// assemble frame
// _q : frame generator object
// _header : raw header
// _payload : raw payload [size: _payload_len x 1]
// _payload_len : raw payload length (bytes)
// _check : data validity check
// _fec0 : inner forward error correction
// _fec1 : outer forward error correction
void gmskframegen_assemble(gmskframegen _q,
unsigned char * _header,
unsigned char * _payload,
unsigned int _payload_len,
crc_scheme _check,
fec_scheme _fec0,
fec_scheme _fec1)
{
// re-create frame generator if properties don't match
if (_q->dec_msg_len != _payload_len ||
_q->check != _check ||
_q->fec0 != _fec0 ||
_q->fec1 != _fec1)
{
// set properties
_q->dec_msg_len = _payload_len;
_q->check = _check;
_q->fec0 = _fec0;
_q->fec1 = _fec1;
// re-create payload packetizer
_q->p_payload = packetizer_recreate(_q->p_payload, _q->dec_msg_len, _q->check, _q->fec0, _q->fec1);
// get packet length
_q->enc_msg_len = packetizer_get_enc_msg_len(_q->p_payload);
_q->payload_len = 8*_q->enc_msg_len;
// re-allocate memory
_q->payload_enc = (unsigned char*) realloc(_q->payload_enc, _q->enc_msg_len*sizeof(unsigned char));
}
// set assembled flag
_q->frame_assembled = 1;
// encode header
gmskframegen_encode_header(_q, _header);
// encode payload
packetizer_encode(_q->p_payload, _payload, _q->payload_enc);
}
// create ofdmflexframesync object
// _M : number of subcarriers
// _cp_len : length of cyclic prefix [samples]
// _taper_len : taper length (OFDM symbol overlap)
// _p : subcarrier allocation (PILOT/NULL/DATA) [size: _M x 1]
// _callback : user-defined callback function
// _userdata : user-defined data structure passed to callback
ofdmflexframesync ofdmflexframesync_create(unsigned int _M,
unsigned int _cp_len,
unsigned int _taper_len,
unsigned char * _p,
framesync_callback _callback,
void * _userdata)
{
ofdmflexframesync q = (ofdmflexframesync) malloc(sizeof(struct ofdmflexframesync_s));
// validate input
if (_M < 8) {
fprintf(stderr,"warning: ofdmflexframesync_create(), less than 8 subcarriers\n");
} else if (_M % 2) {
fprintf(stderr,"error: ofdmflexframesync_create(), number of subcarriers must be even\n");
exit(1);
} else if (_cp_len > _M) {
fprintf(stderr,"error: ofdmflexframesync_create(), cyclic prefix length cannot exceed number of subcarriers\n");
exit(1);
}
// set internal properties
q->M = _M;
q->cp_len = _cp_len;
q->taper_len = _taper_len;
q->callback = _callback;
q->userdata = _userdata;
// allocate memory for subcarrier allocation IDs
q->p = (unsigned char*) malloc((q->M)*sizeof(unsigned char));
if (_p == NULL) {
// initialize default subcarrier allocation
ofdmframe_init_default_sctype(q->M, q->p);
} else {
// copy user-defined subcarrier allocation
memmove(q->p, _p, q->M*sizeof(unsigned char));
}
// validate and count subcarrier allocation
ofdmframe_validate_sctype(q->p, q->M, &q->M_null, &q->M_pilot, &q->M_data);
// create internal framing object
q->fs = ofdmframesync_create(_M, _cp_len, _taper_len, _p, ofdmflexframesync_internal_callback, (void*)q);
// create header objects
q->mod_header = modem_create(OFDMFLEXFRAME_H_MOD);
q->p_header = packetizer_create(OFDMFLEXFRAME_H_DEC,
OFDMFLEXFRAME_H_CRC,
OFDMFLEXFRAME_H_FEC,
LIQUID_FEC_NONE);
assert(packetizer_get_enc_msg_len(q->p_header)==OFDMFLEXFRAME_H_ENC);
// frame properties (default values to be overwritten when frame
// header is received and properly decoded)
q->ms_payload = LIQUID_MODEM_QPSK;
q->bps_payload = 2;
q->payload_len = 1;
q->check = LIQUID_CRC_NONE;
q->fec0 = LIQUID_FEC_NONE;
q->fec1 = LIQUID_FEC_NONE;
// create payload objects (initally QPSK, etc but overridden by received properties)
q->mod_payload = modem_create(q->ms_payload);
q->p_payload = packetizer_create(q->payload_len, q->check, q->fec0, q->fec1);
q->payload_enc_len = packetizer_get_enc_msg_len(q->p_payload);
