雙向放大轉送中繼系統之聯合時間同步與通道估測技術

在這篇論文中，我們考慮一個雙向中繼系統，在此系統中兩個終端點會藉由一個放大轉送中繼點以雙向傳輸方式彼此交換訊息。然而，在雙向中繼協定下，兩個終端點的訊號將通過不同的串聯通道於不同的時間抵達接收端，導致在時間同步和通道估測方面相較於傳統單向中繼系統更為複雜。為了同時處理雙向放大中繼系統之同步與通道估測問題，我們提出一個基於在某種特殊訓練序列安排的聯合時間同步與通道估測技術。而每個終端點所採用的訓練序列是由一完美週期性序列(具有理想的自相關函數)、適當的循環字首以及循環字尾所構成。我們所提出的技術依賴通道首路徑的選擇，而其效能更是高度地依賴閾值的選擇。藉由分析相關器輸出的機率密度函數，我們得到最佳的閾值來區分只含有雜訊的輸出值以及包含通道首路徑增益的輸出值。根據這些閾值，在較低的訊雜比下，所提出技術可提供優於最大似然法則作法之效能，而隨著訊雜比的增加，兩種作法的效能則漸趨一致。透過分析，我們亦展示所提技術所需的計算複雜度遠低於基於最大似然法則的作法，實用價值高。

關鍵字

雙向放大轉送中繼系統；時間同步；通道估測；訓練序列

並列摘要

In this thesis, we consider a two-way relay system where two terminals exchange their information via an amplify-and-forward relay in a bi-directional manner. Due to the two-way relay protocol, signals from both terminals travel through different cascaded channels and this makes synchronization and channel estimation much more complicated than those in conventional one-way relay systems. To cope with these problems, we propose a joint time synchronization and channel estimation scheme based on a specific training sequence arrangement, where each terminal’s training sequence consists of a perfect sequence (with an ideal auto-correlation function) attached by an appropriate cyclic prefix and postfix. The proposed scheme relies on a first channel tap selection process, whose performance is highly dependent on the choice of a threshold to distinguish the signal outputs from noise. By analyzing some possible probability density functions of the correlator output, we derive optimal thresholds for selection of the first channel tap. With these thresholds, the proposed scheme provides better time synchronization performance than the maximum-likelihood approach for low signal-to-noise ratio (SNR) cases; both have similar performance for high SNR cases. It is also shown that the proposed scheme involves much less computational complexity than the maximum-likelihood approach.

並列關鍵字

two-way amplify-and-forward relay systems ； time synchronization ； channel estimation ； training sequence

參考文獻

[1] S. B. Weinstein and P. M. Ebert, “Data transmission by frequency division multiplexing using the discrete Fourier transform,” IEEE Trans. Commun., vol. COM-19, no. 10, pp. 628–634, Oct. 1971.

[3] ANSI, “Very high speed digital subscriber line system requirements,” ANSI/T1E1./9J-007 Aug. 1997.

[5] IEEE, “IEEE standard for local and metropolitan area networks–Part 16: Air interface for fixed broadband wireless access systems,” IEEE Std. 802.16-2004, Oct. 2004.

[7] J. Laneman, D. Tse, and G. Wornell, “Cooperative diversity in wireless networks: efficient protocols and outage behavior,” IEEE Trans. Inform. Theory, vol. 50, no. 12, pp. 3062–3080, Dec. 2004.

[9] S. G. S. Katti and D. Katabi, “Embracing wireless interference: analog network coding,” in Computer Science and Artificial Intelligence Laboratory Technical Report, Feb. 2007.

國際替代計量

雙向放大轉送中繼系統之聯合時間同步與通道估測技術

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