Study On Control Of Nonlinear Dynamics Of Information System

The information system is a complex system. Science of complexity is called the third scientific revolution following on the heels of relativity and quantum physics. The emergence of science of complexity greatly promotes the development of science in depth and indicates the new phase of awareness of human. Since nonlinearity is an important characteristic of complex system, it is the main and effective method to solve questions of complex system with theory of nonlinear dynamics. In this dissertation, control questions unsolvable with traditional method for information system, including neural information system and communicational information system, are studied from the point of view of dynamicsFirst, research on neural information system show, bifurcations of biological systems caused by variation of physiological parameters may be the reason for some neural system diseases. Hence study on stability control of bifurcation holds on an important position in neural science. In this dissertation, a new control method via washout filter controller with linear term is given to realize stability control of Hopf bifurcation in Hodgkin-Huxley neural model. By use of Routh-Hurwitz stability criterion, the range of control coefficient is derived. Further, simulation results demonstrate the effectiveness of the proposed method.Second,from the point of view of dynamics, short-term memory of neural information system works during bistable dynamic regime. And double cycle bifurcation is the onset of bistable dynamic regime. Therefore research on control of location of double cycle bifurcation may provide therapeutic approaches and theory basis for memory problems. A new control method via washout filter controller with cubic term is presented to change location of double cycle bifurcation in this dissertation. By applying of center manifold and normal form theory, we can derive the range of control coefficient of closed system. Consequently, double cycle bifurcation poiont is advanced or delayed along with control coefficient.Finally, based on the former study of two systems with definite mathematic expressions, a new control method is proposed to suppresse nonlinear dynamic behavior in Turbo iterative decoding algorithm of communicational information system. Research show there exist dynamic behaviors in Turbo iterative decoding algorithm such as bifurcation and chaos. Thus decoding performance is seriously affected. In this dissertation, control method with modified Mexican hat wavelet function is developed. By exploiting convergence property of wavelet function, decoding algorithm can avoid the dynamic behavior under low signal-to-noise condition and converges quickly to a fixed point. Simulation results show that the proposed method makes decoding complexity decreased greatly. Moreover, on average, turbo decoding algorithm presents a gain of about 0.3 dB in dynamic region, which is superior to that of the delay feedback method reported.