// decode header
void flexframesync_decode_header(flexframesync _q)
{
#if DEMOD_HEADER_SOFT
// soft decoding operates on 'header_mod' array directly;
// no need to pack bits
#else
// pack 256 1-bit header symbols into 32 8-bit bytes
unsigned int num_written;
liquid_pack_bytes(_q->header_mod, FLEXFRAME_H_SYM,
_q->header_enc, FLEXFRAME_H_ENC,
&num_written);
assert(num_written==FLEXFRAME_H_ENC);
#endif
#if DEBUG_FLEXFRAMESYNC_PRINT
unsigned int i;
// print header (encoded)
printf("header rx (enc) : ");
for (i=0; i<FLEXFRAME_H_ENC; i++)
printf("%.2X ", _q->header_enc[i]);
printf("\n");
#endif
// unscramble header and run packet decoder
#if DEMOD_HEADER_SOFT
// soft demodulation operates on header_mod directly
unscramble_data_soft(_q->header_mod, FLEXFRAME_H_ENC);
_q->header_valid =
packetizer_decode_soft(_q->p_header, _q->header_mod, _q->header);
#else
unscramble_data(_q->header_enc, FLEXFRAME_H_ENC);
_q->header_valid =
packetizer_decode(_q->p_header, _q->header_enc, _q->header);
#endif
// return if header is invalid
if (!_q->header_valid)
return;
// first several bytes of header are user-defined
unsigned int n = FLEXFRAME_H_USER;
// first byte is for expansion/version validation
if (_q->header[n+0] != FLEXFRAME_VERSION) {
fprintf(stderr,"warning: flexframesync_decode_header(), invalid framing version\n");
_q->header_valid = 0;
return;
}
// strip off payload length
unsigned int payload_dec_len = (_q->header[n+1] << 8) | (_q->header[n+2]);
_q->payload_dec_len = payload_dec_len;
// strip off modulation scheme/depth
unsigned int mod_scheme = _q->header[n+3];
// strip off CRC, forward error-correction schemes
// CRC : most-significant 3 bits of [n+4]
// fec0 : least-significant 5 bits of [n+4]
// fec1 : least-significant 5 bits of [n+5]
unsigned int check = (_q->header[n+4] >> 5 ) & 0x07;
unsigned int fec0 = (_q->header[n+4] ) & 0x1f;
unsigned int fec1 = (_q->header[n+5] ) & 0x1f;
// validate properties
if (mod_scheme == 0 || mod_scheme >= LIQUID_MODEM_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), invalid modulation scheme\n");
_q->header_valid = 0;
return;
}
if (check >= LIQUID_CRC_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), decoded CRC exceeds available\n");
_q->header_valid = 0;
return;
}
if (fec0 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), decoded FEC (inner) exceeds available\n");
_q->header_valid = 0;
return;
}
if (fec1 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: flexframesync_decode_header(), decoded FEC (outer) exceeds available\n");
_q->header_valid = 0;
return;
}
// configure payload receiver
if (_q->header_valid) {
// recreate modem
_q->ms_payload = mod_scheme;
_q->bps_payload = modulation_types[mod_scheme].bps;
_q->demod_payload = modem_recreate(_q->demod_payload, _q->ms_payload);
// set new packetizer properties
_q->check = check;
_q->fec0 = fec0;
_q->fec1 = fec1;
// recreate packetizer object
_q->p_payload = packetizer_recreate(_q->p_payload,
_q->payload_dec_len,
_q->check,
_q->fec0,
_q->fec1);
// re-compute payload encoded message length
_q->payload_enc_len = packetizer_get_enc_msg_len(_q->p_payload);
// re-compute number of modulated payload symbols
div_t d = div(8*_q->payload_enc_len, _q->bps_payload);
_q->payload_mod_len = d.quot + (d.rem ? 1 : 0);
// re-allocate buffers accordingly
// (give encoded a few extra bytes to compensate for repacking)
_q->payload_mod = (unsigned char*) realloc(_q->payload_mod, (_q->payload_mod_len )*sizeof(unsigned char));
_q->payload_enc = (unsigned char*) realloc(_q->payload_enc, (_q->payload_enc_len+8)*sizeof(unsigned char));
_q->payload_dec = (unsigned char*) realloc(_q->payload_dec, (_q->payload_dec_len )*sizeof(unsigned char));
if (_q->payload_mod == NULL || _q->payload_enc == NULL || _q->payload_dec == NULL) {
fprintf(stderr,"error: flexframesync_decode_header(), could not re-allocate payload arrays\n");
_q->header_valid = 0;
return;
}
}
#if DEBUG_FLEXFRAMESYNC_PRINT
// print results
printf("flexframesync_decode_header():\n");
printf(" header crc : %s\n", _q->header_valid ? "pass" : "FAIL");
printf(" check : %s\n", crc_scheme_str[check][1]);
printf(" fec (inner) : %s\n", fec_scheme_str[fec0][1]);
printf(" fec (outer) : %s\n", fec_scheme_str[fec1][1]);
printf(" mod scheme : %s\n", modulation_types[mod_scheme].name);
printf(" payload dec len : %u\n", _q->payload_dec_len);
printf(" payload enc len : %u\n", _q->payload_enc_len);
printf(" payload mod len : %u\n", _q->payload_mod_len);
printf(" user data :");
for (i=0; i<FLEXFRAME_H_USER; i++)
printf(" %.2x", _q->header[i]);
printf("\n");
#endif
}
// decode header
void ofdmflexframesync_decode_header(ofdmflexframesync _q)
