Abstract
GNSS (Global Navigation Satellite Systems) multipath has been subject to scientific research for decades and although numerous methods and techniques have already been developed to mitigate this effect, it is still one of the accuracy-limiting factors in many GNSS applications. Since multipath is highly dependent on the individual antenna environment, there is still a need for new methods and further investigations to increase the understanding of this systematic effect. In this paper, the concept of Fresnel zones is applied to two different aspects of multipath. First, Fresnel zones are determined for the line-of-sight transmission between satellite and receiver. By comparing the boundary of the Fresnel zones to an obstruction adaptive elevation mask, potentially diffracted signals can be identified and excluded from the position estimation process. Both the percentage of epochs with fixed ambiguities and the positioning accuracy can be increased by the proposed method. Second, Fresnel zones are used to analyze the multipath induced by a horizontal and spatially-limited reflector. The comparison of simulated and real signal-to-noise (SNR) observations reveals a relationship between the percentage of the overlap of the Fresnel zone and reflector and the occurrence of multipath. It is found that an overlap of 50% is sufficient to induce multipath effects. This is of special interest, since this does not confirm theoretical assumptions of the multipath theory.
Highlights
Sensors 2019, 19, 25 paper, we focus on far-field multipath effects and signal diffraction, and for the sake of simplicity, far-field multipath is referred to as multipath hereafter
The intersection of the ellipsoid with a reflecting surface leads to Fresnel zones, the active scattering regions that cause signal reflection and, in turn, lead to multipath effects after the superimposition with the signal received on the direct signal path
Fresnel zones are determined for the line-of-sight transmission between the satellite and the user antenna
Summary
The signals from GNSS (Global Navigation Satellite Systems) satellites can be used to estimate the position of the user antenna. As a consequence, positioning techniques that only use carrier-phase observations, e.g., as presented in [6], are of special interest, since such approaches eliminate the dominant influence of the code-multipath. In the GNSS reflectometry (GNSS-R) community, ground reflected satellite signals are utilized in order to derive information, such as soil moisture content, snow depth or sea water levels [26,27] In this context, Fresnel zones are used to identify and select the active scattering regions or sensing zones that contribute to the desired quantities. In addition to the signal-to-noise ratio, the possibility of utilizing code-, carrier-phase or Doppler observations has been investigated in the context of GNSS-R applications such as sea surface topography, flood monitoring and tsunami detection [31,32].
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