多经信道环境下LTE及LTE-A系统中的多普勒频偏估计

发布时间：2019-06-04 01:36

【摘要】：近几年来高速铁路的建设在中国如火如荼的展开,高速移动环境下的通信已成为移动通信的又一重要场景。与此同时,伴随着智能手机的普及,移动用户对于数据业务的要求越来越高。作为下一代移动通信标准,3G长期演进LTE(Long Term Evolution),需要满足在高速移动环境下正常的通话和高速数据传输业务。高速移动环境下的通信系统与低速环境有明显不同。用户与基站之间存在较高的相对速度,这会产生较大的多普勒频移和多普勒拓展。其中较为明显的变化就是相干时间缩短,无线通信信道会在短时间内发生剧烈变化。为了抑制多径信道带来的频率选择性衰落,LTE系统下行链路采用正交频分复用技术(Orthogonal Frequency Division Multiplexing, OFDM)作为无线传输技术。然而,OFDM系统对频率偏移十分敏感,即便是很小的频率偏移都会引起较大的误码率。所以,在高速移动环境下,多普勒频偏估计补偿已经成为LTE系统下行链路中亟待解决的重要问题。目前,LTE中OFDM系统的频偏估计在低速场景已经较为成熟,但是高速移动带来的多普勒频率偏移(Carrier Frequency Offset, CFO)比低速场景下更严重,现有的低速场景下的算法已经无法满足系统要求。由于提出新算法难度较大,本文着重研究经典的频偏估计算法,并在经典算法的基础上进行改良,找出更加适合这种特殊环境下的改进算法。在改进载波频率估计算法之前,我们需要充分考虑OFDM系统的原理结构、高速移动环境下信道的模型参数等影响因子。论文在总结当前已存在的经典频偏估计算法的基础上,着重研究了两种算法。其中一种算法估计后在频域补偿,这种算法是在传输符号的序列内插入导频,接收端通过导频序列进行频偏估计。另一种SC算法估计后在时域上进行补偿,这种算法是在一串符号前面插入训练符号用来估计频偏。在这两种算法的基础上,我们提出了三种改良的或适应特殊信道环境的频偏估计算法。
[Abstract]:In recent years, the construction of high-speed railway has been in full swing in China, and the communication in high-speed mobile environment has become another important scene of mobile communication. At the same time, with the popularity of smartphones, mobile users have higher and higher requirements for data services. As the next generation mobile communication standard, 3G long-term evolution LTE (Long Term Evolution), needs to meet the normal call and high-speed data transmission services in high-speed mobile environment. The communication system in high speed mobile environment is obviously different from that in low speed environment. There is a high relative velocity between the user and the base station, which will produce large Doppler shift and Doppler expansion. The obvious change is that the coherence time is shortened, and the wireless communication channel will change dramatically in a short time. In order to suppress the frequency selective fading caused by multi-path channel, (Orthogonal Frequency Division Multiplexing, OFDM) is used as wireless transmission technology in downlink of LTE system. However, the OFDM system is very sensitive to frequency offset, even a very small frequency offset will cause a large bit error rate. Therefore, in high-speed mobile environment, Doppler frequency offset estimation compensation has become an important problem to be solved in the downlink of LTE system. At present, the frequency offset estimation of OFDM system in LTE is more mature in low speed scene, but the Doppler frequency offset (Carrier Frequency Offset, CFO) caused by high speed movement is more serious than that in low speed scene. The existing algorithms in low-speed scenarios have been unable to meet the requirements of the system. Because it is difficult to propose a new algorithm, this paper focuses on the classical frequency offset estimation algorithm, and improves it on the basis of the classical algorithm to find an improved algorithm more suitable for this special environment. Before improving the carrier frequency estimation algorithm, we need to fully consider the principle structure of OFDM system, the model parameters of the channel in high-speed mobile environment and other influencing factors. On the basis of summing up the existing classical frequency offset estimation algorithms, this paper focuses on two algorithms. One of the algorithms compensates in the frequency domain after estimation. This algorithm inserts the pilot into the sequence of the transmission symbol, and the receiver carries on the frequency offset estimation through the pilot sequence. Another SC algorithm compensates in time domain after estimation. This algorithm inserts training symbols in front of a series of symbols to estimate frequency offset. On the basis of these two algorithms, we propose three improved or suitable frequency offset estimation algorithms for special channel environments.
【学位授予单位】：北京邮电大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN929.5

【共引文献】