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// This example demonstrates the functionality of the qdsync object to
// detect and synchronize an arbitrary signal in time in the presence of noise,
// carrier frequency/phase offsets, and fractional-sample timing offsets.
// offsets.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <math.h>
#include <time.h>
#include "liquid.h"
#define OUTPUT_FILENAME "qdsync_cccf_example.m"
// synchronization callback, return 0:continue, 1:reset
int callback(float complex * _buf,
unsigned int _buf_len,
void * _context)
{
printf("callback got %u samples\n", _buf_len);
unsigned int i;
for (i=0; i<_buf_len; i++)
fprintf((FILE*)_context, "y(end+1) = %12.8f + %12.8fj;\n", crealf(_buf[i]), cimagf(_buf[i]));
return 0;
}
int main(int argc, char*argv[])
{
// options
unsigned int seq_len = 80; // 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 nstd = 0.01f;
// 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;
}
// 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; y=[];\n");
// create sync object
qdsync_cccf q = qdsync_cccf_create_linear(seq, seq_len, ftype, k, m, beta, callback, fid);
qdsync_cccf_print(q);
// create interpolator
firinterp_crcf interp = firinterp_crcf_create_prototype(ftype,k,m,beta,0);
// run signal through sync object
float complex buf[k];
for (i=0; i<10*seq_len; i++) {
// generate random symbol
float complex s = i < seq_len ? seq[i] : (rand() & 1 ? 1.0f : -1.0f);
// interpolate symbol
firinterp_crcf_execute(interp, s, buf);
// add noise
unsigned int j;
for (j=0; j<k; j++)
buf[j] += nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// run through synchronizer
qdsync_cccf_execute(q, buf, k);
}
qdsync_cccf_destroy(q);
firinterp_crcf_destroy(interp);
// 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," plot(real(y(1:seq_len)), imag(y(1:seq_len)), '.','MarkerSize',6,'Color',[0 0.2 0.5]);\n");
fprintf(fid," plot(real(y((seq_len+1):end)),imag(y((seq_len+1):end)),'.','MarkerSize',6,'Color',[0 0.5 0.2]);\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);
return 0;
}
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