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//
// Fading generator example
//
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <complex.h>
#include "liquid.h"
#define OUTPUT_FILENAME "debug_fading_generator_example.m"
int main() {
// options
unsigned int h_len=51; // doppler filter length
float fd=0.05f; // maximum doppler frequency
float K=2.0f; // Rice fading factor
float omega=1.0f; // mean power
float theta=0.0f; // angle of arrival
unsigned int n=256; // number of samples
// generate filter
unsigned int i;
float h[h_len];
fir_design_doppler(h_len,fd,K,theta,h);
firfilt_rrrf fi = firfilt_rrrf_create(h,h_len);
firfilt_rrrf fq = firfilt_rrrf_create(h,h_len);
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s, auto-generated file\n\n",OUTPUT_FILENAME);
fprintf(fid,"clear all;\nclose all;\n\n");
for (i=0; i<h_len; i++)
fprintf(fid,"h(%3u) = %12.8e;\n", i+1, h[i]);
// generate complex fading envelope
float complex x, y;
float yi, yq;
float s = sqrtf((omega*K)/(K+1));
float sig = sqrtf(0.5f*omega/(K+1));
float t=0.0f;
for (i=0; i<h_len; i++) {
crandnf(&x);
firfilt_rrrf_push(fi, crealf(x));
firfilt_rrrf_push(fq, cimagf(x));
t += h[i]*h[i];
}
t = sqrtf(t);
for (i=0; i<n; i++) {
crandnf(&x);
firfilt_rrrf_push(fi, crealf(x));
firfilt_rrrf_push(fq, cimagf(x));
// compute outputs
firfilt_rrrf_execute(fi, &yi);
firfilt_rrrf_execute(fq, &yq);
yi /= t;
yq /= t;
y = (yi*sig + s) + _Complex_I*(yq*sig);
printf("%4u: r:%8.5f, angle:%5.2f\n", i, cabsf(y), cargf(y));
fprintf(fid, "y(%4u) = %12.8e + j*%12.8e;\n",i+1,crealf(y),cimagf(y));
}
fprintf(fid,"\n\n");
fprintf(fid,"nfft=1024;\n");
fprintf(fid,"f=[0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"H=20*log10(abs(fftshift(fft(h,nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f,H,'-','LineWidth',2);\n");
fprintf(fid,"xlabel('Normalized frequency');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"\n\n");
fprintf(fid,"t=0:length(y)-1;\n");
fprintf(fid,"R=20*log10(abs(y));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(t,R,'-','LineWidth',2);\n");
fprintf(fid,"xlabel('time [samples]');\n");
fprintf(fid,"ylabel('fading amplitude [dB]');\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
// clean up objects
firfilt_rrrf_destroy(fi);
firfilt_rrrf_destroy(fq);
printf("done.\n");
return 0;
}
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