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ObjectiveThe Message Generation Facility (MGF) is an element of the Galileo Mission Segment (GMS) and is responsible for real-time distribution of the navigation, integrity and SAR messages from the processing facilities to the Up-Link Stations (ULS). The main objective is to route a message to the correct ULS in time for on-board update of navigation data and integrity data for dissemination to users. To perform the Assembly, Integration and Verification (AIV) activities of the MGF, a dedicated test platform, MGF-AIVP, is developed by National Aerospace Laboratory NLR. The MGF-AIVP simulates other Elements in the GMS that are connected to the MGF, in real-time. Its focus is to verify the main objective of the MGF.
ContextThe role of the AIVP is to act as the counterpart of the MGF, simulating the operational environment, in this case a part of the Galileo Mission Segment (GMS). To enable this, the AIVP contains simulation models of all the elements that communicate with the MGF. In this way, the MGF thinks it is running in an operational environment.
As the MGF is communicating in real-time, the AIVP must be able to test the level of real-time guarantee, and hence must be real-time as well. Timing measurements will show the delay of the MGF processing and the interface delays in order to verify MGF performance requirements.
The simulation models are able to set up and maintain the connections to the MGF. Furthermore, depending on the required level of simulation, the models implement (part of) the behaviour of the corresponding element, following the protocols as defined in the GMS Interface Control Documents (ICD). This behaviour is essentially a mix of synchronous (cyclic) messaging by sending models and asynchronous reception of messages by receiving models, everything in real-time.
When a simulation/test run has finished, the results will be analysed to assess the pass/fail criteria of the test. Depending on the complexity of a test scenario, pass/fail criteria are checked automatically in a test script (and logged during the simulation run) or verified in a post-processing step using a dedicated tool.
Another important capability of any test system is the injection of errors for testing the robustness of the unit-under-test. The AIVP features a scripting language to implement test scenarios that command and control the simulation models.
Role of EuroSimThe MGF-AIVP relies for a large part on the simulation framework EuroSim. EuroSim is used to build, schedule and execute the simulation models. The simulation runs realtime at 1000Hz to achieve the required 1 millisecond resolution. Synchronisation within the facility is accomplished via IRIG-B.
The simulation models are designed using the Unified Modelling Language (UML) to allow inheritance and multiple instantiation. As the implementation is done mostly in C++, the models need to comply with the Simulation Model Portability (SMP) standard, through which they are imported in the EuroSim framework.