先得到一个定位初始估计值，再利用建立最大似然方程对这个定位初始估计值进行修正，从而得到更优定位结果值，方法更接近于最大似然方法。-Get the a position initial estimate, re-use to establish the maximum likelihood equations corrected for positioning the initial estimates, resulting in better positioning the resulting value is closer to the maximum likelihood method.