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//
// matched_filter_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "matched_filter_example.m"
// print usage/help message
void usage()
{
printf("matched_filter_example options:\n");
printf(" u/h : print usage/help\n");
printf(" t : filter type: [rrcos], rkaiser, arkaiser, hm3, gmsk, fexp, fsech, farcsech\n");
printf(" k : filter samples/symbol, k >= 2, default: 2\n");
printf(" m : filter delay (symbols), m >= 1, default: 3\n");
printf(" b : filter excess bandwidth factor, 0 < b < 1, default: 0.5\n");
printf(" n : number of symbols, default: 16\n");
}
int main(int argc, char*argv[]) {
// options
unsigned int k=2; // samples/symbol
unsigned int m=3; // symbol delay
float beta=0.7f; // excess bandwidth factor
unsigned int num_symbols=16;
int ftype_tx = LIQUID_FIRFILT_RRC;
int ftype_rx = LIQUID_FIRFILT_RRC;
int dopt;
while ((dopt = getopt(argc,argv,"uht:k:m:b:n:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 't':
if (strcmp(optarg,"gmsk")==0) {
ftype_tx = LIQUID_FIRFILT_GMSKTX;
ftype_rx = LIQUID_FIRFILT_GMSKRX;
} else {
ftype_tx = liquid_getopt_str2firfilt(optarg);
ftype_rx = liquid_getopt_str2firfilt(optarg);
}
if (ftype_tx == LIQUID_FIRFILT_UNKNOWN) {
fprintf(stderr,"error: %s, unknown filter type '%s'\n", argv[0], optarg);
exit(1);
}
break;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'n': num_symbols = atoi(optarg); break;
default:
exit(1);
}
}
if (k < 2) {
fprintf(stderr,"error: %s, k must be at least 2\n", argv[0]);
exit(1);
} else if (m < 1) {
fprintf(stderr,"error: %s, m must be at least 1\n", argv[0]);
exit(1);
} else if (beta <= 0.0f || beta >= 1.0f) {
fprintf(stderr,"error: %s, beta must be in (0,1)\n", argv[0]);
exit(1);
}
unsigned int i;
// derived values
unsigned int num_samples = num_symbols*k;
unsigned int h_len = 2*k*m+1; // transmit/receive filter length
unsigned int hc_len = 4*k*m+1; // composite filter length
// arrays
float ht[h_len]; // transmit filter
float hr[h_len]; // receive filter
float hc[hc_len]; // composite filter
// design the filter(s)
liquid_firdes_prototype(ftype_tx, k, m, beta, 0, ht);
liquid_firdes_prototype(ftype_rx, k, m, beta, 0, hr);
for (i=0; i<h_len; i++) printf("ht(%3u) = %12.8f;\n", i+1, ht[i]);
for (i=0; i<h_len; i++) printf("hr(%3u) = %12.8f;\n", i+1, hr[i]);
#if 0
// generate receive filter coefficients (reverse of transmit)
float hr[h_len];
for (i=0; i<h_len; i++)
hr[i] = ht[h_len-i-1];
#endif
// compute composite filter response
for (i=0; i<4*k*m+1; i++) {
int lag = (int)i - (int)(2*k*m);
hc[i] = liquid_filter_crosscorr(ht,h_len, hr,h_len, lag);
}
// compute filter inter-symbol interference
float rxy0 = liquid_filter_crosscorr(ht,h_len, hr,h_len, 0);
float isi_rms=0;
for (i=1; i<2*m; i++) {
float e = liquid_filter_crosscorr(ht,h_len, hr,h_len, i*k) / rxy0;
isi_rms += e*e;
}
isi_rms = sqrtf( isi_rms / (float)(2*m-1) );
printf(" isi (rms) : %12.8f dB\n", 20*log10f(isi_rms));
// compute relative stop-band energy
unsigned int nfft = 2048;
float As = liquid_filter_energy(ht, h_len, 0.5f*(1.0f + beta)/(float)k, nfft);
printf(" As : %12.8f dB\n", 20*log10f(As));
// generate signal
float sym_in[num_symbols];
float y[num_samples];
float sym_out[num_symbols];
// create interpolator and decimator
firinterp_rrrf interp = firinterp_rrrf_create(k, ht, h_len);
firdecim_rrrf decim = firdecim_rrrf_create( k, hr, h_len);
for (i=0; i<num_symbols; i++) {
// generate random symbol
sym_in[i] = (rand() % 2) ? 1.0f : -1.0f;
// interpolate
firinterp_rrrf_execute(interp, sym_in[i], &y[i*k]);
// decimate
firdecim_rrrf_execute(decim, &y[i*k], &sym_out[i]);
// normalize output
sym_out[i] /= k;
printf(" %3u : %8.5f", i, sym_out[i]);
if (i>=2*m) printf(" *\n");
else printf("\n");
}
// clean up objects
firinterp_rrrf_destroy(interp);
firdecim_rrrf_destroy(decim);
//
// export results
//
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,"k = %u;\n", k);
fprintf(fid,"m = %u;\n", m);
fprintf(fid,"beta = %12.8f;\n", beta);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"num_samples = k*num_symbols;\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++)
fprintf(fid," y(%3u) = %12.8f;\n", i+1, y[i]);
for (i=0; i<h_len; i++) fprintf(fid,"ht(%3u) = %20.8e;\n", i+1, ht[i]);
for (i=0; i<h_len; i++) fprintf(fid,"hr(%3u) = %20.8e;\n", i+1, hr[i]);
for (i=0; i<hc_len; i++) fprintf(fid,"hc(%3u) = %20.8e;\n", i+1, hc[i]);
fprintf(fid,"nfft=1024;\n");
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"Ht = 20*log10(abs(fftshift(fft(ht/k, nfft))));\n");
fprintf(fid,"Hr = 20*log10(abs(fftshift(fft(hr/k, nfft))));\n");
fprintf(fid,"Hc = 20*log10(abs(fftshift(fft(hc/k^2, nfft))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f,Hc,'-','LineWidth',2,...\n");
fprintf(fid," [0.5/k],[-6],'or',...\n");
fprintf(fid," [0.5/k*(1-beta) 0.5/k*(1-beta)],[-100 10],'-r',...\n");
fprintf(fid," [0.5/k*(1+beta) 0.5/k*(1+beta)],[-100 10],'-r');\n");
fprintf(fid,"xlabel('normalized frequency');\n");
fprintf(fid,"ylabel('PSD');\n");
fprintf(fid,"axis([-0.5 0.5 -100 10]);\n");
fprintf(fid,"grid on;\n");
// compute composite filter
fprintf(fid,"figure;\n");
fprintf(fid,"hc = conv(ht,hr)/k;\n");
fprintf(fid,"t = [(-2*k*m):(2*k*m)]/k;\n");
fprintf(fid,"i0 = [0:k:4*k*m]+1;\n");
fprintf(fid,"plot(t, hc, '-s',...\n");
fprintf(fid," t(i0),hc(i0),'or');\n");
fprintf(fid,"xlabel('symbol index');\n");
fprintf(fid,"ylabel('matched filter response');\n");
fprintf(fid,"grid on;\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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