Characterizing Local Effects on Protection Level Concept in Urban Environments

In this paper, the focus is on the characterization of the local effects on satellite based integrity concept in urban environments. For this purpose and to have a better apprehension of the operational environment and techniques best suited for it, one such location, the downtown and suburban area of Munich was selected. The task of collecting navigation data was accomplished using two different receivers at the same time [1]. The first one, used as a reference, was a professional survey-grade NovAtel receiver, able to process the navigation signals broadcast on both L1 and L2 bands and perform Real Time Kinematic measurements. The receiver was combined with an Inertial Measurement Unit (IMU) that guaranteed a positioning accuracy on the order of few centimeters, even during short signal outages. The second one was a survey-grade Septentrio PolaRx2e receiver, able to decode and process the European Geostationary Navigation Overlay Service (EGNOS) integrity messages and output the Horizontal Protection Level (HPL) [2]. A pair of low cost car navigation receivers was also deployed to assess the accuracy in commercial domain. The data from these receivers was post-processed for further reasoning and conclusions. The analysis of this data demonstrated that the poor signal conditions due to the blockage of signals and the presence of multipath limit the integrity performance. The integrity concept has to meet these challenges. Multipath introduces a bias and also adds to the total error variance. So, proper multipath mitigation techniques need to be deployed. The limitation of signal unavailability can be overcome through technologies like EGNOS Data Access Service (EDAS) which recovers integrity data through a different link [3]. The analysis provides the required parameters to develop techniques for automotive applications in harsh and suburban environments.