多載子分碼多重存取(MC-CDMA)結合了多載子傳輸與直序列展頻兩種調變方式，近來已經有一些方法在討論當通道資訊未知的狀況下如何設計MC-CDMA系統。在本論文中，我們考慮更實際的情況，那就是使用者的速度會隨著時間改變。所以，我們將提出一個可以對時變性的通道衰減有穩健性的適應性非集中式濾波器(Adaptive Unscented Filter)。首先，我們假設通道為自回歸(AutoRegressive)隨機程序，接下來用提出的適應性非集中式濾波器經由非線性的方式同時估測這個自回歸程序的參數以及通道增益以達到在時變衰減通道中的穩健性。在通道估測後，我們可以利用估測到的通道以及在估測過程中產生的一些參數來增強等化器的性能。而在這裡我們採用決策回授的方式來作通道估測。用電腦模擬的結果顯示，我們所提出的利用適應性非集中式濾波器所做的決策回授方式可以更穩健並且更準確的追蹤到通道。

Multicarrier code-division multiple access (MC-CDMA) combines multicarrier transmission with direct sequence spread spectrum. Recently, different approaches have been adopted without assuming a perfectly known channel. In this paper, we consider the more realistic case that the velocity of mobile station is time-varying. Thus, we present a channel estimation algorithm called Adaptive Unscented Filter (AUF) that can be robust to the variational fading rate. First, we model the mobile radio channel as an AutoRegressive (AR) random process. Then we jointly estimate the parameters of the AR process and the channel gain using the proposed AUF to achieve the robust estimation under variational fading rate. Following channel estimation, the parameters produced in the computation of AUF are used to enhance the performance of the MMSE equalizer. In tracking mode, we adopt decision-directed scheme based on AUF to track both the dynamics and gains of channel and then to detect the signal using the enhanced MMSE equalizer. Simulation results indicate that the proposed AUF-based decision-directed channel tracking algorithm can track the channel more precisely and robustly than the conventional channel estimator. And the enhanced MMSE method can achieve more robust equalization of MC-CDMA communication systems over the rapid multipath Rayleigh fading channel.

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