【作者】 杨喆；

【导师】 邱玲；

【作者基本信息】 中国科学技术大学 ， 通信与信息系统， 2009， 硕士

【摘要】 随着移动通信系统的不断演进,除传统话音业务之外的移动多媒体业务将逐渐成为未来移动通信系统中的主流业务?对于移动多媒体业务的支持,需要通信系统能够提供极高的数据速率,因此能够极大提高无线系统频谱效率的多天线技术将成为未来高速移动通信系统中的重要技术?理论证明,在点对点的多天线无线传输模型中,当发送端确知信道信息时,利用由多天线提供的额外自由度,系统可以获取可观的空分复用增益,极大提高无线通信系统的数据速率?尤其在多用户多天线系统中,除了可以获得空分增益外,由于较多用户的存在,通过多用户调度,系统可以获取多用户分集增益,使系统获得相比点对点系统更高的吞吐率?以上高速率多天线传输的实现无不极大的依赖于系统对于用户信道信息的获取,但是在实际系统中,反馈完善的信道信息会带来反馈信道无法承受的负担,因此基于有限反馈的多天线系统及其反馈策略就成为了研究的热点?本文聚焦应用于多天线系统中的有限反馈技术?首先,介绍有限反馈技术的发展方向?有限反馈的基本原则?以及现有理论分析的讨论热点,针对不同系统详细介绍不同的反馈策略,对比评价采用不同反馈策略的系统性能;其次,考虑非理想信道信息,包括信道估计误差,信道时延等非理想因素,分析其对于基于码本的多用户有限反馈系统的性能影响,针对非理想信道估计,推导得到使基于码本的多用户有限反馈系统保持固定复用增益时的信道估计性能要求,以及所需反馈比特数变化规律,针对反馈信道时延,以单用户有限反馈系统为例,分别在高信噪比场景下和低信噪比场景下分析推导由于反馈信道延时导致的吞吐率损失;再次,研究现有的LTE系统的码本设计,提出优化的码本设计,利用相关性对于码本进行重排,使系统在反馈信道存在差错的情况下,依靠码本本身的结构,减小由于用户信道和预编码矩阵失配造成的吞吐率和误码率损失?最后,在总结以上研究成果的同时,展望了有限反馈技术在未来移动通信系统中的研究前景?更多还原

【Abstract】 Accompanied by the persistent evolution of the mobile communication system, the mobile media services will gradually become the main-stream services besides the traditional voice service. In order to support the promising services, even higher data rate is urgently required, therefore multiple-input multiple-output technology, aka MIMO, which can greatly improve the spectrum efficiency of the wireless communication systems will, without a doubt ,be the killer application in future mobile communication systems. Theoretically, considerable spatial-multiplexing gain, which will highly enhance the system performance, can be extracted by taking advantage of the extra spatial freedom which is offered by the application of MIMO technology, when perfect channel state information is available at the transmitter in a point-to-point wireless MIMO transmission model. In multiuser systems, because of the multiuser diversity, even higher data rate, compared to the point-to-point system, can be achieved by proper multiuser scheduling that extracts the multiuser diversity gain. However, all of the high rate transmissions mentioned above are totally based on perfect channel state information acquisition at the transmitter. For practical systems, it is unrealistic that the receiver feedbacks the full channel information, which will be regarded as a heavy burden to the system, through the feedback channel with finite data rate. That is why limited feedback based MIMO systems as well as the feedback scheme has become the key point of the research related.In this paper limited feedback scheme in MIMO systems is discussed. Firstly, we introduce the principle, trend, as well as the main topic of limited feedback technology. In terms of different limited feedback schemes used in different systems, an comparison and evaluation is also included in the introduction. Secondly, imperfect channel state information, including channel estimation error and channel delay, is considered. In terms of channel estimation error, in order to guarantee the multiplexing gain of the codebook based multiuser limited feedback systems, the basic requirement of channel estimation as well as the law of feedback bits is analyzed and derived. Taking single-user MIMO system as an example, we analyze the throughput loss caused by feedback delay. An upper bound of throughput loss is presented in high SNR scenario, so as the formulation of the throughput loss in low SNR scenario. Thirdly, we investigate the codebook design in LTE system, and propose an new method for codebook optimization, that will reduce the system performance penalty due to the feedback error. Finally, based on the result we have got, an perspective of limited feedback in future mobile communication is given.更多还原