大规模MIMO系统中抑制导频污染算法的研究

发布时间：2018-06-23 17:02

本文选题：大规模MIMO + 导频污染　；参考：《电子科技大学》2017年硕士论文

【摘要】：多输入多输出(Multiple-Input Multiple-Output,MIMO)是一种多天线技术,它可以在基站和用户之间传输多个数据流,在长期演进技术(Long Term Evolution,LTE)中,时分多址和频分多址模式都可以采用单用户MIMO来提高频谱效率。为了满足新一代移动通信(International Mobile Telecommunication,IMT)的要求,LTEAdvanced引入一种多用户MIMO技术,最大可支持8?8根收发天线,相比于单用户MIMO,它能够获得更大的空间增益、更大的系统平均吞吐率、小区覆盖程度和移动通信系统的稳定性。然而,随着无线移动设备和服务的发展,第四代移动通信系统(the 4th Generation mobile communication technology,4G)仍然无法满足应用需求,比如稀缺的频谱资源和较高的能源消耗。研究者们针对新的无线设备所带来的更高的数据速率和移动性要求开始了第五代移动通信系统(the 4th Generation mobile communication technology,5G)的研究,并且预期在2020年开始商用。所以说,5G时代就要来临了。大规模MIMO相对于4G技术能够提高数个量级的频谱效率,可以利用较大数量的天线来为数个用户在同一时频资源上提供多路信息传输,可以利用定向天线技术集中向特定的方向发送能量来最小化小区内和小区间的干扰。因而大规模MIMO成为5G研究的一个极具前途的技术。在大规模MIMO系统中,一些理论研究和仿真分析也指出了大规模MIMO存在的限制,其中使用时分双工(Time Division Duplexing,TDD)模式时一个最重要的限制因素就是导频污染问题,在一些文献中已经提出了很多在多小区蜂窝系统中抑制导频污染的研究和方法。本文中,我们分析了在TDD的大规模MIMO蜂窝小区中导频污染产生的原因并提出了几种抑制导频污染的方法。首先,简要的给出了TDD大规模MIMO蜂窝小区系统的模型,并基于此模型讨论了导频污染产生的原因和上下行链路数据收发的模式,仿真了在使用正交导频序列和非正交导频序列情况下的系统平均吞吐率。另外介绍了不同的信道估计、信道检测和预编码方式,着重分析了大规模MIMO系统中上下行链路使用匹配滤波、迫零和最小均方误差方式的系统容量性能,结果显示当天线数趋向于无限多时,匹配滤波方式的性能可以逼近最小均方误差方式。其次,为了抑制导频污染,本文提出一种联合时移和小区空间划分的导频序列分配方法(Time Shifted-Cell Sectorization Pilot Assignment,TS-CSPA),该方法通过从时域和空间域两个角度降低导频复用程度来抑制导频污染。文中推导了系统使用该方案时的等效信干比和用户可达速率。仿真结果表明提出的方法能有效的抑制大规模MIMO系统的导频污染,相比于其他几种抑制方法能够在系统性能上获得一定程度的提升。最后,本文提出了基于用户位置信息的导频序列分配方案。所提方案根据用户与基站间的距离以及其在小区基站为极点的极坐标系下的极角大小,对用户进行分层或排序并依次分配导频。该方案通过避免用户复用的导频序列距离过近,从而达到降低导频污染、提高信道条件较差的用户的可达和速率的目的。仿真结果表明,所提方案不仅能够降低系统的导频污染,还能有效缩小不同用户间的性能差距,提高了系统的公平性。
[Abstract]:Multiple-Input Multiple-Output (MIMO) is a multi antenna technology, which can transmit multiple data streams between the base station and the user. In the Long Term Evolution (LTE), the time division multiple access and frequency division multiple access mode can use single user MIMO to improve the spectrum efficiency. In order to satisfy the new generation of mobile communication network, it can satisfy the new generation of mobile communication. As required by International Mobile Telecommunication (IMT), LTEAdvanced introduces a multiuser MIMO technology to support a maximum of 8? 8 transceiver antennas. Compared to single user MIMO, it can gain greater spatial gain, greater system average throughput, cell cover degree and stability of mobile communication systems. The development of mobile devices and services, the fourth generation mobile communication system (the 4th Generation mobile communication technology, 4G) still cannot meet application requirements, such as scarce spectrum resources and high energy consumption. Researchers have begun the fifth generation of higher data rate and mobility requirements for new wireless devices. The research of the 4th Generation mobile communication technology (5G), and is expected to start commercially in 2020. So it says the era of 5G is coming. Large scale MIMO can improve the spectral efficiency of several orders of magnitude relative to 4G technology, and can use a large number of antennas for several users on the same time frequency resource. Providing multi-channel information transmission, we can use directional antenna technology to send energy in a particular direction to minimize interference between cell and cell. Therefore, large-scale MIMO has become a promising technology in 5G research. In large-scale MIMO systems, some theoretical research and simulation analysis also point out the limitations of large-scale MIMO. One of the most important limiting factors for the use of time division duplex (Time Division Duplexing, TDD) is the pilot pollution problem. In some literature, a number of research and methods to suppress pilot pollution in multi cell cellular systems have been proposed. In this paper, we analyzed the pilot pollution production in a large MIMO cellular cell in TDD. Several methods to suppress pilot pollution are proposed. First, a model of TDD large scale MIMO cellular cell system is given briefly. Based on this model, the cause of pilot pollution and the mode of sending and receiving data for uplink and downlink are discussed. The system is simulated in the case of using orthogonal pilot sequence and non orthogonal pilot sequence. In addition, different channel estimation, channel detection and precoding are introduced. The capacity performance of the system with matched filtering, zero forcing and minimum mean square error in the upper and lower links in large scale MIMO systems is analyzed. The results show that the performance of the matched filtering method can be approximated when the antenna number tends to be less than the limit. Secondly, in order to suppress pilot pollution, a pilot sequence allocation method (Time Shifted-Cell Sectorization Pilot Assignment, TS-CSPA) is proposed in order to suppress pilot pollution (Sectorization Pilot Assignment, TS-CSPA). This method reduces pilot pollution by lowering the pilot multiplexing degree from the time domain and space domain. The simulation results show that the proposed method can effectively suppress pilot pollution of large scale MIMO system, and can improve the system performance to a certain extent compared with several other suppression methods. Finally, the pilot sequence based on user location information is proposed. The proposed scheme is based on the distance between the user and the base station and the size of the polar angle in the polar coordinates of the cell base station. The proposed scheme is stratified or ordered and assigned the pilot in turn. This scheme can reduce pilot pollution and improve the channel condition by avoiding the distance of the pilot sequence of the user reused. The simulation results show that the proposed scheme can not only reduce the pilot pollution of the system, but also effectively reduce the performance gap between different users, and improve the fairness of the system.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN919.3

【参考文献】