Multipath mitigation algorithm with hierarchical search based on MEDLL

Multipath mitigation techniques using parametric baseband processing, represented by multipath estimating delay locked loop (MEDLL), have attracted widespread attention by estimating the parameters of direct path and multipath signals simultaneously. The improvement of the estimation accuracy for such techniques, however, is at the cost of the increase of complexity. In order to reduce the resource consumption and speed up the search while maintaining the accuracy, this paper proposes a hierarchical search strategy for the maximum likelihood (ML) estimation of MEDLL. The rough estimates obtained by the former stage of search units serve as the priori information for the next-stage search with a narrower range and a smaller step to achieve refined estimates step by step. The expressions of computational complexities of the original MEDLL and the proposed tree MEDLL (T-MEDLL) with different number of stages are derived analytically, which shows that the computational burden of our approach can be reduced to 30%-50% of that of the traditional blind search with the same delay resolution of 0.01 chip in the presence of a single multipath. In addition, a digital intermediate frequency (IF) GPS signal simulator and a software GPS receiver are developed to test the parameter estimation accuracy and the pseudorange multipath errors of the hierarchical search and the blind search under different multipath scenarios. The results demonstrate that the T-MEDLL can maintain the same performance as MEDLL with significantly reduced implementation complexity.