Feedforward Delay Estimators in Adverse Multipath Propagation for Galileo and Modernized GPS Signals

Abstract

The estimation with high accuracy of the line-of-sight delay is a prerequisite for all global navigation satellite systems. The delay locked loops and their enhanced variants are the structures of choice for the commercial GNSS receivers, but their performance in severe multipath scenarios is still rather limited. The new satellite positioning system proposals specify higher code-epoch lengths compared to the traditional GPS signal and the use of a new modulation, the binary offset carrier (BOC) modulation, which triggers new challenges in the delay tracking stage. We propose and analyze here the use of feedforward delay estimation techniques in order to improve the accuracy of the delay estimation in severe multipath scenarios. First, we give an extensive review of feedforward delay estimation techniques for CDMA signals in fading channels, by taking into account the impact of BOC modulation. Second, we extend the techniques previously proposed by the authors in the context of wideband CDMA delay estimation (e.g., Teager-Kaiser and the projection onto convex sets) to the BOC-modulated signals. These techniques are presented as possible alternatives to the feedback tracking loops. A particular attention is on the scenarios with closely spaced paths. We also discuss how these feedforward techniques can be implemented via DSPs.

A Fast Unambiguous Acquisition Algorithm for BOC-Modulated Signals

“…Depending on the comparator output, the receiver either accepts corresponding code phase or continues to search. The received signal r(t) at the front-end acquisition receiver, after a multipath fading channel with AWGN, can be written as follows [15], [16]:…”

Multipath Mitigation Techniques for Satellite-Based Positioning Applications

“…Several advanced multipath mitigation techniques were also proposed in Bhuiyan (2011), Granados et al (2005), Granados & Rubio (2000), Lohan et al (2006). These techniques, in general, offer better tracking performance than the traditional DLL at a cost of increased complexity.…”

The two-unit CADLL structure multipath performance investigation

“…The representative techniques of this group are Strobe and Edge Correlator, Gated Correlator, High Resolution Correlator and others [5] [6] [7]. Another family of techniques aims at estimating the delayed interfering rays and then cancel them, such as the Multipath Estimating DLL (MEDLL), Projection Over Convex Spaces (POCS) algorithm, the Teager-Kaiser (TK) technique and others [8], [9].…”