多用户多输入多输出系统反馈预编码技术的研究.pdf

上海交通大学 硕士学位论文 多用户多输入多输出系统反馈预编码技术的研究 姓名：李旭 申请学位级别：硕士 专业：通信与信息系统 指导教师：何迪 20090108 上海交通大学硕士学位论文 第 I 页 多用户多输入多输出系统反馈预编码技术的研究多用户多输入多输出系统反馈预编码技术的研究 摘摘 要要 MIMO（Multi-Input Multi-Output，多输入多输出）技术是指在发 射端和接收端分别使用多个发射天线和接收天线的无线通信传输技术 MIMO 技术实质上是为系统提供空间复用增益和空间分集增益，目前针对 MIMO 信道所进行的研究也主要围绕这两个方面空间复用技术可以大大 提高信道容量，而空间分集则可以提高信道的可靠性，降低信道误码率 根据发射端是否能够从接收端获得信道状态信息，MIMO 通信系统可分为 闭环 MIMO 及开环 MIMO 近年来的研究结果表明， 与开环 MIMO 系统相比， 闭环 MIMO 的系统性能，包括系统容量、信噪比、误码率等都能够得到改 善当发射端不知道衰落信道的信道状态信息（CSI）时，发射端需要使 用二维空时编码以保证各信道具有良好的性能而当发射端获得理想信 道信息时，通过预编码，MIMO 信道可被等价分解为多个 SISO 信道，降 低各种处理复杂度。

信道状态信息也使得多用户分集变为可能伴随信 道状态信息，发射端能进行有效的活动用户选择及路由选择信道信息 的获取还能显著增加系统区域容量以及总容量 本文介绍了开环 MIMO 平坦衰落信道下的信号检测技术， 主要包括空 时编码系统和空分复用系统中的信号检测技术而后，进一步介绍了闭 环系统的相关准则和反馈方式分析了单用户 MIMO 预编码技术，对预编 码系统的模型和原理进行了详细的研究讨论了基于迫零、MMSE、SVD 的线性预编码准则，为了减小系统预编码所需的反馈开销，引入具有有 限比特反馈的预编码设计的概念随后对相关的预编码选取准则及设计 方法进行了分析，并通过计算机仿真实验给出具体的性能指标为了解 决矩阵反馈复杂度高且开销大的特点，提出了一种基于 householder 变 上海交通大学硕士学位论文 第 II 页 换的迭代计算和重建方法这一方法可有效的把矩阵的反馈转化为向量 反馈，简化了反馈过程另外在多用户的环境下，对多用户 MIMO 系统下 行链路的预编码方法进行了详细的研究，给出了系统的分析模型提出 了多用户 MIMO 系统与单用户 MIMO 系统之间的异同，其中 CCI（共信道 干扰）的引入是影响多用户系统性能的重要因素。

随后，给出了多用户 预编码的两种编码准则：迫零（ZF）和信泄噪比（SLNR）准则针对用 户接收机设计复杂度高且不易实现的问题，提出一种改进方案，在简化 接收机的同时可以获得更好的系统性能该方案利用维纳滤波的预处理 方法，在发送端对发送数据进行预处理，把各用户接收机的计算任务集 中于发送端该方案中各移动用户接收机不需要预先得到其他用户的信 道信息，降低了用户接收机的复杂度，有利于提高用户终端设备的高效 节能和便携等特性仿真结果表明，与现有的方法相比此方法能有效改 善系统的误码性能，并获得更大的信噪比增益 关键词： 多输入输出，空时编码，预编码，多用户，维纳滤波 上海交通大学硕士学位论文 第 III 页 LIMITED FEEDBACK PRECODING FOR MULTIUSER MIMO SYSTEM ABSTRACT MIMO (Multi-Input Multi-Output) is a wireless communication transmission technology which equips multiple antennas in the transmitter and receiver. MIMO technology is actually to provide spatial multiplexing gain and spatial diversity gain. Many researches on MIMO are focused on these two aspects. Spatial multiplexing increases the channel capacity, and spatial diversity can improve the reliability of the communication system, the bit error rate can also be reduced. MIMO communication systems can be divided into closed-loop MIMO and open-loop MIMO depending on whether the transmitter can get channel state information from the receiver. In recent years, research results show that the former system has better performance than the latter in many aspects, including the capacity of the system, the signal-to-noise ratio, and the bit error rate and so on. When the transmitter does not know the channel state information (CSI), it needs to use the two-dimensional space-time coding to ensure that each channel has a good performance. But when the transmitter gets ideal channel information, by precoding, MIMO channel can be divided into equivalent SISO channels so that we can simplify the complexity of the algorithm. With CSI, transmitter can carry out effectively the activities of the user and routing choice. In this paper, signal detection technology over flat fading MIMO channels for open-loop was studied, including space-time coding system and space multiplexing system. Then, more detailed introduction on the related criteria and feedback methods of closed-loop system was given out, also we analysed the single-user MIMO precoding technology and did some research on its model and principles in detail. Linear precoding criterias such as ZF, 上海交通大学硕士学位论文 第 IV 页 MMSE, SVD were introduced in this paper. In order to reduce the feedback loop’s overhead, we can design the system with limited bits feedback method. After the analysis of some selection criterias for precoding design, the computer simulation also showed us a detailed result of the performance. A new approach based on householder transform was proposed to simplify the feedback complexity. It can turn the feedback from matrix to vectors. And then something about the multiuser MIMO system was researched. Some multiuser precoding criterias like ZF and SLNR were introduced. In addition, because of the complexity and difficulty in practice, a new linear precoding scheme which can simplify the receiver and improve the performance of the system is proposed for the downlink of multiuser MIMO systems. In this scheme, every mobile user doesn’t need to know the other users’ channel information with Wiener filter in the transmitter, and in addition, it can enhance the performance of the system and reduce the complexity in user. It’s helpful to improve the characteristic such as efficiency, economy and portability of the mobile terminal. Simulation results show that the proposed method can improve the performance of BER compared with some existing schemes well. KEY WORDS: Multiple-Input Multiple-Output (MIMO), Space-time Coding, Precoding, Multi-user, Wiener filter 上海交通大学硕士学位论文 第 VII 页 缩略语表 符号符号 说明说明 B3G （Beyond the 3rd Generation） 超第三代移动通信系统 BER （Bit Error Rate） 误码率 BPSK （Binary Phase Shift Key） 二进制相移键控 CDMA （Code Division Multiple Access） 码分多址 CSI （Channel Status Information） 信道状态信息 ICI （Inter Channel/Carrier Interference） 载波间干扰 ISI （Inter Symbol Interference） 符号间干扰/码间干扰 MIMO （。