94 two 6LoWPAN Gateways, a DSNS, a database and a user client as shown in Figure 6-5. The localisation and tracking WSN is the data generator of the system. The outgoing packets contain the RSSI values, which are collected by the target device and transferred to the 6LoWPAN for further processing. The 6LoWPAN Gateway has a location calculation module built-in to obtain the location (xT,yT) of the target
device in the field. The DSNS aims to redirect information for both users and WSNs so that they can find each other and helps to build the connection if necessary. The User client is able to query the DSNS to localise and track using the WSN. All results received are real-time. The components and environment are discussed in detail below.
Figure 6-5 Demonstration system Structure
Localisation and Tracking WSN: The localisation and tracking WSN consists of an
offline tag (measurement object), an online tag (target object) and four Border Routers.
95 1. Border Routers (Figure 6-6 a) are stationary sensor nodes placed in the corners of the target field. They work as receiving towers to continuously listen to the channel so that all the messages from mobile targets can be received and report the RSS values to the 6LoWPAN Gateway. We choose RedBee mc1322x as the demonstrate device.
Figure 6-6 Example of demonstration sensor devices
2. The offline tag (Figure 6-6 b) is designed to draw a radio frequency map of the current field. It is a sensor network device that contains a RF module and a digital accelerometer. For the offline measurement phase, the target area will be segmented into numerous areas depending on the size, for example 8×8 and 2× 5. Then we need to hold the offline tag and start a “snake” path starting from (Figure 6-7) from one corner and stop (detected by accelerometer) at each line crossing to send out a message so that the Border Routers are able to record the radio frequency. Once the offline phase is completed, the RSSI data will be sent to 6LoWPAN Gateway to generate a radio map for the online phase. The tag nod is designed and made by IDC.
96 Figure 6-7 Offline phase "snake move"
3. The online tag (Figure 6-6 c) is designed for tracking the current position of the object. It sends out the RSSI by its RF module to the Border Routers to help them to obtain the RSS, the Border Routers will then send the RSS value to the 6LoWPAN Gateway. Unlike in the offline phase, the accelerometer’s aim is to detect the movement of the device and to wake up the RF module to start sending the message. This increases system efficiency and extends battery life. The online tag is also from IDC.
6LoWPAN Gateway: It consists of three parts: a sensor device acts as a hub to
receive the data from Border Routers; a coordinate calculation module; and a gateway between the two networks. The hub is a Border Routers coordinator and it manages the connection with the 6LoWPAN Gateway. All the data is collected by hub and passed through to the 6LoWPAN Gateway. The 6LoWPAN Gateway of FSN is the component to convert the 6LoWPAN packets to standard IP packets and pass to the coordinate calculation module to calculate the target location by 3NN (3 nearest neighbours) algorithm. We choose two 2008 iMac desktop running windows 7 with Instant Contiki 2.5 loaded by VMware Player to act both 6LoWPAN Gateways. The screenshots of both 6LoWPAN working terminals are shown in Figure 6-8 and Figure 6-9.
97 Figure 6-8 6LowPAN Gateway 1
Figure 6-9 6LowPAN Gateway 2
DSNS: The DSNS is the address redirection server in the FSN. Although the
98 is to provide an indexing mechanism for user to search and choose the desired data source. The DSNS is deployed on a desktop PC in this demonstration.
Figure 6-10 Choose data source
Client: The User Client is an index and presentation software, which is able to
connect to the DSNS and select their desired data source (Figure 6-10). After that, the DSNS will help build the connection and start the data transmission. Users are able to save the data for future use by clicking the start button. The coordinators are displayed in the client interface in Figure 6-11.
99 Figure 6-11 User client with two data source displayed
Discussion
6.4
A 6LoWPAN enabled Federated Sensor Network is a system that uses lightweight IPv6 to identify the individual sensor node in the WSN. It is good for the communication between the sensor node in a WSN and the applications from an external network. In this chapter, the system architecture of the 6LoWPAN Federated Sensor Network is introduced and compared with the solutions presented in Chapters 4 and 5. This is followed by a demonstration for iNet localisation and tracking project, which is an object localisation and tracking system. We involved the 6LoWPAN enabled Federated Sensor Network into the project to support an infrastructure of a future indoor tracking system. From the result, the proposed system shows an ability to handle multiple 6LoWPAN WSNs and provide a functional indexing service for both users and WSNs by DSNS. With the increased popularity of IPv6, applications are able to exchange data with 6LoWPAN devices more conveniently and easily. That is the original design of the Internet of things.
100
SensorML Description
Chapter 7.
for System Implementation
In this chapter, we discuss how to achieve the three types of Federated Sensor Network (FSN) described in Chapters 4-6 using Sensor Model Language (SensorML). After introducing the SensorML, the three FSN systems will be presented in combination with SensorML profiles, including the profiles rules and the detailed description for the three FSN architectures.
Background and motivation
7.1
As one of the Internet of Things (IoT) framework, it is important to present our FSN to the world so we can get more and more people and applications to join our system. The best way for promoting a product is to join a big standard and to be compatible with others, so we choose SensorML as the one to describe our system. With its help, programmers can easily complete any type of FSN and get it deployed on a server for consumer purpose.
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7.1.1 SensorML
SensorML from Open Geospatial Consortium (OGC) is the general model with eXtensible Markup Language (XML) encodings for sensors, observations and measurements. It is developed under the Sensor Web Enablement (SWE) project. The SWE is focused on developing standards to enable the discovery of sensors and corresponding observations, exchange, and processing of sensor observations, as well as the tasking of sensors and sensor systems. SWE presents many opportunities for adding a real-time sensor dimension to the Internet and the Web. This has extraordinary significance for science, environmental monitoring, transportation management, public safety, facility security, disaster management, utilities' Supervisory Control and Data Acquisition (SCADA) operations, industrial controls, facilities management and many other domains of activity. The functionality that OCG has targeted within the Sensor Web includes (Simonis E., 2008):
1. Discovery of sensor systems, observations, and observation processes that meet our immediate needs.
2. Determination of a sensor’s capabilities and quality of measurements.
3. Access to sensor parameters that automatically allow software to process and geo-locate observations.
4. Retrieval of real-time or time-series observations and coverage in standard encodings.
5. Tasking of sensors to acquire observations of interest.
6. Subscription to and publishing of alerts to be issued by sensors or sensor services based upon certain criteria.