Abstract: The autocorrelation method can be used to estimate the precession period of a ballistic radar target in midcourse, for which it is necessary that the upper and lower bounds of the precession period be given in advance. However, the lower bound of the precession period provided may be far less than the true precession period, which will seriously degrade the estimation performance. An improved autocorrelation method is proposed by defining the convex hull of the autocorrelation function(ACF). The difference function between the ACF and the convex hull is obtained, and then the precession period is estimated by searching for the maximum value of the difference function. The theoretical analysis ancl simulation results show that the estimation performance of the proposed method is close to the autocorrelation method when the lower bound is not far less than the true precession period. When the lower bound is far less than the true precession period, the proposed method still has good estimation performance. Usually the ratio of the upper bound to the lower bound is larger than 2, resulting in the computational burden of the proposed method less than 1.4 times of that of the autocorrelation method. Also it is very easy to meet the prior information requirement for the proposed method. Therefore the proposed method can be used widely.

Key words: motion estimation, frequency estimation, autocorrelation, correlation methods, missiles, radar target recognition