// write OFDM symbol
// _q : framing generator object
// _x : input symbols, [size: _M x 1]
// _y : output samples, [size: _M x 1]
void ofdmframegen_writesymbol(ofdmframegen _q,
float complex * _x,
float complex * _y)
{
// move frequency data to internal buffer
unsigned int i;
unsigned int k;
int sctype;
for (i=0; i<_q->M; i++) {
// start at mid-point (effective fftshift)
k = (i + _q->M/2) % _q->M;
sctype = _q->p[k];
if (sctype==OFDMFRAME_SCTYPE_NULL) {
// disabled subcarrier
_q->X[k] = 0.0f;
} else if (sctype==OFDMFRAME_SCTYPE_PILOT) {
// pilot subcarrier
_q->X[k] = (msequence_advance(_q->ms_pilot) ? 1.0f : -1.0f) * _q->g_data;
} else {
// data subcarrier
_q->X[k] = _x[k] * _q->g_data;
}
//printf("X[%3u] = %12.8f + j*%12.8f;\n",i+1,crealf(_q->X[i]),cimagf(_q->X[i]));
}
// execute transform
FFT_EXECUTE(_q->ifft);
// copy result to output, adding cyclic prefix and tapering window
ofdmframegen_gensymbol(_q, _y);
}
void bpacketsync_assemble_pnsequence(bpacketsync _q)
{
// reset m-sequence generator
msequence_reset(_q->ms);
unsigned int i;
for (i=0; i<8*_q->pnsequence_len; i++)
bsequence_push(_q->bpn, msequence_advance(_q->ms));
}
// TODO : test this method
BSYNC() BSYNC(_create_msequence)(unsigned int _g,
unsigned int _k)
{
// validate input
if (_k == 0) {
fprintf(stderr,"bsync_xxxt_create_msequence(), samples/symbol must be greater than zero\n");
exit(1);
}
unsigned int m = liquid_msb_index(_g) - 1;
// create/initialize msequence
msequence ms = msequence_create(m, _g, 1);
BSYNC() fs = (BSYNC()) malloc(sizeof(struct BSYNC(_s)));
unsigned int n = msequence_get_length(ms);
fs->sync_i = bsequence_create(n * _k);
#ifdef TC_COMPLEX
fs->sync_q = bsequence_create(n * _k);
#endif
fs->sym_i = bsequence_create(n * _k);
#ifdef TI_COMPLEX
fs->sym_q = bsequence_create(n * _k);
#endif
msequence_reset(ms);
#if 0
bsequence_init_msequence(fs->sync_i,ms);
#ifdef TC_COMPLEX
msequence_reset(ms);
bsequence_init_msequence(fs->sync_q,ms);
#endif
#else
unsigned int i;
unsigned int j;
for (i=0; i<n; i++) {
unsigned int bit = msequence_advance(ms);
for (j=0; j<_k; j++) {
bsequence_push(fs->sync_i, bit);
#ifdef TC_COMPLEX
bsequence_push(fs->sync_q, bit);
#endif
}
}
#endif
msequence_destroy(ms);
fs->n = _k*n;
return fs;
}
// generate pseudo-random symbol from shift register
// _ms : m-sequence object
// _bps : bits per symbol of output
unsigned int msequence_generate_symbol(msequence _ms,
unsigned int _bps)
{
unsigned int i;
unsigned int s = 0;
for (i=0; i<_bps; i++) {
s <<= 1;
s |= msequence_advance(_ms);
}
return s;
}
// generate p/n sequence
void bpacketgen_assemble_pnsequence(bpacketgen _q)
{
// reset m-sequence generator
msequence_reset(_q->ms);
unsigned int i;
unsigned int j;
for (i=0; i<_q->pnsequence_len; i++) {
unsigned char byte = 0;
for (j=0; j<8; j++) {
byte <<= 1;
byte |= msequence_advance(_q->ms);
}
_q->pnsequence[i] = byte;
}
}
// initialize a bsequence object on an msequence object
// _bs : bsequence object
// _ms : msequence object
void bsequence_init_msequence(bsequence _bs,
msequence _ms)
{
#if 0
if (_ms->n > LIQUID_MAX_MSEQUENCE_LENGTH) {
fprintf(stderr,"error: bsequence_init_msequence(), msequence length exceeds maximum\n");
exit(1);
}
#endif
// clear binary sequence
bsequence_clear(_bs);
unsigned int i;
for (i=0; i<(_ms->n); i++)
bsequence_push(_bs, msequence_advance(_ms));
}
void gmskframegen_write_preamble(gmskframegen _q,
float complex * _y)
{
unsigned char bit = msequence_advance(_q->ms_preamble);
gmskmod_modulate(_q->mod, bit, _y);
// apply ramping window to first 'm' symbols
if (_q->symbol_counter < _q->m) {
unsigned int i;
for (i=0; i<_q->k; i++)
_y[i] *= hamming(_q->symbol_counter*_q->k + i, 2*_q->m*_q->k);
}
_q->symbol_counter++;
if (_q->symbol_counter == _q->preamble_len) {
msequence_reset(_q->ms_preamble);
_q->symbol_counter = 0;
_q->state = STATE_HEADER;
}
}
// recover symbol, correcting for gain, pilot phase, etc.
