The land mobile satellite navigation multipath channel - A statistical analysis

Abstract

In autumn 2002 the German Aerospace Centre (DLR) carried out a high resolution measurement campaign to investigate the land mobile satellite navigation multipath channel. This became necessary because for future wideband navigation systems like Galileo there is not enough knowledge about multipath. High bandwidth navigation signals are strongly disturbed by reflections from structures close to the receiver. To model these effects a very high time resolution is required. Especially for the proposed BOC (Binary Offset Carrier) signal structures the delays of echoes have to be known in ns accuracies. Approaches of the past to describe the multipath effects have resolutions of 50 ns which is not satisfying for high precision positioning. For the measurements a Zeppelin simulated the satellite transmitting a signal down to a measurement van equipped with the receiver and various sensors. During the campaign more than 60 measurements, each lasting for about 15 minutes were taken in several urban, suburban and rural scenarios for car and pedestrian applications in and around Munich. For a sufficient statistic we covered the whole elevation and azimuth range and chose streets containing a relevant mix for each channel type. The measurement signal had a bandwidth of 100 MHz and was transmitted every 3 ms to “sound” the channel, whose impulse response was recorded. For more details on the campaign please refer to [1]. In this paper we will present statistical analyses of the measured data. The raw data has a delay resolution of 10 ns and was post processed with an ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) based super resolution algorithm guaranteeing a delay resolution in ns. We will give detailed information about echo occurrences, birth and death rates, life times of echoes and their power and delay distributions. In addition we have accurate information about their Doppler shifts and bandwidths. We will present dependencies of the channel characteristics (e.g. visibility) on elevation and azimuth and compare different channel types. Furthermore we are able to identify worst case scenarios and can give verified examples, where positioning errors of more than 100 meters occurred due to multipath, when using a standard GPS receiver. The recorded GPS data also allows us to calculate realistic availabilities in these critical scenarios where high buildings or trees often avert the reception of satellite signals. [1] Alexander Steingass. Andreas Lehner, “Measuring GALILEO’s multipath channel”, GNSS 2003, Graz, Austria.