宽带卫星通信系统OFDM同步技术的研究

发布时间：2018-06-13 23:15

本文选题：卫星通信 + OFDM技术　；参考：《吉林大学》2014年硕士论文

【摘要】：宽带卫星通信己成为当前通信的新热点之一，未来的通信是建立在宽带基础上的多媒体通信。宽带卫星通信易受下雨等大气干扰影响，信道特性较差，且频谱资源紧张。正交频分复用(Orthogonal Frequency Division Multiplexing，OFDM)技术具有抗干扰能力强和频带利用率高等特点可以解决上述问题，因而适合应用于卫星通信系统实现高速传输。但是，OFDM的技术优势是建立在各子载波正交的基础上的，对同步误差极为敏感，卫星信道中的多径效应和多普勒频移都会引起同步偏差，因此本文主要研究卫星移动通信系统中OFDM的同步技术。本文首先介绍了宽带卫星移动通信信道特点，并提出本文仿真的信道模型。重点分析了多径效应和多普勒频移，选取郊区环境下宽带卫星移动通信信道模型作为本文仿真环境。而后从OFDM系统的实现过程出发，结合卫星信道特性，重点阐述了OFDM系统中同步偏差产生的原因，理论分析并仿真验证了定时偏差和频率偏差对OFDM系统的影响。采用基于训练序列的方法研究OFDM同步技术，首先进行定时同步，分析并在郊区环境卫星信道下仿真了SchmidlCox方法和Minn方法的原理和性能，在此基础上改进训练序列结构，利用其共轭对称性质实现定时估计，定时峰值尖锐，使定时同步精度有了很大提高。频率同步分为小数频偏估计和整数频偏估计两个过程，一般先进行小数频偏估计，，而后进行校正消除ICI，再进行整数频偏估计。本文深入研究了SchmidlCox的频率同步算法，并基于该算法提出了一种进行多次估值取平均的小数频偏校正方法，其估计性能更准确。对Minn算法进行了研究和性能仿真。对Moose算法和基于导频序列的算法中参数对同步性能的影响进行分析和仿真，基于SchmidlCox整数频偏估计算法的改进思想，给出由Moose算法而来的一种整数频偏估计的改进算法。最后，根据定时同步所采用的训练符号结构，提出了基于共轭关系的小数频偏估计方法和新的整数频偏估计方法，对接收端解调信号误码率进行仿真，该算法频率同步性能与Minn算法基本一致。
[Abstract]:Broadband satellite communication has become one of the new hotspots in current communication. The future communication is multimedia communication based on broadband. Wideband satellite communications are vulnerable to atmospheric interference such as rain, so the channel characteristics are poor, and the spectrum resources are scarce. The orthogonal Frequency Division Multiplexing OFDM (OFDM) technology can solve the above problems because of its strong anti-jamming ability and high frequency band efficiency, so it is suitable for high speed transmission in satellite communication systems. However, the advantages of OFDM are based on the orthogonal subcarriers, which are sensitive to synchronization errors. The multipath effect and Doppler frequency shift in satellite channels will cause synchronization errors. Therefore, this paper mainly studies the synchronization technology of OFDM in satellite mobile communication system. In this paper, the characteristics of wideband satellite mobile communication channel are introduced, and the channel model simulated in this paper is presented. The multipath effect and Doppler shift are analyzed, and the channel model of wideband satellite mobile communication in suburban environment is selected as the simulation environment. Based on the realization process of OFDM system and the characteristics of satellite channel, the causes of synchronization bias in OFDM system are discussed, and the effects of timing error and frequency deviation on OFDM system are analyzed and verified by simulation. The OFDM synchronization technology is studied based on training sequence. Firstly, timing synchronization is carried out. The principle and performance of SchmidlCox method and Minn method are analyzed and simulated in suburban environment satellite channel, and the structure of training sequence is improved. The timing estimation is realized by using its conjugate symmetry property, and the timing peak is sharp, so the precision of timing synchronization is greatly improved. Frequency synchronization is divided into two processes: fractional frequency offset estimation and integer frequency offset estimation. Generally, the fractional frequency offset estimation is carried out first, then the ICI is corrected and the integer frequency offset estimation is carried out. In this paper, SchmidlCox's frequency synchronization algorithm is studied in depth, and based on this algorithm, a new method of decimal frequency offset correction based on multiple estimations is proposed. The estimation performance is more accurate. Minn algorithm is studied and simulated. The effect of parameters on synchronization performance in Moose algorithm and pilot sequence based algorithm is analyzed and simulated. Based on the improved SchmidlCox integer frequency offset estimation algorithm, an improved integer frequency offset estimation algorithm based on Moose algorithm is presented. Finally, according to the training symbol structure used in timing synchronization, a new integer frequency offset estimation method and a new integer frequency offset estimation method based on conjugate relation are proposed, and the bit error rate of demodulated signal at the receiver is simulated. The frequency synchronization performance of this algorithm is basically consistent with that of Minn algorithm.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN927.2

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