{
#if OFDMFLEXFRAME_H_SOFT
# if 0
unsigned int i;
// copy soft bits
for (i=0; i<8*OFDMFLEXFRAME_H_ENC; i++)
_q->header_enc[i] = _q->header_mod[i];
# else
// TODO: ensure lengths are the same
memmove(_q->header_enc, _q->header_mod, 8*OFDMFLEXFRAME_H_ENC);
# endif
// unscramble header using soft bits
unscramble_data_soft(_q->header_enc, OFDMFLEXFRAME_H_ENC);
// run packet decoder
_q->header_valid = packetizer_decode_soft(_q->p_header, _q->header_enc, _q->header);
#else
// pack 1-bit header symbols into 8-bit bytes
unsigned int num_written;
liquid_repack_bytes(_q->header_mod, OFDMFLEXFRAME_H_BPS, OFDMFLEXFRAME_H_SYM,
_q->header_enc, 8, OFDMFLEXFRAME_H_ENC,
&num_written);
assert(num_written==OFDMFLEXFRAME_H_ENC);
// unscramble header
unscramble_data(_q->header_enc, OFDMFLEXFRAME_H_ENC);
// run packet decoder
_q->header_valid = packetizer_decode(_q->p_header, _q->header_enc, _q->header);
#endif
#if 0
// print header
printf("header rx (enc) : ");
for (i=0; i<OFDMFLEXFRAME_H_ENC; i++)
printf("%.2X ", _q->header_enc[i]);
printf("\n");
// print header
printf("header rx (dec) : ");
for (i=0; i<OFDMFLEXFRAME_H_DEC; i++)
printf("%.2X ", _q->header[i]);
printf("\n");
#endif
#if DEBUG_OFDMFLEXFRAMESYNC
printf("****** header extracted [%s]\n", _q->header_valid ? "valid" : "INVALID!");
#endif
if (!_q->header_valid)
return;
unsigned int n = OFDMFLEXFRAME_H_USER;
// first byte is for expansion/version validation
if (_q->header[n+0] != OFDMFLEXFRAME_PROTOCOL) {
fprintf(stderr,"warning: ofdmflexframesync_decode_header(), invalid framing version\n");
_q->header_valid = 0;
}
// strip off payload length
unsigned int payload_len = (_q->header[n+1] << 8) | (_q->header[n+2]);
// strip off modulation scheme/depth
unsigned int mod_scheme = _q->header[n+3];
if (mod_scheme == 0 || mod_scheme >= LIQUID_MODEM_NUM_SCHEMES) {
fprintf(stderr,"warning: ofdmflexframesync_decode_header(), invalid modulation scheme\n");
_q->header_valid = 0;
return;
}
// strip off CRC, forward error-correction schemes
// CRC : most-significant 3 bits of [n+4]
// fec0 : least-significant 5 bits of [n+4]
// fec1 : least-significant 5 bits of [n+5]
unsigned int check = (_q->header[n+4] >> 5 ) & 0x07;
unsigned int fec0 = (_q->header[n+4] ) & 0x1f;
unsigned int fec1 = (_q->header[n+5] ) & 0x1f;
// validate properties
if (check >= LIQUID_CRC_NUM_SCHEMES) {
fprintf(stderr,"warning: ofdmflexframesync_decode_header(), decoded CRC exceeds available\n");
check = LIQUID_CRC_UNKNOWN;
_q->header_valid = 0;
}
if (fec0 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: ofdmflexframesync_decode_header(), decoded FEC (inner) exceeds available\n");
fec0 = LIQUID_FEC_UNKNOWN;
_q->header_valid = 0;
}
if (fec1 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: ofdmflexframesync_decode_header(), decoded FEC (outer) exceeds available\n");
fec1 = LIQUID_FEC_UNKNOWN;
_q->header_valid = 0;
}
// print results
#if DEBUG_OFDMFLEXFRAMESYNC
printf(" properties:\n");
printf(" * mod scheme : %s\n", modulation_types[mod_scheme].fullname);
printf(" * fec (inner) : %s\n", fec_scheme_str[fec0][1]);
printf(" * fec (outer) : %s\n", fec_scheme_str[fec1][1]);
printf(" * CRC scheme : %s\n", crc_scheme_str[check][1]);
printf(" * payload length : %u bytes\n", payload_len);
#endif
// configure payload receiver
if (_q->header_valid) {
// configure modem
if (mod_scheme != _q->ms_payload) {
// set new properties
_q->ms_payload = mod_scheme;
_q->bps_payload = modulation_types[mod_scheme].bps;
// recreate modem (destroy/create)
_q->mod_payload = modem_recreate(_q->mod_payload, _q->ms_payload);
}
// set new packetizer properties
_q->payload_len = payload_len;
_q->check = check;
_q->fec0 = fec0;
_q->fec1 = fec1;
// recreate packetizer object
_q->p_payload = packetizer_recreate(_q->p_payload,
_q->payload_len,
_q->check,
_q->fec0,
_q->fec1);
// re-compute payload encoded message length
_q->payload_enc_len = packetizer_get_enc_msg_len(_q->p_payload);
#if DEBUG_OFDMFLEXFRAMESYNC
printf(" * payload encoded : %u bytes\n", _q->payload_enc_len);
#endif
// re-allocate buffers accordingly
_q->payload_enc = (unsigned char*) realloc(_q->payload_enc, _q->payload_enc_len*sizeof(unsigned char));
_q->payload_dec = (unsigned char*) realloc(_q->payload_dec, _q->payload_len*sizeof(unsigned char));
// re-compute number of modulated payload symbols
div_t d = div(8*_q->payload_enc_len, _q->bps_payload);
_q->payload_mod_len = d.quot + (d.rem ? 1 : 0);
#if DEBUG_OFDMFLEXFRAMESYNC
printf(" * payload mod syms: %u symbols\n", _q->payload_mod_len);
#endif
}
}
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]; // recieved 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;
}
