Modeling Of Communication Systems For NCS Over IP Network And Its Application

Internet has been developed rapidly and becomes an important part of today's social life. Because of the great requirement of network applications, the network system is often immersed in the status of congestion. In existing TCP/IP protocols, TCP relies on packet dropping as the indication of congestion. This mechanism is appropriate for TCP traffic which has little or no sensitivity to delay or loss of individual packets. Packet dropping mechanism may lead to poor performances for low-bandwidth delay-sensitive applications like telnet, web-browsing. To improve the performances of IP networks with low-bandwidth delay-sensitive TCP traffic, this thesis introduces the packet marking as the indication of congestion and builds a dynamic model with RED/ECN for a simple IP network. This model is well validated by comparing its analytical results with the NS simulation results.Networked control systems (NCS) have become an important domain in the field of process control engineering. To describe the external characteristics of complicated communication subsystem in NCS, this thesis proposes a simplified dynamic model, consisting of a variable-period sampler and variable transport delay, to denote the packet dropping in data transmission and network-induced time delay. This simplified model has been well validated by simulation results.Based on the above simplified model, this thesis constructs a simulation system for a single-input-single-output NCS and presents the event driven version of regular PID control algorithm. Simulation results expose the limitation of the event driven PID when heavy data dropping occurs. Therefore, this thesis proposes an improve scheme. Simulation results show its strong robustness.