在時變多路徑通道之低複雜度載波間互擾效應消除於正交分頻多工系統

Abstract

本篇論文應用在正交分頻多工（OFDM）系統於時變頻率選擇衰變通道. 隨著符號長度的增加，OFDM可抵抗對於多重路徑干擾的效應。然而在行動通訊的應用上，時變通道破壞了子載波間的正交性，造成載波間的互相干擾（ICI）因而降低系統效能。在本篇論文中，利用線性模型去近似時變通道。基於這個假設，我們解出線性的通道參數進而重建通道矩陣，目的去消除載波間的互相干擾。模擬結果顯示所提出的方法可有效抑制因時變通道所造成的ICI效應以及降低錯誤率在高雜訊比仍高居不下的現象。

This thesis considers an orthogonal frequency division multiplexing (OFDM) system over frequency selective time-varying fading channels. As the symbol duration increases, OFDM is robust to channel multipath dispersion. However, for mobile applications, channel variations within an OFDM block period destroy the orthogonality between subcarriers; the effect, known as Intercarrier Interference (ICI), will degrade the system performance. In this thesis, a linear model is assumed for the channel variation because of its simplicity. Based on the assumption, the proposed method solves the linear channel parameters of each path and creates a channel matrix which can be used for ICI cancellation. The simulation results show that the proposed method can effectively suppress the ICI effects induced by the time variant channels and reduce the error floor of bit error rate (BER).