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// This example tests the performance for detecting and decoding frames
// with the qdsync_cccf object.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "qdsync_cccf_performance_example.m"
int main(int argc, char*argv[])
{
// options
unsigned int seq_len = 1024; // number of sync symbols
unsigned int k = 2; // samples/symbol
unsigned int m = 7; // filter delay [symbols]
float beta = 0.3f; // excess bandwidth factor
int ftype = LIQUID_FIRFILT_ARKAISER;
float threshold = 0.10f;//
unsigned int min_trials = 10; //
unsigned int max_trials = 100; //
unsigned int min_missed = 4; //
float SNRdB = -25.0f;
// generate synchronization sequence (QPSK symbols)
float complex seq[seq_len];
unsigned int i;
for (i=0; i<seq_len ; i++) {
seq[i] = (rand() % 2 ? 1.0f : -1.0f) * M_SQRT1_2 +
(rand() % 2 ? 1.0f : -1.0f) * M_SQRT1_2 * _Complex_I;
}
// interpolate sequence
firinterp_crcf interp = firinterp_crcf_create_prototype(ftype,k,m,beta,0);
unsigned int num_symbols = seq_len + 2*m + 3*seq_len;
unsigned int buf_len = num_symbols * k;
float complex buf_0[buf_len];
float complex buf_1[buf_len];
for (i=0; i<num_symbols; i++) {
// generate random symbol
float complex s = i < seq_len ? seq[i] : 0;
// interpolate symbol
firinterp_crcf_execute(interp, s, buf_0 + i*k);
}
firinterp_crcf_destroy(interp);
// create sync object and run signal through
qdsync_cccf q = qdsync_cccf_create_linear(seq, seq_len, ftype, k, m, beta, NULL, NULL);
qdsync_cccf_set_threshold(q, threshold);
while (SNRdB <= 5.0f) {
float nstd = powf(10.0f, -SNRdB/20.0f) * M_SQRT2;
unsigned int t;
unsigned int num_trials = 0;
unsigned int num_missed = 0;
while (1) {
for (t=0; t<min_trials; t++) {
// copy buffer and add noise
for (i=0; i<buf_len; i++)
buf_1[i] = buf_0[i] + nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// run through synchronizer
qdsync_cccf_reset(q);
qdsync_cccf_execute(q, buf_1, buf_len);
num_missed += qdsync_cccf_is_detected(q) ? 0 : 1;
}
num_trials += min_trials;
if (num_missed >= min_missed)
break;
if (num_trials >= max_trials)
break;
}
float pmd = (float)num_missed / (float)num_trials;
printf("SNR: %8.3f dB, missed %3u / %3u (%5.1f%%)\n", SNRdB, num_missed, num_trials, pmd*100);
if (num_missed < min_missed)
break;
SNRdB += 1.0f;
}
qdsync_cccf_destroy(q);
#if 0
// open file for storing results
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all; close all;\n");
// export results
fprintf(fid,"seq_len = %u;\n", seq_len);
fprintf(fid,"figure('color','white','position',[100 100 800 800]);\n");
fprintf(fid,"hold on;\n");
fprintf(fid,"hold off;\n");
fprintf(fid,"legend('Preamble','Payload');\n");
fprintf(fid,"grid on; xlabel('real'); ylabel('imag');\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
#endif
return 0;
}
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