二维扩频关键技术研究

【作者】 潘文生；

【导师】 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】 直接序列扩频(DSSS)是第三代移动通信的核心技术,本文主要讨论的广义二维扩频技术(2DSS)是直接序列扩频与多载波码分多址(MC-CDMA)技术的有机结合,它是移动通信领域中一种新兴的扩频多址技术。 广义二维扩频将正交频分复用(OFDM)应用于CDMA中,使之同时具有这两者的优点。它先将原始数据进行DS扩频,再进行离散多载波扩频,将信息调制到相互正交的子载波上传输。这一技术能有效地抗多径引起的符号间干扰(ISI),并且有频率分集的优点,在移动通信领域中具有广阔的应用前景。 本文在第二章提出了一个较为完整的广义二维扩频系统总体模型,并通过对接收机和发射机的分析阐明了广义二维扩频的基本原理。 为了提高数据传输率,本文在第三章将M-ary扩频与广义二维扩频技术有机的结合起来,提出了M-ary二维扩频技术,给出了接收机和发射机模型。并在瑞利衰落信道条件下分析了该方法的性能。 在第三代移动通信技术中,为了克服多径传输引起的频率选择性衰落,通常采用RAKE接收机进行直接序列扩频信号的接收。RAKE接收机先将各个多径的信号分别检测出来,然后利用各种不同的合并技术将各个检测出来的信号合并后恢复出发射的原始信息。当多径延时小于RAKE接收机的分辨率时,RAKE接收机不能准确捕获出每一条径,且RAKE接收机需要捕获每一条径,其计算十分复杂。考虑到直接序列扩频是广义二维扩频的一种特例,利用广义二维扩频接收信号的方法,本文提出了时频二维联合解扩DS-CDMA信号的算法。 本文第四章详细的阐述了时频二维联合解扩DS-CDMA信号算法的基本原理,并给出了该算法的接收机结构和信道估计方法。为了充分利用多径能量,本文对DS-CDMA信号的时频二维联合解扩算法提出了改进。最后本文在不同的信道条件下,利用COSSAP通信仿真软件,对DS-CDMA信号的不同解扩算法进行了仿真对比。仿真结果表明在多径时延小于RAKE接收机分辨率的情况下,由于RAKE接收机能分辨的每一条多径,从时域上看由两条或两条以上不同时延的多径组成,从频域上看其有频率选择性,本文提出的时频二维联合解扩算法的性能优于理想的RAKE接收的性能。更多还原

【Abstract】 Direct sequence spread spectrum (DSSS) technology is the key technology for the third generation mobile communication systems. In this paper, we discuss the general two-dimensional spread spectrum (2DSS) technology, which is the combination of DSSS and multi-carrier code division multiple access (MC-CDMA). This is a novel spread spectrum access method in mobile communication.2DSS applies orthogonal frequency division multiplexing (OFDM) into CDMA, thus it has advantages of both of them. It spreads the original data stream by DSSS, then spreads the spread signal by discrete multi-carrier (DMC) technology, finally, modulates them to orthogonal sub-carrier for transmission. This technology will have brilliant future for its efficiency in canceling ISI and its advantage of frequency diversity.A whole model of 2DSS is present in the second chapter and its function is showed by analysis of its receiver and transmitter.In order to improve the rate of transmitting information, the M-ary 2DSS is proposed in the third chapter. It is the combination of M-ary spread spectrum and 2DSS. The models of its receiver and transmitter are drawn. And we analyze its performance under Rayleigh channel.Among technologies concerning the third generation mobile communication, the rake receiving technology is accepted in order to counteract the frequency selective fading caused by the signal multi-path propagandizing. The rake receiver detects all the multi-path signals respectively, and combines all the detected signals to recover the transmitted information by the transmitter. When the delay between multi-paths is less than the resolving power of the rake receiver, the receiver can’t acquire each path accurately, and the receiver has to acquire each path that makes the receiver complicated. Considering that the DSSS technology is a special example of the 2DSS technology, a de-spread method of DS-CDMA based on time-frequency 2DSS is brought forward in the paper.The basal principle of the de-spread method of DS-CDMA based on更多还原