【作者】 李争；

【导师】 朱光喜；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2006， 硕士

【摘要】 随着无线通信需求的日益增长和实现技术的日新月异,无线通信技术向更高数据传输速率,更大系统容量,更高频谱利用率和更适合各种信道条件的方向发展。分布式系统由于能够在移动端只有单天线的情况下通过合作分集实现传统的多天线(MIMO)系统所能够带来的显著的分集增益而引起学者们越来越浓厚的研究兴趣。本文在采用合作分集的分布式系统中将空时编码引入,这种分布式空时编码系统是本文的主要研究方向。本文首先提出并分析了分布式空时编码系统的物理层信号同步问题。物理层信号同步包括定时同步和频率同步。在分布式空时编码系统中,信号同步问题有它自身的独特性,这是由于分布式空时编码系统中存在多个节点或发送端,因此可能存在多个时钟偏差以及频率偏移,使得接收端无法同时进行定时同步和频率同步。本文接下来将分布式空时分组编码与正交频分复用相结合建立起分布式空时分组编码正交频分复用系统(DSTBC-OFDM)。DSTBC-OFDM系统能抑制多个时钟偏差给系统性能带来的影响,这是因为正交频分复用技术本身对时钟偏差并不敏感。如何抑制多个载波频率偏移给DSTBC-OFDM系统性能带来的严重影响是本文研究的关键问题。本文最后提出了一种简单的频域均衡技术来抑制多个载波频率偏移给系统性能带来的影响。仿真结果表明这种均衡技术在各分布式发送端间的载波频率之差较小时具有优异的性能,同时,通过把接收端的频率设置为各发送端频率的平均值可以获得更好的性能。更多还原

【Abstract】 The world of wireless communications is rapidly evolving. New wireless technologies which improve the transmission rate, system capacity, spectrum efficiency of the wireless system and which are more adapted to channel conditions are continuing to emerge. Distributed system attracts more and more research interests because it can achieve the significant benefit of diversity as in traditional MIMO system through cooperative diversity when there is only one antenna at the mobile terminal. This thesis involves space-time coding into distributed system with cooperative diversity. The distributed space-time coded system is mainly investigated in this thesis.The thesis first proposes and investigates the problem of synchronization of signal in physical layer in distributed space-time coded system. In distributed space-time coded system, the problem of synchronization is unique. Because there exists multiple nodes or transmitters in the distributed space-time coded system, there may exist multiple timing offsets and frequency offsets. Thus, it is impossible for the receiver to synchronize to multiple transmitters at the same time.The thesis combines the distributed space-time coding with orthogonal frequency-division multiplexing to construct the DSTBC-OFDM system. The DSTBC-OFDM system can mitigate the influence of the multiple timing offsets, because OFDM is not sensitive to timing offsets.How to mitigate the serious interference caused by the multiple carrier frequency offsets in DSTBC-OFDM system is the key problem in the thesis. Finally the thesis proposes a simple frequency domain equalization technology to mitigate the interference caused by the multiple carrier frequency offsets. The simulation results show that the equalization technique is quite effective when the carrier frequency difference between the distributed transmitters is small, and moreover, by setting the receiver’s frequency to the mean value of the transmitters’frequencies, a better performance can be obtained.更多还原