傳播對室外多輸入多輸出系統容量影響之研究

Abstract

多輸入多輸出系統的技術概念發射端與接收端信號的結合處理獲得高速率通道傳輸容量。該系統於多路徑環境下可利用路徑的低相關性達到相當高的通道容量。本論文採用頻域向量通道響應系統模擬四對四的多輸入多輸出系統，於台灣國立交通大學校園內對主波導性、阻擋波導性及非波導性環境進行通道響應實地量測並計算其通道容量。對於通道容量而言，吾人發現於傳播環境中，天線間距、傳輸接收端的距離、區域散射波以及頻寬都有很大的影響。然而陣列擺向在非波導性環境下有顯著的影響，主波導性則是影響較小。對於相關特性而言，相關特性跟周遭環境有很大的關連。量測環境越複雜，由多重路徑信號造成的入射角度擴展均方根越大與通道容量呈現正相關的現象。我們並結合一實體統計空-時通道模型與量測結果評估通道容量，一如預期通道容量與量測傳輸距離、區域散射波及天線間距有關係。

Large capacity is obtained via the potential decorrelation among MIMO spatial radio channels. A fully correlated MIMO radio channel only offers one equivalent subchannel for transmission and a completely decorrelated MIMO spatial radio channel potentially offer multiple subchannels depending on the antenna array arrangement and propagation effects. In this paper, effects of propagation conditions such as LOS, OLOS and NLOS, propagation distance, local scatterer distributions, signal bandwidth and antenna array element spacing on 4x4 MIMO capacity are investigated through extensive measurement in macrocellular environments. It is found that the rms AOA (Angle-of-Arrival) and number of multipath components (MCPS) are the two fundamental parameters to affects the capacity. Environments under rich scattering signals such as NLOS condition and existing of local scatterers exhibiting a high rms angular spread of AOA ensures a high probability of achieving independent fading and hence boosts capacity. The increase of the array element spacing decreases the correlation among spatial channels, i.e., increasing the capacity. It is also found that the increase of signal bandwidth will increase the signal resolution and hence number of MPCs increases, which enhances the capacity. It seems that the capacity is independent of propagation distance and angular spread of AOD.