- 學位論文
正交空時編碼之多輸入多輸出正交分頻多工系統中之通道盲估測
Blind Channel Estimation for Orthogonal Space-Time Block Coded MIMO-OFDM systems
摘要
正交分頻多工最近引起相當大的興趣因為它能在頻率選擇性衰落通道中以高資料率傳輸. 在多輸出多輸入無線通信系統中,空時編碼利用在空間分集及抵抗衰落已經是一個很強大的方法. 該論文研究具有多個發射天線的正交分頻多工系統中的通道盲估測.全文共分成三個部分. 在第一部分,我們探討已存在利用子空間的通道估測方法. 雖然這方法提供良好的效能但是對大部分時空碼來說,當只有一根接收天線此方法是無法得到唯一解. 為了解決此問題,我們也提出一個改善的估測方法. 在第二部分,我們提出一個新的利用子空間的通道估測方法. 此方法是利用正交時空碼的特性誘導出零空間來估測通道. 我們也探討它的唯一性問題. 在第三部分中,我們提出一個修改的方法,能夠使用較少的接收資訊及較低的複雜度就能估測通道. 我們還提供了實驗數據,此能證明我們的方法是可行的.
並列摘要
Orthogonal frequency division multiplexing (OFDM) has recently received con- siderable interest for its advantages in high-bit-rate transmissions over frequency- selective fading channels. Space-time block coding (STBC) has emerged as a powerful approach to exploit spatial diversity and to combat fading in multiple-input multiple- output (MIMO) wireless communication systems This thesis studies the blind channel estimation for OFDM systems with multiple transmit antennas. The thesis consists of three parts. In the rst part, we review an existing channel estimation method us- ing subspace. This method though gives good performance but for many orthogonal STBCs (OSTBCs), it cannot uniquely identify the channels when only one receive antenna is available. In order to solve this issue, we propose an improved method. In the second part, we propose a new subspace-based method for blind channel esti- mation. The proposed method exploits the null space induced by the OSTBCs with rare < 1. The identi ability is also studied. In the third part, we introduce a modi- cation of the proposed method so that fewer received blocks are needed. Moreover the modi ed method has low computational complexity. We also provide numerical simulation to verify the performance of the proposed methods.