void ofdmframesync_rxsymbol(ofdmframesync _q)
{
// apply gain
unsigned int i;
for (i=0; i<_q->M; i++)
_q->X[i] *= _q->R[i];
// polynomial curve-fit
float x_phase[_q->M_pilot];
float y_phase[_q->M_pilot];
float p_phase[2];
unsigned int n=0;
unsigned int k;
float complex pilot = 1.0f;
for (i=0; i<_q->M; i++) {
// start at mid-point (effective fftshift)
k = (i + _q->M2) % _q->M;
if (_q->p[k]==OFDMFRAME_SCTYPE_PILOT) {
if (n == _q->M_pilot) {
fprintf(stderr,"warning: ofdmframesync_rxsymbol(), pilot subcarrier mismatch\n");
return;
}
pilot = (msequence_advance(_q->ms_pilot) ? 1.0f : -1.0f);
#if 0
printf("pilot[%3u] = %12.4e + j*%12.4e (expected %12.4e + j*%12.4e)\n",
k,
crealf(_q->X[k]), cimagf(_q->X[k]),
crealf(pilot), cimagf(pilot));
#endif
// store resulting...
x_phase[n] = (k > _q->M2) ? (float)k - (float)(_q->M) : (float)k;
y_phase[n] = cargf(_q->X[k]*conjf(pilot));
// update counter
n++;
}
}
if (n != _q->M_pilot) {
fprintf(stderr,"warning: ofdmframesync_rxsymbol(), pilot subcarrier mismatch\n");
return;
}
// try to unwrap phase
for (i=1; i<_q->M_pilot; i++) {
while ((y_phase[i] - y_phase[i-1]) > M_PI)
y_phase[i] -= 2*M_PI;
while ((y_phase[i] - y_phase[i-1]) < -M_PI)
y_phase[i] += 2*M_PI;
}
// fit phase to 1st-order polynomial (2 coefficients)
polyf_fit(x_phase, y_phase, _q->M_pilot, p_phase, 2);
// filter slope estimate (timing offset)
float alpha = 0.3f;
p_phase[1] = alpha*p_phase[1] + (1-alpha)*_q->p1_prime;
_q->p1_prime = p_phase[1];
#if DEBUG_OFDMFRAMESYNC
if (_q->debug_enabled) {
// save pilots
memmove(_q->px, x_phase, _q->M_pilot*sizeof(float));
memmove(_q->py, y_phase, _q->M_pilot*sizeof(float));
// NOTE : swapping values for octave
_q->p_phase[0] = p_phase[1];
_q->p_phase[1] = p_phase[0];
windowf_push(_q->debug_pilot_0, p_phase[0]);
windowf_push(_q->debug_pilot_1, p_phase[1]);
}
#endif
// compensate for phase offset
// TODO : find more computationally efficient way to do this
for (i=0; i<_q->M; i++) {
// only apply to data/pilot subcarriers
if (_q->p[i] == OFDMFRAME_SCTYPE_NULL) {
_q->X[i] = 0.0f;
} else {
float fx = (i > _q->M2) ? (float)i - (float)(_q->M) : (float)i;
float theta = polyf_val(p_phase, 2, fx);
_q->X[i] *= liquid_cexpjf(-theta);
}
}
// adjust NCO frequency based on differential phase
if (_q->num_symbols > 0) {
// compute phase error (unwrapped)
float dphi_prime = p_phase[0] - _q->phi_prime;
while (dphi_prime > M_PI) dphi_prime -= M_2_PI;
while (dphi_prime < -M_PI) dphi_prime += M_2_PI;
// adjust NCO proportionally to phase error
nco_crcf_adjust_frequency(_q->nco_rx, 1e-3f*dphi_prime);
}
// set internal phase state
_q->phi_prime = p_phase[0];
//printf("%3u : theta : %12.8f, nco freq: %12.8f\n", _q->num_symbols, p_phase[0], nco_crcf_get_frequency(_q->nco_rx));
// increment symbol counter
_q->num_symbols++;
#if 0
for (i=0; i<_q->M_pilot; i++)
printf("x_phase(%3u) = %12.8f; y_phase(%3u) = %12.8f;\n", i+1, x_phase[i], i+1, y_phase[i]);
printf("poly : p0=%12.8f, p1=%12.8f\n", p_phase[0], p_phase[1]);
#endif
}
// 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;
}
// 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;
}
//
// AUTOTEST: static channel filter, blind equalization on QPSK symbols
