void HMM::viterbi_update(uint32_t* y,
double* T1, int* T2, double* aux,
int t_start, int t_end) {
for(int t = t_start; t < t_end; t++) {
if(t == 0) {
update_log_parameters();
// Initialize T1[0]
vadd(nu_log, 1, g_log + y[0], os, T1, 1, hs);
} else {
double* T1p_ = T1 + (t-1)*hs;
double* T1_ = T1 + t*hs;
int* T2_ = T2 + t*hs;
for(int s = 0; s < hs; s++) { // for each current state
// mlt with transitions: aux = T1prev * Q (for every previous state)
vadd(T1p_, 1, Q_log + s, hs, aux, 1, hs);
// find best previous state
int maxi;
maxvi(aux, 1, T1_ + s, &maxi, hs);
T2_[s] = maxi;
// update with emission g[s, y[t]]
T1_[s] += g_log[s*os + y[t]];
}
}
}
}
void HMM::viterbi_backtrack(int n, double* T1, int* T2, uint32_t* x, double* logprob) {
int maxi;
int t = n-1;
maxvi(T1 + t*hs, 1, logprob, &maxi, hs);
x[t] = maxi;
for(int t = n-2; t >= 0; t--) {
x[t] = T2[(t+1)*hs + x[t+1]];
}
}
/* navigation bit synchronization ----------------------------------------------
* check synchronization of navigation bit
* args : double IP I correlation output (IP data)
* double oldIP I previous correlation output
* sdrnav_t *nav I/O navigation struct
* return : int 1:synchronization 0: not synchronization
*-----------------------------------------------------------------------------*/
extern int checksync(double IP, double IPold, sdrnav_t *nav)
{
int i,corr=0,maxi;
/* BeiDou MEO/IGSO satellite (secondary code is NH20) */
if (nav->ctype==CTYPE_B1I&&nav->sdreph.prn>5) {
shiftdata(&nav->bitsync[0],&nav->bitsync[1],sizeof(int),nav->rate-1);
nav->bitsync[nav->rate-1]=(IP<0?-1:1);
/* correlation between NH20 */
for (i=0;i<nav->rate;i++)
corr+=nav->ocode[i]*nav->bitsync[i];
/* if synchronization success */
if (abs(corr)==nav->rate) {
nav->synci=nav->biti; /* synchronization bit index */
return 1;
}
/* other satellite */
} else {
if (IPold*IP<0) {
nav->bitsync[nav->biti]+=1; /* voting bit position */
/* check vote count */
maxi=maxvi(nav->bitsync,nav->rate,-1,-1,&nav->synci);
/* if synchronization success */
if (maxi>NAVSYNCTH) {
/* synchronization bit index */
nav->synci--; /* minus 1 index*/
if (nav->synci<0) nav->synci=nav->rate-1;
return 1;
}
}
}
return 0;
}