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
q->payload_dec = (unsigned char*) malloc(q->payload_len*sizeof(unsigned char));
q->payload_mod_len = 0;
// reset state
ofdmflexframesync_reset(q);
// return object
return q;
}
// 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
}
}
// decode header and re-configure payload decoder
void gmskframesync_decode_header(gmskframesync _q)
{
// pack each 1-bit header symbols into 8-bit bytes
unsigned int num_written;
liquid_pack_bytes(_q->header_mod, GMSKFRAME_H_SYM,
_q->header_enc, GMSKFRAME_H_ENC,
&num_written);
assert(num_written==GMSKFRAME_H_ENC);
// unscramble data
unscramble_data(_q->header_enc, GMSKFRAME_H_ENC);
// run packet decoder
_q->header_valid = packetizer_decode(_q->p_header, _q->header_enc, _q->header_dec);
#if DEBUG_GMSKFRAMESYNC_PRINT
printf("****** header extracted [%s]\n", _q->header_valid ? "valid" : "INVALID!");
#endif
if (!_q->header_valid)
return;
unsigned int n = GMSKFRAME_H_USER;
// first byte is for expansion/version validation
if (_q->header_dec[n+0] != GMSKFRAME_VERSION) {
fprintf(stderr,"warning: gmskframesync_decode_header(), invalid framing version\n");
_q->header_valid = 0;
return;
}
// strip off payload length
unsigned int payload_dec_len = (_q->header_dec[n+1] << 8) | (_q->header_dec[n+2]);
// strip off CRC, forward error-correction schemes
// CRC : most-significant 3 bits of [n+3]
// fec0 : least-significant 5 bits of [n+3]
// fec1 : least-significant 5 bits of [n+4]
unsigned int check = (_q->header_dec[n+3] >> 5 ) & 0x07;
unsigned int fec0 = (_q->header_dec[n+3] ) & 0x1f;
unsigned int fec1 = (_q->header_dec[n+4] ) & 0x1f;
// validate properties
if (check >= LIQUID_CRC_NUM_SCHEMES) {
fprintf(stderr,"warning: gmskframesync_decode_header(), decoded CRC exceeds available\n");
check = LIQUID_CRC_UNKNOWN;
_q->header_valid = 0;
}
if (fec0 >= LIQUID_FEC_NUM_SCHEMES) {
fprintf(stderr,"warning: gmskframesync_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: gmskframesync_decode_header(), decoded FEC (outer) exceeds available\n");
fec1 = LIQUID_FEC_UNKNOWN;
_q->header_valid = 0;
}
// print results
#if DEBUG_GMSKFRAMESYNC_PRINT
printf(" properties:\n");
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_dec_len);
#endif
// configure payload receiver
if (_q->header_valid) {
// set new packetizer properties
_q->payload_dec_len = payload_dec_len;
_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);
#if DEBUG_GMSKFRAMESYNC_PRINT
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_dec_len*sizeof(unsigned char));
}
//
}
// create GMSK frame synchronizer
// _callback : callback function
// _userdata : user data pointer passed to callback function
gmskframesync gmskframesync_create(framesync_callback _callback,
void * _userdata)
{
gmskframesync q = (gmskframesync) malloc(sizeof(struct gmskframesync_s));
q->callback = _callback;
q->userdata = _userdata;
q->k = 2; // samples/symbol
q->m = 3; // filter delay (symbols)
q->BT = 0.5f; // filter bandwidth-time product
#if GMSKFRAMESYNC_PREFILTER
// create default low-pass Butterworth filter
q->prefilter = iirfilt_crcf_create_lowpass(3, 0.5f*(1 + q->BT) / (float)(q->k));
#endif
unsigned int i;
// frame detector
q->preamble_len = 63;
q->preamble_pn = (float*)malloc(q->preamble_len*sizeof(float));
q->preamble_rx = (float*)malloc(q->preamble_len*sizeof(float));
float complex preamble_samples[q->preamble_len*q->k];
msequence ms = msequence_create(6, 0x6d, 1);
gmskmod mod = gmskmod_create(q->k, q->m, q->BT);
for (i=0; i<q->preamble_len + q->m; i++) {
unsigned char bit = msequence_advance(ms);
// save p/n sequence
if (i < q->preamble_len)
q->preamble_pn[i] = bit ? 1.0f : -1.0f;
// modulate/interpolate
if (i < q->m) gmskmod_modulate(mod, bit, &preamble_samples[0]);
else gmskmod_modulate(mod, bit, &preamble_samples[(i-q->m)*q->k]);
}
