運用狀態化簡最大事後機率等化器消除OFDM系統在時變通道上的子載波間干擾

Abstract

正交分頻多工（OFDM）移動傳輸的效能受到都普勒擴展導致子載波間干擾(ICI)而削弱。不同類型的等化器經常用來減輕子載波間干擾。雖然最大事後機率（MAP）等化器提供了最佳的性能，但計算複雜度比別人大上許多。從之前的研究，我們知道，每個子載波在一個OFDM符號，面臨到的ICI效應不盡相同。因此開發了一個簡單的ICI指標來表示每個子載波的ICI的嚴重性級別。在這裡，我們提出了子載波的自適應MAP均衡器框架，以減少計算的複雜性。除此之外，我們更進一步的將格狀解碼(Trellis Decoding)化簡，基於狀態劃分(State Partitioning)將兩個或兩個以上的狀態合併成一個超級狀態，以減少狀態數，通過這個降低狀態數的解碼方法，性能與原方法可相互媲美。

The performance of mobile transmission based on orthogonal frequency-division multiplexing (OFDM) is impaired by inter-carrier interference (ICI) caused Doppler spread. Different types of equalizers are often used to mitigate ICI. Among them, the Maximum A-Posteriori Probability (MAP) equalizer offers optimal performance, though the computational complexity is also much greater than others’. From previous studies, we know that each subcarrier in one OFDM symbol faces different ICI situations. A simple ICI indicator was also developed to indicate the severity level of ICI on each subcarrier. Here, we proposed a per-subcarrier adaptive framework for the MAP equalizer to reduce the computational complexity. Moreover, based on state partitioning, it’s easy to use a technique to reduce the number of trellis states by merging two or more states into a super-state. The performance of the simplified MAP equalizer with a reduced trellis is comparable to that of the original MAP equalizer.