摘要
由於其簡易的安裝和移動性，無線區域網路 (wireless local area network，簡稱WLAN)相對於傳統的有線的區域網路已經變成另一種可行的方式。而IEEE 802.11a是一種高速率的無線區域網路的標準，其運用現在很熱門的正交頻域多工 (orthogonal frequency division multiplexing，簡稱OFDM)的技術。在這篇論文裡我們根據IEEE 802.11a的標準，結合頻率、時間、和框架的同步，加上通道的估計和訊號的偵測與解碼。我們考慮有可加性白色高斯雜訊 (additive white Gaussian noise，簡稱AWGN) 的多路徑通道 (multipath channel)，而這個通道在一個封包 (packet) 之內是不變的，但對於不同的封包通道就不同。正交頻域多工系統的一個很重要的問題便是同步，包括了頻率同步 (frequency synchronization) ，時間同步 (timing synchronization) 與傳輸框同步 (frame synchronization) 的研究。我們將採用IEEE 802.11a 標準的實體層 (physical layer) 來從事頻率，時間，和傳輸框同步的最大可能性估計 (maximum likelihood estimation) 研究。我們利用IEEE 802.11a的10個短訓練符號 (training symbol) 和2個長訓練符號，導出上述的同步的演算法。再結合先前推導過的通道估計和訊號偵測與解碼，我們建立出了一個基頻的接收器。模擬結果顯示我們的基頻接收器與之前的演算法比較，有著類似的表現，但是需要較少的複雜度。且相較於完美同步的例子，非完美同步的例子下，其錯誤率會飽和至一穩定值。而且對於不同的傳輸速率而言，其表現不只會受到傳輸速率影響，同時也會受到錯誤更正碼碼率的影響。

Wireless local area network (WLAN) are now becoming a viable
alternative to traditional wired solutions, due to the advantage
of ease of installation and mobility. IEEE 802.11a is a high-rate
WLAN standard, based on the popular orthogonal frequency division
multiplexing (OFDM) technology. In this thesis we manage to
combine frequency, timing, and frame synchronization plus channel
estimation and detection based on the 802.11a standard. The
channel considered is a multipath channel with additive white
Gaussian noise (AWGN) and is assumed to be quasi-static. Based on
the maximum likelihood (ML) criterion, we have derived estimator
algorithms to conduct the above mentioned synchronization tasks.
Jointly with previous proposed channel estimation and combined
detection/decoding algorithms, an entire baseband receiver has
been obtained. Simulation results show that our baseband receiver
performs similarly as those previously proposed best methods, but
requires lower complexity.

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