臺灣博碩士論文加值系統

頻率偏移破壞OFDM系統子載波間之正交性，導致系統承受子載波間干擾(Inter-Carrier Interference, ICI)問題。本研究探討在使用ICI自消機制之OFDM系統下實現CFO估測。本文所提出的方法首先將收集到的信號時間樣本建構成快取向量來估測CFO。本研究亦開發一時間取樣篩選機制以紓緩在CFO估測前所涉及之等化過程中可能產生之雜訊放大效應。電腦模擬結果顯示本研究所提之方法能有效估測CFO。

Frequency discrepancy destroys the orthogonality among subcarriers, resulting in the system suffering from the inter-carrier interferences (ICI). This study presents a CFO estimation algorithm for OFDM system using a general ICI self-cancellation scheme. The proposed approach first collects the receive time samples to construct snapshot vectors for the CFO estimation. This study also develops a time sample selection scheme to mitigate the noise enhancement in the involved equalization process before the CFO estimation algorithm. Computer simulations show that the proposed algorithm can effectively estimate the CFO.

目錄
指導教授推薦書
口試委員會審定書
致謝 iii
中文摘要 iv
Abstract v
目錄 vi
圖目錄 viii
第一章 序論 1
1.1 研究動機與背景 1
1.2 研究方法與目的 2
1.3 論文架構 3
第二章 OFDM系統簡介 4
2.1 OFDM簡介 4
2.1.1 OFDM系統功能簡述 4
2.1.2 串列轉並列（S/P） 5
2.1.3 符元間干擾（ISI） 6
2.2 OFDM調變原理 12
2.3 OFDM系統模型 14
2.4 OFDM之優缺點 15
第三章 CFO產生之ICI問題與ICI自消 17
3.1 子載波間干擾（ICI） 17
3.1.1 差動相位位移鍵（DPSK） 21
3.2 ICI自消除演算法 23
3.2.1 ICI自消預先編碼 23
3.2.2 使用ICI自消除機制效能模擬 26
第四章 使用子空間法之頻移估測 28
4.1 T-MUSIC演算法 28
4.1.1 系統模型 28
4.1.2 頻移估測法 31
4.1.3 篩選特定時間取樣 33
4.2 決策回授之頻移估測法 35
4.3 模擬結果 37
第五章 結論 42
參考文獻 43

 
圖目錄
圖2.1-1 OFDM系統簡易架構圖 5
圖2.1-2 OFDM與FDM之頻譜分佈 6
圖2.1-3 簡易訊號傳輸模型 7
圖2.1-4 Precoder系統架構圖 8
圖2.1-5 決策回授系統架構圖 9
圖2.1-6 CP示意圖 11
圖2.1-7 小於保護區間 12
圖2.1-8 大於保護區間 12
圖2.2-1 OFDM調變與解調之架構圖 13
圖3.1-1 (a)時域訊號長度與取樣週期關係 17
圖3.1-1 (b)頻域子載波間距與取樣頻率關係 18
圖3.1-2 ICI 干擾分析圖 20
圖3.1-3 QPSK 21
圖3.2-1 ICI自消除方法架構圖 23
圖3.2-2 ICI自消係數比較 25
圖3.2-3 (a) 未使用ICI自消機制不同CFO對系統影響 (b) 使用ICI自消機制不同CFO對系統影響 27
圖4.1-1 (a) 等化因子在 之分布 (b) 等化因子在 之分佈 34
圖4.2-1不同CFO效能比較圖 36
圖4.3-1 (a) CFO=0.3之虛擬頻譜估測圖 (b) CFO=-0.47之虛擬頻譜估測圖 38
圖4.3-2 不同ICI自消階數之MSE比較圖 39
圖4.3-3 系統於不同CFO時效能比較(a) CFO=0.1 (b) CFO=0.6 (c) CFO=1.2 41

[1] R. W. Chang and R. A. Gibby, “A theoretical study of performance of an orthogonal multiplexing data transmission scheme,” IEEE Trans. Commun., vol. COM-16, pp.529 -540, Aug. 1968.
[2] IEEE Std. 802.11b, Part 11：Wireless LAN medium access control (MAC) and physical layer (PHY) specifications：high-speed physical layer in the 2.4GHz Band, 1999.
[3] European Telecommunication Standard Institute, “Radio Broadcast Systems；Digital Audio Broadcasting (DAB) to Mobile, Portable and Fixed Receivers,” (Draft) prevision ETS 300 401, Mar. 1994.
[4] R. W. Chang and R. A. Gibby, “A theoretical study of performance of an orthogonal multiplexing data transmission scheme,” IEEE Trans. Commun., vol. COM-16, pp.529 -540, Aug. 1968.
[5] R. Li and G. Stette, “Time-limited orthogonal multicarrier modulation schemes”, IEEE Trans. Commun., vol. 43, pp.1269 -1272 , 1995.
[6] Y. Zhao, J.-D. Leclercq and S.-G. Häggman, “Intercarrier Interference compression in OFDM communication systems by using correlative coding,” IEEE Trans. Commun. Lett., vol.2, no.7, pp. 214-216, Aug. 1998.
[7] Y. Zhao and S.-G. Häggman, “Sensitivity to Doppler Shift and Carrier Frequency Errors in OFDM Systems -- The Consequences and Solutions,” in Proc. IEEE 46th Vehicular Technology Conf., Atlanta GA, pp.1564-1568, 1996.
[8] Yuping Zhao, Sven-Gustav Häggman, “Intercarrier Interference Self-Cancellation Scheme for OFDM Mobile Communication systems.” IEEE Trans. Communications, vol. 49, no. 7, pp.1185-1191, July 2001.
[9] 賴重安, “OFDM系統子載波間干擾自消除機制研究,” 長庚大學電機研究所碩士論文, 2013.
[10] Kwang Done Choe, Si Chul Kim, and S. K. Park, “Pre-Scrambling Method for PAPR Reduction in OFDM Communication Systems. ” IEEE Transactions on Consumer Electronics, vol.50, no. 4, November 2004.
[11] Yung-Yi Wang, “A Subspace-Based CFO Estimation Algorithm for General ICI Self-Cancellation Precoded OFDM Systems” IEEE Transactions on wireless communications, vol. 12, no. 8. August 2013.
[12] Miin-Jong Hao, “Decision Feedback Frequency Offset Estimation and Tracking for General ICI Self-Cancellation Based OFDM Systems,” IEEE Transactions on Broadcasting, vol. 53, no. 2, June 2007.