void ofdmoqamframe64sync_execute_plcplong1(ofdmoqamframe64sync _q, float complex _x)
{
// cross-correlator
float complex rxy;
firfilt_cccf_push(_q->crosscorr, _x);
firfilt_cccf_execute(_q->crosscorr, &rxy);
rxy *= _q->g;
#if DEBUG_OFDMOQAMFRAME64SYNC
windowcf_push(_q->debug_rxy, rxy);
#endif
_q->timer++;
if (_q->timer < _q->num_subcarriers-8) {
return;
} else if (_q->timer > _q->num_subcarriers+8) {
#if DEBUG_OFDMOQAMFRAME64SYNC_PRINT
printf("warning: ofdmoqamframe64sync could not find second PLCP long sequence; resetting synchronizer\n");
#endif
ofdmoqamframe64sync_reset(_q);
return;
}
if (cabsf(rxy) > 0.7f*(_q->rxy_thresh)*(_q->num_subcarriers)) {
#if DEBUG_OFDMOQAMFRAME64SYNC_PRINT
printf("rxy[1] : %12.8f at input[%3u]\n", cabsf(rxy), _q->num_samples);
#endif
//
float complex * rc;
windowcf_read(_q->input_buffer, &rc);
memmove(_q->S1b, rc, 64*sizeof(float complex));
// estimate frequency offset
float complex rxy_hat=0.0f;
unsigned int j;
for (j=0; j<64; j++) {
rxy_hat += _q->S1a[j] * conjf(_q->S1b[j]) * hamming(j,64);
}
float nu_hat1 = -cargf(rxy_hat);
if (nu_hat1 > M_PI) nu_hat1 -= 2.0f*M_PI;
if (nu_hat1 < -M_PI) nu_hat1 += 2.0f*M_PI;
nu_hat1 /= 64.0f;
#if DEBUG_OFDMOQAMFRAME64SYNC_PRINT
printf("nu_hat[0] = %12.8f\n", _q->nu_hat);
printf("nu_hat[1] = %12.8f\n", nu_hat1);
#endif
nco_crcf_adjust_frequency(_q->nco_rx, nu_hat1);
/*
printf("exiting prematurely\n");
ofdmoqamframe64sync_destroy(_q);
exit(1);
*/
_q->state = OFDMOQAMFRAME64SYNC_STATE_RXSYMBOLS;
}
}
// recover symbol, correcting for gain, pilot phase, etc.
void wlanframesync_rxsymbol(wlanframesync _q)
{
// apply gain
unsigned int i;
for (i=0; i<64; i++)
_q->X[i] *= _q->R[i];
// polynomial curve-fit
float x_phase[4] = {-21.0f, -7.0f, 7.0f, 21.0f};
float y_phase[4];
float p_phase[2];
// update pilot phase
unsigned int pilot_phase = wlan_lfsr_advance(_q->ms_pilot);
y_phase[0] = pilot_phase ? cargf(-_q->X[43]) : cargf( _q->X[43]);
y_phase[1] = pilot_phase ? cargf(-_q->X[57]) : cargf( _q->X[57]);
y_phase[2] = pilot_phase ? cargf(-_q->X[ 7]) : cargf( _q->X[ 7]);
y_phase[3] = pilot_phase ? cargf( _q->X[21]) : cargf(-_q->X[21]);
// unwrap phase
if ( (y_phase[1]-y_phase[0]) > M_PI ) y_phase[1] -= 2*M_PI;
if ( (y_phase[1]-y_phase[0]) < -M_PI ) y_phase[1] += 2*M_PI;
if ( (y_phase[2]-y_phase[1]) > M_PI ) y_phase[2] -= 2*M_PI;
if ( (y_phase[2]-y_phase[1]) < -M_PI ) y_phase[2] += 2*M_PI;
if ( (y_phase[3]-y_phase[2]) > M_PI ) y_phase[3] -= 2*M_PI;
if ( (y_phase[3]-y_phase[2]) < -M_PI ) y_phase[3] += 2*M_PI;
#if 0
printf(" x = [-21 -7 7 21]; y = [%6.3f %6.3f %6.3f %6.3f];\n", y_phase[0], y_phase[1], y_phase[2], y_phase[3]);
#endif
// fit phase to 1st-order polynomial (2 coefficients)
polyf_fit(x_phase, y_phase, 4, p_phase, 2);
// compensate for phase offset
// TODO : find more computationally efficient way to do this
for (i=0; i<64; i++) {
float fx = (i > 31) ? (float)i - (float)(64) : (float)i;
float theta = polyf_val(p_phase, 2, fx);
_q->X[i] *= cexpf(-_Complex_I*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;
if (dphi_prime > M_PI) dphi_prime -= M_2_PI;
if (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];
}
int main() {
// options
unsigned int num_channels=8; // number of channels
unsigned int m=2; // filter delay
float As=-60; // stop-band attenuation
unsigned int num_frames=25; // number of frames
// create objects
firpfbch_crcf c = firpfbch_crcf_create_kaiser(LIQUID_ANALYZER, num_channels, m, As);
//firpfbch_crcf_print(c);
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\nclose all;\n\n");
fprintf(fid,"num_channels=%u;\n", num_channels);
fprintf(fid,"num_frames=%u;\n", num_frames);
fprintf(fid,"x = zeros(1,%u);\n", num_channels * num_frames);
fprintf(fid,"y = zeros(%u,%u);\n", num_channels, num_frames);
unsigned int i, j, n=0;
float complex x[num_channels]; // time-domain input
