_create_kaiser(nfft, window_size, beta); // generate signal (filter with frequency offset) unsigned int h_len = 91; // filter length float fc = 0.07f; // filter cut-off frequency float f0 = 0.20f; // filter center frequency float As = 60.0f; // filter stop-band attenuation float h[h_len]; // filter coefficients liquid_firdes_kaiser(h_len, fc, As, 0, h); // add frequency offset for (i=0; i<h_len; i++) h[i] *= cosf(2*M_PI*f0*i); firfilt_rrrf filter = firfilt_rrrf_create(h, h_len); firfilt_rrrf_set_scale(filter, 2.0f*fc); for (i=0; i<num_samples; i++) { // generate random sample float x = randnf(); // filter float y = 0; firfilt_rrrf_push(filter, x); firfilt_rrrf_execute(filter, &y); // add noise y += nstd * randnf(); // push resulting sample through periodogram spgramf_accumulate_psd(q, &y, alpha, 1); } // compute power spectral density output float psd[nfft]; spgramf_write_accumulation(q, psd); // destroy objects firfilt_rrrf_destroy(filter); spgramf_destroy(q); // // export output file // FILE * fid = fopen(OUTPUT_FILENAME,"w"); fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME); fprintf(fid,"clear all;\n"); fprintf(fid,"close all;\n\n"); fprintf(fid,"nfft = %u;\n", nfft); fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n"); fprintf(fid,"H = zeros(1,nfft);\n"); fprintf(fid,"noise_floor = %12.6f;\n", noise_floor); for (i=0; i<nfft; i++) fprintf(fid,"H(%6u) = %12.4e;\n", i+1, psd[i]); fprintf(fid,"figure;\n"); fprintf(fid,"plot(f, H, '-', 'LineWidth',1.5);\n"); fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n"); fprintf(fid,"ylabel('Power Spectral Density [dB]');\n"); fprintf(fid,"grid on;\n"); fprintf(fid,"ymin = 10*floor([noise_floor-20]/10);\n"); fprintf(fid,"ymax = 10*floor([noise_floor+80]/10);\n"); fprintf(fid,"axis([-0.5 0.5 ymin ymax]);\n"); fclose(fid); printf("results written to %s.\n", OUTPUT_FILENAME); printf("done.\n"); return 0; }