Estimation And Control Over Wireless Communication Network

In wireless networked control system, WNCS , the real-time information exchanges take place over a wireless network between plant, sensors, controller, and actuators. As the deployment of wireless networks allows fully mobile operation, flexible installation and rapid deployment, while reducing maintenance costs, control over wireless network has many compelling applications. However, as in all forms of control over networks, WNCS is also a challenging task because wireless network inevitably introduces random delays, data packet dropouts, clock jetter, etc. in the feedback loop, which will degrade the system performance and even make system unstability, and the wireless channels are even more unreliable because of time varying channel gains and interferences, fading channels, nodes mobility and time-varying network topologies. As it's impossible to slove these problems by using conventional control theory directly, new theories and methods need to be developed.In this dissertation, the properties of packet delays in wireless network are analysised firstly. The medium access control, MAC, of IEEE802.11b is modeled as two dimension markov process. Based on this model, the probability distribution of packet delays in unsaturated situation can be obtained. Hide terminal and packets forwarding are inevitable in ad hoc wireless network, the properties of packet delays in such wireless network are also studied. A node access control strategy is proposed to keep the end to end packet delays in desired range.State estimation is impormant in the implemention of networked control, so the problem of remote state estimation over lossy network links is researched. To realize remote estimation with sensor scheduling and measurement loss, a time-varying Kalman filter is proposed. Statistical properties of the estimation error are studied, the expectation of the estimation error covariance is proved to have upper and lower bounds, convergence conditions and methods to calculate these bounds are also presented. The optimal sensor selection probability is also found by using gradient search method. When the remote estimator schedules the transmission of sensors using optimal probability, the best estimation performance can be obtained. Several numerical examples are proposed to verify the results.To realize real-time control and obtain optimal performance, suitable control strategy should be adopted. In this dissertation, a new time-slotted control strategy to wireless networked control system is presented. By dividing the control period into several time slots, and using these time slots to drive the actuator, the networked control system can be modeled as a type of linear jump system, and the model of WNCS is simlified. Time-slotted networked control system can be modeled as markov jump linear system when slots switching and packet dropouts are markov processes, stochastic stability condition of time-slotted networked control system is established by using linear matrix inequality (LMI) approach, and H_∞controller synthesis method is obtained by solving a convex optimization problem.Synthesis algorithms of LQR states feedback controller and output feedback controller for time-slotted networked control system are presented, the parameters which have effect on system performance are analysised by numerical simulation. To deal with the time-varing of packet delays in WNCS, time-slotted controller with adaptive adjust is proposed, in which a packet delays predictor is used to predictive packet delays distribution in current session, decision maker implements synthesis algorithms to get new control parameters, and time-slotted controller updates to new parameters to obtain optimal performance.Networked controller with bounded delays is also studied in this dissertation, stochastic stability and synthesis method to robust H_∞controller of such system are presented by finding optimal solution to a coupled linear matrix inequalities.Finally, the results of the dissertation are summarized and further research problems are pointed out.