Design and performance evaluation of a LoRa-based mobile emergency management system (LOCATE)

Smartphone devices can play a key role on emergency scenarios thanks to their pervasiveness, and the possibility to convey emergency requests from the involved people to the rescue teams. At the same time, the effective utilization of such devices on critical scenarios with limited mobile Internet access is challenging. As an alternative, several recent research studies have proposed Emergency Communication System (ECS) based on short-range Device-to-Device (D2D) solutions available on Commercial Off The Shelf (COTS) devices (e.g. Wi-Fi Direct); however, the target of these solutions is constituted by small indoor areas, since the scalability on large-scale environments is often a problem. In this paper, we overcome such issue by proposing LOCATE, a novel phone-based ECS enabling long-range communication among survivors and rescue teams over critical environments where 3/4G cellular connectivity is not available and the traditional geo-localization technologies (e.g. the GPS) provide only partial coverage of the environment. The proposed system consists of a mobile application connected to a LoRa transceiver via Bluetooth Low Energy (BLE); through the app, users can send emergency requests that are re-broadcasted by other peers until reaching a rescue personnel who is able to handle the emergency. Three novel contributions are provided in this paper. First, we provide extensive measurements of the LoRa technology, and investigate its suitability for ECS-related applications. Second, we describe the LOCATE prototype and the enabling algorithms; specifically, we propose a novel multi-hop dissemination algorithm which maximizes the probability to deliver an emergency request to the destination (e.g. rescue personnel) within a user-defined temporal threshold, while minimizing the number of message re-transmissions. Third, we extensively evaluate the LOCATE performance through OMNeT++ simulations, assessing the capability of the dissemination protocol to spread out the emergency requests over large-scale scenarios, and through experiments, assessing the capability of LoRa-based trilateration technique to provide accurate GPS-free localization. The results demonstrate that the LOCATE protocol is able to minimize the time required to handle the emergency when compared to other dissemination strategies (e.g. flooding, continuous, once-per-contact), and they highlight the considerable improvement provided by the LoRa technology over other D2D solutions available on COTS smartphones (e.g. Wi-Fi Direct).