室內環境下極化分集多輸入多輸出系統之通道模型與量測分析

Abstract

在本論文中，我們使用四種極化分集技術並探討在多輸入多輸出系統之通道特性和傳輸效能。目前一般多輸入多輸出系統的天線設置方法，是在傳送與接收兩端皆採用垂直極化。然而，正交極化具有好的隔離效果，在室內的環境下，傳送與接收兩端天線都採用對稱的正交極化方式，通道容量會比傳統上的極化方式來得高。 依據量測的資料，我們分析與討論影響通道容量的參數，包括特徵值與相關係數等，另外還提出一種新的方法來分析通道容量，此法針對不同的極化型態並考慮天線的接收功率和極化的影響。數值分析結果證明，這個通道容量分析方法會非常貼近實際室內環境的通道容量。 在無線通訊系統中，結合正交分頻多工與多輸入多輸出的系統在頻率選擇衰落(frequency-selective fading)通道的環境下能提升資料傳輸速率。VBLAST是一種藉由使用多根天線傳送來得到高速傳輸速率的空間多工架構。我們使用下一世代無線網路的規格(IEEE 802.11n)的通道模型作為模擬的通道。當傳輸天線的數量增加，不同天線間互相干擾的情況會變嚴重；此外，在相關性通道內，干擾消除的動作沒辦法表現良好。因此，增加天線數量可以提升系統效能，但在相關性通道下卻不盡然。

In this thesis we have discussed four polarization diversity antenna configurations of MIMO schemes in their channel characteristics or transmission performance. For a general MIMO system, we usually use vertically co-polarized antenna arrays at both transmitter and receive ends. However, we know that using cross-polarized antenna scheme symmetrically in both ends; the capacity is higher than conventional antenna polarization scheme under the indoor environment due to the high isolation between orthogonal polarizations. According to measurement data, we analyze and discuss some factors that can affect the channel capacity, like eigenvalues and correlation coefficients etc. Besides, we also propose a novel analysis method of channel capacity including the normalization received power and polarization effect for different polarization schemes. Simulation results show that our proposed analysis method is close to the realistic measurement of the indoor environment. The combination of MIMO signal processing with OFDM is regarded as a promising solution for enhancing the data rates of wireless communication systems operating in frequency-selective fading environments. VBLAST is a spatial multiplexing scheme and can provide huge data rate by using multiple antennas. Channel model adopted by next-generation WLAN standard (IEEE 802.11n) is used in our simulation. In the correlated channel, the interference cancellation cannot work well when more antennas are used. Consequently, using more antennas cannot guarantee the higher performance in the correlated channel.