//
void autotest_eqlms_cccf_blind()
{
// parameters
float tol = 2e-2f; // error tolerance
unsigned int k = 2; // samples/symbol
unsigned int m = 7; // filter delay
float beta = 0.3f; // excess bandwidth factor
unsigned int p = 7; // equalizer order
float mu = 0.7f; // equalizer bandwidth
unsigned int num_symbols = 400; // number of symbols to observe
// create sequence generator for repeatability
msequence ms = msequence_create_default(12);
// create interpolating filter
firinterp_crcf interp = firinterp_crcf_create_prototype(LIQUID_FIRFILT_ARKAISER,k,m,beta,0);
// create equalizer
eqlms_cccf eq = eqlms_cccf_create_rnyquist(LIQUID_FIRFILT_ARKAISER,k,p,beta,0);
eqlms_cccf_set_bw(eq, mu);
// create channel filter
float complex h[5] = {
{ 1.00f, 0.00f},
{ 0.00f, -0.01f},
{-0.11f, 0.02f},
{ 0.02f, 0.01f},
{-0.09f, -0.04f} };
firfilt_cccf fchannel = firfilt_cccf_create(h,5);
// arrays
float complex buf[k]; // filter buffer
float complex sym_in [num_symbols]; // input symbols
float complex sym_out[num_symbols]; // equalized symbols
// run equalization
unsigned int i;
unsigned int j;
for (i=0; i<num_symbols; i++) {
// generate input symbol
sym_in[i] = ( msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2 ) +
( msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2 ) * _Complex_I;
// interpolate
firinterp_crcf_execute(interp, sym_in[i], buf);
// apply channel filter (in place)
firfilt_cccf_execute_block(fchannel, buf, k, buf);
// apply equalizer as filter
for (j=0; j<k; j++) {
eqlms_cccf_push(eq, buf[j]);
// decimate by k
if ( (j%k) != 0 ) continue;
eqlms_cccf_execute(eq, &sym_out[i]);
// update equalization (blind operation)
if (i > m + p)
eqlms_cccf_step(eq, sym_out[i]/cabsf(sym_out[i]), sym_out[i]);
}
}
// compare input, output
unsigned int settling_delay = 285;
for (i=m+p; i<num_symbols; i++) {
// compensate for delay
j = i-m-p;
// absolute error
float error = cabsf(sym_in[j]-sym_out[i]);
if (liquid_autotest_verbose) {
printf("x[%3u] = {%12.8f,%12.8f}, y[%3u] = {%12.8f,%12.8f}, error=%12.8f %s\n",
j, crealf(sym_in [j]), cimagf(sym_in [j]),
i, crealf(sym_out[i]), cimagf(sym_out[i]),
error, error > tol ? "*" : "");
if (i == settling_delay + m + p)
printf("--- start of test ---\n");
}
// check error
if (i > settling_delay + m + p)
CONTEND_DELTA(error, 0.0f, tol);
}
// clean up objects
firfilt_cccf_destroy(fchannel);
eqlms_cccf_destroy(eq);
msequence_destroy(ms);
}
// 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;
q->m = 7; // filter delay (symbols)
q->beta = 0.3f; // excess bandwidth factor
unsigned int i;
// generate p/n sequence
q->preamble_pn = (float complex*) malloc(64*sizeof(float complex));
q->preamble_rx = (float complex*) malloc(64*sizeof(float complex));
msequence ms = msequence_create(7, 0x0089, 1);
for (i=0; i<64; i++) {
q->preamble_pn[i] = (msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2) +
(msequence_advance(ms) ? M_SQRT1_2 : -M_SQRT1_2)*_Complex_I;
}
msequence_destroy(ms);
// create frame detector
unsigned int k = 2; // samples/symbol
q->detector = qdetector_cccf_create_linear(q->preamble_pn, 64, LIQUID_FIRFILT_ARKAISER, k, q->m, q->beta);
