在本篇論文中，我們基於正交分頻多工雙向放大轉送中繼系統提出一種新的前置資料設計，此前置資料中包含兩個訓練符元，用於時間同步、載波頻率偏移估測與通道估測。第一個訓練符元包含一個具有良好特性的特殊複數序列，其序列與自己的共軛複數循環位移做Hadamard乘積會是一個近似完美序列。第二個訓練符元中，我們將兩個不完全Zadoff-Chu序列擺放在頻域交錯的子載波集合上，使此兩個序列在時域及頻域上能彼此區隔。我們將所提出的前置資料用於雙向中繼系統中的其中一個終端點，在相同的前置資料中將第一個訓練符元做適當的循環位移後可用於另一個終端點，藉由第一個訓練符元我們利用自相關與交相關來得到不受載波頻率偏移影響的初步時間同步，接著可以由第二個訓練符元來完成載波頻率偏移估測、精確的時間同步以及通道估測。與現存的相關技術比較下，我們所提出之方法可以得到較好的效能，且不會有太大的運算複雜度增加。

In this thesis, a novel preamble structure of two time-domain training signals is proposed for time synchronization, carrier frequency offset (CFO) estimation, and channel estimation in orthogonal frequency-division multiplexing (OFDM)-based two-way amplify-and-forward (AF) relay systems. The first training signal consists of a specific complex sequence with a nice property that the Hadamard product of the sequence and its complex-conjugate circular-shift version (excluding the zero-shift case) is a near-perfect sequence. The second training signal is a sequence whose frequency-domain counterpart is formed by placing two partial Zadoff-Chu sequences proposed recently on subcarriers in an interleaved manner, where these two sequences are separable in both of the frequency and time domains. Using the proposed preamble for one terminal of the two-way system and a similar preamble with the first training signal circularly shifted appropriately for the other terminal, we can conduct CFO-immune coarse time synchronization for both terminals based on auto-correlation and cross-correlation in the first half of the training period, and then perform CFO estimation, fine time synchronization, and channel estimation in the second half. As compared to existing related works, the proposed approach achieves better performance with a little increase in the computational complexity.

Abstract i
Contents ii
List of Figures iv
List of Tables vi
I. INTRODUCTION 1
II. SYSTEM MODEL 3
III. RELATED WORKS 6
A. A Related Work for OFDM Systems [11] 6
B. A Related Work for Cooperative Systems [12] 8
C. Some Related Works for Two-Way AF Relay Systems 11
IV. The PROPOSED METHODS 12
A. Motivation 12
B. The Preamble Design 13
C. Coarse Timing Estimation 16
D. CFO Estimation and Compensation 17
E. Joint Fine Timing Estimation and Channel Estimation 18
V. SIMULATION RESULTS 20
VI. CONCLUSION 30
REFERENCES 31

