| Chaos, a random yet deterministic process in nonlinear dynamical system, is widely used in areas such as chaotic communications, chaotic control and chaotic life science, and many others. This dissertation, based on the theories of nonlinear dynamics and modem communications, and with an aim to apply the excellent chaos characteristics to the communication system to efficiently improve its performance, focuses its study on chaotic correlation synchronization, enhanced FM-DCSK modulation, optimal chaotic sequences designing, VD-Rake receiver and arithmetic separating of chaotic signals and noise. As a nonlinear system, the chaotic communication system will be analyzed on the nonlinear systemic theory. The rest of the dissertation will be arranged as follows.In Chapter 2, three chaos synchronization ways are surveyed. First, the principle of chaotic drive-response synchronization is introduced, and the conditions of chaos and synchronization of drive-response systems are derived. Then, the theory of chaotic coupled synchronization is presented. Computer simulations show that coupled synchronization is more simple, credible, and more robust to noise than chaotic drive-response synchronization. Finally, the synchronize schemes for digital multiple-access communication, called correlation-based synchronization, is discussed. Threshold value synchronization is proposed, and a novel method to survey the threshold-value is described. Computer simulations supports the credibility of synchronization, with the time needed for synchronization reduced by 50%.In chapter 3, two robust noncoherent chaotic digital modulation schemes are in detail described. QCSK modulation, which is based on the idea of QPSK, is introduced. By utilizing the main advantages of orthonormalization and power conservation from Hilbert transformation, it is found that bit error rate is close to that of DCSK system, but transmission speed is one time higher than that of DCSK system, and the system's output variance is effectively reduced.Another method to reduce the BER of the DSCK system is the FM-DCSK modulation. Compared with DCSK modulation, the FM-DCSK modulation changed the chaotic signals with random magnitude into the signal with constant magnitude and random frequency, thus the systemic noise performance is achieved. In Enhanced FM-DCSK technique, instead of transmitting only one information-bearing signal after the reference signal, N bits will be transmitted using the same reference and the date rate is increased. The performance of the system using Enhanced FM-DCSK technique is evaluated in context of noise, multipath channels.In Chapter 4, the performance of asynchronous systems with multilevel spreadingcodes based on periodical repetition of quantized chaotic time series is presented, focusing on the DS-CDMA systems. Some computer simulations for four kinds of chaos-based sequences are given to examine the results that chaos-based sequences outperform the classical spreading sequences (maximum-length and Gold sequences) and the chaos-based sequences from the Chevbyshev maps (k=3,7,11) is the best among them. As the result of these optimization effort, two design means toward sequences optimization are obtained, in which one is based on the entropy theory, the other is on minimizing the average possible error. The design results arise from the simulations.Some key techniques for chaos-based DS-CDMA systems are studied in Chapter 5. Systemic optimizing is achieved by combining the three main parts respect to systemic performance under the conditions that the bit error rate is minimized. Optimizing arithmetic and Optimizing results is shown. With the notion of variable step-size in reference [105], a variable step-size decorrelating Rake detector, which is robust against the variation of the power of received signals, is proposed. The system characteristic with VD-Rake is much better than that with D-Rake.Finally, in Chapter 6, the noise reduction methods based on manifold decomposing for chaotic communication schemes ar...
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