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//
// packetizer_soft_example.c
//
// This example demonstrates the functionality of the packetizer object
// for soft-decision decoding. Data are encoded using two forward error-
// correction schemes (an inner and outer code) before noise and data
// errors are added. The decoder then tries to recover the original data
// message. Only the outer code uses soft-decision decoding.
//
// SEE ALSO: fec_soft_example.c
// packetizer_example.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include "liquid.h"
// print usage/help message
void usage()
{
printf("packetizer_example [options]\n");
printf(" u/h : print usage\n");
printf(" n : input data size (number of uncoded bytes): 8 default\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[]) {
// 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
// read command-line options
int dopt;
while((dopt = getopt(argc,argv,"uhn:v:c:k:")) != EOF){
switch (dopt) {
case 'h':
case 'u': usage(); return 0;
case 'n':
n = atoi(optarg);
if (n < 1) {
printf("error: packet length must be positive\n");
usage();
exit(-1);
}
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);
}
}
unsigned int i;
unsigned int k = packetizer_compute_enc_msg_len(n,check,fec0,fec1);
packetizer p = packetizer_create(n,check,fec0,fec1);
packetizer_print(p);
// initialize arrays
unsigned char msg_org[n]; // original message
unsigned char msg_enc[k]; // encoded message
unsigned char msg_rec[8*k]; // received message (soft bits)
unsigned char msg_dec[n]; // decoded message
int crc_pass;
// initialize original data message
for (i=0; i<n; i++)
msg_org[i] = rand() % 256;
// encode packet
packetizer_encode(p,msg_org,msg_enc);
// convert to soft bits and add 'noise'
for (i=0; i<k; i++) {
msg_rec[8*i+0] = (msg_enc[i] & 0x80) ? 255 : 0;
msg_rec[8*i+1] = (msg_enc[i] & 0x40) ? 255 : 0;
msg_rec[8*i+2] = (msg_enc[i] & 0x20) ? 255 : 0;
msg_rec[8*i+3] = (msg_enc[i] & 0x10) ? 255 : 0;
msg_rec[8*i+4] = (msg_enc[i] & 0x08) ? 255 : 0;
msg_rec[8*i+5] = (msg_enc[i] & 0x04) ? 255 : 0;
msg_rec[8*i+6] = (msg_enc[i] & 0x02) ? 255 : 0;
msg_rec[8*i+7] = (msg_enc[i] & 0x01) ? 255 : 0;
}
// flip first bit (ensure error)
msg_rec[0] = 255 - msg_rec[0];
// add noise (but not so much that it would cause a bit error)
for (i=0; i<8*k; i++) {
int soft_bit = msg_rec[i] + (int)(20*randnf());
if (soft_bit > 255) soft_bit = 255;
if (soft_bit < 0) soft_bit = 0;
msg_rec[i] = soft_bit;
}
// decode packet
crc_pass =
packetizer_decode_soft(p,msg_rec,msg_dec);
// clean up allocated objects
packetizer_destroy(p);
// print results
printf("original message: [%3u] ",n);
for (i=0; i<n; i++)
printf(" %.2X", (unsigned int) (msg_org[i]));
printf("\n");
printf("encoded message: [%3u] ",k);
for (i=0; i<k; i++)
printf(" %.2X", (unsigned int) (msg_enc[i]));
printf("\n");
#if 0
printf("received message: [%3u] ",k);
for (i=0; i<k; i++)
printf("%c%.2X", msg_rec[i]==msg_enc[i] ? ' ' : '*', (unsigned int) (msg_rec[i]));
printf("\n");
#endif
//if (verbose) {
if (1) {
// print expanded result (print each soft bit value)
for (i=0; i<k; i++) {
unsigned char msg_cor_hard = 0x00;
printf("%5u: ", i);
unsigned int j;
for (j=0; j<8; j++) {
msg_cor_hard |= (msg_rec[8*i+j] > 127) ? 1<<(8-j-1) : 0;
unsigned int bit_enc = (msg_enc[i] >> (8-j-1)) & 0x01;
unsigned int bit_rec = (msg_rec[8*i+j] > 127) ? 1 : 0;
//printf("%1u %3u (%1u) %c", bit_enc, msg_rec[i], bit_rec, bit_enc != bit_rec ? '*' : ' ');
printf("%4u%c", msg_rec[8*i+j], bit_enc != bit_rec ? '*' : ' ');
}
printf(" : %c%.2X\n", msg_cor_hard==msg_enc[i] ? ' ' : '*', (unsigned int) (msg_cor_hard));
}
} // verbose
printf("decoded message: [%3u] ",n);
for (i=0; i<n; i++)
printf("%c%.2X", msg_dec[i] == msg_org[i] ? ' ' : '*', (unsigned int) (msg_dec[i]));
printf("\n");
printf("\n");
// count bit errors
unsigned int num_sym_errors=0;
unsigned int num_bit_errors=0;
for (i=0; i<n; i++) {
num_sym_errors += (msg_org[i] == msg_dec[i]) ? 0 : 1;
num_bit_errors += count_bit_errors(msg_org[i], msg_dec[i]);
}
//printf("number of symbol errors detected: %d\n", num_errors_detected);
printf("number of symbol errors received: %4u / %4u\n", num_sym_errors, n);
printf("number of bit errors received: %4u / %4u\n", num_bit_errors, n*8);
if (crc_pass)
printf("(crc passed)\n");
else
printf("(crc failed)\n");
return 0;
}
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