Design Of Chaotic System And Its Application In Secure Communication

The chaos theory,relativity theory and quantum mechanics are known as the three most famous scientific discoveries of the physics field in the last century.The foundation of chaos theory has not only extended the research area of nonlinear theory,but also provided a new technique for many research fields such as medicine,economy and engineering.For example,the traditional secure communication systems have many shortcomings including vulnerable to interference,high energy consumption in terminals and limitation of frequency band.A chaotic system has the properties of easy implementation,unpredictability and ergodicity.With these significant properties,the chaos-based secure communication systems can reduce or even overcome these shortcomings of traditional secure communication systems.With the fast development of chaos theory,researchers found that many existing chaotic systems have performance drawbacks in practical applications.First,the chaotic ranges of many existing chaotic systems are small and discontinuous.This means that there are many periodic windows in these chaotic ranges.Small interference to the parameters may make the parameters fall into the periodic windows and this will lead to the corresponding chaotic systems loss chaotic behaviors.Besides,many existing chaotic systems have low levels of complexity.This may lead to that their chaotic behaviors can be estimated using some artificial intelligence techniques.These drawbacks of existing chaotic systems may cause the defects of chaos-based practical applications.To accommodate these drawbacks of existing chaotic systems,this thesis proposes a high-dimensional(HD)chaotic system construction method.This method can produce new HD chaotic systems using lower dimensional chaotic systems as seed maps.Using different chaotic systems as seed maps,this method produces many different examples of HD chaotic system.Property analysis and performance evaluation are performed to these examples of new chaotic systems in aspects of the trajectory,Lyapunov exponent and sample entropy.The results demonstrate that,compared with existing chaotic systems,these newly produced chaotic systems have much larger chaotic ranges,more complex chaotic behaviors,and thus are more suitable for many practical applications such as secure commination.Using the newly produced HD chaotic systems,this thesis further proposes a newdifferential chaos shift keying(DCSK)secure communication system.This system can transmit two bits of data using the same reference signal in one signal frame.The first half of a signal frame is the reference signal while its second half is the information signal.In the sender,a time delay bock is used to implement continuous signal transmission.In the receiver,the transmitted data are recovered by demodulating the signal frames.This thesis calculates the theoretical bit error rates of the proposed system in noisy channels using the Gaussian estimation method,and simulates the proposed system in the MATLAB software.The comparison results demonstrate that the proposed secure communication system has simpler structure,smaller bit error rates and more stable system structure than several existing secure communication systems such as the HE-DCSK and RS-DCSK.