A Ubiquitous Model for Wireless Sensor Networks Monitoring
Summary (3 min read)
1. Introduction
- Wireless sensors are tiny devices that are able to measure several environmental and vital variables.
- A new emerging technology called wireless sensor networks (WSNs) has become a trend in technological research [11, 19].
- Due to the heterogeneity of recent mobile devices and platforms, the construction of a Web service to interconnect these devices in a platform independent way require open technologies and protocols.
- Section 3 introduces and describes the overall system architecture and the interaction between its modules.
3. System Architecture
- The proposed four-tier architecture is based on the following main components: a Web service, a gateway, a relational database, and a mobile client application.
- RESTful architectures are based on HTTP to communicate over the network.
- Based on this analysis, several fields of the database were defined to store all the relevant data needed to remotely access and monitor a WSN.
- The gateway can have more than one IPv6 interface and at least one 6LoWPAN interface to allow the communications between the regular IPv6 node and the WSN.
- For real-time monitoring the mobile application sends requests over the Internet to a HTTP service running on the gateway computer that query the WSN and responds directly to the smartphone.
4. Construction of the Proposed Model
- The proposed model architecture was constructed in a real environment with all the needed components for a full WSN monitoring solution.
- The development process of the server-side components of the proposed model is described, including a database, a Web service, a push notifications system, and an end-to-end connectivity between mobile devices and sensor nodes.
4.1 Database Design
- Based on the requirements analysis, the MySQL Database Management System (DBMS) was chosen for data storage [22].
- In the context of WSNs, the performance of the database is an important issue due to the large amount of data collected by the sensors.
- The user table stores information about user credentials such as username and password.
- The third group of tables is formed by the tables sensor_data, report and data_report that store the collected data by the sensors for each parameter as well as the maximum, minimum and average values for each sensor parameter grouped by day, month or year.
- These events are scheduled to work after each day, month and year.
4.2 REST Web Service
- To enable the exchange of information between the database and the mobile devices, a RESTful Web service was built.
- The Web service has a modular architecture and generic implementation in order to be scalable and accessed through several mobile 35 platforms.
- A REST Web service can be defined as a set of resources, available through HTTP interfaces accessed using well-defined HTTP methods such as GET and POST.
- It implements the annotations presented on the specification providing a Java API for RESTful Web services development.
- The client may request the resource representation in XML or JSON media types.
4.3 Push Notifications
- One of the main features of the proposed WSN monitoring architecture is the push notification system.
- The push notification system is focused on the Android operating system because it is an open platform and integrates well the RESTful Web service and the mobile application.
- The C2DM technology is part of the Android platform and provides libraries and APIs for developing push-enabled applications.
- 38 Then, a unique registration ID is generated by the authentication server and sent to the mobile device.
- By doing this, the computational costs of polling are on the server side instead of stressing the mobile devices, resulting in significant energy and bandwidth savings.
4.4 End-to-End Connectivity
- In order to access real-time data from the wireless sensor network, a multiplatform software application was developed and deployed in the gateway computer enabling the mobile users to request sensor measures.
- When the mobile client application requests data from the 6LoWPAN WSN, the software application deployed in the gateway computer handles the HTTP request and retrieves data directly from the WSN using the UDP transport protocol.
- The requested data is transmitted through the IEEE 802.15.4 interface, connected to the gateway via USB.
- Then, the gateway 39 application converts the collected data to XML format and forwards it to the smartphone over HTTP using an IEEE 802.11g wireless network with Internet connection.
- On the client side, the Android application parses the received data and presents it to the user.
5. Android Application
- The Android OS is an open mobile operating system, developed and supported by Google.
- It was built from scratch, specifically for mobile devices and is based on Linux kernel.
- The Android System Development Kit (SDK) provides libraries and APIs that enable developers to create Android applications and take advantage of hardware capabilities available on the devices using Java programming language.
- Through the APIs, developers can use functionalities such as text messaging or accelerometers in order to build richer and immersive applications.
- Since Android is an open platform, it integrates well with emerging technologies and Web services.
5.1 Android User Interface
- The user interface was designed following the Android User Interface Guidelines [6] in order to be consistent with the operating system interface and other Android applications.
- If the user authentication is successful, a new screen is presented with the tab bar at the top where the user could choose between three tabs: Sensors tab, History tab and Settings tab.
- At the bottom of the screen, sensed data is presented graphically as indicated by “5”.
- If the user switches to the History tab, a new screen is shown, which presents an interface that allows the user to choose a time interval as indicated by Fig.
- The settings menu provides the following application options: enable or disable data updates; define the updates frequency; and enable or disable push notifications.
6. Performance Evaluation and Demonstration
- In order to evaluate and demonstrate the architecture and mobile application, a 6LoWPAN wireless sensor network laboratory testbed was constructed.
- The motes are capable of sensing air temperature and humidity, luminosity and battery voltage readings.
- A 6LoWPAN gateway is used to provide IPv6 end-to-end connectivity between the sensor network and the Internet.
- The smartphone used to evaluate the proposed architecture and mobile application was the Samsung Galaxy S, running Android 2.3 with a 1.0 GHz CPU and a Li-Ion 1500mAh battery.
- As expected, the lower the polling rate, the lower the battery consumption of the smartphone, but more updates missed by the monitoring application.
7. Conclusion
- This paper proposed a ubiquitous wireless sensor networks monitoring solution allowing users to receive latest sensor readings as well as historical measures on their 46 smartphones.
- Since it is based on REST interfaces and XML/JSON messaging, the architecture is platform independent and supported in the majority of current mobile devices.
- The proposed architecture was evaluated and demonstrated using a real wireless sensor testbed and an Android mobile application.
- The experiments showed that the solution is reliable and the push notification system has a significant impact on smartphone’s energy savings.
- In an outdoor environment, factors such as energy management, security and weather conditions should be considered.
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"A Ubiquitous Model for Wireless Sen..." refers background in this paper
...Based on this kind of sensors, a recent network approach, known as wireless sensor networks (WSNs), has become an important field of research....
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402 citations
"A Ubiquitous Model for Wireless Sen..." refers background in this paper
...In this context, a new emerging technology called wireless sensor networks (WSNs) has become a trend in technological research [11, 19]....
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330 citations
"A Ubiquitous Model for Wireless Sen..." refers background in this paper
...It is now widely used in several areas since it provides a wide range of environment monitoring and military surveillance applications among others [1, 2]....
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