Christophe Ouzeau

Degraded Modes Resulting From The Multi-Constellation Use Of GNSS Christophe Ouzeau

The International Civil Aviation Organization (ICAO) has defined the concept of GlobalNavigation Satellite System (GNSS), which corresponds to the set of systems allowing toperform satellite-based navigation while fulfilling ICAO requirements. The US Global Positioning Sysem (GPS) is a satellite-based navigation system whichconstitutes one of the components of the GNSS. Currently, this system broadcasts a civilsignal, called L1 C/A, within an Aeronautical Radio Navigation Services (ARNS) band. The GPSis being modernized and will broadcast two new civil signals: L2C (not in an ARNS band) andL5 in another ARNS band. Galileo is the European counterpart of GPS. It will broadcast three signals in an ARNSband: Galileo E1 OS (Open Service) will be transmitted in the GPS L1 frequency band andGalileo E5a and E5b will be broadcasted in the same 960-1215 MHz ARNS band than that ofGPS L5. GPS L5 and Galileo E1, E5a, E5b components are expected to provide operationalbenefits for civil aviation use. However, civil aviation requirements are very stringent and upto now, the bare systems alone cannot be used as a means of navigation. For instance, theGPS standalone does not implement sufficient integrity monitoring. Therefore, in order to ensure the levels of performance required by civil aviation in terms ofaccuracy, integrity, continuity of service and availability, ICAO standards define differentsystems/algorithms to augment the basic constellations. GPS, Galileo and the augmentationsystems could be combined to comply with the ICAO requirements and complete the lack ofGPS or Galileo standalone performance. In order to take benefits of new GNSS signals, and to provide the service levelrequired by the ICAO, the architecture of future combined GNSS receivers must bestandardized. The European Organization for Civil Aviation Equipment (EUROCAE) WorkingGroup 62, which is in charge of Galileo standardization for civil aviation in Europe, proposesnew combined receivers architectures, in coordination with the Radio Technical Commissionfor Aeronautics (RTCA). The main objective of this thesis is to contribute to the efforts made by the WG 62 byproviding inputs necessary to build future receivers architecture to take benefits of GPS, Galileo and augmentation systems. In this report, we propose some key elements of thecombined receivers' architecture to comply with approach phases of flight requirements. In case of perturbation preventing one of the needed GNSS components to meet aphase of flight required performance, it is necessary to be able to switch to another availablecomponent in order to try to maintain if possible the level of performance in terms ofcontinuity, integrity, availability and accuracy. That is why future combined receivers mustbe capable of detecting the impact of perturbations that may lead to the loss of one GNSScomponent, in order to be able to initiate a switch. These perturbations are mainlyatmospheric disturbances, interferences and multipath. In this thesis we focus on theparticular cases of interferences and ionosphere perturbations. The interferences are among the most feared events in civil aviation use of GNSS. Detection, estimation and removal of the effect of interference on GNSS signals remain openissues and may affect pseudorange measurements accuracy, as well as integrity, continuityand availability of these measurements. In literature, many different interference detectionalgorithms have been proposed, at the receiver antenna level, at the front-end level. Detection within tracking loops is not widely studied to our knowledge. That is why, in thisthesis, we address the problem of interference detection at the correlators outputs. Theparticular case of CW interferences detection on the GPS L1 C/A and Galileo E1 OS signalsprocessing is proposed