正交分頻多工與多重存取系統中符元時序偏移之估測與補償

Abstract

近幾年對於傳輸效率的需求越來越高，因此採用上行多用戶傳輸方法是非常重要的。正交分頻多工以及正交分頻多址已經被廣泛地應用在無線通訊標準上，然而正交分頻多址對於同步錯誤是非常敏感的，其中載波頻率偏移和符元時序偏移將使子載波間失去正交性。在這篇論文中，我們將介紹福元時序偏移的估測與補償。在接收端接收到的訊號，會是每個用戶分別帶有不同符元時序偏移的訊號疊加。這些符元時序偏移將會導致接收訊號有載波間干擾以及用戶間干擾，而這些干擾會大幅的降低系統的表現。因此對於上行正交分頻多址中，符元時序偏移的估測與補償會非常重要，而且是一個具有挑戰性的議題。在這篇論文中，我們首先提出載波間干擾與用戶間干擾的補償演算法，可以降低位元錯誤率。接下來我們提出基於指標對符元時序偏移與通道的共同估測子，我們還提出了一個新的指標區塊結構，可以提升估測的表現。最後，模擬圖放置於各章節的後面，從模擬結果可以證明我們的方法，亦可與其他方法進行比較。

In recent years, the demand for high transmission efficiency is increasing, so adopting uplink multi-user transmission (UL MU) is more important. Orthogonal frequency-division multiplexing (OFDM) and orthogonal frequency-division multiple access (OFDMA) have been widely adopted in many wireless communication standards. However, the OFDMA-based systems are sensitive to the synchronization error, including carrier frequency offset (CFO) and symbol timing offset (STO), which destroys the orthogonality among the subcarriers. In this thesis, we focus on the estimation and compensation of the STO. At the receiver, the received signal is a superposition of signals from all active users with individual STO. The STO introduces both inter-carrier interference (ICI) and multi-user interference (MUI), which seriously degrade the performance of systems. Hence, the estimation and compensation of STO and interferences are challenging tasks in uplink OFDMA systems. In the thesis, we frst propose a ICI and MUI compensation algorithm which can improve the BER. Next, we propose a pilot-based joint STO and channel estimator. Moreover, we also propose a pilot structure to further improve the estimation performance. Simulations are carried out to verify the performance of the proposed methods.