qdetector_cccf_set_threshold(q->detector, 0.5f);
// 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,k,q->m,q->beta);
#if FLEXFRAMESYNC_ENABLE_EQ
// create equalizer
unsigned int p = 3;
q->equalizer = eqlms_cccf_create_lowpass(2*k*p+1, 0.4f);
eqlms_cccf_set_bw(q->equalizer, 0.05f);
#endif
// create down-coverters for carrier phase tracking
q->mixer = nco_crcf_create(LIQUID_NCO);
q->pll = nco_crcf_create(LIQUID_NCO);
nco_crcf_pll_set_bandwidth(q->pll, 1e-4f); // very low bandwidth
// header demodulator/decoder
q->header_dec = (unsigned char *) malloc(FLEXFRAME_H_DEC*sizeof(unsigned char));
q->header_decoder = qpacketmodem_create();
qpacketmodem_configure(q->header_decoder,
FLEXFRAME_H_DEC,
FLEXFRAME_H_CRC,
FLEXFRAME_H_FEC0,
FLEXFRAME_H_FEC1,
LIQUID_MODEM_QPSK);
q->header_mod_len = qpacketmodem_get_frame_len(q->header_decoder);
q->header_mod = (float complex*) malloc(q->header_mod_len*sizeof(float complex));
// header pilot synchronizer
q->header_pilotsync = qpilotsync_create(q->header_mod_len, 16);
q->header_sym_len = qpilotsync_get_frame_len(q->header_pilotsync);
q->header_sym = (float complex*) malloc(q->header_sym_len*sizeof(float complex));
// payload demodulator for phase recovery
q->payload_demod = modem_create(LIQUID_MODEM_QPSK);
// create payload demodulator/decoder object
q->payload_dec_len = 64;
int check = LIQUID_CRC_24;
int fec0 = LIQUID_FEC_NONE;
int fec1 = LIQUID_FEC_GOLAY2412;
int mod_scheme = LIQUID_MODEM_QPSK;
q->payload_decoder = qpacketmodem_create();
qpacketmodem_configure(q->payload_decoder, q->payload_dec_len, check, fec0, fec1, mod_scheme);
//qpacketmodem_print(q->payload_decoder);
//assert( qpacketmodem_get_frame_len(q->payload_decoder)==600 );
q->payload_sym_len = qpacketmodem_get_frame_len(q->payload_decoder);
// allocate memory for payload symbols and recovered data bytes
q->payload_sym = (float complex*) malloc(q->payload_sym_len*sizeof(float complex));
q->payload_dec = (unsigned char*) malloc(q->payload_dec_len*sizeof(unsigned char));
// reset global data counters
flexframesync_reset_framedatastats(q);
#if DEBUG_FLEXFRAMESYNC
// set debugging flags, objects to NULL
q->debug_enabled = 0;
q->debug_objects_created = 0;
q->debug_qdetector_flush = 0;
q->debug_x = NULL;
#endif
// reset state and return
flexframesync_reset(q);
return q;
}
int main(int argc, char*argv[]) {
// options
unsigned int m=5; // shift register length, n=2^m - 1
char filename[64] = ""; // output filename
int dopt;
while ((dopt = getopt(argc,argv,"uhm:f:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'm': m = atoi(optarg); break;
case 'f':
// copy output filename string
strncpy(filename,optarg,64);
filename[63] = '\0';
break;
default:
exit(1);
}
}
// ensure output filename is set
if (strcmp(filename,"")==0) {
fprintf(stderr,"error: %s, filename not set\n", argv[0]);
exit(1);
}
// validate m
if (m < 2) {
fprintf(stderr,"error: %s, m is out of range\n", argv[0]);
exit(1);
}
// create and initialize m-sequence
msequence ms = msequence_create_default(m);
msequence_print(ms);
unsigned int n = msequence_get_length(ms);
unsigned int sequence[n]; // sequence
signed int rxx[n]; // auto-correlation
