Statistical GNSS performance assessment as part of the ALEGRO Ground Based Augmentation System inside Research Harbour Rostock

Kurzfassung

In the Research Port Rostock the Institute of Communication and Navigation of the German Aerospace Center deployed and operates an experimental Ground Based Augmentation System (GBAS). The first prototype of this GBAS system was developed under the project acronym ALEGRO to support positioning and navigation of marine users by the provision of phase based differential GNSS service. In time the implemented GBAS System is limited on a one receiver station system but will be extended by a second station up the end of 2009 for GBAS integrity monitoring. For the development and operation of GBAS the assessment of Global Navigation Satellite System (GNSS) signal and positioning quality at reference station site has to be considered as one elementary task before augmentation and correction data are derived and provided to marine users. Based on the decomposition of GNSS related measurements like e.g. ranges, phases, amplitudes and Signal to Noise Ratios (SNR) different quality parameters are derived in real time. Related to the fact that GBAS are normally placed at reference locations with low multipath effects, the influence of the environment in form of shadowing and reflections should be strongly limited. Daily derived statistics of quality parameters like e.g. code and carrier phase noise, SNR and power noise are used to derive values ranges of their regular (undisturbed) behaviour and to describe dependencies between them. For this purpose inside the ALEGRO processing system a statistical processor system operates to determine statistical parameters from 24 h measurements and derived real time quality parameters. They are used to model the regular value ranges and to identify thresholds for integrity monitoring in a next step. Such data are foreseen to support the monitoring of the GBAS operational system itself and to tune the measuring models used in the algorithms dealing with the provision of augmentation data and with the prediction and verification of the expected positioning accuracy and integrity in the GBAS environmental field. The paper will discuss the results of a 1 month measurement campaign. Under regular GNSS operation and signal propagation conditions it will be demonstrated that the quality parameters are reproducible at successive days. On basis of selected measuring examples it will be shown that the exact quantitative knowledge and description of the reference behaviour enables the detection of signal disturbances during GBAS operation. Besides the investigation of single quality parameters a special attention has been given on the description of dependencies between various quality parameters and their relation to satellite elevation and signal strength.