Multipath Estimating Techniques Performance Analysis

In Global Navigation Satellite Systems, resilience to multipath remains an important open issue, being the limiting factor in several applications due to the environment specific nature of such harsh propagation conditions. In order to as-sess the multipath impact into the final system performance, accurate metrics are required. The multipath error envelope (MPEE), even if easy to handle, is limited to the study of the bias of a receiver architecture in a noise free environment. Moreover, when it is a flat zero-valued line, the MPEE becomes less informative about the parameter estimation performance. Considering an unbiased estimator, an alternative way to char-acterize an architecture is to evaluate its mean square error (MSE) and compare it to the corresponding Cramer-Rao bound (CRB). In this work, a methodology to use both aforementioned tools is presented. First, the MPEE, which is an understandable metric. Secondly, the MSE convergence to the CRB, where one can clearly interpret the estimation performance in terms of signal-to-noise ratio or minimum path separation. These tools are then applied to a range of known multipath mitigation techniques. In addition, a new alternating projection multipath mitigation approach is proposed and analyzed.

1. Introduction

The design of new Global Navigation Satellite Systems (GNSS) architectures implies a trade-off between different performance criteria. Estimation accuracy, computational cost or robustness to multipath are examples of key GNSS receiver design criteria. Among them, resilience to mul-tipath still remains an important open issue, indeed being the limiting factor in several applications due to the environment specific nature of such harsh propagation conditions. There are many ways to tackle the multipath issue: one is to use choke ring or specific antenna arrays to filter out the multipath, assuming that one knows its direction of arrival; another is to use signal processing techniques such as Multipath Estimating Delay Lock Loop (MEDLL) [1] or Multipath Mitigation Technique (MMT) [2]; or a method of the family of algorithms which try to exploit the distortion of the correlation function, such as Vision Correlator [3], Pulse Aperture Correlator (PAC) [4], etc.