// initialize sequence
unsigned int i;
for (i=0; i<n; i++)
sequence[i] = msequence_advance(ms);
// reset sequence
msequence_reset(ms);
// create and initialize first binary sequence on m-sequence
bsequence bs1 = bsequence_create(n);
bsequence_init_msequence(bs1, ms);
// create and initialize second binary sequence on same m-sequence
bsequence bs2 = bsequence_create(n);
bsequence_init_msequence(bs2, ms);
// when sequences are aligned, autocorrelation is equal to length
unsigned int k=0;
rxx[k++] = 2*bsequence_correlate(bs1, bs2) - n;
// when sequences are misaligned, autocorrelation is equal to -1
for (i=0; i<n-1; i++) {
bsequence_push(bs2, msequence_advance(ms));
rxx[k++] = 2*bsequence_correlate(bs1, bs2)-n;
}
// clean up memory
bsequence_destroy(bs1);
bsequence_destroy(bs2);
msequence_destroy(ms);
//
// generate auto-correlation plot
//
// open output file
FILE * fid = fopen(filename,"w");
if (fid == NULL) {
fprintf(stderr,"error: %s, could not open file \"%s\" for writing.\n", argv[0], filename);
exit(1);
}
// print header
fprintf(fid,"# %s : auto-generated file (do not edit)\n", filename);
fprintf(fid,"# invoked as :");
for (i=0; i<argc; i++)
fprintf(fid," %s",argv[i]);
fprintf(fid,"reset\n");
fprintf(fid,"set terminal postscript eps enhanced color solid rounded\n");
fprintf(fid,"set xrange [-1:%u];\n", n+1);
fprintf(fid,"set size ratio 0.3\n");
fprintf(fid,"set xlabel 'delay (number of samples)'\n");
fprintf(fid,"set nokey # disable legned\n");
//fprintf(fid,"set grid xtics ytics\n");
//fprintf(fid,"set grid linetype 1 linecolor rgb '%s' lw 1\n", LIQUID_DOC_COLOR_GRID);
fprintf(fid,"set multiplot layout 2,1 scale 1.0,1.0\n");
fprintf(fid,"# sequence\n");
fprintf(fid,"set ylabel 'sequence'\n");
fprintf(fid,"set yrange [-0.1:1.1]\n");
fprintf(fid,"plot '-' using 1:2 with steps linetype 1 linewidth 4 linecolor rgb '%s'\n",LIQUID_DOC_COLOR_BLUE);
for (i=0; i<n; i++) {
fprintf(fid," %6u %6u\n", i, sequence[i]);
}
fprintf(fid,"e\n");
fprintf(fid,"# auto-correlation\n");
fprintf(fid,"set ylabel 'auto-correlation'\n");
fprintf(fid,"set yrange [%f:1.1]\n", -5.0f / (float)n);
fprintf(fid,"plot '-' using 1:2 with lines linetype 1 linewidth 4 linecolor rgb '%s'\n",LIQUID_DOC_COLOR_GREEN);
for (i=0; i<n; i++) {
fprintf(fid," %6u %12.4e\n", i, (float)rxx[i] / (float)n);
}
fprintf(fid,"e\n");
fprintf(fid,"unset multiplot\n");
// close output file
fclose(fid);
printf("results written to %s.\n", filename);
return 0;
}
void ofdmoqamframe64sync_rxpayload(ofdmoqamframe64sync _q,
float complex * _Y0,
float complex * _Y1)
{
unsigned int j=0;
unsigned int t=0;
int sctype;
unsigned int pilot_phase = msequence_advance(_q->ms_pilot);
// gain correction (equalizer)
unsigned int i;
for (i=0; i<_q->num_subcarriers; i++) {
_Y0[i] *= _q->G[i];// * _q->zeta;
_Y1[i] *= _q->G[i];// * _q->zeta;
}
// TODO : extract pilots
for (i=0; i<_q->num_subcarriers; i++) {
sctype = ofdmoqamframe64_getsctype(i);
if (sctype==OFDMOQAMFRAME64_SCTYPE_PILOT) {
// pilot subcarrier : use p/n sequence for pilot phase
float complex y0 = ((i%2)==0 ? _Y0[i] : _Y1[i]) / _q->zeta;
float complex y1 = ((i%2)==0 ? _Y1[i] : _Y0[i]) / _q->zeta;
