int main(int argc, char*argv[])
{
srand(time(NULL));
// options
unsigned int k=2; // filter samples/symbol
unsigned int m=5; // filter delay (symbols)
float beta=0.3f; // bandwidth-time product
float dt = 0.0f; // fractional sample timing offset
unsigned int num_sync_symbols = 64; // number of synchronization symbols
float SNRdB = 20.0f; // signal-to-noise ratio [dB]
float dphi = 0.02f; // carrier frequency offset
float phi = 2*M_PI*randf(); // carrier phase offset
int dopt;
while ((dopt = getopt(argc,argv,"uhk:m:n:b:t:F:t:S:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'k': k = atoi(optarg); break;
case 'm': m = atoi(optarg); break;
case 'n': num_sync_symbols = atoi(optarg); break;
case 'b': beta = atof(optarg); break;
case 'F': dphi = atof(optarg); break;
case 't': dt = atof(optarg); break;
case 'S': SNRdB = atof(optarg); break;
default:
exit(1);
}
}
unsigned int i;
// validate input
if (beta <= 0.0f || beta >= 1.0f) {
fprintf(stderr,"error: %s, bandwidth-time product must be in (0,1)\n", argv[0]);
exit(1);
} else if (dt < -0.5f || dt > 0.5f) {
fprintf(stderr,"error: %s, fractional sample offset must be in [-0.5,0.5]\n", argv[0]);
exit(1);
}
// derived values
unsigned int num_symbols = num_sync_symbols + 2*m + 10;
unsigned int num_samples = k*num_symbols;
float nstd = powf(10.0f, -SNRdB/20.0f);
// arrays
float complex seq[num_sync_symbols]; // synchronization pattern (symbols)
float complex s0[k*num_sync_symbols]; // synchronization pattern (samples)
float complex x[num_samples]; // transmitted signal
float complex y[num_samples]; // received signal
float complex rxy[num_samples]; // pre-demod correlation output
float dphi_hat[num_samples]; // carrier offset estimate
// create transmit/receive interpolator/decimator
firinterp_crcf interp = firinterp_crcf_create_prototype(LIQUID_FIRFILT_RRC,k,m,beta,dt);
// generate synchronization pattern (BPSK) and interpolate
for (i=0; i<num_sync_symbols + 2*m; i++) {
float complex sym = 0.0f;
if (i < num_sync_symbols) {
sym = rand() % 2 ? -1.0f : 1.0f;
seq[i] = sym;
}
if (i < 2*m) firinterp_crcf_execute(interp, sym, s0);
else firinterp_crcf_execute(interp, sym, &s0[k*(i-2*m)]);
}
// reset interpolator
firinterp_crcf_reset(interp);
// interpolate input
for (i=0; i<num_symbols; i++) {
float complex sym = i < num_sync_symbols ? seq[i] : 0.0f;
firinterp_crcf_execute(interp, sym, &x[k*i]);
}
// push through channel
for (i=0; i<num_samples; i++)
y[i] = x[i]*cexpf(_Complex_I*(dphi*i + phi)) + nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// create cross-correlator
bpresync_cccf sync = bpresync_cccf_create(s0, k*num_sync_symbols, 0.05f, 11);
bpresync_cccf_print(sync);
// push signal through cross-correlator
float rxy_max = 0.0f; // maximum cross-correlation
float dphi_est = 0.0f; // carrier frequency offset estimate
int delay_est = 0; // delay estimate
for (i=0; i<num_samples; i++) {
// correlate
bpresync_cccf_push(sync, y[i]);
bpresync_cccf_execute(sync, &rxy[i], &dphi_hat[i]);
// detect...
