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//
// firpfbch_crcf_analysis_example.c
//
// Example of the analysis channelizer filterbank. The input signal is
// comprised of several signals spanning different frequency bands. The
// channelizer downconverts each to baseband (maximally decimated), and
// the resulting spectrum of each is plotted.
//
#include <stdio.h>
#include <math.h>
#include <complex.h>
#include "liquid.h"
#define OUTPUT_FILENAME "firpfbch_crcf_analysis_example.m"
int main() {
// options
unsigned int num_channels = 8; // number of channels
unsigned int m = 4; // filter delay
float As = 60; // stop-band attenuation
unsigned int num_frames = 25; // number of frames
//
unsigned int i;
unsigned int k;
// derived values
unsigned int num_samples = num_frames * num_channels;
// data arrays
float complex x[num_samples]; // time-domain input [size: num_samples x 1 ]
float complex y[num_samples]; // channelized output [size: num_channels x num_frames]
// initialize input with zeros
for (i=0; i<num_samples; i++)
x[i] = 0.0f;
// generate input signal(s)
unsigned int num_signals = 4;
float fc[4] = {0.0f, 0.25f, 0.375f, -0.375f}; // center frequencies
float bw[4] = {0.035f, 0.035f, 0.035f, 0.035f}; // bandwidths
unsigned int pulse_len = 137;
float pulse[pulse_len];
for (i=0; i<num_signals; i++) {
// create pulse
liquid_firdes_kaiser(pulse_len, bw[i], 50.0f, 0.0f, pulse);
// add pulse to input signal with carrier offset
for (k=0; k<pulse_len; k++)
x[k] += pulse[k] * cexpf(_Complex_I*2*M_PI*fc[i]*k) * bw[i];
}
// create prototype filter
unsigned int h_len = 2*num_channels*m + 1;
float h[h_len];
liquid_firdes_kaiser(h_len, 0.5f/(float)num_channels, As, 0.0f, h);
#if 0
// create filterbank channelizer object using internal method for filter
firpfbch_crcf q = firpfbch_crcf_create_kaiser(LIQUID_ANALYZER, num_channels, m, As);
#else
// create filterbank channelizer object using external filter coefficients
firpfbch_crcf q = firpfbch_crcf_create(LIQUID_ANALYZER, num_channels, 2*m, h);
#endif
// channelize input data
for (i=0; i<num_frames; i++) {
// execute analysis filter bank
firpfbch_crcf_analyzer_execute(q, &x[i*num_channels], &y[i*num_channels]);
}
// destroy channelizer object
firpfbch_crcf_destroy(q);
//
// export results to file
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"num_channels = %u;\n", num_channels);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"num_frames = %u;\n", num_frames);
fprintf(fid,"h_len = 2*num_channels*m+1;\n");
fprintf(fid,"num_samples = num_frames*num_channels;\n");
fprintf(fid,"h = zeros(1,h_len);\n");
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = zeros(num_channels, num_frames);\n");
// save prototype filter
for (i=0; i<h_len; i++)
fprintf(fid," h(%6u) = %12.4e;\n", i+1, h[i]);
// save input signal
for (i=0; i<num_samples; i++)
fprintf(fid," x(%6u) = %12.4e + 1i*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
// save channelized output signals
for (i=0; i<num_frames; i++) {
for (k=0; k<num_channels; k++) {
float complex v = y[i*num_channels + k];
fprintf(fid," y(%3u,%6u) = %12.4e + 1i*%12.4e;\n", k+1, i+1, crealf(v), cimagf(v));
}
}
// plot results
fprintf(fid,"\n");
fprintf(fid,"nfft = 1024;\n"); // TODO: use nextpow2
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"H = 20*log10(abs(fftshift(fft(h/num_channels,nfft))));\n");
fprintf(fid,"X = 20*log10(abs(fftshift(fft(x,nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," plot(f, H, 'Color', [0 0.5 0.25], 'LineWidth', 2);\n");
fprintf(fid," axis([-0.5 0.5 -100 10]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid," ylabel('Prototype Filter PSD');\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," plot(f, X, 'Color', [0 0.25 0.5], 'LineWidth', 2);\n");
fprintf(fid," axis([-0.5 0.5 -100 0]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid," ylabel('Input PSD');\n");
// compute the PSD of each output and plot results on a square grid
fprintf(fid,"n = ceil(sqrt(num_channels));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"for i=1:num_channels,\n");
fprintf(fid," Y = 20*log10(abs(fftshift(fft(y(i,:),nfft))));\n");
fprintf(fid," subplot(n,n,i);\n");
fprintf(fid," plot(f, Y, 'Color', [0.25 0 0.25], 'LineWidth', 1.5);\n");
fprintf(fid," axis([-0.5 0.5 -120 20]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," title(num2str(i-1));\n");
fprintf(fid,"end;\n");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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