近幾年來，正交分頻多工(Orthogonal Frequency Division Multiplexing, OFDM) 技術已經被廣泛的應用在許多不同類型的數位通訊系統中。全球互通微波存取(WiMAX)則是結合了定點無線寬頻與行動無線寬頻兩種應用的技術。IEEE 802.16e即針對WiMAX系統應用於移動性環境而設計的標準。
無線通訊系統要維持良好的性能表現，一個很重要的步驟就是運用有限的領航訊號(pilot)進行通道估測。由於使用者的移動速度造成通道的變化，加上802.16e的領航訊號在頻域上不完全規則的排列方式，這些因素都增加了通道估測的困難度。
在本論文中，我們提出可適性通道估測的作法，讓系統可以自行估算速度以及雜訊的大小，決定通道估測的方式。在低速時，判斷雜訊的影響來決定用線性內插或是離散傅利葉通道估測法；當使用者速度提高時，則考慮消去子載波之間的干擾(ICI)效應，藉由適當切換通道估測的作法，以得到好的系統性能表現以及節省運算量。
模擬結果顯示，本論文所提出的可適性通道估測作法，能有效節省計算量，並提供良好的系統效能。

Recent years, Orthogonal Frequency Division Multiplexing (OFDM) has been widely applied to various digital communication systems. WiMAX (Worldwide Interoperability for Microwave Access) holds a combination of fixed and mobile broadband wireless access techniques. And IEEE 802.16e is the specification designed for WiMAX system in application of mobile environments. In order to achieve robust performance, one of the most important steps is the channel estimation procedure based on limited number of pilot signals. Owing to the channel’s time variant characteristic caused by user’s mobility and irregular arrangement of pilot signals in 802.16e system, the exact channel-estimation is more difficult to achieve for this system.
In this thesis, considering the effects of high mobility and AWGN, we proposed an adaptive channel estimation scheme so that the mobile stations can choose proper channel estimation process in order to reduce the computational complexity for the downlink signal-reception. The basic idea is that, when in low speed, the linear interpolation or DFT-Based channel estimation will be adopted depending on the amount of CINR and, when in high mobility, the ICI reduction method will be processed to maintain good performance. Simulation results show that the proposed adaptive channel estimation scheme can save computational complexity and keep good system performance.

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