高速移動環境下DVB-T數位電視廣播之同步

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姓名

林韋丞(Wei-cheng Lin) 查詢紙本館藏

畢業系所

通訊工程學系

論文名稱

高速移動環境下DVB-T數位電視廣播之同步
(Synchronization for DVB-T in High-mobility Environment)

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摘要(中)

正交分頻多工（OFDM）調變技術普遍被無線通訊規格所採用，其中包含DVB-T，因為OFDM具有較高的頻譜使用效率、較簡單的通道等化及在符元前端插入前置循環字首來抵抗多重路徑干擾(ISI)。然而，OFDM系統對於非同步產生的影響相當敏感，例如符元時序偏移、載波頻率偏移及取樣率偏移。為了解決同步產生的問題，相關方法已被提出來估測及解決OFDM的同步問題，主要為使用前置循環字首訊號相關性之時域估測法及使用Pilots相關性之頻域估測法，不過大部份的演算法假設在靜止環境下，此時發射及接收端為靜止不動的，其通道脈衝響應為非時變，但當發射及接收端處於高速移動環境下時，此時所使用的演算法就不適用，因為通道脈衝響應會隨時間改變。
本論文首先研究探討在高速移動環境下DVB-T系統所面臨的問題，當接收機最大的移動速度高達300 km/hr，此時時變通道會產生都普勒擴展(Doppler Spread)的現象，將破壞子載波間的正交性及訊號間的相關性，一般的靜態環境下的方法已不適用，因此本論文設計一套適用於高速移動環境下DVB-T接收機的同步方法，並使用Modelsim軟體進行驗證且實現於FPGA平台。

摘要(英)

OFDM technique is adopted in many standards, including DVB-T, since it exhibits outstanding characteristics in terms of efficiency in spectral utilization, simplicity in equalization and immunity in Inter-Symbol-Interference (ISI). However OFDM system performance is sensitive to synchronization errors including symbol timing offset, carrier frequency offset and sampling clock frequency offset. Typical methods exploiting the correlation of cyclic-prefix in time domain and the correlation of continual pilots in frequency domain have been proposed for estimating and correcting the synchronization errors for OFDM systems. In these methods the channel model is generally assumed to be static, i.e., the transmitter and receiver are in stationary positions and the channel impulse response is time invariant. This assumption is violated especially when the receiver and/or transmitter are in high-mobility environment, i.e., the channel impulse response becomes time varying significantly.
In this thesis, we focus on studying on the synchronization problems of DVB-T system when the receiver is in mobility as high as to 300 km/hr. In this scenario, significant time-varying channel impulse response due to large Doppler spread is noticed which causes the loss of subcarrier orthogonality and signal correlation, and the performance of typical synchronization algorithms is evaluated. Finally, a synchronization method, which is more suitable to high-mobility reception, is designed for DVB-T receiver. The implementation of synchronization systems is verified with Modelsim tool and real-time implementation on FPGA hardware.

關鍵字(中)

★ 高速移動
★ 同步
★ 歐規數位電視地面廣播
★ 正交分頻多工

關鍵字(英)

★ High-mobility
★ Synchronization
★ OFDM
★ DVB-T

論文目次

中文摘要
英文摘要
誌謝
目錄
圖目錄
表目錄
第一章緒論
1.1 研究背景與動機
1.2 章節提要
第二章歐規數位電視地面廣播系統簡介
2.1 OFDM簡介
2.1.1 OFDM調變原理
2.1.2 OFDM基頻離散等效模型
2.2 DVB-T系統規格與參數
2.3 DVB-T系統2K模式及8K模式比較
2.4 DVB-T接收機架構
第三章高速移動環境下之同步
3.1 通道模型
3.2 時間同步
3.2.1 符元時序偏移探討
3.2.2 延遲相關器
3.3 載波頻率同步
3.3.1 載波頻率偏移探討
3.3.2 小數倍載波頻率偏移估測
3.3.3 整數倍載波頻率偏移估測
3.3.4 高速移動環境下之載波頻率同步
3.3.5 模擬結果及效能比較
3.4 取樣率同步
3.4.1 取樣率偏移探討
3.4.2 再取樣器之基本原理
3.4.3 取樣率偏移估測
3.4.4 高速移動環境下之取樣率同步
3.4.5 模擬結果及效能比較
第四章歐規數位電視地面廣播接收機設計
4.1 通道估測與等化
4.1.1 最小平方法通道估測
4.1.2 通道響應內插
4.1.3 零值逼近通道等化
4.2 載波間干擾(ICI)壓抑技術
4.2.1 載波間干擾量(ICI)估測
4.2.2 載波間干擾量(ICI)壓抑
4.3 接收機分集技術
4.4 軟式腓特比解碼器
4.5 模擬結果與效能比較
第五章電腦模擬結果與硬體設計
5.1 同步收斂情形
5.2 同步與非同步效能比較
5.3 同步系統技術硬體設計
第六章結論與未來發展
參考文獻

參考文獻

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指導教授

陳逸民(Yih-min Chen)

審核日期

2008-7-10

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