摘要
扩频通信具有良好的保密性和抗干扰能力,在现代通信系统中得到了广泛的应用,而以混沌为基础的扩频通信技术在近年也得到了广泛的研究。
混沌动力学的发现为扩频序列研究提供了新的思路。混沌是在非线性系统中,由于其系统内部相互作用所产生的类随机过程。这种过程是非周期的,是一种貌似无规则的运动,虽然不收敛但是有界,并且具有初值敏感性。由此可以产生数量众多相关特性优良的伪随机序列。
本文对扩频通信中PN码的随机性进行了综合研究和探讨。随后围绕着混沌数字扩频序列展开研究,系统地介绍了混沌二进制序列的产生方法、特点和应用性能。以Logistic和Tent序列为代表,为了获得扩频通信中优良的伪随机特性码组,采用了多比特抽取的量化方法。对混沌映射的迭代结果进行截断和量化处理,分析了混沌序列的平衡性、自相关、互相关特性及旁瓣均方值、峰值等特性,并应用计算机仿真。结果表明混沌序列很适合作为扩频通信系统中的伪随机码,验证了混沌在扩频系统中应用的可行性。
通过分析影响扩频通信性能的关键参数,提出了扩频序列的筛选准则,给出了混沌序列的筛选方法和得到优良混沌序列码组的具体步骤,并对两种混沌序列的码组性能和传统的Gold序列作了比较和分析,分析结果得出,优选后混沌扩频序列的相关性能优于传统的伪随机扩频序列,有利于解决扩频移动通信中的抗干扰及多用户检测等关键问题,从而使混沌扩频系统的抗干扰能力和抗破译能力得到增强。
Due to excellent ability of security and anti-jamming, spread spectrum communication has a great deal of applications in modern communication system. The modulation technology based on chaos has been studied in recent years. The discovery of chaotic dynamic system offers the broad way of PN sequence. Chaos is a convinced and random kind course that appears in the nonlinear system. It is a non-periodic and an irregular course. It is not convergence but have a bound and sensitive to its initial value. So it can generate enough PN sequence with good correlation property.
This paper centers on research of the chaotic digital spread-spectrum sequence. First, we introduced the chaotic digital spread-spectrum sequence's production method, the characteristic and the application performance, and made the PN characteristic simulation on the several kinds of chaotic spread-spectrum sequence produced by chaos mappings. We take Logistic and Tent sequence as representative with traditional Gold sequence. In the comparison we study their performance of balance performance of run, performance of auto-correlation, performance of cross-correlation, performance of side lobe, performance of peak value. We can come to a conclusion that chaotic sequences adapt to the spreading codes of Code Division Multiple Access. The work showed that the feasibility of the use of chaotic sequence in Spread Spectrum Communication system.
In order to gain a good properly group of pseudorandom sequences in code division multiple access communication, an optimization algorithm based on the optimized chaotic spread-spectrum sequences is proposed. The method based on the properties of spread-spectrum sequences and multiple access performance index are presented, and 2 kinds of optimized sequences obtained by repealing a truncated and quantized chaotic time series are compared with classical Gold sequences in performance. The computer simulations show that Code Division Multiple Access system based on these optimized chaotic spreading sequences perform much better than the conventional pseudorandom ones. It is very useful in solving key problems related to correlation characteristics in Code Division Multiple Access mobile communications, such,multiple access interference and multi-user detection, so the anti-jamming ability and security of the chaotic communications are greatly improved.
引文
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