if (cabsf(rxy[i]) > 0.6f) {
printf("****** preamble found, rxy = %12.8f (dphi-hat: %12.8f), i=%3u ******\n",
cabsf(rxy[i]), dphi_hat[i], i);
}
// retain maximum
if (cabsf(rxy[i]) > rxy_max) {
rxy_max = cabsf(rxy[i]);
dphi_est = dphi_hat[i];
delay_est = (int)i - (int)2*k*m + 1;
}
}
// destroy objects
firinterp_crcf_destroy(interp);
bpresync_cccf_destroy(sync);
// print results
printf("\n");
printf("rxy (max) : %12.8f\n", rxy_max);
printf("dphi est. : %12.8f ,error=%12.8f\n", dphi_est, dphi-dphi_est);
printf("delay est.: %12d ,error=%3d sample(s)\n", delay_est, k*num_sync_symbols - delay_est);
printf("\n");
//
// export results
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all\n");
fprintf(fid,"close all\n");
fprintf(fid,"num_samples = %u;\n", num_samples);
fprintf(fid,"num_symbols = %u;\n", num_symbols);
fprintf(fid,"k = %u;\n", k);
fprintf(fid,"x = zeros(1,num_samples);\n");
fprintf(fid,"y = zeros(1,num_samples);\n");
fprintf(fid,"rxy = zeros(1,num_samples);\n");
for (i=0; i<num_samples; i++) {
fprintf(fid,"x(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"rxy(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(rxy[i]), cimagf(rxy[i]));
}
fprintf(fid,"t=[0:(num_samples-1)]/k;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," plot(t,real(y), t,imag(y));\n");
fprintf(fid," axis([0 num_symbols -2 2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('received signal');\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," plot(t,abs(rxy));\n");
fprintf(fid," axis([0 num_symbols 0 1.5]);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('correlator output');\n");
fprintf(fid," grid on;\n");
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
return 0;
}
void bpresync_test(bpresync_cccf _q,
float complex * _x,
unsigned int _n,
float _SNRdB,
float _dphi_max,
float * _rxy_max,
float * _dphi_err,
float * _delay_err,
unsigned int _num_trials,
unsigned int _verbosity)
{
unsigned int max_delay = 64;
float gamma = powf(10.0f, _SNRdB/20.0f);
float nstd = 1.0f;
// Farrow filter (for facilitating delay)
unsigned int h_len = 49;
unsigned int order = 4;
float fc = 0.45f;
float As = 60.0f;
firfarrow_crcf fdelay = firfarrow_crcf_create(h_len, order, fc, As);
unsigned int num_samples = _n + max_delay + (h_len-1)/2;
float complex y[num_samples];
unsigned int t;
for (t=0; t<_num_trials; t++) {
unsigned int delay = rand() % max_delay; // sample delay
float dt = randf() - 0.5f; // fractional sample delay
float dphi = (2.0f*randf() - 1.0f) * _dphi_max; // carrier frequency offset
float phi = 2*M_PI*randf(); // carrier phase offset
// reset binary pre-demod synchronizer
bpresync_cccf_reset(_q);
// reset farrow filter
firfarrow_crcf_clear(fdelay);
firfarrow_crcf_set_delay(fdelay, dt);
unsigned int i;
unsigned int n=0;
// generate signal: delay
for (i=0; i<delay; i++) {
firfarrow_crcf_push(fdelay, 0.0f);
firfarrow_crcf_execute(fdelay, &y[n++]);
}
// generate signal: input sequence
for (i=0; i<_n; i++) {
firfarrow_crcf_push(fdelay, _x[i]);
firfarrow_crcf_execute(fdelay, &y[n++]);
}
// generate signal: flush filter
while (n < num_samples) {
firfarrow_crcf_push(fdelay, 0.0f);
firfarrow_crcf_execute(fdelay, &y[n++]);
}
// add channel gain, carrier offset, noise
for (i=0; i<num_samples; i++) {
y[i] *= gamma;
y[i] *= cexpf(_Complex_I*(phi + i*dphi));
y[i] += nstd*( randnf() + randnf()*_Complex_I )*M_SQRT1_2;
}
// push through synchronizer
_rxy_max[t] = 0.0f;
_dphi_err[t] = 0.0f;
_delay_err[t] = 0.0f;
for (i=0; i<num_samples; i++) {
// push through correlator
float complex rxy;
float dphi_est;
bpresync_cccf_push(_q, y[i]);
bpresync_cccf_correlate(_q, &rxy, &dphi_est);
// retain maximum
if ( cabsf(rxy) > _rxy_max[t] ) {
_rxy_max[t] = cabsf(rxy);
_dphi_err[t] = dphi_est - dphi;
_delay_err[t] = (float)i - (float)(_n + delay + (h_len-1)/2) + 1.0f + dt;
}
}
if (_verbosity == 0) {
// do nothing
} else if (_verbosity == 1) {
// print progress bar
if ( (t%100)==0 || t==_num_trials-1 ) {
float percent = (float)(t+1) / (float)_num_trials;
unsigned int bars = (unsigned int) (percent*60);
printf("[");
for (i=0; i<60; i++)
printf("%c", i < bars ? '#' : ' ');
printf("] %5.1f%%\r", percent*100);
fflush(stdout);
}
} else {
// print every trial
printf(" %6u: rxy_max=%12.8f, dphi-err=%12.8f, delay-err=%12.8f\n",
t, _rxy_max[t], _dphi_err[t], _delay_err[t]);
}
}
// destroy Farrow filter
firfarrow_crcf_destroy(fdelay);
}
