Multipath Channel Modelling for Satellite Navigation Systems
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Beschreibung
The first GPS satellite was launched in February 1978. The envisaged goal of the USA was to operate a globally available navigation system with an outstanding accuracy. Controlled by the US military, this accuracy was artificially degraded for civil users at the beginning. But techniques where found to overcome this degradation and even reduce the influence of several other error sources, leading to an accuracy which allows numerous civil applications. For example GPS makes road toll payment or avionic landing systems realizable without any ground based infrastructure today. However the required position accuracy is often not easy to guarantee. One error source still impedes applications where sub-meter accuracy is needed: multipath reception. Thereby signal echoes from objects in the near surrounding of a navigation receiver can cause positioning errors of several tens of meters. So far neither system design improvements nor advanced receiver techniques succeeded in solving this problem. The main emphasis of this thesis is to provide detailed models for the multipath environment in satellite navigation systems. The effect of multipath causing position errors in navigation receivers is well understood. It strongly depends on the power, excess delay and phase of the echo signals. Thereby especially the timely variation of these parameters is relevant. So far existing L-band models are not accurate enough. They are based on channel measurements of insufficient delay resolution and on physical simulations with a too low level of environmental detail. In this thesis two worldwide unique measurement campaigns are presented which are the basis to realistically and accurately model the multipath channel for satellite navigation systems. These models are necessary to simulate the critical environments for the test of new signal structures and for the development of multipath mitigation and estimation techniques for future highly accurate receivers.
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