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//
// bpacketsync_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <getopt.h>
#include "liquid.h"
int callback(unsigned char * _payload,
int _payload_valid,
unsigned int _payload_len,
framesyncstats_s _stats,
void * _userdata)
{
printf("callback invoked, payload (%u bytes) : %s\n",
_payload_len,
_payload_valid ? "valid" : "INVALID!");
// copy data if valid
if (_payload_valid) {
unsigned char * msg_dec = (unsigned char*) _userdata;
memmove(msg_dec, _payload, _payload_len*sizeof(unsigned char));
}
return 0;
}
// print usage/help message
void usage()
{
printf("bpacketsync_example [options]\n");
printf(" u/h : print usage\n");
printf(" n : input data size (number of uncoded bytes): 8 default\n");
printf(" e : bit error rate of channel, default: 0\n");
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();
}
int main(int argc, char*argv[]) {
srand(time(NULL));
// options
unsigned int n=8; // original data message length
crc_scheme check = LIQUID_CRC_32; // data integrity check
fec_scheme fec0 = LIQUID_FEC_HAMMING74; // inner code
fec_scheme fec1 = LIQUID_FEC_NONE; // outer code
float bit_error_rate = 0.0f; // bit error rate
// read command-line options
int dopt;
while((dopt = getopt(argc,argv,"uhn:e:v:c:k:")) != EOF){
switch (dopt) {
case 'h':
case 'u': usage(); return 0;
case 'n': n = atoi(optarg); break;
case 'e': bit_error_rate = atof(optarg); break;
case 'v':
// data integrity check
check = liquid_getopt_str2crc(optarg);
if (check == LIQUID_CRC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported CRC scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
case 'c':
// inner FEC scheme
fec0 = liquid_getopt_str2fec(optarg);
if (fec0 == LIQUID_FEC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported inner FEC scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
case 'k':
// outer FEC scheme
fec1 = liquid_getopt_str2fec(optarg);
if (fec1 == LIQUID_FEC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported outer FEC scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
default:
exit(1);
}
}
// validate input
if (n == 0) {
fprintf(stderr,"error: %s, packet length must be greater than zero\n", argv[0]);
exit(1);
} else if (bit_error_rate < 0.0f || bit_error_rate > 1.0f) {
fprintf(stderr,"error: %s, channel bit error rate must be in [0,1]\n", argv[0]);
exit(1);
}
// create packet generator
bpacketgen pg = bpacketgen_create(0, n, check, fec0, fec1);
bpacketgen_print(pg);
unsigned int i;
// compute packet length
unsigned int k = bpacketgen_get_packet_len(pg);
// initialize arrays
unsigned char msg_org[n]; // original message
unsigned char msg_enc[k]; // encoded message
unsigned char msg_rec[k+1]; // received message
unsigned char msg_dec[n]; // decoded message
// create packet synchronizer
bpacketsync ps = bpacketsync_create(0, callback, (void*)msg_dec);
bpacketsync_print(ps);
// initialize original data message
for (i=0; i<n; i++)
msg_org[i] = rand() % 256;
//
// encode packet
//
bpacketgen_encode(pg,msg_org,msg_enc);
//
// channel
//
// add delay
msg_rec[0] = rand() & 0xff; // initialize first byte as random
memmove(&msg_rec[1], msg_enc, k*sizeof(unsigned char));
liquid_lbshift(msg_rec, (k+1)*sizeof(unsigned char), rand()%8); // random shift
// add random errors
for (i=0; i<k+1; i++) {
unsigned int j;
for (j=0; j<8; j++) {
if (randf() < bit_error_rate)
msg_rec[i] ^= 1 << (8-j-1);
}
}
//
// run packet synchronizer
//
// push random bits through synchronizer
for (i=0; i<100; i++)
bpacketsync_execute_byte(ps, rand() & 0xff);
// push packet through synchronizer
for (i=0; i<k+1; i++)
bpacketsync_execute_byte(ps, msg_rec[i]);
//
// count errors
//
unsigned int num_bit_errors = 0;
for (i=0; i<n; i++)
num_bit_errors += count_bit_errors(msg_org[i], msg_dec[i]);
printf("number of bit errors received: %4u / %4u\n", num_bit_errors, n*8);
// clean up allocated objects
bpacketgen_destroy(pg);
bpacketsync_destroy(ps);
return 0;
}
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