[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.
[2] R. van Nee and R. Prasad, OFDM for Wireless Multimedia Communications. Norwood, MA: Artech House, 2000.
[3] IEEE Standard for Information Technology-Telecommunications and Information Exchange Between Systems Local and Metropolitan Area Networks-Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, IEEE Std. 802.11-2012 (Revision of IEEE std. 802.11-2007), Mar. 2012, pp. 1-2793.
[4] IEEE Standard for Air Interface for Broadband Wireless Access Systems, IEEE Std. 802.16-2012 (Revision of IEEE Std. 802.16-2009), Aug. 2012, pp. 1-2542.
[5] “Technical specification group radio access network; Physical layer aspects for evolved universal terrestrial radio access (UTRA) (Release 7),” Cedex, France, 3GPP TR 25.814, V7.1.0, Sep. 2006.
[6] U. Reimers, “DVB-T: The COFDM-based system for terrestrial television,” Electron. Commun. Eng. J., vol. 9, no. 1, pp. 28-32, Feb.1997.
[7] S. Zhang, S.-C. Liew, and P. P. Lam, “Physical-layer network coding,” in Proc. MobiCom 2006, Los Angeles, California, Sept. 2006, pp. 358-365.
[8] S. G. S. Katti and D. Katabi, “Embracing woreless interference: analog network coding,” Computer Science and Artificial Intelligence Laboratory, Technical Report, Feb. 2007.
[9] C. E. Shannon, “Two-way communication channels,” in Proc. 4th Berkeley Symp. Math. Stat. Prob., 1961, pp. 611-644.
[10] B. Rankov and A. Wittneben, “Spectral efficient signaling for half-duplex relay channels,” in Proc. 2005 Asilomar Conf. Signals, Systems, and Computers, Pacific Grove, California, Oct./Nov. 2005, pp. 1066-1071.
[11] Y. Liu, H. Yu, F. Ji, F. Chen, and W. Pan, “Robust timing estimation method for OFDM systems with reduced complexity,” IEEE Commun. Letters, vol. 18, no. 11, pp. 1959-1962, Nov. 2014.
[12] C.-L. Wang, H.-C. Wang, and Y.-Y. Chen, “A synchronization scheme based on partial Zadoff-Chu sequences for cooperative MIMO OFDM systems,” in Proc. IEEE Wireless Communications and Networking Conf., Paris, France, Apr. 2012.
[13] G.Wang, F. Gao, and C. Tellambura, “Joint frequency offset and channel estimation methods for two-way relay networks,” in Proc. 2009 IEEE Global Telecommun. Conf. (GLOBECOM 2009), Honolulu, Hawaii, USA, Nov./Dec. 2009.
[14] G.Wang, F. Gao, Y. Wu, and C. Tellambura, “Joint CFO and channel estimation for CP-OFDM modulated two-way relay networks,” in Proc. 2010 IEEE Wireless Commun. And Networking Conf. (WCNC 2010), Sydney, Australia, Apr. 2010.
[15] G. Wang, F. Gao, Y. Wu, and C. Tellambura, “Superimposed pilot based joint CFO and channel estimation for CP-OFDM modulated two-way relay networks,” in Proc. 2010 IEEE Global Telecommun. Conf. (GLOBECOM 2010), Miami, Florida, USA, Dec. 2010.
[16] G. Wang, F. Gao, Y. Wu, and C. Tellambura, “Joint CFO and channel estimation for OFDM-based two-way relay networks,” IEEE Trans. Wireless Commun., vol. 10, no. 2, pp. 456-465, Feb. 2011.
[17] C.-L. Wang, P.-C. Chiu, and H.-C. Wang, “Joint time synchronization and channel estimation for two-way amplify-and-forward relay systems,” in Proc. 2014 IEEE Global Telecommun. Conf. (GLOBECOM 2014), Austin, Texas, USA, Dec. 2014.
[18] S. Chang and B. Kelley, “An efficient time synchronization scheme for broadband two-way relaying networks based on physical-layer network coding,” IEEE Commun. Letters, vol. 16, no. 9, pp. 1416-1419, Sep. 2012.
[19] Z. Jiang, H. Wang, and Z. Ding, “Joint symbol timing and channel estimation in two-way multiple antenna relay networks,” in Proc. 2012 IEEE Veh. Technol. Conf. –Fall (VTC 2012-Fall), Quebec City, Canada, Sep. 2012.
[20] C.-L. Wang, H.-C. Wang, and Y.-H. Chen, “A synchronization scheme based on interleaved partial Zadoff-Chu sequences for cooperative MIMO OFDM systems,” in Proc. 2013 IEEE Veh. Technol. Conf. –Fall (VTC 2013-Fall), Las Vegas, NV, Sep. 2013.
[21] M. Morelli, and U. Mengali, “An improved frequency offset estimator for OFDM applications,” IEEE Commun. Letters, vol. 3, no. 3, pp. 75-77, 1999.