在現代社會中，筆記型電腦及智慧型手機已成為生活中不可或缺的一部分。
隨著行動裝置的普及，對通訊的需求也越來越大。為了滿足人類的需求，最
有效的改善方式是增加無線通訊傳輸通道的容量(Channel capacity)。其中最
有效的方法是增加傳輸頻寬，也就是使用寬頻(Wide-band)無線通訊，然而在
實際使運用中，頻寬是有限的。另一種有有效的方式是使用多輸出多輸入系
統(MIMO)，利用增加天線數量來提供更多的通道容量。此系統的特色是傳輸
通道的容量會與傳輸及接收天線的數量呈線性增加。在多重存取通道(multipleaccess
channel)中，多使用者多輸出多輸入系統(multi-user MIMO)可以進一步增
加頻寬使用效率。
近年來，時間空間碼已被證明是可以有效提高頻譜效率及降低錯誤率的
方法。從1998年起，Alamouti、Tarokh及Oggier等人提出各種時間空間碼的設
計，並不斷加以改進。隨著對於資料傳輸率的要求越來越高，傳統上假設通
道是頻率非選擇性通道(Frequency-nonselective fading channel)已不太適用。因
此，對於多重路徑的環境，我們可以有更多的分集增益。
在本論文中，我們推算了在多使用者頻率選擇快速衰減通道下線性調變的
時間空間碼的設計準則。接著我們依照此準則來建構一個時間空間碼。此時間
空間碼編碼器是利用可除性代數所設計的最佳編碼器。接下來我們推導出在多
使用者頻率選擇快速衰減通道下此時間空間碼的分集與多工增益的權衡。

In this thesis, we derived the rank design criteria of a space-time coding scheme for linear modulation over multiple access frequency-selective fast fading channel with oversampling technique. We introduced a multi-user space-time code constructed by division algebra.
Then we evaluated the diversity and multiplexing gain tradeoff for multiple access frequency-selective fast fading channel.
We showed that the diversity and multiplexing gain tradeoff with a temporal code is better than the optimal one without a temporal code for low to medium multiplexing gains.

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