Mobile Device-to-Device Communication for Crisis Scenarios Using Low-Cost LoRa Modems

We present an approach to enable long-range device-to-device communication between smartphones in crisis situations. Our approach is based on inexpensive and readily available microcontrollers with integrated LoRa hardware that we empower to receive and forward messages via Bluetooth, Wi-Fi, or a serial connection by means of a dedicated firmware, called rf95modem. The developed firmware cannot only be used in crisis scenarios but also in a variety of other applications, such as providing a communication fallback during outdoor activities, geolocation-based games or broadcasting of local information. We present two applications to show the benefits of our approach. First, we introduce a novel device-to-device LoRa chat application that works on both Android and iOS as well as on traditional computers like notebooks using a console-based interface. Second, we demonstrate how other infrastructure-less technology can benefit from our approach by integrating it into the DTN7 delay-tolerant networking software. Furthermore, we present the results of an in-depth experimental evaluation of approach consisting of (i) real-world device-to-device LoRa transmissions in urban and rural areas and (ii) scalability tests based on simulations of LoRa device-to-device usage in a medium-sized city with up to 1000 active users. The firmware, our device-to-device chat application, our integration into DTN7, as well as our code fragments of the experimental evaluation and the experimental results are available under permissive open-source licenses.