正交分頻多工為第四代行動通訊 ( 4G ) 的主要技術，然而隨著無線通訊技術的進步與人們對行動通訊的使用方式改變，高速資料傳輸及低時間延遲等需求成為目前的趨勢，進而發展出第五代行動通訊 ( 5G )。其中可以利用多輸入多輸出的技術來提升頻譜效率及毫米波頻段的使用來增加頻寬，結合兩者優點可在實務上增加資料的傳輸速率。 本論文將會旨在多輸入多輸出系統（Multi-input Multi-output, MIMO）的正交分頻多工系統（Orthogonal Frequency Division Multiplexing, OFDM）與其調變原理做介紹，並參考LTE Downlink相關規格，著墨於訊框架構和通道估測等化。以軟體定義無線電（Software Defined Radio, SDR）方式設計，利用發射機兩根天線與接收機兩根天線來實現訊號即時傳輸。又以觀測經過通道後不同增益和距離帶來的影響，來探討本論文系統的品質。 ;Orthogonal Frequency Division Multiplexing (OFDM) is the main technology of the fourth generation mobile communication (4G).However, with the advancement of wireless communication technology and the changes of using mobile, high-speed data transmission and low time delay requirements have become the current trend.The technology of Multiple-Input And Multiple-Output can be used to improve the spectrum efficiency and the use of Multi-mode Wideband to increase the bandwidth. Combining the advantages of the two can increase the data transmission speed in practice. The main purpose of the paper is to introduce OFDM MIMO system and its modulation principle refer to the specifications of LTE Downlink. It will also focus on the frame structure, channel estimation and channel equalization.By using two antennas of the transmitter and two antennas of the receiver to realize real-time signal transmission and implemented on Software Defined Radio (SDR) and observe the influence of different gains after passing through the channel to discuss the quality of the system in this paper.