float complex p = (pilot_phase ? 1.0f : -1.0f);
float phi_hat =
ofdmoqamframe64sync_estimate_pilot_phase(y0,y1,p);
_q->y_phase[t] = phi_hat;
t++;
#if DEBUG_OFDMOQAMFRAME64SYNC_PRINT
printf("i = %u\n", i);
printf("y0 = %12.8f + j*%12.8f;\n", crealf(y0),cimagf(y0));
printf("y1 = %12.8f + j*%12.8f;\n", crealf(y1),cimagf(y1));
printf("phi_hat = %12.8f\n", phi_hat);
#endif
/*
printf("exiting prematurely\n");
ofdmoqamframe64sync_destroy(_q);
exit(1);
*/
}
}
assert(t==4);
// pilot phase correction
/*
_q->y_phase[0] = cargf(_q->X[11]); // -21
_q->y_phase[1] = cargf(_q->X[25]); // -7
_q->y_phase[2] = cargf(_q->X[39]); // 7
_q->y_phase[3] = cargf(_q->X[53]); // 21
*/
// try to unwrap phase
for (i=1; i<4; i++) {
while ((_q->y_phase[i] - _q->y_phase[i-1]) > M_PI)
_q->y_phase[i] -= 2*M_PI;
while ((_q->y_phase[i] - _q->y_phase[i-1]) < -M_PI)
_q->y_phase[i] += 2*M_PI;
}
// fit phase to 1st-order polynomial (2 coefficients)
polyf_fit(_q->x_phase, _q->y_phase, 4, _q->p_phase, 2);
//nco_crcf_step(_q->nco_pilot);
float theta_hat = nco_crcf_get_phase(_q->nco_pilot);
float phase_error = _q->p_phase[0] - theta_hat;
while (phase_error > M_PI) phase_error -= 2.0f*M_PI;
while (phase_error < -M_PI) phase_error += 2.0f*M_PI;
pll_step(_q->pll_pilot, _q->nco_pilot, 0.1f*phase_error);
#if DEBUG_OFDMOQAMFRAME64SYNC_PRINT
// print phase results
for (i=0; i<4; i++) {
printf("x(%3u) = %12.8f; y(%3u) = %12.8f;\n", i+1, _q->x_phase[i], i+1, _q->y_phase[i]);
}
printf("p(1) = %12.8f\n", _q->p_phase[0]);
printf("p(2) = %12.8f\n", _q->p_phase[1]);
#endif
#if DEBUG_OFDMOQAMFRAME64SYNC
windowf_push(_q->debug_pilotphase, _q->p_phase[0]);
windowf_push(_q->debug_pilotphase_hat, theta_hat);
#endif
// compensate for phase shift due to timing offset
float theta;
_q->p_phase[0] = theta_hat;
_q->p_phase[1] = 0.0f;
for (i=0; i<_q->num_subcarriers; i++) {
// TODO : compute phase for delayed symbol (different from non-delayed symbol)
theta = polyf_val(_q->p_phase, 2, (float)(i)-32.0f);
_Y0[i] *= liquid_cexpjf(-theta);
_Y1[i] *= liquid_cexpjf(-theta);
}
nco_crcf_step(_q->nco_pilot);
// strip data subcarriers
for (i=0; i<_q->num_subcarriers; i++) {
sctype = ofdmoqamframe64_getsctype(i);
if (sctype==OFDMOQAMFRAME64_SCTYPE_NULL) {
// disabled subcarrier
} else if (sctype==OFDMOQAMFRAME64_SCTYPE_PILOT) {
// pilot subcarrier
} else {
// data subcarrier
if ((i%2)==0) {
// even subcarrier
_q->data[j] = crealf(_Y0[i]) +
cimagf(_Y1[i]) * _Complex_I;
} else {
// odd subcarrier
_q->data[j] = cimagf(_Y0[i]) * _Complex_I +
crealf(_Y1[i]);
}
// scaling factor
_q->data[j] /= _q->zeta;
j++;
}
}
assert(j==48);
#if DEBUG_OFDMOQAMFRAME64SYNC
for (i=0; i<48; i++)
windowcf_push(_q->debug_framesyms,_q->data[i]);
#endif
if (_q->callback != NULL) {
int retval = _q->callback(_q->data, _q->userdata);
if (retval == -1) {
printf("exiting prematurely\n");
ofdmoqamframe64sync_destroy(_q);
exit(0);
} else if (retval == 1) {
#if DEBUG_OFDMOQAMFRAME64SYNC_PRINT
printf("resetting synchronizer\n");
#endif
ofdmoqamframe64sync_reset(_q);
} else {
// do nothing
}
}
}
// autotest helper function
// _n : sequence length
// _dt : fractional sample offset
// _dphi : carrier frequency offset
