正交分頻多工通信系統於時變與多重路徑衰減通道之通道估測與訊號偵測設計

Abstract

在本篇論文中，探討了數種正交多工分頻系統於時變與多重路徑衰減通道的通道估測與訊號偵測技術。在單個正交多工分頻系統符元內的通道變化，將會破壞次載波彼此間的正交性，而其所造成次載波間的干擾會使系統效能下降。此效能誤差量將會隨著移動的速度、載波頻率或是符元的持續時間增加而變的嚴重。基於現有的通道估測與訊號偵測方法，我們提出了一些改進的方式。所提出的訊號偵測方法利用了時變通道內隱含的時間多樣性，而不是只將其視為次載波間的干擾。它的效能較一般次載波干擾消去法優異，並且擁有可接受的複雜度。而所提出的通道估測方法基於適當的數學模型假設。此數學模型可以有效減少所需估計的參數，使估測可行並且更為精準。

In this thesis, several methods for channel estimation and data detection of OFDM systems in time-varying and multipath fading channels are investigated. Channel variations over an OFDM symbol destroy the orthogonality between subcarriers. The corresponding intercarrier-interference (ICI) degrades the system performance. This error floor becomes more severe as mobile speed, carrier frequency, or symbol duration increases. Based on the existing channel estimation methods and the data detection methods, several modifications to improve the system performances or to reduce the system computational complexities are proposed. The proposed data detection methods exploit time diversity involved in the nature of the time-varying channels. Thus, the proposed methods outperform the conventional methods, like ICI cancellation method and least square (LS) detection. For implementation, the proposed methods are modified to have acceptable complexities. The proposed channel estimation methods are based on appropriate mathematical models. The estimated parameters can be reduced by using these mathematical models. Therefore, channel estimation in fast fading channels becomes feasible and trackable.