OFDM系统中ICI消除算法的研究

发布时间：2018-12-23 18:07

【摘要】：正交频分复用(Orthogonal Frequency Division Multipletxing,OFDM)技术由于其在抵抗码间串扰(Inter-Symbol Interference,ISI)以及频谱的利用率上有着巨大的优势而闻名,从而在现代的通信技术中得到了广泛的应用。然而,做出该贡献的最大“功臣”是该技术的子载波间的正交性,该正交性的出现,使得不同子载波在频谱上相互重叠。伴随着最近几年相关技术的增长,OFDM技术的应用越来越广泛,它已成为第4代移动通信(4th Generation,4G)的关键技术。然而,无论哪一项技术都会有着自己的不足之处,OFDM技术也不例外,它同样存在这一些缺点:由于OFDM系统在子载波间是相互重叠的,以及对子信道间的正交性的严格要求,使得该系统对频偏变得十分的“恐惧”,换句话说,假如子载波之间的正交没有得到百分之百的满足,那么将有可能导致其存在载波间干扰(Inter-Carrier Interference,ICI)。随着近几年通信以及各领域技术的不断增长,人们对通信技术的要求也在不断地提高,频谱资源的需求也不断增加,从而导致子载波之间的间隔被不断的变小,那么可想而知的是,正交性变得更加的脆弱,ICI的程度更严重。因此,研究载波间干扰消除技术就显得十分有必要。本文以OFDM系统为主要的研究背景,通过对载波间干扰消除算法为核心进行研究,在前人提出的消除算法的基础之上进行了改进。论文的主要工作内容包括:1、深入研究理解OFDM系统的不足之处,着手分析造成OFDM系统ICI的主要原因,以及ICI对OFDM系统在性能上的影响,并从数学公式推导上分析ICI对系统造成的具体的影响。2、介绍国内外对于ICI消除算法的研究,从理论分析和仿真两个方面来进行算法性能的比较。其中,主要的研究算法有:基于频域的编码技术的自消除算法、时域加窗算法、基于双路径下共轭消除算法(Conjugate Cancellation,CC)等。3、针对频域的编码技术的自消除算法,做两个方面改进。第一,针对该技术在频谱利用率上的不足进行了改进,使得由传统的50%的效率提升到75%。该方法的主要思想是:将发送信道在经过IFFT之后运用信号处理知识将奇偶载波分开发送,这样由于载波频偏的特性,使得前半段发送的奇载波的频偏因子只有后半段的偶载波的频偏因子的一半,而后半段偶载波再进行传统的编码自消除技术。第二,在性能以及频谱的利用率上进一步做了改进,使得频谱利用率相比与传统的编码技术不降低的情况下误码性能得到显著提高。该方法的主要思想是:在基于第一个方法的基础上,在发送端,传输三段数据即:奇数载波数据、偶数载波数据、偶数载波数据。由于后两段数据的重传,可以利用他们来大致粗估计出相应的频偏因子,在接收端进行补偿。
[Abstract]:Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multipletxing,OFDM) technology has been widely used in modern communication technology because of its great advantages in resisting inter-symbol crosstalk (Inter-Symbol Interference,ISI) and spectrum efficiency. However, the greatest contribution is the orthogonality between the subcarriers of the technique, which makes the different subcarriers overlap each other in the spectrum. With the increase of related technologies in recent years, OFDM technology has been used more and more widely. It has become the key technology of the 4th generation mobile communication (4th Generation,4G). However, no matter which technology has its own shortcomings, OFDM technology is no exception, it also has these shortcomings: because the OFDM system overlaps each other in subcarriers, and the strict requirements for orthogonality between sub-channels, In other words, if the quadrature between subcarriers is not satisfied 100%, it may lead to the existence of intercarrier interference (Inter-Carrier Interference,ICI). With the continuous growth of communication and technology in various fields in recent years, the demand for communication technology is also increasing, and the demand for spectrum resources is also increasing, which leads to the continuous decrease of the spacing between subcarriers. What can be imagined then is that orthogonality becomes more fragile and ICI is more serious. Therefore, the study of inter-carrier interference cancellation technology is very necessary. In this paper, OFDM system as the main research background, through the inter-carrier interference cancellation algorithm as the core research, on the basis of the previous proposed elimination algorithm to improve. The main contents of this paper are as follows: 1. Deeply study and understand the shortcomings of OFDM system, analyze the main causes of ICI in OFDM system, and the influence of ICI on the performance of OFDM system. And from the mathematical formula analysis of the specific impact of ICI on the system. 2, introduced the domestic and foreign research on the ICI elimination algorithm, from the theoretical analysis and simulation to compare the performance of the algorithm. Among them, the main algorithms are: the self-cancellation algorithm based on frequency-domain coding technology, the time-domain windowed algorithm, the conjugate elimination algorithm based on dual-path (Conjugate Cancellation,CC), etc. Make two improvements. Firstly, we improve the efficiency of this technology from 50% to 75%. The main idea of this method is to separate the odd and even carriers by using the signal processing knowledge after the transmission channel passes through the IFFT, which is due to the characteristics of the carrier frequency offset. The frequency offset factor of the odd carrier transmitted in the first half is only half the frequency offset factor of the even carrier in the second half, and the second half of the even carrier carries on the traditional coding self-cancellation technique. Secondly, the performance and spectrum efficiency are further improved, which makes the performance of BER improve significantly compared with the traditional coding technology. The main idea of this method is: on the basis of the first method, three segments of data are transmitted at the transmitter: odd carrier data and even carrier data. Because of the retransmission of the latter two segments of data, they can be used to roughly estimate the corresponding frequency offset factors and compensate at the receiving end.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.53

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