void detector_cccf_runtest(unsigned int _n,
float _dt,
float _dphi)
{
// TODO: validate input
unsigned int i;
// fixed values
float noise_floor = -80.0f; // noise floor [dB]
float SNRdB = 30.0f; // signal-to-noise ratio [dB]
unsigned int m = 11; // resampling filter semi-length
float threshold = 0.3f; // detection threshold
// derived values
unsigned int num_samples = _n + 2*m + 1;
float nstd = powf(10.0f, noise_floor/20.0f);
float gamma = powf(10.0f, (SNRdB + noise_floor)/20.0f);
float delay = (float)(_n + m) + _dt; // expected delay
// arrays
float complex s[_n]; // synchronization pattern (samples)
float complex x[num_samples]; // resampled signal with noise and offsets
// generate synchronization pattern (two samples per symbol)
unsigned int n2 = (_n - (_n%2)) / 2; // n2 = floor(n/2)
unsigned int mm = liquid_nextpow2(n2); // mm = ceil( log2(n2) )
msequence ms = msequence_create_default(mm);
float complex v = 0.0f;
for (i=0; i<_n; i++) {
if ( (i%2)==0 )
v = msequence_advance(ms) ? 1.0f : -1.0f;
s[i] = v;
}
msequence_destroy(ms);
// create fractional sample interpolator
firfilt_crcf finterp = firfilt_crcf_create_kaiser(2*m+1, 0.45f, 40.0f, _dt);
// generate sequence
for (i=0; i<num_samples; i++) {
// add fractional sample timing offset
if (i < _n) firfilt_crcf_push(finterp, s[i]);
else firfilt_crcf_push(finterp, 0.0f);
// compute output
firfilt_crcf_execute(finterp, &x[i]);
// add channel gain
x[i] *= gamma;
// add carrier offset
x[i] *= cexpf(_Complex_I*_dphi*i);
// add noise
x[i] += nstd * ( randnf() + _Complex_I*randnf() ) * M_SQRT1_2;
}
// destroy fractional sample interpolator
firfilt_crcf_destroy(finterp);
// create detector
detector_cccf sync = detector_cccf_create(s, _n, threshold, 2*_dphi);
// push signal through detector
float tau_hat = 0.0f; // fractional sample offset estimate
float dphi_hat = 0.0f; // carrier offset estimate
float gamma_hat = 1.0f; // signal level estimate (linear)
float delay_hat = 0.0f; // total delay offset estimate
int signal_detected = 0; // signal detected flag
for (i=0; i<num_samples; i++) {
// correlate
int detected = detector_cccf_correlate(sync, x[i], &tau_hat, &dphi_hat, &gamma_hat);
if (detected) {
signal_detected = 1;
delay_hat = (float)i + (float)tau_hat;
if (liquid_autotest_verbose) {
printf("****** preamble found, tau_hat=%8.6f, dphi_hat=%8.6f, gamma_hat=%8.6f\n",
tau_hat, dphi_hat, gamma_hat);
}
}
}
// destroy objects
detector_cccf_destroy(sync);
//
// run tests
//
// convert to dB
gamma = 20*log10f(gamma);
gamma_hat = 20*log10f(gamma_hat);
if (liquid_autotest_verbose) {
printf("detector autotest [%3u]: signal detected? %s\n", _n, signal_detected ? "yes" : "no");
printf(" dphi : estimate = %12.6f (expected %12.6f)\n", dphi_hat, _dphi);
printf(" delay : estimate = %12.6f (expected %12.6f)\n", delay_hat, delay);
printf(" gamma : estimate = %12.6f (expected %12.6f)\n", gamma_hat, gamma);
}
// ensure signal was detected
CONTEND_EXPRESSION( signal_detected );
// check carrier offset estimate
CONTEND_DELTA( dphi_hat, _dphi, 0.01f );
// check delay estimate
CONTEND_DELTA( delay_hat, delay, 0.2f );
// check signal level estimate
CONTEND_DELTA( gamma_hat, gamma, 2.0f );
}