Design and Optimization of Wireless Remote Monitoring and Control System Using the ZigBee Protocol

Abstract: This thesis presents the design and the optimization of a wireless remote monitoring and control system utilizing the ZigBee protocol.From the system architecture point of view, the remote wireless monitoring and control system is mainly combined by 3 parts, the wireless sensor network, the message gateway and the web service. In order to increase the system flexibility and the reconfigurability, each part communicates with each other by using the standard communication protocols.The wireless sensor network of the system can be deployed in many different locations. The network includes the sensor module, the message relay, the control module and the network coordinator. The sensor module calculates the sensor information (e.g., temperature) periodically and sends the message to the network coordinator. If the radio link of the sensor module is not long enough to reach the coordinator, a message relay could be utilized in between to forward the message to the destination. Meanwhile, the message relay can be utilized as a control module as well. For example, when connected with the air conditioning system (radiator or ventilation), the control device can generate control signal to adjust the temperature and the relative humidity. The network coordinator is the root of the network. When the network coordinator receives the sensor information from the sensor module, it forwards the message to the connected gateway. On the other hand, the coordinator also receives the control command from the gateway. When the control command is received, the network coordinator forwards the control command to the corresponding control device of the wireless sensor network to execute the command. Generally speaking, it is the wireless sensor network part provides the sensor information and executes the control commands in the system.The gateway works as a translator and synchronizer between the wireless sensor network and the web service. It communicates with the wireless sensor network via the connection of the network coordinator. When receiving the sensor information from the wireless sensor network, the gateway forwards the message to the web service through the Internet. On the other hand, the gateway also receives control commands from the web service. When the gateway receives the control command from the web service, it forwards the command to the network coordinator of the wireless sensor network. Moreover, the gateway also works as a local monitoring and control agent. The gateway can be utilized to monitor and control the local sensor network without login to the web service. During the network deployment, the gateway needs to be equipped for each wireless sensor network. Different gateways can communicate with the web service via the Internet at the same time.The web service contains the sensor information uploaded from different locations. When the control command is received from the user configuration, the web service forwards the control command to the correct local server. From the user point of view, the web service is a website which can be accessed by a normal web browser. Users can register the website to apply for monitoring and control privilege. The monitoring function provides the graphical presentation of the sensor information from different locations. The control function of the system includes the ON/OFF control, temperature control and humidity control.In order to increase the system reliability, extra optimizations are developed in different parts of the system. In the wireless sensor network, the power consumption of the battery powered sensor module is optimized. A method is discovered to manage the network topology and the message forwarding pattern. Moreover, an alternative routing algorithm is designed which could be utilized by the coordinator to communicated with the sensor network. This method is verified to be much more efficient than the original algorithm utilized by the sensor network. Finally, a general purpose communication reliability enhancement framework is developed for the wireless sensor network. It helps the wireless sensor network to handle the exceptions without interference to the sensor network applications. In the gateway part, the Internet connection status is checked all the time. When the Internet connection is broken, sensor messages sent from the coordinators are buffered in the gateway to avoid the message lost.Finally, the remote monitoring and control system has received a nomination for the Swedish Embedded Award 2010 and been demonstrated at the Scandinavia Embedded Conference 2010 in Stockholm.