Formula for STA

[yeyoe]

I didn't find the code about STA part.So, I attemp to recode the STA code. But in the paper, about formula (8), I can't get the closed-form solution about x(t). To my knowledge, the formula (8) is a GMM formula, which need EM algorithm to get the solution iteratively( not a closed-form solution ). So, please offer the solution of x(t) or the way to get the solution. THKS! BEST WISHES