Generating Hibird Chaotic Spectrum Sequences And Performance Analysis

Code Division Multiple Access is one kind of new and mature wireless communication technique, which has a great deal of applications in modern communication system. Designing a sufficient number of spread spectrum codes, which have excellent characteristics, are the basis of CDMA technology in order to meet the needs of many users. Commonly used in CDMA systems address code is generated by the maximum length of a linear shift register sequences such as m and Gold sequences, though easily to implement they have a length and quantity limited number of defects.The discovery of chaotic phenomenon and the maturity of chaotic theory offer the broad way of PN sequence. The chaos phenomenon is one kind of convinced and random course that appears in nonlinear system, which has the characteristic of a non-periodic, non-convergence and highly sensitive to initial values. Making use of chaotic mapping can generate enough PN sequence with good correlation property.This paper mainly centers on research of the chaotic digital spread-spectrum sequence. With Logistic and Chebyshev sequence represented, the balance, relevance and side-lobe peak and mean square value and other properties of performance of chaotic sequences are analyzed and simulated. On the basis of study, the optimization algorithm was complied to prepare for optimizing the chaotic sequence, and the optimal sequences are applied to CDMA system model, finally gives the BER performance in single user and multi-user circumstances under Additive White Gaussian Noise channel. The simulation results show that these chaotic sequences are suitable as address code in the CDMA communication system.Based on the analysis of the performance of chaotic sequence, aiming at overcoming the shortcoming that the spreading spectrums sequences generated by traditional single chaotic map has low complexity and poor performance against by intercepted, a method for generating chaotic spread-spectrum sequences based on the series hybrid mapping model was proposed, then do the simulation analysis about the performance of sequence such as correlation, balance, run-length and so on. In the sequence optimization process, this paper offers a method according to the initial value area to produce source sequence as a search target. Then make the simulation in the circumstances that optimal sequences are applied to CDMA system. The results of simulation show that the chaotic spread-spectrum sequences generated by the proposed method have good performance and more secure for communication.