A Dissertation Submitted to Shanghai Jiao Tong University
梦稿本for the Degree of Master
RESEARCH ON CHANNEL TEST AND PRE-CODING FOR MIMO WIRELESS SYSTEMS
Author: Dawei WU
Supervisor: Chen HE
Shanghai Jiao Tong University
初中物理新课程标准Dec. 2010
摘 要
由于多输入多输出（Multiple Input Multiple Output, MIMO）系统通过空间复用实现了更高数据速率的传输，许多无线通信系统，如IEEE802.11n WLAN、基于IEEE 802.16e 的Mobile WiMAX TM Wave 2 和LTE（Long‐Term Evolution）等移动无线通信系统近来都已经采用了MIMO技术。分析表明，MIMO系统的性能在很大程度上受到无线信道特性，特别是空间相关性的影响。 地磁指数预报
为了设计新一代MIMO通信系统，需要对现有工作频点以及未来可能被选用的工作频点的无线信道特征有深刻的了解。只有获得无线信道准确的空时频三维信息，才可以设计合适的多天线传输技术。通过对无线信道参数的测试，可以从中获得信道的空间相关、信道矩阵条件数以及信道容量等信息。因此，MIMO 信道参数的测试具有重要意义。 另一方面，MIMO系统存在着共信道干扰（CCI），为了消除或减少CCI，可以采用预编码技术对发射信号进行处理。预编码处理需要发射端获得信道状态信息（CSI），对于FDD系统，发射端可以通过反馈链路获得信道状态信息，而TDD 系统则可以利用信道的互易性直接获得CSI。若假设发射端已知精确的信道状态信息，在设计预编码矩阵时，通常主要考虑提高系统的BER性能或考虑提升传输速率逼近信道容限。若发射端获得的是非理想信道状态信息，设计预编码时主要考虑在信道矩阵误差不超出一定范围的条件下，提升预编码设计方法的鲁棒性。 本文提出了一种基于Agilent 公司的EDA软件ADS TM与仪器互联的MIMO信道测试方案，与现有的其它测试方案相比，该方案成本低，灵活性好，易于扩展，可以对不同的频率和带宽进行信道测试。利用现场测试获取的信道参数，可以进行信道时间相关性、频率相关性、空间相关性、信道容量以及标识信道质量的条件数的分析。而且利用所获得的信道矩阵，可以进行后续章节中预编码算法性能的验证。
本文对非理想信道条件下的矢量预编码技术进行了研究。通过几何均值分解可以获得增益相等的平行子信道，在此基础上采用矢量预编码的方法，可以进一步改善系统的性能。同时，由于实际系统中获得的CSI存在时延等误差，需要在设计预编码的过程中考虑信道误差矩阵的统计信息，从而产生具有鲁棒性的预编
码设计方法。计算机仿真表明，本文中提出的鲁棒的预编码算法比传统的预编码算法具有更好的BER性能。
关键词：MIMO，信道参数，条件数，线性预编码，矢量预编码
ABSTRACT人道主义干涉
Multiple Input Multiple Output (MIMO) systems have been shown to improve data capacity through spatial multiplexing. Due to the potential improvement in system performance, many wireless systems, including the IEEE 802.11n wireless LAN, IEEE 802.16e-basedMobile WiMAX™Wave 2 and the Long-Term Evolution (LTE) mobile wireless system, have recently adopted the use of MIMO technology. Research has shown that, the performance of MIMO systems is greatly affected by the channel property, especially the spatial correlation.
七夕之国
In order to design brand-new communication systems, it is necessary to have a deep understanding on the property of the wireless channel, both for the adopted radio frequency and the would-be candidates. Only with accurate information on spatial, temporal and frequency aspects of the wireless channel, can we design proper MIMO technologies. By testing the channel coefficients, we can analyze the spatial- correlation, condition number and channel capacity for wireless channel. Therefore the channel coefficients test is of great importance.
磁流On another side, to eliminate or reduce the co-channel interference (CCI) in MIMO system, pre-coding is utilized in base station for signal processing. Channel state information (CSI) is needed when performing pre-coding. For FDD system, the transmitter can get CSI through feedback, while for TDD systems, CSI can be obtained by channel reciprocity. When the transmitter gets the exact CSI, the pre-coding matrix should be considered to improve the system performance or approach the capacity limit. If the transmitter only knows imperfect CSI, the pre-coding design should take the error information into account to make the design a robust scheme.
We propose a novel test program, which is based on the interconnection of Agilent’s EDA software ADS TM and RF test instruments. Compared with other existing test program, the proposed one is more flexible and cost-saving. We can setup different frequency and signal bandwidth in this test ben
ch. Using channel coefficient,
we can calculate temporal, spatial and frequency correlation and determine the channel quality indication—condition number. Furthermore, the obtained channel matrix can be used to verify the proposed pre-coding algorithm in the following chapter.
We also discuss the robust pre-coding scheme in this thesis. Geometric mean decomposition (GMD), which is dedicated to decomposing the channel into sub-channel with equal gain, combined with vector pre-coding can get better system performance. The transmitter obtains imperfect CSI due to estimation errors, feedback error etc., so we should consider the statistical information of channel error when designing pre-coding matrix and optimum perturbation vector. Simulation results show that the proposed pre-coding algorithm is more robust to imperfect CSI than conventional pre-coder.
Keywords: MIMO, channel coefficients, condition number, linear pre-coding, vector pre-coding
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