Advanced signal processing strategies for resilient satellite navigation using multi-correlator structures

Abstract

Positioning and timing has become a crucial component in a broad field of applications. This spans from positioning and navigation in aeronautics, maritime, and automobile applications to system critical time synchronization of power grids or mobile telecommunication networks. On a global scale, this is achieved already today with global navigation satellite systems (GNSSs). However, environmental conditions can affect their performance and reliability. A well-known threat in this context is the multipath propagation. Objects in the nearer receiver environment reflect the satellite signals, which can cause errors or even failure of conventional GNSS receivers. A second threat are atmospheric effects, in particular due to the ionosphere. Solar radiation ionizes the remaining atoms and molecules in this layer of the atmosphere. The resulting free electrons introduce additional signal delays. As this effect is frequency-dependent, it can be largely eliminated with a multi-frequency receiver using the ionosphere-free combination. Unfortunately, other errors, such as multipath errors, tend to be amplified in this process. Multipath propagation depicts therewith a limiting factor in GNSS. In the literature, a large number of approaches have been proposed in the past to mitigate the effect of multipath. They vary in effectiveness and complexity depending on the application and requirements they were developed for. Nevertheless, a certain gap has been identified in the literature regarding solutions, that are effective, provide a good noise performance, and are of feasible complexity. In this work, a multipath mitigating algorithm has been developed, that is designed to fill this gap. Propagation characteristics are estimated in the form of a line-of-sight (LOS) delay and an impulse response that represents multipath components. This enables an improved delay estimation. The approach will be analyzed with synthetic data, hardware emulations, as well as actual measurement data, confirming that it fulfills the design criteria. In addition, the integration into an advanced vector tracking (VT) receiver architecture has been shown. The joint processing of all satellites increases reliability in challenging environments and depicts with the increased multipath resilience of the proposed algorithm a strong combination. Moreover, the extension to simultaneously processing multiple frequencies has been explored. The therewith achieved observability of the ionospheric delays is used to actively estimate this effect. The multipath resilience of the underlying developed algorithm allows for an accurate estimation, also in multipath environments. Last but not least, the extension to antenna arrays has been explored. The therewith additionally available spatial domain allows to overcome the temporal resolution limit that was limiting the effectiveness of the proposed solution against short delay multipaths.