在時變多路境環境下OFDM用於克服ICI效應之低複雜度加窗技術

Abstract

正交分頻載波多工系統使用在時變及頻率選擇性通道，會造成相當大的子載波間干擾效應現象。在這種高速的移動環境下行動通訊會遭受極大的都卜勒效應，系統受到的快速衰減影響相當大，傳統的非時變通道傳道解調架構由於無法克服這個問題，而使得錯誤率大幅提升。 此篇論文我們利用ICI效應產生之機制，提出一個等化器之演算法。此等化器作用方式分為二個階段，在第一階段我們使用時域加窗的方式來抑制ICI效應，並且在第二階段採用疊代估測法的方式來估測頻域符號。模擬結果顯示我們提出的等化器在頻率選擇性通道中其效能及其複雜度比起傳統的線性MMSE估測法均有獲得改善。

Orthogonal frequency division multiplexing (OFDM) systems may experience significant inter-carrier interference (ICI) when used in time- and frequency-selective, or doubly selective, channels. In high mobility environment mobile communication suffers from critical Doppler effect, the performance is decreasing due to fast fading. The structure of the traditional demodulation system in time-invariant channel can not conquer this problem, so that the BER is rapidly rising. In this thesis we take the advantage of the mechanism generated by ICI effect, and we proposed calculating method of the equalizer. This method contains two stages, the first stage applies time-domain windowing to restrict ICI support, and the second stage uses iterative estimation to estimate finite-alphabet frequency-domain symbols. Simulation results indicate that our equalizer has significant performance and complexity advantages over the classical linear MMSE estimator in doubly selective channels.