TDD系统中大规模MIMO导频污染削弱技术研究

发布时间：2018-09-10 14:13

【摘要】：大规模MIMO是5G中的关键技术,其阵列天线增益,能在同一时频资源下支持大量的数据流,成倍的提高系统容量和传输速率,已经成为了当今通信领域研究的热点。在TDD系统的大规模MIMO中因为上下行链路具有互易性,基站端只要获得上行预编码矩阵,下行就可以利用转置后的预编码矩阵进行传输。基站处理方便,并且能充分利用大规模MIMO的天线增益,提高系统频谱效率和能效。但是,因为导频序列有限,基站对目标用户进行导频估计的时候,就会受到相邻小区用户的干扰,出现导频污染问题,并且导频污染并不会随着基站天线的增加而降低,这严重限制了大规模MIMO多天线的性能。因此,本文从大规模MIMO TDD系统的概念和传输模式,分析多小区导频污染的原因,然后通过多小区复用不同的导频,来研究导频污染问题,最后提出改进的方案和调度流程,对导频污染进行分析验证。主要工作如下:首先,介绍课题的研究背景,对大规模MIMO系统中导频污染问题的研究现状进行归类总结,给出本文的研究意义和研究内容;从MIMO信道模型、信道容量和天线间的相关性进行分析,介绍大规模MIMO的基本模型和传输原理。分析讨论常用的用于信道检测的线性预编码,并对检测性能进行仿真分析。然后,论文对TDD系统的传输模式和导频帧结构进行了介绍,引出了大规模MIMO TDD系统中的导频污染问题。详细分析了导频污染的原因、导频污染对大规模MIMO系统性能的影响,并进行仿真验证。结果表明,存在导频污染的多小区系统,系统的可达和速率并不会随着天线数的增加而提高,仅取决于小区间的交叉增益值,交叉增益值越大,导频污染越严重。基于导频污染的分析,提出了多小区的导频复用方案,通过多小区复用不同的导频,对系统的能量效率进行分析。仿真表明高的导频复用因子可以提高系统的能量效率,进而提高系统的和速率,减轻了导频污染,但前提条件是牺牲多的导频资源。最后,论文基于导频的功率控制提出了改进的系统模型和导频调度方案。通过对小区用户的界定,将容易受到导频干扰的边缘用户进行导频的调度,从而避开了同时使用相同导频的用户。最后通过多小区线性预编码对改进方案下系统的能量效率、频谱效率和系统可达和速率进行仿真分析。仿真结果表明,相比于导频污染系统,改进方案能达到减轻小区导频污染的效果。
[Abstract]:Large-scale MIMO is a key technology in 5G. Its antenna array gain, which can support a large number of data streams under the same time-frequency resource, has become a hot topic in the field of communication. In large scale MIMO of TDD system, because of the reciprocity between uplink and downlink, the base station can transmit by transposed precoding matrix as long as the uplink precoding matrix is obtained. The base station is convenient to process and can make full use of the antenna gain of large scale MIMO to improve the spectral efficiency and energy efficiency of the system. However, because of the limited pilot sequence, when the base station carries out pilot estimation of the target user, it will be interfered by the adjacent cell users, and the pilot pollution will not be reduced with the increase of the base station antenna. This severely limits the performance of large-scale MIMO multi-antennas. Therefore, from the concept and transmission mode of large-scale MIMO TDD system, this paper analyzes the causes of multi-cell pilot pollution, then studies the pilot pollution problem through multi-cell multiplexing different pilot frequencies, and finally puts forward an improved scheme and scheduling flow. The pilot pollution is analyzed and verified. The main work is as follows: firstly, the research background of the subject is introduced, and the research status of pilot pollution in large-scale MIMO system is classified and summarized. The research significance and content of this paper are given. The correlation between channel capacity and antenna is analyzed, and the basic model and transmission principle of large scale MIMO are introduced. The linear precoding used in channel detection is discussed, and the detection performance is simulated. Then, the transmission mode and pilot frame structure of TDD system are introduced in this paper, and the pilot pollution problem in large scale MIMO TDD system is introduced. The causes of pilot pollution and the influence of pilot pollution on the performance of large scale MIMO system are analyzed in detail and verified by simulation. The results show that in the multi-cell system with pilot pollution, the reachability rate of the system does not increase with the increase of the number of antennas, but only depends on the cross-gain value of the interval. The greater the cross-gain value, the more serious the pilot pollution. Based on the analysis of pilot frequency pollution, a multi-cell pilot multiplexing scheme is proposed. The energy efficiency of the system is analyzed by multi-cell multiplexing different pilots. The simulation results show that the high pilot multiplexing factor can improve the energy efficiency of the system, thus improve the sum rate of the system and reduce the pilot pollution, but the precondition is to sacrifice more pilot resources. Finally, the paper presents an improved system model and pilot scheduling scheme based on pilot power control. By defining the cell users, the edge users who are susceptible to pilot interference are scheduled for pilot frequency, thus avoiding the users who use the same pilot frequency at the same time. Finally, the energy efficiency, spectrum efficiency and reachability rate of the system under the improved scheme are simulated and analyzed by multi-cell linear precoding. The simulation results show that compared with pilot pollution system, the improved scheme can reduce pilot pollution.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TN919.3;TN929.5

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