I. Introduction
With the rise of smartphones and tablets in the recent years, the daily use of location-based services (LBS) became a matter of course. Every day, mobile applications installed on billions of mobile devices interact with reactive LBS in order to support the users in their daily life through the provision of location-specific content. All the popular mobile applications for point of interest search, travel guidance or weather forecasts - to mention just a few - are based on this principle to make the required information available upon request by the user. In contrast, proactive LBS [1] are built upon the idea to proactively support the user with location-specific content. While better known as Geofencing, a proactive LBS constantly monitors the position of each mobile device and triggers a content update every time the user enters or leaves a dedicated zone, called geofence. Proactive LBS became popular in the context of location-based marketing [2]–[5]. Thereby, potential customers are notified about location-based coupons or ads while entering a commercial district, mall or retail store. Furthermore, location-based reminders [6], [7] - nowadays mostly integrated in calendar or notes applications - became a core feature of mobile operating systems. Other potential application fields are the location-based automation [8], urban planning [9], fleet management [10], car-to-x systems [11], in-car-infotainment systems [12], parking [13] or delivery services [14].