Adaptive controllers for level-crossing sampling: Conditions and comparison

When wireless sensors are used for control purposes (e. g. room temperature control), energy efficiency of the sensors is of great interest, because the energy must come from a (limited) battery or from energy harvesting. Since message transmission is the most critical point regarding energy efficiency, event-based sampling is a typical method for reducing the message rate. Levelcrossing sampling, also known as send-on-delta sampling, is the most popular type of event-based sampling. Some technical processes are time-variant. The controller parameters should then be updated regularly to reach good control performance. Adaptive controllers are able to estimate the current process parameters and optimize the controller parameters automatically. Adaptive control and event-based sampling have hardly been examined together. One focus of this paper is the analysis of preconditions which must be fulfilled to apply adaptive controllers in conjunction with level-crossing (or event-based) sampling sampling. Further, performance measures are discussed which are the basis for a qualitative comparison of such controllers. This paper finally compares two adaptive control strategies with respect to level-crossing sampling.