對角線加權式時空段碼正交分頻多工系統與其通道估計

Abstract

時空段碼正交分頻多工系統因擁高傳輸效率與分集增益(diversity gain)等優勢而於近年來廣受推崇。在本篇論文中，我們針對四根傳輸天線的時空段碼，討論其傳輸矩陣結構是否正交與其傳輸率，並在此提出一種非正交的複數時空段碼Block Diagonal (BD)。在其通道估計方面，我們應用Giannakis所提出的時空正交分頻多工調變之半盲式通道估計，為改善其估計值，phase direct (PD)將被使用以使此通道估計演算法更趨於理想。PD是在我們得到通道功率(振幅)響應之後解得其相角響應，在時空段碼正交分頻多工中，其通道功率響應必須透過矩陣與向量的運算取得。此外，在非正交複數信號時空段碼中，當傳輸矩陣不可逆時，會無法求得通道功率響應，為解決此問題，我們對時空段碼傳輸矩陣的對角線元素統一乘上一正實常數 ，為公平起見，所有可使用此半盲式通道估計之時空段碼的傳輸矩陣都會經此處理。最後，電腦模擬將會驗證PD確實對通道估計有所改善，展示並討論 值對於通道估計均方誤差、雜訊與位元錯誤率等的影響。

Space-time block coded orthogonal frequency division multiplexing (STBC OFDM) has become popular recently for its high data rate transmission and diversity gain. In this thesis, we focus on STBCs with four transmit antennas and discuss about whether their transmission matrices are orthogonal and their transmission rate. A novel kind of complex non-orthogonal STBC called Block Diagonal (BD) will be proposed. The semi-blind channel estimation proposed by Giannakis is adopted for the STBC OFDM. To improve the performance of estimator, we use phase direct (PD), which is to solve phase ambiguities after the channel power response is obtained. We get channel power response through matrix and vector computation in STBC OFDM. In complex non-orthogonal STBCs, however, channel power response cannot be obtained when transmission matrix is singular. To solve this problem, we multiply a positive real constant to the diagonal elements of their transmission matrices, not only in non-orthogonal models but also in all STBCs that can be implemented in the semi-blind channel estimation. Finally, in computer simulations, we can see that PD really improves the estimator. The effect of on channel estimate mean square error, noise and bit error rate performance will also be exhibited and discussed.