Data collection and visualization

the packet (data packet or control packet). This part also performs the packet decryption in case secured transmission is used.

Packet Injector puts the required command from Network Control in a request packet and sends this packet to the destination node(s).

Database stores all information of nodes and interfaces with other components.

Alert checks the pre-defined conditions and sends warning messages to users when a condition is matched.

Logger records all pre-defined values of nodes to a file after the database is updated.

The GUI has many panels to provide the interface between users and the network. It includes the following parts:

o Statistics Measurements contains processes which calculate packet reception rate, message rate, etc.

o Topology Viewer displays the network topology with related metrics.

o Data Display shows all the information extracted from packets and measurements in a table.

o Graph Display shows the conventional values after analyzing values such as temperature, humidity, or battery level of each node in charts.

o Network Control allows users to manage each node by sending specific commands to that node.

o Network Status displays the status of the network and configuration of nodes.

o Setting is the interface where users can change the parameters of the logging process, and customize displayed parameters of the network topology, etc.

All these parts will be discussed in detail in the next sections.

Because WiSeCoMaSys is always in operation with an embedded application of WSN, it can be used in many applications such as:

Habitat monitoring [WPT⁺08].

Environmental condition monitoring in data warehouses, storages or harbors [SWT⁺09-08].

Tracking and monitoring of logistic items inside containers or other transport vehicles [JBL⁺07] [TKB⁺06].

5.2 Data collection and visualization

5.2.1 Data collection

As mentioned in Chapter 4, the environmental conditions are sensed and packed in data packets for transmission from a source node to the WiSeCoMaSys (which acts as the sink). Along the path to the destination, besides the original information, some additional information can be added to the data packet for many purposes:

Debugging: debug parameters can be added into the data packets so that they can be analyzed by WiSeCoMaSys.

Management: information such as hop count can be updated.

Aggregation: multiple sensed values of many nodes can be packed into one data packet to reduce the overhead.

WiSeCoMaSys allows analyzing all information sources above.

5.2.2 Centralized control and management

WiSeCoMaSys is a centralized system, which bridges the information flow between users and the deployed WSN. The advantage of a centralized system here is that users can have a full picture of the running sensor network. The control and management can be carried out from users or complicated algorithms can be executed to find the best solution and reconfigure the network.

However, WiSeCoMaSys is designed in such a way that it can influence each individual node in the network with separate parameters. This helps users to achieve a better customization and optimization.

5.2.3 Data visualization

In this section, the visualization including network topology and sensed data are described.

5.2.3.1 Topology building Vector aggregation

In order to build a real-time network topology, WiSeCoMaSys uses the technique of vector aggregation which is popular in [SUR10] [RJD⁺08] [MVi10]. The key point of this technique is that each data packet has to carry some additional information of the BNN and RSSI between a node and its BNN. In the design discussed in Chapter 3, this information is also included in the data packet. Because WiSeCoMaSys receives all data packets from all nodes, it can build the topology by using the BNN field (shown in Figure 5.2). Moreover, WiSeCoMaSys also supports displaying the backup topology because the ODEUR⁺ routing protocol [SWT⁺09-08] has a backup BNN.

This technique requires that the link quality (e.g., RSSI or LQI) has to be available in lower layers. If the hardware platforms do not support RSSI or LQI measurement, an arbitrary value can be used instead of RSSI and the link quality between nodes cannot be displayed in this case.

Figure 5.2: a) Information in vector. b) Vector aggregation.

Topology viewer

In Figure 5.3, the Topology Viewer component has two panels: one topology panel displays the network topology and the legend panel is used for settings of the topology panel.

5.2 Data collection and visualization 75

Figure 5.3: Topology viewer.

In the topology panel, the status data of each node is updated when WiSeCoMaSys receives and analyzes a packet from a node. There are three kinds of nodes in this panel:

the red node is the gateway, the blue nodes are the normal nodes and the pink nodes are the anchor nodes (see the localization part in Chapter 4). Each pair of nodes is connected by a solid line with the RSSI indicating that link quality. A gradient color is used to specify the health of the link from good to bad quality: a green line means the link is good and a red one means the link is bad (see Figure 5.3).

The big light blue circle around a node indicates that WiSeCoMaSys has just received a packet from that node, while a small cyan circle indicates the node that is currently selected for management or control from the operator.

The legend panel provides an interface for users to customize the display in the topology panel. Users can choose the settings to display sensed values, backup BNN, battery, etc.

WiSeCoMaSys can also use a timer in this component to detect which nodes leave the network by setting a timeout interval. If WiSeCoMaSys does not receive any packets from a node after this timeout, it considers that the node is disconnected from the network. However, this feature only works in the automatic data mode in which nodes report packets periodically (see Chapter 4).

5.2.3.2 Data Display panel

In the design, there is a private node database for each sensor node which stores all the information WiSeCoMaSys collects from that node. Besides that, this database also contains the measured parameters which are the processed results of the Statistics Measurement.

When a data packet or control packet is received, the measurement (e.g., PRR, delay or data rate) is executed and the corresponding node database is updated. The database can be updated by the event of receiving packets or by using a timer. However, because the receiving frequency can be different in each application, WiSeCoMaSys uses receiving events. Moreover, updates based on events utilize the resources better than that based on timers, especially when the frequency of events of receiving packets is not high.

The Data Display component is a table which is seen on the tab Database of WiSeCoMaSys (shown in Figure 5.4). It has many columns and rows which display all information about the nodes such as:

Fixed information: for example, containerID and packageID when nodes are deployed inside containers.

Sensed values: temperature, humidity, battery, etc.

Status of nodes: connected or disconnected Measured parameters: PRR, message rate, etc.

Figure 5.4: Data Display component.

5.2.3.3 Graph panel

Another visual method for data is displaying the parameters in graphs. This can be used to observe the change of environment over time. For example, a monitoring application can be deployed to find out the point of time in a day when the temperature of goods changes most. This feature is provided in the Graph Display component of WiSeCoMaSys. The Graph Display component also has two parts: one for displaying the charts, and the other for settings (shown in Figure 5.5).

The J-Freechart library [JFC10] is integrated in this component to provide a rich feature set for the display. With this component, real time data of a specific node or multiple