The Influences Of The Time-delay And The Data-packet Dropout On The Stability Of Greenhouse WSN Measurement And Control System

In comparion with the wired network technique,the new-emerging wireless sensor network(WSN) technique had the advantage of flexible placement,convenient extension,self-organized network,low price, ect...Greenhouses using the WSN technique belonged to the frontier-technique of the development of facility agriculture,it was more competitive than prevalent greenhouses using the field bus technique.But, WSN was more susceptable to system time-delay and data-packet dropout.Compared with wired networks,the time-delay and the packet-dropping rate as important factors for the influence of control system stability,the analysis of the influence of WSN stability by them from researchers all over the world was not so much.Combing with the characteristics of greenhouse WSN measurement and control system,taking temperature and humidity as the research object,we established information transmission model of temperature and humidity in this paper.Then,record the single control circuit of temperature and humidity by incorporating the decouping technique.In order to ensure the stability of the whole greenhouse WSN measurement and control system,we used for reference from the method of research for the time-delay and the packet-dropping rate by network control system,in combination with Lyapunov stability and special conditions for greenhouses,judged the stability of the temperature and humidity control model.Then,the linear matrix inequality with time-delay variable and the packet-dropping rate variable can be derived,which meets the stability of measurement and control systems.Finally,by using LMI(linear matrix inequality) of Matlab to feasible solution analysis,the critical value of the time-delay and the packet-dropping rate were calculated,which can provide theoretical evidence to establish stable greenhouse WSN measurement and control systems.The WSN measurement and control system simulation model can be established through the TrueTime box.And through the simulation experiment,we got the following results:when the time-delay and the packet-dropping rate of greenhouse WSN measurement and control system were less than the calculated critical value,the whole system was stable;the system stability decreased with the time-delay and the packet-dropping rate increased;when the time-delay and the packet-dropping rate were more than the calculated critical value,the whole system was unstable and can break down.