二维扩频通信及其抗干扰技术研究

【作者】 戚骥；

【导师】 李少谦； 唐友喜；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2005， 硕士

【摘要】 当前多载波无线通信技术得到了广泛的研究,二维扩频技术在时域、频域上对原始信号同时进行了频谱扩展,是对传统的一维时域直接序列扩频和多载波扩频的推广。本论文全面研究了二维扩频通信系统在衰落信道下的实现方案,分别提出了导引辅助的相干检测和时频码片级差分检测方案以充分利用其时频域扩频结构,并对扩频系统抗宽带干扰的原理及算法进行了深入研究。本文首先介绍了多载波通信系统的特点以及二维扩频技术的研究现状,总结了需要进一步解决的问题,指出了本文的研究方向。本文的第二部分针对衰落信道下二维扩频通信系统进行了研究。目前对衰落信道下的二维扩频通信系统研究尚浅,已有的研究都是基于加性高斯白噪声(Additive White Gaussian Noise, AWGN)信道或假定已知衰落信道参数,而其非相干检测方案的研究也很少。本文从可实现的角度出发,对相干检测的二维扩频通信系统提出了一种数据和导引符号重叠的相干解调方案,对非相干检测的二维扩频通信系统,在简述了码片级差分检测优点的基础上提出了时频码片级差分的二维扩频通信方案,分析了上述两种方案在多径衰落信道中的误码率性能,并对两种方案的性能进行了对比,分析结果表明时频码片级差分检测同时具有抵抗信道时间和频率双选择性衰落的能力,并体现了优于相干解调方案的性能。扩频通信以其抗干扰能力强著称,近年来,宽带的非平稳干扰对扩频系统的影响越来越引起人们的重视,在本文第三部分中,重点研究了一类常见的宽带类型干扰——线性调频干扰,详述了采用时频分析抑制宽带干扰的原理,提出采用仿射傅里叶变换替代现有大多数文献采用的分数阶傅里叶变换以改进现有的线性调频干扰抑制算法并对仿射傅里叶变换算法进行了仔细的研究和改进,得出了可用于实际信号处理的高效算法并分析了算法的设计原理,对于将该算法用于二维扩频作了简单的分析。最后,本文分析了窄带干扰对二维扩频通信系统在AWGN 信道下的影响,证明了二维扩频通信对抗窄带干扰的性能和一维扩频相近,指出扩频码的设计是需要进一步研究的工作。更多还原

【Abstract】 Multicarrier wireless communications have been widely investigatedrecently, and two dimensional spread spectrum technology spreads theoriginal signal in time and frequency domain simultaneously, which is theextension of traditional direct sequence spread spectrum and multicarrierspread spectrum. This dissertation will propose two methods which canfully utilize the time-frequency spread spectrum structure to implement2D-SS over fading channel, one is pilot symbol assisted coherentdetection and the other one is time-frequency chip-level differentialdetection. The theories and algorithms for the spread spectrum system toresist wideband interference have also been deeply discussed in thisthesis.First we introduce the characteristics of multicarrier wirelesscommunications and the research background of two dimensional spreadspectrum, and then summarize the questions to be further studied.2D-SS system under fading channel will be studied in the 2nd part ofthis dissertation. There aren’t many researches in this field, all theexisted results are based on AWGN channel or on that the channelparameters are already known, and the study of 2D-SS non-coherentdetection method is still weak. In this paper, we propose two practicable2D-SS schemes, one is pilot symbol assisted coherent detection whichadds the pilot symbol and the data symbol orthogonally, another one ischip-level time-frequency non-coherent detection precedes with a briefintroduction of the merits of chip-level differential detection. The BERperformance of these two schemes over multipath fading channels areanalyzed and compared, the results indicate that time-frequencychip-level differential detection is capable of resisting time and frequencydual selective fading, and is better than the coherent detection schemeproposed in this thesis in the time frequency dual selective fadingchannel.Spread spectrum communications is well known by its anti-jamming更多还原