# Integration of a Mobile Node into a Hybrid Wireless Sensor Network for Urban Environments +
## 3 Mobile Node
### Integration with the H-Wsn  
The data acquired by the sensors on the Mobile node are available to any user through the database, like the data from any other sensor in the static network. The Wireless Sensor Network is then transformed into a Hybrid Wireless Sensor Network (H-WSN), managing data from both static and mobile nodes indifferently. Figure 9 shows the integration of the Mobile node (in the right-hand side) with a static WSN (in the left-hand side), resulting in a H-WSN. The Receiver node acts as a mobile sink, granting coverage for the Transmitter nodes whenever 3G or Wi-Fi coverage is available without the need for multi-hop routing or dynamic relocation methods, which can reduce operating lifetime of the nodes due to increased communication. By transforming the WSN into H-WSN the resulting system gains flexibility, since a Mobile node can be deployed to obtain data from an area not covered by static nodes (for instance, in cases where some pieces of evidence make the area worth studying after the original deployment of the network). Robustness can also be increased with the use of a Mobile node to substitute malfunctioning static nodes.  
Figure 8: Frame in networked mode with gas sensors data: (**a**) Frame with data from two sensors. (**b**) Frame with data from three sensors.  
Figure 9: Integration of the Mobile node to create a Hybrid-Wireless Sensor Network.  
The external database is the input for an HMI developed for this application using LabVIEW (see Figure 10), making possible to present the information obtained by the different sensors, and related to their locations. The user can configure what sensors' information is shown, according to the deployed nodes, including static nodes. For instance, Figure 10 shows how the user can see the available measurements for CO\({}_{2}\), CO, O\({}_{2}\), NH\({}_{3}\), ozone (O\({}_{3}\)), atmospheric pressure, relative humidity and temperature, at the beginning of a route.  
The data gathered from the Transmitter nodes are presented to the user associated to their locations. In the case of the Mobile node this location is dynamic, but from the point of view of the WSN it is presented as another node. The HMI has been designed to be compatible with ruggedized tablets running Windows 7. This way, users can also move, either with the Mobile node, or on another vehicle.  
The use-case in this article is based on measuring gas levels in an urban scenario, but some other applications are feasible. The Mobile node has been designed to accept as many types of Transmitter nodes as possible, without any modifications in hardware. The Mobile node provides an interface with the network, via an additional Receiver node, and power supply by using a battery bank. Although power supply by photovoltaic panels is still possible, depending on the application it might be unpractical. So far, only the Laser node is to be integrated in the mobile node. This flexibility in the configuration of the sensor suite allows for adaptation to other applications through the modification of the set of sensors and the selection of the platform to carry the Mobile node, allowing for collaborative efforts towards Cyber-Physical System integrating sensors, vehicles or humans. For instance, search and rescue applications present opportunities for this approach [60].