自编码直接序列扩频机制与改进模型研究

【作者】 陈仲林；

【导师】 周亮；

【作者基本信息】 电子科技大学 ， 密码学， 2004， 硕士

【摘要】 现代电子对抗技术可以准确估计直接序列扩频通信的载波频率、符号周期甚至扩频码本身,为达到更低截获率和更高抗干扰的通信目的,必需研究新的直扩通信技术。自编码直扩通信是Lim Nguyen在1999年首次提出的一种利用信源数据构作扩频序列的随机直扩技术,此技术在自编码扩频机制,最佳扩频序列设计、自编码同步等方面还需要进一步认识和研究。本文总结了自编码直扩通信的研究成果,补充完善了部分理论推导,特别对自编码扩频存在的特有自干扰现象进行了仿真分析并且对三种主要的性能提升技术――纠错码技术、预编码技术和信源随机化处理进行了技术总结。本文论证了自编码直扩通信的可行性,指出自干扰是导致通信性能门限较高的主要原因。本文针对基本自编码直扩系统的扩频序列无严格的0/1平衡特性,建立了三种都能达到扩频序列平衡、但系统误码性能不同的改进模型。通过对基本模型的理论分析,本文指出在高信噪比时应采用纠错码外部反馈改进型,而在低信噪比时应采用纠错码级联改进型,仿真结果验证了这一结论。此外本文还介绍了改善性能的预编码技术和信源随机化技术。本文对自编码直扩单用户和多用户系统中扩频序列的相关性和碰撞概率进行了分析和计算机仿真,指出改善相关性的一个有效方法是由信源数据挑选已证明有良好相关性的已知序列,如Gold序列,为减少多用户应用时的序列碰撞概率,挑选函数的取值应具有等概分布特性并且有尽可能大的序列集合。更多还原

【Abstract】 Modern electronic counterwork technic could exactly estimate the carrier frequency , signal period, even the pseudo-random (PN) sequence itself of direct sequence spread spectrum (DSSS). It is urgency to investigate a new DSSS to achieve lower Low Probability of Detection(LPD) and higher Anti-Jamming.At 1999, Lim Nguyen first brought forward a novel self-encoded spread spectrum(SESS) system, which spread spectrum sequence is full builded by the source data. It needs to better understand and study on some problems,such as the best codes of its spread sequence, communication synchronization and so on.In this article, in addition to summarize some results, renew some formulas, especially simulate and analyze the self-interference(SI) unusual existing in SESS, we sum up the mostly performance improvement technology, namely error-correct code,transmitter-based precoding and source randomness. On this way we demonstrate SESS’s feasibility and point out it is the SI which is main reason leading to high communicate performance limit. Aiming at spread sequence isn’t strict balance in the basic SEDS system, we set up three improved models,which can make the sequence balance ,at the same time their BER performances is different. We consider,via analyzing the basic model in theory, that it should adopt mod. External model when there is high SNR, otherwise it should adopt SEDS+ECC mode.which is verified in latter simulation. Additional two improved models,namly transmitter precoding and source randomness are also introduced.Comparing some SESS systems which has different co-correlation on single user and multi-user conditions, we indicate the efficient means is to pick out the proved good correction sequences,such as Gold sequence, to amend correlation. To reduce sequences collision in multi-user condition, The corresponding value of function G should have equal distributing and SESS sequence family should as large as it can.更多还原