gmskmod_destroy(mod);
msequence_destroy(ms);
#if 0
// print sequence
for (i=0; i<q->preamble_len*q->k; i++)
printf("preamble(%3u) = %12.8f + j*%12.8f;\n", i+1, crealf(preamble_samples[i]), cimagf(preamble_samples[i]));
#endif
// create frame detector
float threshold = 0.5f; // detection threshold
float dphi_max = 0.05f; // maximum carrier offset allowable
q->frame_detector = detector_cccf_create(preamble_samples, q->preamble_len*q->k, threshold, dphi_max);
q->buffer = windowcf_create(q->k*(q->preamble_len+q->m));
// create symbol timing recovery filters
q->npfb = 32; // number of filters in the bank
q->mf = firpfb_rrrf_create_rnyquist( LIQUID_FIRFILT_GMSKRX,q->npfb,q->k,q->m,q->BT);
q->dmf = firpfb_rrrf_create_drnyquist(LIQUID_FIRFILT_GMSKRX,q->npfb,q->k,q->m,q->BT);
// create down-coverters for carrier phase tracking
q->nco_coarse = nco_crcf_create(LIQUID_NCO);
// create/allocate header objects/arrays
q->header_mod = (unsigned char*)malloc(GMSKFRAME_H_SYM*sizeof(unsigned char));
q->header_enc = (unsigned char*)malloc(GMSKFRAME_H_ENC*sizeof(unsigned char));
q->header_dec = (unsigned char*)malloc(GMSKFRAME_H_DEC*sizeof(unsigned char));
q->p_header = packetizer_create(GMSKFRAME_H_DEC,
GMSKFRAME_H_CRC,
GMSKFRAME_H_FEC,
LIQUID_FEC_NONE);
// create/allocate payload objects/arrays
q->payload_dec_len = 1;
q->check = LIQUID_CRC_32;
q->fec0 = LIQUID_FEC_NONE;
q->fec1 = LIQUID_FEC_NONE;
q->p_payload = packetizer_create(q->payload_dec_len,
q->check,
q->fec0,
q->fec1);
q->payload_enc_len = packetizer_get_enc_msg_len(q->p_payload);
q->payload_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
#if DEBUG_GMSKFRAMESYNC
// debugging structures
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_x = NULL;
q->debug_fi = NULL;
q->debug_mf = NULL;
q->debug_framesyms = NULL;
#endif
// reset synchronizer
gmskframesync_reset(q);
// return synchronizer object
return q;
}
// 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
}
// create flexframesync object
// _callback : callback function invoked when frame is received
// _userdata : user-defined data object passed to callback
flexframesync flexframesync_create(framesync_callback _callback,
void * _userdata)
{
flexframesync q = (flexframesync) malloc(sizeof(struct flexframesync_s));
q->callback = _callback;
q->userdata = _userdata;
unsigned int i;
// generate p/n sequence
msequence ms = msequence_create(6, 0x005b, 1);
for (i=0; i<64; i++)
q->preamble_pn[i] = (msequence_advance(ms)) ? 1.0f : -1.0f;
msequence_destroy(ms);
// interpolate p/n sequence with matched filter
q->k = 2; // samples/symbol
q->m = 7; // filter delay (symbols)
q->beta = 0.25f; // excess bandwidth factor
float complex seq[q->k*64];
firinterp_crcf interp = firinterp_crcf_create_rnyquist(LIQUID_FIRFILT_ARKAISER,q->k,q->m,q->beta,0);
for (i=0; i<64+q->m; i++) {
// compensate for filter delay
if (i < q->m) firinterp_crcf_execute(interp, q->preamble_pn[i], &seq[0]);
else firinterp_crcf_execute(interp, q->preamble_pn[i%64], &seq[q->k*(i-q->m)]);
}
firinterp_crcf_destroy(interp);
// create frame detector
float threshold = 0.4f; // detection threshold
float dphi_max = 0.05f; // maximum carrier offset allowable
q->frame_detector = detector_cccf_create(seq, q->k*64, threshold, dphi_max);
q->buffer = windowcf_create(q->k*(64+q->m));
// create symbol timing recovery filters
q->npfb = 32; // number of filters in the bank
q->mf = firpfb_crcf_create_rnyquist(LIQUID_FIRFILT_ARKAISER, q->npfb,q->k,q->m,q->beta);
q->dmf = firpfb_crcf_create_drnyquist(LIQUID_FIRFILT_ARKAISER,q->npfb,q->k,q->m,q->beta);
// create down-coverters for carrier phase tracking
q->nco_coarse = nco_crcf_create(LIQUID_NCO);
q->nco_fine = nco_crcf_create(LIQUID_VCO);
nco_crcf_pll_set_bandwidth(q->nco_fine, 0.05f);
// create header objects
q->demod_header = modem_create(LIQUID_MODEM_BPSK);
