网络拥塞控制模型Hopf分岔的PD控制

网络拥塞会导致信息丢失,时延增加,甚至系统崩溃。由于无线接入网络中的时变衰落和分组错误率,使得TCP协议在网络拥塞控制更加复杂。TCP Westwood是专门为高速无线网络设计的,大大提高了网络带宽的利用率,改善了网络性能。TCP Westwood/AQM拥塞控制的连续流体流模型被引用,源端采用TCP Westwood拥塞控制协议,路由器端采用主动队列管理(AQM)机制中的随机早期检测(RED)算法。为了延迟无线接入网络拥塞控制模型中霍普夫(Hopf)分岔现象的发生,采用比例微分(PD)控制器,通过选择通信延迟作为分岔参数,分析无线网络系统中的Hopf分岔行为,并由理论分析得知当分岔参数超过临界值时系统发生Hopf分岔。利用中心流形和规范型理论,推导得出系统发生Hopf分岔的条件和反映Hopf分岔性质,方向和周期的参数,数值仿真验证理论分析的准确性,表明PD控制器的有效性。

Hopf Bifurcation in a Network Congestion Control Model Based onPD Controller

Network congestion may lead to information loss,delay increase,or even congestion collapse.Due to the time-varying fading and packet error rate in wireless access network,network congestion control is more complex with TCP protocol.TCP Westwood,which will increase bandwidth utilization and improve performance of network,is specially designed for high-speed wireless network.The continuous fluid flow model of TCP Westwood/AQM is applied in congestion control system.The source end adopts the TCP Westwood protocol,and the router end adopts the RED algorithm in the Active Queue Management(AQM)mechanism.In order to delay the onset of Hopf bifurcation,a proportional-derivative(PD)controller is used to a congestion control model of TCP Westwood/AQM.The Hopf bifurcation behavior is analyzed by choosing communication delay as the bifurcation parameter and a Hopf bifurcation occurs when the parameter passes through a critical value.The conditions of Hopf bifurcation and the parameters reflecting the nature,direction and period of Hopf bifurcation are derived by using the central popularity and normative theory.Numerical simulations verify the accuracy of theoretical analysis and show the effectiveness of the PD controller.