Maritime GBAS: Improvement of Positioning Accuracy and Reliability by Integrity Monitoring

Abstract

Ground Based Augmentation Systems (GBAS) supporting phase-based DGNSS or pseudolite-augmented positioning are sufficient approaches to fulfil IMO requirements (International Maritime Organisation) on future GNSS for vessel navigation in port areas. With respect to the “safety of life” character of maritime traffic and transport processes, the GBAS must be enriched with a self-monitoring system assessing the augmentation service provided in real time in relation to specific user requirements. The build-up of the experimental GBAS in the vicinity of the Research Port Rostock and the development of monitoring algorithm were realised in the frame of the projects ALEGRO (FKZ V230-630-08-TIFA-560) and ASMS (FKZ 50NA0735). At begin of this paper the architecture of the experimental GBAS and the developed integrity monitoring concept will be described. At both stations – at reference and integrity monitoring station – different independent, but hierarchical composed tests are executed to evaluate the quality of signals and the performance of the provided GBAS services. The assessment results were logical linked in a central software module generating the final integrity message RTCM 4083 for the users. A critical point is the optimal choice of performance key identifiers used during the hierarchical composed tests. Based on outlier detection it should be ensured, that only high-quality satellite signals are used to provide GBAS augmentation signals and to support P-DGNSS based positioning. The selection of high-quality satellite signals reduces the number of available signals for positioning and increases the dilution of precision (DOP). Scope of this paper is to investigate the influence of the satellite selecting procedures on the reachable positioning accuracy. The derived results are used to optimise the control and configuration of the techniques realising the selection of satellite signals used for augmentation and positioning.