# An Interactive Real-Time Locating System Based on Bluetooth Low-Energy Beacon Network +
###### Abstract
This capability can then be used to implement a variety of location-based services such as determining the current physical location or distributing messages at specific points of interest. Although the iBeacon protocol is useful in providing unidirectional communication from the beacon devices to the smartphones, we find it helpful in some use cases if the reverse communication path exists (i.e., from smartphones to the beacon devices). Currently, to respond to the beacon messages, the smartphone users need to rely on their own mobile Internet connections to communicate with the backend system. Although the mobile Internet services are popular these days, in some cases they may not be always available or too costly. Even if there is a free Wi-Fi service, users are often required to log on before they can use the service. The inconvenience motivates us to design an interactive real-time locating system that only relies on the BLE technology, in which beacon devices not only broadcast beacon messages, but also receive and relay messages from the users. On receiving a message from a specific user, our beacon device detects the presence of the user, and then forwards the presence state to the backend system via the Bluetooth mesh network consisting of beacon devices. By combining the broadcast and mesh topologies in the BLE network, our experimental system can serve as an infrastructure for developers to implement a variety of interactive applications such as tracking VIP customers at the airport, or tracking an elder with Alzheimer's disease in the neighborhood. Let us describe a possible use case of our system. An airport company sets up a real-time locating system by deploying a sufficient number of beacon devices in the airport building. The locating service as part of the airport infrastructure can then be leased to airline operators. When a VIP customer of a specific airline arrives at the parking area, he opens the smartphone app provided by the airline. By receiving the beacon advertisements, the app performs locating and then pinpoints the customer on the floor plan. At the same time, the app broadcasts the presence message of the customer which includes the encrypted user ID and his current location. As soon as any beacon device discovers the presence message, it immediately forwards the presence message hop-by-hop over the Bluetooth beacon network to the backend server. As a consequence, the backend server is notified that the VIP customer has arrived at the parking area. The backend server then responds with a customer-specificwelcome message and sends it to the smartphone of the VIP customer over the Bluetooth beacon network, letting him know that the airline is aware of his presence and may send a staff to assist him. Through the Bluetooth beacon network, the airline can also provide other information to the VIP customer such as his flight status, or offer him some shopping coupons when he is about to pass through the shop having sales promotion. The VIP customer can also ask for help by pressing a button in the app. Since the real-time location of the customer is tracked, even if he has left the location where he asked for help, the airline staff can still reach him at his real-time location. Overall, this paper makes the following contributions:  
* We combine the broadcast and mesh topology options of Bluetooth to extend the applicability of beacon solutions. Smartphone users are able to interact with the backend system with a single and pervasive network technology--Bluetooth. * The user experience of Bluetooth beacon-based applications is enhanced because our system can work without smartphone users' Internet connections. In other words, smartphone users only need to turn on the Bluetooth interface to enjoy the interactive locating services without paying a time on their phone bills. * We implemented a real-time locating system solely based on Bluetooth. The feasibility and usefulness of our work have been verified through extensive experiments.