Improving GNSS Shadow Matching with Diffraction Modelling

authored by: Anat Schaper
Abstract: Positioning with Global Navigation Satellite System (GNSS) in urban areas is still a challenging task. A large number of signals is affected by obstacles such as buildings, trees or vehicles which leads to diffraction, reflection, multipath, or even signal blockages. Especially the cross street accuracy suffers in urban environments since signals from behind the buildings are more likely to be affected compared to signals following the direction of the street.

This thesis focuses on combining diffraction with Shadow Matching (SM). For this purpose, the occurrence and extent of diffraction are analysed in a typical urban area of Hanover using a 3D building model and two static long term GNSS experiments. A Knife Edge Diffraction (KED) model is utilised to determine the signal strength loss caused by diffraction. The obtained information is considered to design a new and more sophisticated SM scoring scheme incorporating diffraction.

Results show that the majority of observations can be modelled accurately if the building's eave closest to the signal is considered as sole diffraction source. Larger discrepancies are observed as soon as more than the first Fresnel zone is obstructed and the signal strengths fluctuate at a low level.
Integrating the signal strengths predicted with the KED model into a SM results in improvements of up to 85% in the horizontal plane and 97% in cross track direction compared to scoring schemes considering diffraction only in a simplified form.
Organisation(s): Institute of Geodesy
Type: Master's thesis
Publication date: 10.11.2021
Publication status: Published
: Details in the research portal "Research@Leibniz University"

BibTeX

@mastersthesis{ffd8ca5bf12048459464fab961206b4a,
title = "Improving GNSS Shadow Matching with Diffraction Modelling",
abstract = "Positioning with Global Navigation Satellite System (GNSS) in urban areas is still a challenging task. A large number of signals is affected by obstacles such as buildings, trees or vehicles which leads to diffraction, reflection, multipath, or even signal blockages. Especially the cross street accuracy suffers in urban environments since signals from behind the buildings are more likely to be affected compared to signals following the direction of the street.This thesis focuses on combining diffraction with Shadow Matching (SM). For this purpose, the occurrence and extent of diffraction are analysed in a typical urban area of Hanover using a 3D building model and two static long term GNSS experiments. A Knife Edge Diffraction (KED) model is utilised to determine the signal strength loss caused by diffraction. The obtained information is considered to design a new and more sophisticated SM scoring scheme incorporating diffraction.Results show that the majority of observations can be modelled accurately if the building's eave closest to the signal is considered as sole diffraction source. Larger discrepancies are observed as soon as more than the first Fresnel zone is obstructed and the signal strengths fluctuate at a low level.Integrating the signal strengths predicted with the KED model into a SM results in improvements of up to 85% in the horizontal plane and 97% in cross track direction compared to scoring schemes considering diffraction only in a simplified form.",
author = "Anat Schaper",
year = "2021",
month = nov,
day = "10",
language = "English",
school = "Institute of Geodesy",
}