Beamforming Analysis and DOA Estimation Techniques in Wireless MIMO-OFDM Communications

[[abstract]]在無線通訊系統快速發展之下，頻寬效益和通訊品質已經成為研發人員有興趣的研究方向。多重路徑衰減、多重存取干擾以及一些傳輸的難題都是應該被處理解決的。 智慧型天線的科技是一個可以接受的解決方法，這個機制主要是使用一組固定的天線元件集合來達成。結合每個天線元件所收到的訊號，利用波束成型演算法可以產生某個特定方向的波束場型，如此一來便能完全的接收到想要的訊號並且進一步的去抑制干擾。 在本篇論文裡面，主要討論研究的方向是基於正交分頻多工系統搭配智慧型天線。智慧型天線技術包含了到達角度估測以及波束成型。在天線陣列的接收端，到達角度估測的演算法用來估測所有的使用者個數以及分別的來源角度，然而這些角度可以分類為兩種，分別為信號源以及干擾源的角度。接下來這些估測出來的到達角度資訊將會被丟入波束成型演算法，因此波束成型演算法可以正確的計算適當的權重去達成波束成型。波束成型技術就像是一個空間濾波器，他可以設計一組權重把主要的波束朝向信號源角度，然而把零點朝向干擾源角度。因此，利用智慧型天線將會使正交分頻多工系統的位元錯誤率有明顯的改善。[[abstract]]In the rapid development of wireless communication systems, the bandwidth efficiency and communication quality have become interesting issues for researchers. Some transmission difficulties should be coped with, including multipath fading, multiple-access interference and so on. Smart antenna that uses a ?xed set of antenna elements is the technology for an acceptable solution. The signals from these antenna elements are combined to form a particular beam pattern that can keep the desired signal and suppress the interference. In this thesis, the orthogonal frequency division multiplexing (OFDM) system with smart antenna is considered and investigated. The smart antenna technique contains direction-of-arrival (DOA) estimation and beamforming. At the receiver end, DOA algorithm is employed to estimate the number of total impinging signals and their angles. However, these angles contain desired and interference directions. And then the estimated DOA information is applied to the beamforming algorithm. As a result, the beamforming algorithm could calculate appropriate weight to accomplish beamforming. The beamforming technique is just the spatial ?ltering which could design the weights to form main beam toward the desired signal direction, and form a null toward the interference direction. Therefore, the bit error rate performance of the OFDM system would have great improvement with smart antenna.[[note]]碩