在信道自相关特性的多普勒频偏估计算法的基础上，分析了存在的估计性能不受信噪比和频偏变化 影响的最优相关间隔。利用该特性提出一种逐次缩小搜索范围的迭代（CIO，correlation唱interval optimized）算法，实 现对其搜索和最大多普勒频偏的估计。通过仿真证明理论分析的正确及算法的有效性。与传统基于相关估计算 法相比，该算法自适应于信噪比和频偏变化，估计性能基本上独立于信噪比和频偏的变化，实现多普勒频偏的 直接性能估计。

In this paper,  at first research of relation between correlation-interval and estimation accuracy is carried out,  and the optimal correlation-interval is proved to be existent that is adaptive to signal-to-noise ratio and velocity varieties. Then some special characteristics of the optimal correlation-interval are explored. Based on them an iterative correlation-interval optimized (CIO) algorithm is proposed.  It optimizes the correlation- interval and calculates the Doppler spread by increasing the resolution on time-domain iteratively.  Simulation results show that contrasted to conventional schemes the proposed approach is less sensitive to signal-to-noise ratio and velocity varieties,  and can improves the performance dramatically in low signal-to-noise ratio environment in which the conventional schemes has a poor performance. It achieves the high accurate estimation of Doppler spread directly.