q->p_header = packetizer_create(FLEXFRAME_H_DEC,
FLEXFRAME_H_CRC,
FLEXFRAME_H_FEC0,
FLEXFRAME_H_FEC1);
assert(packetizer_get_enc_msg_len(q->p_header)==FLEXFRAME_H_ENC);
// frame properties (default values to be overwritten when frame
// header is received and properly decoded)
q->ms_payload = LIQUID_MODEM_QPSK;
q->bps_payload = 2;
q->payload_dec_len = 1;
q->check = LIQUID_CRC_NONE;
q->fec0 = LIQUID_FEC_NONE;
q->fec1 = LIQUID_FEC_NONE;
// create payload objects (overridden by received properties)
q->demod_payload = modem_create(LIQUID_MODEM_QPSK);
q->p_payload = packetizer_create(q->payload_dec_len, q->check, q->fec0, q->fec1);
q->payload_enc_len = packetizer_get_enc_msg_len(q->p_payload);
q->payload_mod_len = 4 * q->payload_enc_len;
q->payload_mod = (unsigned char*) malloc(q->payload_mod_len*sizeof(unsigned char));
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
q->payload_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
#if DEBUG_FLEXFRAMESYNC
// set debugging flags, objects to NULL
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_x = NULL;
#endif
// reset state
flexframesync_reset(q);
return q;
}
// create OFDM flexible framing generator object
// _M : number of subcarriers, >10 typical
// _cp_len : cyclic prefix length
// _taper_len : taper length (OFDM symbol overlap)
// _p : subcarrier allocation (null, pilot, data), [size: _M x 1]
// _fgprops : frame properties (modulation scheme, etc.)
ofdmflexframegen ofdmflexframegen_create(unsigned int _M,
unsigned int _cp_len,
unsigned int _taper_len,
unsigned char * _p,
ofdmflexframegenprops_s * _fgprops)
{
// validate input
if (_M < 2) {
fprintf(stderr,"error: ofdmflexframegen_create(), number of subcarriers must be at least 2\n");
exit(1);
} else if (_M % 2) {
fprintf(stderr,"error: ofdmflexframegen_create(), number of subcarriers must be even\n");
exit(1);
}
ofdmflexframegen q = (ofdmflexframegen) malloc(sizeof(struct ofdmflexframegen_s));
q->M = _M; // number of subcarriers
q->cp_len = _cp_len; // cyclic prefix length
q->taper_len = _taper_len; // taper length
// allocate memory for transform buffers
q->X = (float complex*) malloc((q->M)*sizeof(float complex));
// allocate memory for subcarrier allocation IDs
q->p = (unsigned char*) malloc((q->M)*sizeof(unsigned char));
if (_p == NULL) {
// initialize default subcarrier allocation
ofdmframe_init_default_sctype(q->M, q->p);
} else {
// copy user-defined subcarrier allocation
memmove(q->p, _p, q->M*sizeof(unsigned char));
}
// validate and count subcarrier allocation
ofdmframe_validate_sctype(q->p, q->M, &q->M_null, &q->M_pilot, &q->M_data);
// create internal OFDM frame generator object
q->fg = ofdmframegen_create(q->M, q->cp_len, q->taper_len, q->p);
// create header objects
q->mod_header = modem_create(OFDMFLEXFRAME_H_MOD);
q->p_header = packetizer_create(OFDMFLEXFRAME_H_DEC,
OFDMFLEXFRAME_H_CRC,
OFDMFLEXFRAME_H_FEC,
LIQUID_FEC_NONE);
assert(packetizer_get_enc_msg_len(q->p_header)==OFDMFLEXFRAME_H_ENC);
// compute number of header symbols
div_t d = div(OFDMFLEXFRAME_H_SYM, q->M_data);
q->num_symbols_header = d.quot + (d.rem ? 1 : 0);
// initial memory allocation for payload
q->payload_dec_len = 1;
q->p_payload = packetizer_create(q->payload_dec_len,
LIQUID_CRC_NONE,
LIQUID_FEC_NONE,
LIQUID_FEC_NONE);
q->payload_enc_len = packetizer_get_enc_msg_len(q->p_payload);
q->payload_enc = (unsigned char*) malloc(q->payload_enc_len*sizeof(unsigned char));
q->payload_mod_len = 1;
q->payload_mod = (unsigned char*) malloc(q->payload_mod_len*sizeof(unsigned char));
// create payload modem (initially QPSK, overridden by properties)
q->mod_payload = modem_create(LIQUID_MODEM_QPSK);
// initialize properties
ofdmflexframegen_setprops(q, _fgprops);
// reset
ofdmflexframegen_reset(q);
// return pointer to main object
return q;
}
