發(fā)布時(shí)間：2019-04-04 13:00

【摘要】：隨著用戶(hù)數(shù)量的不斷擴(kuò)大以及多媒體業(yè)務(wù)的大量涌現(xiàn),第三代移動(dòng)通信系統(tǒng)已不能滿(mǎn)足未來(lái)移動(dòng)通信的發(fā)展需要,因此3GPP組織啟動(dòng)了3G技術(shù)的長(zhǎng)期演進(jìn)(Long Term Evolution, LTE)工作。OFDM作為L(zhǎng)TE物理層的關(guān)鍵技術(shù)之一,不僅能夠提供較高的數(shù)據(jù)傳輸速率,而且還具有較強(qiáng)的抗多徑衰落和抗符號(hào)間干擾能力。但是,OFDM在具有這些獨(dú)特優(yōu)勢(shì)的同時(shí),存在著對(duì)載波頻偏十分敏感的缺點(diǎn)。另一方面,OFDM在接收端一般采用相干檢測(cè),準(zhǔn)確的信道狀態(tài)信息必不可少,然而在高速移動(dòng)場(chǎng)景下,傳播路徑復(fù)雜,信號(hào)衰落嚴(yán)重,信道己由傳統(tǒng)的慢時(shí)變轉(zhuǎn)變?yōu)榭鞎r(shí)變,因此,信道估計(jì)是OFDM系統(tǒng)需要解決的又一關(guān)鍵問(wèn)題。基于此,本文研究分析了快時(shí)變信道條件下的OFDM系統(tǒng)頻率同步與信道估計(jì)技術(shù)。 論文首先介紹了OFDM系統(tǒng)模型和無(wú)線(xiàn)信道的仿真模型,在此基礎(chǔ)上,分析推導(dǎo)了載波頻偏對(duì)OFDM系統(tǒng)的影響,然后對(duì)基于循環(huán)前綴的頻率同步技術(shù)和基于訓(xùn)練序列的頻率同步技術(shù)做出了分析比較,研究了訓(xùn)練序列對(duì)頻率同步性能的影響。其次,針對(duì)快時(shí)變信道的特點(diǎn),分析了傳統(tǒng)LS算法和MMSE算法的局限性,對(duì)基于基擴(kuò)展模型的信道估計(jì)算法做了重點(diǎn)介紹,并給出了數(shù)據(jù)符號(hào)位置的信道插值算法。最后,考慮到頻率同步與信道估計(jì)技術(shù)的內(nèi)在聯(lián)系,對(duì)比分析了傳統(tǒng)聯(lián)合估計(jì)算法和基于基擴(kuò)展模型的聯(lián)合估計(jì)算法的性能差異,并且詳細(xì)推導(dǎo)了快時(shí)變信道條件下聯(lián)合估計(jì)算法的理論界。仿真結(jié)果表明,基于訓(xùn)練序列的頻率同步性能要明顯好于基于循環(huán)前綴的頻率同步性能,并且通過(guò)改變訓(xùn)練序列的種類(lèi)、長(zhǎng)度和插入位置可以進(jìn)一步提高同步性能,另一方面,基于基擴(kuò)展模型的信道估計(jì)算法以及頻偏和信道聯(lián)合估計(jì)算法在快時(shí)變信道條件下能夠提供較為理想的估計(jì)性能。
[Abstract]:With the continuous expansion of the number of users and the emergence of a large number of multimedia services, the third generation of mobile communication systems can no longer meet the development needs of future mobile communications. Therefore, the 3GPP organization initiated the long-term evolution of 3G technology, (Long Term Evolution,. As one of the key technologies in the physical layer of LTE, LTE can not only provide high data transmission rate, but also can resist multipath fading and inter-symbol interference. However, while OFDM has these unique advantages, it has the disadvantage that it is very sensitive to carrier frequency offset. On the other hand, OFDM generally uses coherent detection at the receiver, and accurate channel state information is necessary. However, in high-speed mobile scenario, the propagation path is complex and the signal fading is serious. The channel has changed from traditional slow-time to fast-time-varying. Therefore, channel estimation is another key problem to be solved in OFDM system. Based on this, the frequency synchronization and channel estimation techniques for OFDM systems under fast time-varying channel conditions are studied and analyzed in this paper. Firstly, the OFDM system model and the simulation model of wireless channel are introduced. On the basis of this, the influence of carrier frequency offset on OFDM system is analyzed and deduced. Then the frequency synchronization technology based on cyclic prefix is analyzed and compared with the frequency synchronization technology based on training sequence, and the influence of training sequence on the performance of frequency synchronization is studied. Secondly, according to the characteristics of fast time-varying channel, the limitations of traditional LS algorithm and MMSE algorithm are analyzed, and the channel estimation algorithm based on the basis extension model is introduced emphatically, and the channel interpolation algorithm of data symbol position is given. Finally, considering the inherent relationship between frequency synchronization and channel estimation technology, the performance differences between the traditional joint estimation algorithm and the joint estimation algorithm based on the basis-extended model are compared and analyzed. The theory of joint estimation algorithm under fast time-varying channel conditions is deduced in detail. The simulation results show that the performance of frequency synchronization based on training sequence is obviously better than that based on cyclic prefix, and the synchronization performance can be further improved by changing the type, length and insertion position of training sequence. The channel estimation algorithm based on the basis-spread model and the joint frequency offset and channel estimation algorithms can provide ideal estimation performance under fast time-varying channel conditions.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TN929.53

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