  In this article we focus on estimating the quadratic covariation of
continuous semimartingales from discrete observations that take place at
asynchronous observation times. The Hayashi-Yoshida estimator serves as
synchronized realized covolatility for that we give our own distinct
illustration based on an iterative synchronization algorithm. We consider
high-frequency asymptotics and prove a feasible stable central limit theorem.
The characteristics of non-synchronous observation schemes affecting the
asymptotic variance are captured by a notion of asymptotic covariations of
times. These are precisely illuminated and explicitly deduced for the important
case of independent time-homogeneous Poisson sampling.
