Performance Evaluation of the Multipath Estimating Delay Lock Loop

Abstract

When using narrow correlator spacing in a GPS receiver, the C/A-code tracking errors are on the order of a decimeter. In the presences of multipath signals, tracking errors can be on the order of a few meters. In many differential GPS applications, multipath is the most significant source of error. In a previous paper, the authors demonstrated that it is possible to reduce multipath errors greatly by using the Multipath Estimating Delay Lock Loop (MEDLL). Since then, MEDLL has been implemented into a multichannel receiver that calculates the pseudorange multipath errors in real time. This paper reviews the multipath problem in the GPS receiver and the theory of the MEDLL. Two experiments carried out to evaluate the MEDLL are described. First, measurements were collected simultaneously with the MEDLL receiver and a standard NovAtel narrow-correlator receiver over a short baseline. Second, the same receivers were connected to a GPS signal simulator so a multipath signal could be introduced in a controlled enviroment.