室內傳環境及天線擺設對多輪入多輸出系統容量之影響分析與量測

Abstract

通訊系統為了提高傳輸速率，因而在發射端與接收端使用了多單元天線架構，稱之為多輸入多輸出系統，其系統容量比傳統的一對一天線要來的高。該系統於多路徑環境下利用路徑的低相關性能得到相當高的容量。本論文採用頻域向量通道響應系統模擬八對八及四對四的多輸入多輸出系統，於國立交通大學工程四館內進行量測與分析。對於通道容量而言，吾人發現了下列的幾個現象: (1) 當發射天線單元間距的標準差在一到1.5個波長之間，不規則天線架構能比規則天線系統得到較高的通道容量; (2) 系統容量會隨著天線單元間距的增加而增加，但在超過了一個波長之後，天線單元間距對於系統容量就沒有顯著的影響; (3) 系統容量和接收端的擴散角度成正相關;(4) 高的訊號頻寛能得到較大的通道容量;(5) 位於接收端附近的散射體能增加系統的通道容量。

Multiple-input-multiple-output (MIMO) systems have the potential to achieve very high capacities, depending on the propagation environment. The use of multiple antennas offers extended range and higher throughputs than conventional single antenna communication systems. Large capacity is obtained via the potential decorrelation in the MIMO radio propagation channel since a fully correlated MIMO radio channel only offers one subchannel, while a completely decorrelated MIMO radio channel potentially offers multiple subchannels. The decorrelation effect is dependent on propagation and array arrangement. In this paper, effects of transmitting antenna spacing, multipath angular spreading, signal bandwidth and Tx-Rx distance on the MIMO capacity are investigated through measuremts in indoor environments such as along corridors and classrooms. It is found that (1) When the standard deviation of Tx element spacing is ranging from 1λ to 1.5λ, unequally antenna array spacing may have larger capacity than that of the equal spacing; (2)The MIMO capacity increases as the array element spacing increases and it saturates when the spacing is larger than one wavelength. This reveals that the correlation distance between the elements in indoor environments is about one wavelength; (3) Capacity is increased when the propagation distance decreases, or when rms angle spread increases, or when number of received paths increases. (4) Higher signal bandwidth obtains higher capacity, since more multipath components are resolved, which leads to less spatial correlation.