Real time performance monitoring and noise analysis in an operational WAM system

Wide Area Multilateration (WAM) systems are complex systems and suffer from several typse of interference that vary over time. To ensure reliable operation and high data quality, a continuous verification approach is needed. The typical quality metrics in Asterix Cat 20 data are not fully sufficient to determine the operational capability of a WAM system. Different parameters are needed additionally to characterise system performance. This approach also allows detecting small changes and degradations of the system over time that may not only be caused by system intrinsic effects, but also by external evolution, like RF environment, different traffic patterns and equipment mix, or different surveillance infrastructure. This paper shows crucial low level parameters and their real time evaluation within the operational system like a)propagation path effects (especially for low level targets) b) probability of telegram reception and error rate c) interrogation efficiency d) accuracy and outlier rate of timing measurements e) system synchronisation monitoring f) measurement and track noise characterisation g) comparison against other metrics (e.g. ADS-B and the side effects thereof) h) aircraft transponder anomaly monitoring Based on these analyses, optimized data output strategies are proposed how to convey the maximum amount of information into Asterix reports for further processing. A more detailed definition of some fields will become necessary, especially when the MLAT data is fed into a sensor data fusion.