An Adaptive Multipath Mitigation Architecture for GPS System

In this paper, a multipath mitigation tracking system is presented for static GPS applications. It is comprised of four function blocks, those being (1) adaptive path estimator (APE), (2) multipath interference reproducer (MPIR), (3) Rake-based delay locked loop (RB-DLL), and (4) Rake-based phase locked loop (RB-PLL). Only the short delay condition with delay less than 1.5 PN chip is considered here, because GPS pseudorange error envelope decreases to zero for delay time greater than 1.5 PN chip. In order to estimate reflection profile in the correlation domain, the FFT-based circular correlation and block average method (BAM) are utilized to offer significant savings in computational complexity. The APE estimates the delayed profiles and coefficients of the reflection signals. With the path parameters from APE, the corresponding multipath arms are activated to accomplish the multipath reproduction. These replica profiles are used for subtracting the reflection components from carrier and code discriminators before sending it into the Rake-based carrier/code tracking loops. Simulation results shows that our proposed method provides a better performance in terms of multipath error envelop and carrier-phase error. Key-Words: Global Positioning System (GPS) Receiver, adaptive path estimator (APE), multipath interference reproducer (MPIR), Rake-based delay locked loop (RB-DLL), and Rake-based phase locked loop (RB-PLL)