- freely available
Sensors 2018, 18(5), 1637; https://doi.org/10.3390/s18051637
- 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 dime 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.
- We identify some potential problems of deploying the Bluetooth locating system, and propose possible solutions to solve/mitigate the problems.
2. Related Work
2.1. Locating Systems and Applications Based on Bluetooth Low Energy (BLE)
2.2. Implementations of Bluetooth Mesh Networking
2.3. Bluetooth Beacon Technology
3. System Design
3.1. System Architecture
- Mobile App: a locating application running on mobile users’ smartphones. It listens to the beacon messages sent by the Mesh Beacons to figure out the current location of the mobile user. It responds to the received beacon message by broadcasting the mobile user’s encrypted presence message.
- Mesh Beacon: a beacon device that can send, receive, and relay messages in the Bluetooth beacon network. Specifically, it not only broadcasts beacon messages, but also receives presence message from Mobile Apps, and relays the presence message to the Application Server.
- Mesh Router: a gateway device between the Bluetooth beacon network and the rest of the network. It is responsible for collecting the presence messages from the Mobile Apps within the range of the Bluetooth beacon network. Once the Mesh Router receives a presence message, it will upload the presence state to the Application Server through hypertext transfer protocol (HTTP), and send an acknowledgement message back to the Mobile App in response to receiving the presence message from a specific user.
- Application Server: a shared HTTP server for the Mesh Routers from several Bluetooth beacon networks. It buffers the presence states of the mobile users, and forwards the presence states to the Cloud Database.
- Cloud Database: a real-time database in the cloud environment. It is responsible for keeping the history records of all the mobile users’ presence states.
3.2. Flow of Operations
- When the Mobile App discovers a beacon message from a certain Mesh Beacon, it locates itself based on the Major/Minor values embedded in the message. In our design, the Mobile App directly looks up a built-in location table to resolve the Major/Minor values, so the name of the detected location can be shown on the user interface immediately.
- Once the locating process has completed, the Mobile App composes the presence message containing the encrypted user ID and the detected Major/Minor values, and then broadcasts the presence message. The objective of broadcasting the presence message is to inform the backend system that this specific user has shown up at a particular location.
- As soon as any Mesh Beacon hears the presence message, it uses the managed-flood-based approach to rebroadcast the presence message. The purpose of rebroadcasting the presence message is to relay it to the Mesh Router. The managed-flood-based approach can make sure that once a specific presence message has been broadcasted by a Mesh Beacon, the Mesh Beacon will not rebroadcast it again.
- When the Mesh Router hears the presence message originated from a certain Mobile App, it uploads the content in the presence message to the Application Server. Meanwhile, it sends an acknowledgement message back to the Mobile App by broadcast.
- When any Mesh Beacon hears the acknowledgement message, it rebroadcasts the message by using the managed-flood-based approach again. The purpose of rebroadcasting the acknowledgement message is to relay it to the Mobile App.
- (Continue from item 4) When the Application Server receives the presence state from the Mesh Router, it forwards the presence state to the Cloud Database. In the Cloud Database we are able to see the locating history for all the mobile users.
- When the acknowledgement message from the Mesh Router has been received at the Mobile App, the Mobile App displays a welcome message indicating that the backend system is aware of the user’s presence.
3.3. Messages in the Beacon Network
- Type 1: beacon messages sent by the Mesh Beacons
- Type 2: presence messages sent by the Mobile Apps
- Type 3: presence messages forwarded by the Mesh Beacons
- Type 4: acknowledgement messages sent by the Mesh Router.
4. Implementation and Experiments
4.1. Implementation and Deployment of Our Prototype System
4.2. Experiment 1
4.3. Experiment 2
4.4. Experiment 3
4.5.1. The Communication Range of Bluetooth Beacons
4.5.2. Contention on Advertising Channels and Interference from Wi-Fi
4.5.3. Problems Related to a Large Deployment Area
Conflicts of Interest
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|Mobile App||Apple iOS version 10.2|
|Mesh Beacon and Mesh Router||RedBear Duo development board (with Bluetooth V4.1 and IEEE 802.11n Wi-Fi)|
|Application Server||Node.js web server on Linux Ubuntu 14.04|
|Cloud Database||Google Firebase|
|Locations||Timestamp of the Locating Record|
|User 1||User 2|
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