於快速時變環境中，正交分頻多工系統需要在傳送信號中插入較密集的導引信號，用以追蹤通道響應變化。無論如何，增加導引信號的密度，相對的也會降低系統的傳輸量。因此，我們提出一個建構在「虛擬導引信號」上的演算法，此演算法能有效追蹤快速變化的通道響應，並且不需增加更多的導引信號。我們在信號區塊中，挑選出某些資料信號，並將它們視為虛擬導引信號。接收端會考量虛擬導引信號所有可能的組合，並且求出其可能的組合所對應之資料虛列與metric。其中，對應至最小metric的資料序列，則被選擇為偵測的資料序列。除此之外，我們也提出兩個改良的方法，用來減少搜尋的次數。
對於快速時變通道而言，在一個正交分頻多工信號的週期中，通道是時變的假設是不合理的。於一個正交分頻多工信號的週期中，時變的通道響應會導致次載波間的干擾(ICI)。此現象會破壞載波間的正交性，並降低系統的效能。為了減少次載波間的干擾之影響，我們提出一個簡單且有效的次載波間干擾自我消除演算法。此演算法可以很容易地結合我們的虛擬導引信號演算法，並且不會影響原始系統架構與複雜度。模擬結果也證明所提出的演算法的效能。

In fast time-variant environments, an orthogonal frequency-division multiplexing (OFDM) system needs to insert denser pilot symbols among transmitted symbols for tracking the variation of a channel. However, increasing pilot-symbol density leads to the reduction of the transmission throughput. In this work, we propose an algorithm based on pseudopilots which can effectively track fast-varying channel responses without increasing more pilot-symbols.
Within a block of symbols, we choose some data symbols and regard them as pseudopilot symbols. The receiver considers all the possible patterns of the pseudopilots and associates each of them with a data sequence and a corresponding metric. The associated data sequence whose metric is minimum is selected as the detected data sequence.
In addition, we also propose two modified schemes to reduce the number of search.
For fast time-varying channel, it is unpractical to assume the channel is time-invariant within an OFDM symbol duration. The time-variation during one OFDM symbol interval causes inter-subchannel interference (ICI), which destroys the orthogonality among subchannels and degrade the system performance. To reduce the ICI effect, based on [24] we propose a modified ICI self-cancellation algorithm, which is simple and efficient. The modified ICI self-cancellation algorithm can be readily incorporated into our pseudopilot algorithm without affecting the original system architecture and complexity. The simulation validates the efficiency of the proposed algorithms.

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