float complex y[num_channels]; // channelized output
// create nco: sweeps entire range of frequencies over the evaluation interval
nco_crcf nco_tx = nco_crcf_create(LIQUID_VCO);
nco_crcf_set_frequency(nco_tx, 0.0f);
float df = 2*M_PI/(num_channels*num_frames);
printf("fr/ch:");
for (j=0; j<num_channels; j++) printf("%3u",j);
printf("\n");
for (i=0; i<num_frames; i++) {
// generate frame of data
for (j=0; j<num_channels; j++) {
nco_crcf_cexpf(nco_tx, &x[j]);
nco_crcf_adjust_frequency(nco_tx, df);
nco_crcf_step(nco_tx);
}
// execute analysis filter bank
firpfbch_crcf_analyzer_execute(c, x, y);
printf("%4u : ", i);
for (j=0; j<num_channels; j++) {
if (cabsf(y[j]) > num_channels / 4)
printf(" x ");
else
printf(" . ");
}
printf("\n");
// write output to file
for (j=0; j<num_channels; j++) {
// frequency data
fprintf(fid,"y(%4u,%4u) = %12.4e + j*%12.4e;\n", j+1, i+1, crealf(y[j]), cimagf(y[j]));
// time data
fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", n+1, crealf(x[j]), cimag(x[j]));
n++;
}
}
// destroy objects
nco_crcf_destroy(nco_tx);
firpfbch_crcf_destroy(c);
// plot results
fprintf(fid,"\n\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," plot(1:length(x),real(x),1:length(x),imag(x));\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('signal');\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," plot(20*log10(abs(y.')/num_channels));\n");
fprintf(fid," xlabel('time (decimated)');\n");
fprintf(fid," ylabel('channelized energy [dB]');\n");
fprintf(fid,"n=min(num_channels,8);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"for i=1:n\n");
fprintf(fid," subplot(n,1,i);\n");
fprintf(fid," plot(1:num_frames,real(y(i,:)),1:num_frames,imag(y(i,:)));\n");
fprintf(fid," axis off;\n");
fprintf(fid," ylabel(num2str(i));\n");
fprintf(fid,"end;\n");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
// 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
}
void wlanframesync_execute_rxlong1(wlanframesync _q)
{
_q->timer++;
if (_q->timer < 64)
return;
// run fft
float complex * rc;
windowcf_read(_q->input_buffer, &rc);
// estimate S1 gain, adding backoff in gain estimation
wlanframesync_estimate_gain_S1(_q, &rc[16-2], _q->G1b);
// compute S1 metrics
float complex s_hat;
wlanframesync_S1_metrics(_q, _q->G1b, &s_hat);
s_hat *= _q->g0; // scale output by raw gain estimate
// rotate by complex phasor relative to timing backoff
//s_hat *= cexpf(_Complex_I * 2.0f * 2.0f * M_PI / 64.0f);
s_hat *= cexpf(_Complex_I * 0.19635f);
// save second 'long' symbol statistic
_q->s1b_hat = s_hat;
// rotate by complex phasor relative to timing backoff
//s_hat *= liquid_cexpjf((float)(_q->backoff)*2.0f*M_PI/(float)(_q->M));
#if DEBUG_WLANFRAMESYNC_PRINT
printf(" s_hat : %12.8f <%12.8f>\n", cabsf(s_hat), cargf(s_hat));
#endif
// check conditions for s_hat
float s_hat_abs = cabsf(s_hat);
float s_hat_arg = cargf(s_hat);
if (s_hat_arg > M_PI) s_hat_arg -= 2.0f*M_PI;
if (s_hat_arg < -M_PI) s_hat_arg += 2.0f*M_PI;
// check conditions for s_hat:
// 1. magnitude should be large (near unity) when aligned
// 2. phase should be very near zero (time aligned)
if (s_hat_abs > WLANFRAMESYNC_S1B_ABS_THRESH &&
fabsf(s_hat_arg) < WLANFRAMESYNC_S1B_ARG_THRESH)
{
#if DEBUG_WLANFRAMESYNC_PRINT
printf(" acquisition S1[b]\n");
#endif
// refine CFO estimate with G1a, G1b and adjust NCO appropriately
float nu_hat = wlanframesync_estimate_cfo_S1(_q->G1a, _q->G1b);
nco_crcf_adjust_frequency(_q->nco_rx, nu_hat);
#if DEBUG_WLANFRAMESYNC_PRINT
printf(" nu_hat[1]: %12.8f\n", nu_hat);
#endif
// TODO : de-rotate S1b by phase offset (help with equalizer)
// estimate equalizer with G1a, G1b
wlanframesync_estimate_eqgain_poly(_q);
// set state
_q->state = WLANFRAMESYNC_STATE_RXLONG1;
// reset timer
_q->timer = 0;
}
// set state
_q->state = WLANFRAMESYNC_STATE_RXSIGNAL;
// reset timer
_q->timer = 0;
}
