【摘要】：正交頻分復(fù)用(Orthogonal Frequency Division Multipletxing,OFDM)技術(shù)由于其在抵抗碼間串?dāng)_(Inter-Symbol Interference,ISI)以及頻譜的利用率上有著巨大的優(yōu)勢而聞名,從而在現(xiàn)代的通信技術(shù)中得到了廣泛的應(yīng)用。然而,做出該貢獻的最大“功臣”是該技術(shù)的子載波間的正交性,該正交性的出現(xiàn),使得不同子載波在頻譜上相互重疊。伴隨著最近幾年相關(guān)技術(shù)的增長,OFDM技術(shù)的應(yīng)用越來越廣泛,它已成為第4代移動通信(4th Generation,4G)的關(guān)鍵技術(shù)。然而,無論哪一項技術(shù)都會有著自己的不足之處,OFDM技術(shù)也不例外,它同樣存在這一些缺點:由于OFDM系統(tǒng)在子載波間是相互重疊的,以及對子信道間的正交性的嚴格要求,使得該系統(tǒng)對頻偏變得十分的“恐懼”,換句話說,假如子載波之間的正交沒有得到百分之百的滿足,那么將有可能導(dǎo)致其存在載波間干擾(Inter-Carrier Interference,ICI)。隨著近幾年通信以及各領(lǐng)域技術(shù)的不斷增長,人們對通信技術(shù)的要求也在不斷地提高,頻譜資源的需求也不斷增加,從而導(dǎo)致子載波之間的間隔被不斷的變小,那么可想而知的是,正交性變得更加的脆弱,ICI的程度更嚴重。因此,研究載波間干擾消除技術(shù)就顯得十分有必要。本文以O(shè)FDM系統(tǒng)為主要的研究背景,通過對載波間干擾消除算法為核心進行研究,在前人提出的消除算法的基礎(chǔ)之上進行了改進。論文的主要工作內(nèi)容包括:1、深入研究理解OFDM系統(tǒng)的不足之處,著手分析造成OFDM系統(tǒng)ICI的主要原因,以及ICI對OFDM系統(tǒng)在性能上的影響,并從數(shù)學(xué)公式推導(dǎo)上分析ICI對系統(tǒng)造成的具體的影響。2、介紹國內(nèi)外對于ICI消除算法的研究,從理論分析和仿真兩個方面來進行算法性能的比較。其中,主要的研究算法有:基于頻域的編碼技術(shù)的自消除算法、時域加窗算法、基于雙路徑下共軛消除算法(Conjugate Cancellation,CC)等。3、針對頻域的編碼技術(shù)的自消除算法,做兩個方面改進。第一,針對該技術(shù)在頻譜利用率上的不足進行了改進,使得由傳統(tǒng)的50%的效率提升到75%。該方法的主要思想是:將發(fā)送信道在經(jīng)過IFFT之后運用信號處理知識將奇偶載波分開發(fā)送,這樣由于載波頻偏的特性,使得前半段發(fā)送的奇載波的頻偏因子只有后半段的偶載波的頻偏因子的一半,而后半段偶載波再進行傳統(tǒng)的編碼自消除技術(shù)。第二,在性能以及頻譜的利用率上進一步做了改進,使得頻譜利用率相比與傳統(tǒng)的編碼技術(shù)不降低的情況下誤碼性能得到顯著提高。該方法的主要思想是:在基于第一個方法的基礎(chǔ)上,在發(fā)送端,傳輸三段數(shù)據(jù)即:奇數(shù)載波數(shù)據(jù)、偶數(shù)載波數(shù)據(jù)、偶數(shù)載波數(shù)據(jù)。由于后兩段數(shù)據(jù)的重傳,可以利用他們來大致粗估計出相應(yīng)的頻偏因子,在接收端進行補償。
[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.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN929.53

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