双码本波束成形相关技术研究

1、 双码本波束成形相关技术研究重庆大学博士学位论文学生姓名：王丹指导教师：杨士中院士专业：通信与信息系统学科门类：工学重庆大学通信工程学院二 O一四年十月 Study on Double Codebook Beamforming Technique A Thesis Submitted to Chongqing Universityin Partial Fulfillment of the Requirement for theDoctors Degree of EngineeringByDan WangSupervised by Prof. Shizhong YangSpecialty: Co

2、mmunication and Information SystemCollege of Communication Engineering of Chongqing University, Chongqing, China October 2014 中文摘要摘要多天线技术能够利用空间自由度实现空间分集和复用，有效提高频谱利用率。其中，波束成形是在多天线系统中实现空分多址的主要技术，主要分为两类，一类是长时的波束成形技术，它应用于小间距的多根天线阵列，主要原理是利用空间信道的强相关性及波的干涉原理产生强方向性的辐射方向图，使辐射方向图的主瓣自适应地指向用户来波方向；另一类是短时的波束成形技术，

3、它的主要原理是基于实时的信道冲击响应，利用天线阵元之间的弱相关性构建信号处理算法，当发送端和接收端都具有完整的信道信息，短时波束成形技术能够简单有效地实现MIMO信道的最大分集增益。当天线距离在半波长到 10倍波长之间，角度扩散不大时，为长时波束成形和短时波束成形结合起来提供了条件，因而，能使二者结合的双码本技术被引入到 LTE-Advanced（LTE-A）系统中，它同时用两个码本分别指示长时波束成形特性（码本 1）和短时波束成形特性（码本 2）。此外，由于长时特性和短时特性的变化周期不相同，决定了二者反馈周期也不同，这样就可以延长长时特性码本的反馈周期，从而减小平均反馈量，提高资源利用率。

4、虽然在 LTE-A中定义了双码本发送方案，但是双码本估计和反馈等都是双码本技术中亟待解决的关键问题。本论文就是围绕着双码本波束成形技术的研究展开的，通过对相关理论研究，提出了一系列解决方案。总的来说，本文主要研究内容和贡献如下：首先，研究了双码本波束成形技术的码本设计特性和码本估计算法。在宽带信号的正交频分多路复用（Orthogonal Frequency Division Multiplexing，OFDM）系统中，不同子载波之间存在频率偏移，所以在利用不同载波上的信道信息进行独立码本估计时存在偏差，本文提出相关估计算法，利用宽带信号中多个载波之间的相关性，将不同载波的信道信息聚焦到某个参考

5、频点上获得等效的信道信息。此外，在将多采样点估计获得的信道矩阵进行平均来获得统计信道信息时，引入采样点时刻的信噪比作为加权因子进行加权平均，可以克服由于个别噪声干扰较大的采样信息带来的估计性能恶化现象。通过理论分析和数值仿真得出，在信号带宽较小时，优化算法对系统性能提升较小，主要得益于加权平均；当信号带宽较大时，系统性能提升较明显。接着，在双码本波束成形系统中，分析由于 IQ（in-phase/quadrature-phase）不平衡对波束成形系统带来的影响，推导了在 IQ不平衡情况下引起的码本估计偏差以及双码本估计特性。为了消除 IQ不平衡对码本估计的影响，本文给出了一种完整的收发端 IQ不

6、平衡估计和补偿算法，通过该算法能够对收发端 IQ不平衡参数进行分步估计补偿，校正该因素引起的码本估计误差，从而提高系统性能。I 重庆大学博士学位论文然后，通常情况下为了减小上行反馈资源，对代表长时信道特征的码本 1采用较长的反馈周期，然而信道变化快慢具有时变性，如果采用固定的反馈周期会影响码本 1的准确性，因此本文利用修正的非等间距灰色预测算法对信道方向指示（CDI）信息进行预测，提出一种自适应反馈策略。此外，由于码本 2估计实时性要求较高，过时的信道估计会严重降低码本 2的估计性能，因此本文利用卡尔曼预测算法对信道估计矩阵进行预测，并且引入灰色预测算法对预测时用到的状态转移矩阵进行修正，从而

7、提高码本 2的估计性能。最后，重点研究在大规模天线阵列（Massive MIMO）系统模型下，随着天线数的增加，信道信息估计与反馈信息的复杂度成倍增加，同时，Massive MIMO系统中天线阵通常呈二维阵列分布，信道的方向性估计也需要扩展成二维方向估计。针对上述特性，本文提出基于在二维信道方向估计下的双码本波束成形技术方案，包括双码本设计和双码本估计方案。最后通过仿真验证该方案的有效性，并对多种码本估计算法进行对比仿真，从复杂度和性能两方面进行比较分析，其中似 ESPRIT原理的码本估计算法复杂度较低，且性能也接近改进的二维双码本估计算法。关键词：双码本，波束成形，IQ不平衡，大规模天线（M

8、assive MIMO）II 英文摘要ABSTRACT Multi-antenna technology can make use of spatial degrees of freedom to achievespatial diversity and multiplexing, effectively improve the spectrum utilization. Amongthem, beamforming is a main technology to implement space division multiple access inMIMO system, mainly di

9、vided into two categories. One is a long-term beamformingtechnology, applied to a closely spaced antenna array. The main principle is to use thestrong correlation of spatial channel and interference principle of waves producingdirectional radiation pattern, so that the main lobe of the radiation pat

10、tern adaptivelydirects to users. The other is a short-term beamforming technology, based on real-timechannel impulse response, using a weak correlation between antenna array elements tobuild signal processing algorithms. With complete channel information in the senderand receiver, beamforming techno

