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Contact Tracing with the Exposure Notification Framework in the German Corona-Warn-App

Digital Contact Tracing (CT) protocols based on Bluetooth are best implemented at the system level to save resources and preserve security aspects. Combined with a government-monitored software platform, these CT-protocols can then be used to support controlling pandemics such as COVID-19. However, it is unclear how these protocols have to be parameterized to ensure the most accurate and reliable CT.This paper describes how we derived optimal parameters for a decentralized CT from extensive measurement campaigns that we carried out together with Deutsche Telekom (DT) and SAP under the supervision of the Robert Koch Institut (RKI). We examined the Google/Apple Exposure Notification Framework (ENF), which in combination with the front-end, i.e., the German Corona-Warn-App (CWA), enables digital CT in Germany. With centimeter accurate optical reference systems we show that optimal parameters are application-specific. However, they cause impractical high resource costs. In contrast, optimized general parameters offer an everyday compromise between energy costs, applicability, accuracy, and reliability of the ENF.