Detecting relative position of user devices and mobile access points

Free Internet access in urban public transportation fleets by means of WiFi hotspots is becoming a common service in a growing number of cities. Users of the public bus WiFi service will get the network memorised in their mobile devices and, as they move from buses to streets, their devices will switch Internet access from WiFi to cellular. If a bus passes by the user while he or she is on the street, the mobile device will connect to the bus WiFi hotspot, breaking the cellular connection and initiating a short-lived WiFi connection. This disruption of the user experience can be avoided if the mobile access point (AP) learns whether the user device is inside or outside the bus and decides to accept its connection request or not. In this paper, we evaluate if a mobile AP (installed on the buses) can detect the relative position of a user device. We collected a large dataset of WiFi-usage and mobility patterns from a real-world public bus fleet in Porto, Portugal, to identify features from which the mobile AP can detect if a user device is inside or outside the bus. We tested RSSI and bus speed as features feed into a classifier, and observed that RSSI is a poor indicator whereas bus speed presents some correlation to whether a connection is established inside or outside the bus. Finally, we propose and evaluate the trade-offs of a mechanism (running on the mobile AP) that decides whether a device should be allowed to connect or not.