11、logy can easily and effectively achieve maximumdiversity gain. When the distance of antenna is between half and 10 times of thewavelength, and the azimuth spread is small, the long-term and short-term beamformingtechnology can work together. Therefore, double codebook technique is introduced intothe

12、 LTE-Advanced (LTE-A) system, which indicates the long-term and short-termbeamforming characteristics by two codebooks respectively. Further, since the changespeeds of long-term and short-term characteristics are not the same, two estimation andfeedback periods of them are different. Hence the feedb

13、ack period of long-termcodebook can be extended to reduce the average amount of feedback and improve theresource efficiency.Although the double codebook is defined in LTE-A, the estimationand feedback of double codebook are the key problems to be solved.This thesis studies double codebook beamformin

14、g technology, and based on therelevant theoretical research proposes a series of solutions. The main contributions areorganized as follows:Firstly, it analyzes the design characteristics and estimation algorithm of doublecodebook. In the OFDM system of wideband signal, frequency offset exists betwee

15、ndifferent subcarrier, so there is codebook estimation deviation in the independent use ofthe channel information carried on the different carriers. The thesis proposes a coherentestimation algorithm based on the correlation between multi-carriers of wideband signal,focusing the different channel in

16、formation to a reference frequency for the equivalentchannel information. What is more, weighted average of the channel information atdifferent sample times is proposed, which take the SNR (Signal Noise Ratio) as theIII 重庆大学博士学位论文weighting factor. As a result, a large deviation due to some poor samp

17、les can beovercome. Through theoretical analysis and numerical simulation, coherent estimationalgorithm can improve performance, especially for wider band signals.Secondly, it studies the effect of IQ (in-phase / quadrature-phase) imbalance on thedouble codebook beamforming system, and derives the c

18、odebook estimate deviationcaused by imbalance. According to signal processing theory, the character of codebookestimation with IQ imbalance is deduced, and a complete joint Tx_Rx IQ imbalanceestimation algorithm is proposed, which can estimate and compensate Tx_Rx IQimbalance parameters step by step

19、 so as to improve system capacity.Thirdly, in order to reduce the uplink feedback resource, the feedback period offirst codebook for long-term codebook is usually longer. However, due to thetime-varying channel change speed, a constant feedback cycle will affect the accuracyof the codebook 1. Thus i

20、t proposes an adaptive feedback strategy of that codebookbased on improved non-equidistant gray prediction algorithm. Further, the short-termcodebook estimation with higher real-time requirement may be severely degraded bythe outdated channel information. Kalman prediction algorithm is introduced to

21、 predictthe channel estimate matrix, and the state transition matrix is corrected by grayprediction algorithm, so as to improve the estimation accuracy.Finally, in Massive MIMO system model, with the increasing number of antennas,the channel estimation information is multiplied with complexity of th

22、e feedbackinformation. In addition, antenna array of massive MIMO is always a two-dimensionalstructure, and channel direction estimation also needs to be expanded intotwo-dimensional direction estimation. Thus, a double codebook design and estimationscheme is proposed based on the two-dimensional ch

23、annel estimation principle, andeffectiveness of the scheme is verified by simulation. With a variety of codebookestimation algorithm simulation comparison, the thesis also compares the performanceand complexity of three estimation algorithms. Among them, the complexity ofestimation algorithm based o

24、n ESPRIT principle is the lowest, and the performance isalso close to the improved two-dimensional double codebook estimation algorithm.Keywords： Double codebook, beamforming, IQ imbalance, Massive MIMOIV 目录目录中文摘要.I英文摘要. III符号对照表 .IX1.绪论. 11.1研究背景 . 11.2波束成形技术的发展和研究现状. 31.2.1长时波束成形技术的发展和研究进展 . 31.2.

25、2短时波束成形技术的发展和研究进展 . 41.3双码本技术的发展和研究现状. 51.3.1单码本设计的发展. 51.3.2双码本设计的发展. 61.4论文的结构和内容安排 . 72.双码本波束成形基本原理 . 92.1引言 . 92.2 MIMO系统下波束成形系统模型 . 92.2.1 SU-MIMO系统模型 . 92.2.2 MU-MIMO系统模型. 102.3双码本设计分析 . 112.3.1 GoB码本 . 112.3.2 Clustered GoB（CGoB）码本. 132.3.3自适应（AC）码本. 142.4 LTE-A中双码本性能研究. 152.4.1 LTE-A中双码本定义.

26、152.4.2 LTE-A中双码本特性分析. 172.5性能仿真分析及讨论 . 192.5.1反馈开销分析. 192.5.2性能分析. 202.6本章小结 . 233.双码本估计算法及性能研究 . 253.1引言 . 253.2双码本反馈系统模型 . 263.3双码本联合码本估计 . 26V 重庆大学博士学位论文3.3.1基于性能优化准则的选择. 273.3.2基于 DOA估计的选择 . 293.4双码本独立码本估计 . 303.4.1独立码本估计算法. 313.4.2基于信号相关性的码本估计. 323.5仿真结果及讨论 . 343.6本章小结 . 374. IQ不平衡对波束成形技术的性能影响研究. 394.1引言 . 394.2 IQ不平衡时的系统模型. 404.2.1发送端 IQ不平衡模型. 404.2.2接收端 IQ不平衡模型. 414.3 IQ不平衡下的码本估计. 424.3.1 IQ不平衡下码本估计特性. 434.3.2 IQ不平衡下码本估计误差. 454.4 IQ不平衡估计与补偿. 504.4.1接收端 IQ不平衡估计与补偿. 514.4.2信道响应和发送端 IQ不平衡联合估计. 544.5性