The Research Of DCSK Modulation System Base On Chaos Theory

Since the 1970's, there has been a great deal of research effort spent on studying chaotic systems and the properties of the chaotic signals generated. Characterized by their wideband,impulse-like autocorrelation and low cross-correlation properties, chaotic signals are useful spread-spectrum signals for carrying digital information. chaotic signals can be generated using simple circuitries, thus lowering the cost of transceivers. Chaos communication is a rather new field in the communication research. There has been significant interest in recent years in exploiting chaotic dynamics in communications. Topics which have been studied include chaotic modulation for transmission of information, chaotic spreading codes for multi-user access in spreading spectrum system, chaotic encryption for security.More specifically,this dissertation focuses mainly on the frist topic.Frist of all, an overview of fundamentals and applications of chaotic systems is given, with particular emphasis on engineering applications to communications. The historical motivation of the use of chaos in this context is introduced. Recent advances and future challenging problems are surveyed. Based on discrete implementation of chaotic signals and traditional communication theory, we regard the chaotic signals as random variable, the error performance of CSK and DCSK in AWGN channels and the error performance of DCSK in Rayleigh fading channel is studied analytically . Then ,analysis performance expressions of the bit error rates of DCSK in Ricean channels are derived. The analytical and simulation results are compared.Finally,the scheme of time-delay-based multiple access DCSK system which F. C. M. Lau put forward is discussed in this paper.For reduce the disturb of different users ,a modified multiple access DCSK scheme which make use of the orthogonal properity of Walsh is proposed . Through combing chaotic sequences with Hadamard Matrix, transmitter generatesvery good orthogonal signals. Noncoherent detection is given at the receiver,and analysis performance expressions of the bit error rates are derived in the paper. Compared with conventional multi-user DCSK communication systems, the modified multi-user communication system which can mitigate multi-user interference effectively is better than conventional multi-user DCSK communication systems in bit error rate performance.