【作者】 蒋文娟；

【导师】 贾志成；

【作者基本信息】 河北工业大学 ， 通信与信息系统， 2007， 硕士

【摘要】 在码分多址(CDMA)系统中,扩频序列自相关和互相关特性的好坏很大程度上决定了系统自干扰(SI)、多址接入干扰(MAI)和邻区干扰(ACI)的大小,从而直接影响着系统性能。因此,扩频序列设计是扩频通信系统的核心课题之一。目前人们研究的伪随机码主要是二元码:m序列、Gold序列和M序列等。随着二元序列研究的深入,人们发现二元序列存在着如地址码数量过少,相关性能改善已经达到极限等缺点,从而无法适应移动用户数量的不断增加且无法满足用户对通信质量要求的不断提高。为了改变这种现状,众多学者开始研究多相序列,其中以日本学者Suehiro的多相序列理论较为典型,按其构造方法得到的多相序列具有更优的相关性能和更多的地址码数量。本论文首先对多相正交序列的基本理论知识进行分析,给出了序列相关性能定义,包括周期相关、非周期相关、奇周期相关特性等。以四相正交序列为例对其自相关和互相关进行计算并对序列的平衡性能进行分析,以二相序列为基础给出了四相序列平衡性的定义。接着,将伪周期的概念与多相正交序列结合,使多相正交序列的长度、序列数目在很大程度上改善了,并对改造后的序列利用蒙特卡罗方法进行了仿真,仿真结果表明:改造后的序列在误码率性能上优于原序列和64长的Walsh序列。本论文还研究了AWGN信道条件下多相正交序列在直扩系统中的应用。将QPSK调制用于直扩系统,运用Simulink工具搭建生成多相正交序列波模型的系统以及生成发射系统、接收系统和误码率仿真的系统,理论和仿真结果表明:由于接收系统每码片采样约4个点,可以获得额外增益,所以误码率仿真结果略小于理论值。最后,本论文将多相正交序列用于扩频通信系统,并对在Nakagami衰落信道中的性能进行了分析:数学分析表明其误码性能与扩频码的相关性是密切联系的。采用蒙特卡罗方法把多相正交序列扩频码在Nakagami信道中进行了仿真,在m取不同值可以模拟瑞利衰落信道、莱斯衰落信道,当m取到一定大的值时衰落明显减小。更多还原

【Abstract】 In Code Division Multiple Access ( CDMA ) systems, the auto-correlation and cross-correlation properties of the spreading sequences employed play an important role on the level of the self-interference(SI), multiple access interference(MAI) and adjacent cell interference(ACI),and therefore directly influence the performance and capacity of the systems. Therefore, the spreading sequences designs are one of the key points of the spreading-spectrum communication systems. At present the main spreading sequence are duality sequences, it includes m sequence, Gold sequence and M sequence. The research for duality sequences have been abroad and thoroughly. But the duality sequences have some disadvantages that there are few address-codes and the correlation properties can not be improved further. Therefore, the increase of mobile users and higher communication quality can not be satisfied. To change the actuality, a lot of scholars begin to study polyphase sequences. The polyphase sequences construction method of Suehiro from Japan is typical. According this method, polyphase sequences with more excellent correlation properties can be gotten and more address-code can also be gotten.First of all, in this thesis, the basic theory knowledge of polyphase orthogonal sequences is given and the correlation properties of polyphase sequences are studied detailedly, including the periodic correlation property, aperiodic correlation property and the odd periodic correlation property. Especially, the auto-correlation and cross-correlation properties of quadriphase sequence are computed and analyzed. According to duality sequences, the balance definition of quadriphase sequence is given.Next, the concept of pseudoperiodic sequences is associated with the polyphase orthogonal sequences; both the length and the family size of polyphase orthogonal sequences are extended. The polyphase sequences are simulinked by using Monte Carlo method. The result of simulation indicates that the BER performances of the extended sequences are better than the original sequences and the length of 64 Walsh sequence. The applications of polyphase orthogonal sequences to the DS-CDMA systems in AWGN channel are considered in this thesis. The modulated of QPSK is used in DS-CDMA system. The model of DS-CDMA is constructed, including polyphase orthogonal sequence wave, transmitted system received system. The result of simulation shows that the BER simulation value is less than theoretic value, owing to each chip sampling of received system about four can get extra plus.In the end, the performance of spread spectrum communication system in Nakagami fading channel with polyphase orthogonal spreading sequences is evaluated: the BER of spread spectrum communication system in Nakagami fading channel is correlative to spread codes’correlation properties by mathematic analysis; Using Monte Carlo method for polyphase orthogonal sequences have simulinked. According to different m values, we can get Rayleigh channel, Rician channel, when m go beyond someone value, declining is clearly minish.更多还原