Informationssystem Forschung

Implementing Real-time Signal Monitoring within a GNSS Software Receiver

Einrichtung	Universität der Bundeswehr München
Fakultät	Luft- und Raumfahrttechnik
Studiengang	Luft- und Raumfahrttechnik
Institut	Space Technology and Space Applications (ISTA)

Art des Eintrags	Konferenzbeitrag
Titel	Implementing Real-time Signal Monitoring within a GNSS Software Receiver
Verantwortlich	Dipl.-Ing. Carsten Stöber
Verantwortlich / Ansprechpartner	Dipl.-Ing. Carsten Stöber
Weiteres	Stöber, C., Kneißl, F., Krämer, I., Pany, T., Hein, G.W.
Stichworte	Software Receiver, Signal Monitoring, GPS, Galileo, GNSS
Zusammenfassung	Problematic distortions of received GNSS signals are a critical issue for all users. Signal anomalies caused by the signal generating hardware, so called “evil waveforms” (EWF), Multipath effects or interfering signals lead to a deformation of the correlation function within a GNSS receiver. To identify hazardous distortions multi-correlator techniques can be employed and by using the gathered data it is possible to protect a user against the mentioned signal anomalies. The aim of this paper will be a demonstration of some capabilities of the software receiver developed at the University FAF Munich. It will describe aspects of the implementation of monitoring algorithms within the receiver and furthermore the results derived from the implemented algorithms will be presented. One of the core problems while developing a GNSS software receiver is to make it work in realtime. Furthermore adding additional capabilities, like signal monitoring in realtime, will enhance this problem. Apart from this a software receiver is well suited to implement all kinds of monitoring algorithms because of the “direct” access to all possible needed data. Hence after finishing the realtime capable GNSS software receiver it is the next logical step to implement monitoring functionality. To detect deviations of the correlation function from its “nominal” shape a multi-correlator module was developed for the software receiver. It provides a variety of correlator measurements at distinct Doppler and code phase offsets. On high power standard PC hardware it provides correlator measurements for all satellites in view simultaneously. On low power hardware it can work either in multiplexing mode switching between different satellites or it delivers measurements for a single satellite. Using the correlator output different metrics, mathematical combinations of the correlator measurements, are formed within the monitoring module. The functionality is not limited to a special system due to the high flexibility of the software receiver. Currently GPS C/A, L2 Civil Signal, GIOVE-A E1/E5a and SBAS signals are monitored. To identify signal distortions the calculated metric values are compared towards thresholds which depend on satellite, frontend/antenna and site. Thus deriving the thresholds is a complex and time-consuming issue. To overcome this problem, and to make the monitoring work even if inexperienced users are operating the software, the receiver employs different self calibration stages. In the most rapid mode it uses the median of the last (predefined) number of epochs to protect the user against suddenly occurring hazardous signal errors. After gathering enough measurements the receiver finishes the self calibration process and switches to the precise monitoring mode by forming elevation angle depending thresholds. The paper will describe the used techniques, experimental results and practical application more detailed. It will also give a short foreside to the integration of additional monitors like verification of the satellite orbits into the same module.
Dokument	Ansehen
Zeitangaben	publiziert: 2008-04-25
Sprache	englisch

Geldgeber	DLR / BWB
Geldgeber-URL	http://www.dlr.de
Projektnummer	1241

Titel Sammelwerk / Konferenz	ENC GNSS 2008
Ort der Konferenz	Toulouse, France
Zusatz-Infos	ENC GNSS 2008 Conference, April 22-25, Toulouse, France

Mitglieder der Arbeitsgruppe / Co-Autoren	Hein Günter W., Univ. Prof. Dr.-Ing. Kneissl Felix, Dipl. Math. Krämer Isabelle, Dipl.-Inf. Pany Thomas, Dr.