【作者】 王树斌；

【导师】 张春业；

【作者基本信息】 山东大学 ， 通信与信息系统， 2011， 硕士

【摘要】 随着科技的发展,基于3G技术的个人移动通信已经进入实用阶段,基于CDMA的扩频技术是第三代无线个人通信系统的一项主要技术。CDMA通信系统的扩频技术的基础是要构造一个具有良好互相关和自相关特性的扩频码,并要求扩频码具有尽可能多的编码序列,以满足更多用户的需求。扩频序列的性能直接影响到扩频系统的性能,因此选用的扩频序列成为扩频通信系统的关键所在。现在扩频通信系统使用的是由最大长度线性移位寄存器生成的m序列和Gold序列,但它们仍然存在序列长度有限和数量有限等缺陷。混沌动力学的发现为扩频序列的使用和研究提供了崭新思路,混沌是在非线性动态系统中出现的确定性的非周期的现象,类似随机的过程,是一种貌似无规则的运动,有界但不收敛,对初值具有及其敏感的依赖性。正是由于混沌表现出的非周期,宽频谱和对初始值非常敏感的特性,可以用它来产生长度非常大的序列和数目巨大的码元,这使得混沌所产生扩频伪随机码在扩频通信领域有着比传统扩频码更好的特性,使频谱资源得到最大限度的复用。本文分析传统在用的m序列和Gold序列的各项性能,并分析了Tent, Chebyshev, Logistic,改进Logistic等典型混沌映射的性能。在此基础上用一种新的方法产生混沌序列,那就是借助于连续混沌的离散化产生混沌序列,这使已经被人们广泛深入研究的连续混沌可以用来产生混沌序列,用于产生混沌序列的混沌动力学模型可选择的范围大大增加。本文设计了一个切换混沌系统和一个超混沌系统,并按照一定规则,对混沌信号进行处理,以此为基础产生了混沌扩频序列,对产生的混沌扩频序列的自相关、互相关特性及旁瓣、峰值、移位性能等特性进行了分析。对于切换混沌系统和超混沌系统我们用全新的实现方式,基于FPGA平台进行实验验证,在示波器上观测到了与计算机仿真完全一致的结果。基于FPGA平台的实现更加稳定,可靠,具有更好的可移植性,为混沌扩频序列的真正实际应用进行了探索。随后我们在MATLAB平台上对优选后的扩频序列进行了实验分析,参照蒙特卡罗通信系统仿真模型,通过对影响扩频通信性能的关键参数进礼优选,对其误码性能进行了分析和仿真。证明所设计的切换混沌系统序列和超混沌序列比一般混沌序列和Gold序列具有较好的性能。这对扩频通信中的扩频码的研究和发展有一定的参考价值,也为混沌理论在通信系统中的工程应用提供了一定的实验依据,有利于促进混沌通信的发展。更多还原

【Abstract】 With the development of science and technology, the 3G-based individual mobile communication has been put into pragmatic period and the CDMA-based spread spectrum has become the key technology in the third generation of the individual mobile communication system. The basis of the CDMA spread spectrum is the construction of the sound code with mutual correlation and self-correlation. And the code should contain spread spectrum sequence as more as possible in order to meet the demand of more customers. The performance of the spread spectrum sequence has the direct influence to the spread spectrum system and the spread spectrum sequence has become the key issue in spread spectrum communication system. The present spread spectrum communication system uses the m-code and Gold-system generated from the maximal length linear shift register, yet they still have the drawbacks of length and quantity limitation. The discovery of the chaotic dynamics provides the new ideas for the use and research of the spread spectrum sequence. Chaos is the certain acyclic phenomenon appeared in the non-linear dynamic system and it’s similar with the stochastic process. It looks like irregular motion and it is limited yet not converged. It has sensitive reliance to the original values. Based on its non-periodicity, wide frequency and sensitivity to the original values, the chaos can be used in producing very long sequence and large-quantity code element. It makes the pseudo-random code has more advantaged than the traditional spread spectrum communication system and it makes the multiplexing to the maximum.This paper analyses all kinds of performance of the traditional m-code and Gold-mode and performance of the typical chaos mapping, such as Tent, Chebyshev. Logistic and the improved Logistic. On this basis, a new method can be used to produce chaos sequence, i.e. the chaos sequence can be produced by applying the discretization of the continuous chaos. Thus, the widely used continuous chaos can be used to produce chaos sequence and the range of the chaotic dynamics model can be greatly extended. This paper designs a switching chaos system and a ultra chaos system. The systems deal with the chaos signals according to certain rules and they produce chaos spread spectrum sequence. This paper also analyses characteristics of the mutual correlation, self-correlation, sidelobe, crest value and shift performance. We apply for the new methods to shift the chaos system and the ultra chaos system and we have got the result from the use of the FPGA platform, which is in accordance with the computer simulation. The application of FPGA platform is more convenient, reliable and transferable, and it explores the practical application of chaos spread spectrum sequence. Later we apply the experimental analysis on the optimized spread spectrum sequence on the MATLAB platform. By referring to the Monte Carlo communication system, we select the key parameters in influencing spread spectrum communication performance and analyse and simulate the error code performance. It proves that the designed shift sequence has more advantages in distinguishing the chaos sequence, ultra-chaos sequence, normal chaos sequence and Gold sequence. It provides great value for the research and development of the spectrum-spreading code and certain experimental evidence for the application of chaos system in communication system, which is quite beneficial for the development of the chaos communication.更多还原