【作者】 闫川；

【导师】 柳平；

【作者基本信息】 汕头大学 ， 信号与信息处理， 2007， 硕士

【摘要】 当今社会，随着个人通信技术的迅猛发展，人们对通信的要求也越来越高。在第三代移动通信技术中由于基于扩频技术的CDMA具有抗干扰，抗多径等优越性，越来越受到人们的关注，而对一个扩频系统，信源端的扩频码性能将直接影响到系统的性能，因此就信源端来说，提高扩频码的性能将成为扩频通信系统的关键。混沌动力学的发现为扩频序列的研究提供了新的思路。混沌现象是在非线性动态系统中出现的确定性的，类似随机的过程，这种过程非周期，是一种貌似无规则的运动，不收敛但有界，且对初值具有及其敏感的依赖性，这些独具特色的性质使得混沌在通信应用领域尤其在伪随机码的产生方面有着很好的应用前景。本文首先对扩频通信系统进行了深入的研究，分析了扩频通信系统的结构原理，在此基础上对扩频系统中的常用码进行了阐述，然后介绍了混沌的基本特点和性能分析，以序列的相关性能和方差为出发点，将混沌引入扩频通信，基于logistic混沌映射，提出了一种改进的混沌扩频序列产生方法，该方法由给定初值代入混沌映射，然后对每个迭代点进行L比特量化，通过截短得到新的混沌扩频序列。得到的序列与传统混沌扩频码和GOLD码作了比较，并在DS-CDMA系统中作了仿真验证。用同样的方法对另一经典混沌Tent映射做了类似的处理，也得到了满意的结果，由此验证了该方法的可行性。该方法不但减少了迭代次数，加快了运算速度，并且可以产生任意长度的扩频序列，地址数远远大于现有的GOLD码。系统误码率也有所降低，通过实验还得到了最优的二进制量化阶数。这些对于扩频通信中扩频码的研究和发展具有一定的参考价值。更多还原

【Abstract】 Today, with the fast fierce development of personal communication technology, people havea higher request upon communication. The CDMA system based on spread spectrum technologywill be attached more importance for its advantage of anti-jam and anti multi-access. For aspread spectrum communication, the performance of system will be directly decided by thespread spectrum code of the generator. Thus for the signal source, how to improve theperformance of spread spectrum code become an important issue for a spread spectrumcommunication system.New idea was proposed for spread spectrum sequence research by the discovery on chaoticdynamics. Chaotic phenomenon is a determinate and random process in non-linear dynamicsystem, which is non-periodic, non-convergent, but limitary, depending on initial valuesensitively. This particular characteristic of chaos makes it fit for communication especially inapplications of generating the spread spectrum codes. The research on spread spectrumcommunication was firstly conducted in this article, secondly the theorem of communication wasanalyzed, and the usual code in spread spectrum system was also studied. Then finally the basiccharacteristic of chaos was introduced. It was substituted in the spread spectrum communicationaccording to the correlation and variance of spread spectrum sequence.Based on the logistic-map, an optimized method of generating the spread-spectrumsequences was proposed. In this method, an initial value was given and iterated in the logisticmap, then L bit qualification was done to every point, in this way, new spread spectrum sequencewould be achieved by shorten. It was compared with conventional chaotic code and GOLD codeand finally simulated in the DS-CDMA systems. Another classic chaotic map (Tent map) wasdone by the same way; a satisfied answer was got too. By this method, the advantage was asfollows: the iterative times were reduced and the calculating speed was improved. Thespread-spectrum sequences could be reshaped with any length. The address number of thesesequences was larger than gold sequence in being and The BER (bit error ratio) was reduced. Atlast the best quantification order was got by many experiment. These results had some referencevalues to the research on spread spectrum code in spread spectrum communication.更多还原