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//
// flexframesync_example.c
//
// This example demonstrates the basic interface to the flexframegen and
// flexframesync objects used to completely encapsulate raw data bytes
// into frame samples (nearly) ready for over-the-air transmission. A
// 14-byte header and variable length payload are encoded into baseband
// symbols using the flexframegen object. The resulting symbols are
// interpolated using a root-Nyquist filter and the resulting samples are
// then fed into the flexframesync object which attempts to decode the
// frame. Whenever frame is found and properly decoded, its callback
// function is invoked.
//
// SEE ALSO: flexframesync_reconfig_example.c
// framesync64_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <getopt.h>
#include <assert.h>
#include "liquid.h"
void usage()
{
printf("flexframesync_example [options]\n");
printf(" u/h : print usage\n");
printf(" s : signal-to-noise ratio [dB], default: 20\n");
printf(" F : carrier frequency offset, default: 0.01\n");
printf(" n : payload length [bytes], default: 480\n");
printf(" m : modulation scheme (qpsk default)\n");
liquid_print_modulation_schemes();
printf(" v : data integrity check: crc32 default\n");
liquid_print_crc_schemes();
printf(" c : coding scheme (inner): h74 default\n");
printf(" k : coding scheme (outer): none default\n");
liquid_print_fec_schemes();
printf(" d : enable debugging\n");
}
// flexframesync callback function
static int callback(unsigned char * _header,
int _header_valid,
unsigned char * _payload,
unsigned int _payload_len,
int _payload_valid,
framesyncstats_s _stats,
void * _userdata);
int main(int argc, char *argv[])
{
//srand( time(NULL) );
// options
modulation_scheme ms = LIQUID_MODEM_QPSK; // mod. scheme
crc_scheme check = LIQUID_CRC_32; // data validity check
fec_scheme fec0 = LIQUID_FEC_NONE; // fec (inner)
fec_scheme fec1 = LIQUID_FEC_NONE; // fec (outer)
unsigned int payload_len = 480; // payload length
int debug_enabled = 0; // enable debugging?
float noise_floor = -60.0f; // noise floor
float SNRdB = 20.0f; // signal-to-noise ratio
float dphi = 0.01f; // carrier frequency offset
// get options
int dopt;
while((dopt = getopt(argc,argv,"uhs:F:n:m:v:c:k:d")) != EOF){
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 's': SNRdB = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 'n': payload_len = atol(optarg); break;
case 'm': ms = liquid_getopt_str2mod(optarg); break;
case 'v': check = liquid_getopt_str2crc(optarg); break;
case 'c': fec0 = liquid_getopt_str2fec(optarg); break;
case 'k': fec1 = liquid_getopt_str2fec(optarg); break;
case 'd': debug_enabled = 1; break;
default:
exit(-1);
}
}
// derived values
unsigned int i;
float nstd = powf(10.0f, noise_floor/20.0f); // noise std. dev.
float gamma = powf(10.0f, (SNRdB+noise_floor)/20.0f); // channel gain
// create flexframegen object
flexframegenprops_s fgprops;
flexframegenprops_init_default(&fgprops);
fgprops.mod_scheme = ms;
fgprops.check = check;
fgprops.fec0 = fec0;
fgprops.fec1 = fec1;
flexframegen fg = flexframegen_create(&fgprops);
// create flexframesync object
flexframesync fs = flexframesync_create(callback,NULL);
if (debug_enabled)
flexframesync_debug_enable(fs);
// assemble the frame (NULL pointers for default values)
flexframegen_assemble(fg, NULL, NULL, payload_len);
flexframegen_print(fg);
// generate the frame in blocks
unsigned int buf_len = 256;
float complex x[buf_len];
float complex y[buf_len];
int frame_complete = 0;
float phi = 0.0f;
while (!frame_complete) {
// write samples to buffer
frame_complete = flexframegen_write_samples(fg, x, buf_len);
// add noise and push through synchronizer
for (i=0; i<buf_len; i++) {
// apply channel gain and carrier offset to input
y[i] = gamma * x[i] * cexpf(_Complex_I*phi);
phi += dphi;
// add noise
y[i] += nstd*( randnf() + _Complex_I*randnf())*M_SQRT1_2;
}
// run through frame synchronizer
flexframesync_execute(fs, y, buf_len);
}
// export debugging file
if (debug_enabled)
flexframesync_debug_print(fs, "flexframesync_debug.m");
flexframesync_print(fs);
// destroy allocated objects
flexframegen_destroy(fg);
flexframesync_destroy(fs);
printf("done.\n");
return 0;
}
static int callback(unsigned char * _header,
int _header_valid,
unsigned char * _payload,
unsigned int _payload_len,
int _payload_valid,
framesyncstats_s _stats,
void * _userdata)
{
printf("******** callback invoked\n");
// count bit errors (assuming all-zero message)
unsigned int bit_errors = 0;
unsigned int i;
for (i=0; i<_payload_len; i++)
bit_errors += liquid_count_ones(_payload[i]);
framesyncstats_print(&_stats);
printf(" header crc : %s\n", _header_valid ? "pass" : "FAIL");
printf(" payload length : %u\n", _payload_len);
printf(" payload crc : %s\n", _payload_valid ? "pass" : "FAIL");
printf(" payload bit errors : %u / %u\n", bit_errors, 8*_payload_len);
return 0;
}
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