Study of Event-based Sampling Techniques and Their Influence on Greenhouse Climate Control with Wireless Sensors Network

Abstract

During last years, event-based sampling and control are receiving special attention from researchers in wireless sensor networks (WSN) and networked control systems (NCS). The reason to deserve this attention is due to event-based strategies reduce the exchange of information between sensors, controllers, and actuators. This reduction of information is equivalent to extend the lifetime of battery-powered wireless sensors, to reduce the computational load in embedded devices, or to cut down the network bandwidth (Miskowicz, 2005). Event-based systems are becoming increasingly commonplace, particularly for distributed real-time sensing and control. A characteristic application running on an event-based operating system is that where state variables are updated asynchronously in time, e.g., when an event of interest is detected or because of delays in the computation and/or communication tasks (Sandee, 2005). Event-based control systems are currently being presented as solutions to many control problems (Arzen, 1999); (Sandee, 2005); (Miskowicz, 2005); (Astrom, 2007); (Henningsson et al., 2008). In event-based control systems, it is the proper dynamic evolution of system variables what decides when the next control action will be executed, whereas in a time-based control system, the autonomous progression of the time is what triggers the execution of control actions (Astrom & Wittenmark 1997). Current distributed control systems impose restrictions on the system architecture that makes difficult the adoption of a paradigm based on events activated per time. Especially, in the case of closed-loop control using computer networks or buses, as happens with field buses, local area networks, or even Internet. An alternative to these approaches consists of using event-based controllers that are not restricted to the synchronous occurrence of controller actions. The utilization of synchronous sampling period is one of the severest conditions that control engineers impose on the software implementation. As discussed 14