相關性多輸入多輸出通道之解構與分析

Abstract

在通訊系統中要能有效率地提升資料傳送速度，除了擴張頻寬之外，在理論上也可以透過增加傳送、接收兩端的天線數目，形成所謂的多輸入多輸出（Multiple-Input Multiple-Output, MIMO）系統，來提升通道容量。然而在MIMO系統中，對於通道的統計性質假設與現實環境不合，例如未考慮天線所看到的通道彼此之間的相關性，則會高估此種系統理論上的潛力。 在本論文中將回顧文獻中數種應用於分析MIMO系統所使用的解析通道模型，其中Weichselberger等人所提出之模型有許多解析通道模型之一般化的形式，故將特別著重此模型討論。除了介紹Weichselberger模型的數學型式外，本論文亦提出模型的物理詮釋，將實際的電波傳播現象與模型參數連接起來。為了檢視模型在戶外到室內環境的適用性，以及前述之物理詮釋是否合理，在本論文中以以通用信號量測儀器組合出以正交多工分頻信號為基礎的MIMO通道探測儀，所得到實地量測結果，並以通道容量做為衡量標準，驗證模型的適用性與物理詮釋的合理性。除了驗證模型之外，也可以透過模型的參數，了解不同環境、系統組態、以及天線陣列種類對於MIMO通道特性的影響。

Prediction in theory shows that data rate can be efficiently further raised by adding multiple antennas to both of the transmitter and receiver in addition to expanding transmission bandwidth, forming so called Multiple-Input Multiple-Output (MIMO) system. However, improper channel modeling, such as lacking in consideration of correlation in channels between antennas, may leads to over-optimistic results. In this thesis several analytic MIMO channel models are reviewed. Emphasis is laid on the model proposed by Weichselberger et al. since it encompasses various analytic models. In addition to the math formulation, the physical interpretation is proposed to link the model parameters to physical wave propagation phenomenon. With MIMO channel capacity as evaluation metric, and the MIMO OFDM-based channel sounder developed with general-purposed equipments, the validity of both physical interpretation and the statistical behavior of the model are examined in an outdoor-to-indoor environment. In addition, with the model parameters estimated with measurement results, one may have a view on the characteristics of MIMO channel seen by the system with some specific configurations.