Efficient Estimation of Stochastic Volatility Using Noisy Observations:   A Multi-Scale Approach
  With the availability of high frequency financial data, nonparametric estimation of volatility of an asset return process becomes feasible. A major problem is how to estimate the volatility consistently and efficiently, when the observed asset returns contain error or noise, for example, in the form of microstructure noise. The former (consistency) has been addressed heavily in the recent literature, however, the resulting estimator is not quite efficient. In Zhang, Mykland and Ait-Sahalia (2003), the best estimator converges to the true volatility only at the rate of n^{-1/6}. In this paper, we propose an estimator, the {\it Multi-scale Realized Volatility (MSRV)}, which converges to the true volatility at the rate of n^{-1/4}, which is the best attainable. We have shown a central limit theorem for the MSRV estimator, which permits setting intervals for the true integrated volatility on the basis of MSRV. 
Lan Zhang