Formal Monitoring of Risk-based Geo-fences

Abstract

This work proposes a novel risk-based geo-fencing approach. Multiple, adjacent geo-fences are each assigned a specific risk level. An UAS with a low confidence level would be restricted to an area with no or very low risk. However, an UAS with a high confidence level could be allowed to exit such a geo-fence and cross over to another geo-fence with a different risk level. This approach enables different scenarios for the use of geo-fences and requirements for entering, flying, and leaving geo-fences of specific risk. Moreover, using runtime monitoring, the UAS can be assigned a dynamic confidence level, which represents the current and prior system health, system performance, or possibly environmental conditions. This results in a structured methodology for the independent assurance of geo-fences corresponding to specific and possibly dynamic confidence levels of an UAS. The geo-fencing problem as well as the risk-based approach is formalized in the specification language Lola, which provides a concise unambiguous mathematical foundation. Specified properties can be checked at runtime due to automatically generated monitors. This results in a trustworthy implementation, possibly enabling cost-effective UAS operation in accordance to upcoming regulations. Finally, a simulation is used as proof of concept to show the feasibility of the presented approach.