目前正交分頻多工技術已被廣泛的應用在多種不同的通訊系統上，以無線網路為例，藉由此技術的保護區間訊號可以有效降低多路徑通道對於系統效能的影響。雖然正交分頻多工技術非常適合運用在無線網路上，不過首先便是要能克服符碼時間偏移的問題。由於符碼時間偏移不僅會破壞系統子載波間的正交性，不當的符碼時間估測值亦會影響接收端的DFT運算，因而引起嚴重的位元錯誤率效能下降。所以本論主要研究應用於無線網路架構的符碼時間估測演算法－延遲與相關演算法，並進一步簡化其架構。由於簡化後的符碼時間估測演算法有較低的運算量，因此適合運用於低功率的無線個域網路IEEE P802.15上。

Nowadays, the OFDM system is widely used in different communication systems. For example, wireless network can abate the multipath effect by using guard interval signal in OFDM system. Even though OFDM is suitable for being applied in wireless network, we have to overcome the problem of symbol timing offset. Because symbol timing offset not only ruins the orthogonality among the subcarriers, but also affects the result of DFT computation in receiver. This thesis is to study the delay and correlate algorithm which is the symbol timing estimation algorithm in wireless network. Based on the algorithm and then to simplify its processing, the simplified structure can reduce the computation in symbol timing estimation and good for mobile devices. Finally, we make use of this merit being applied to the IEEE P802.15 system that emphasized the lower power consumption.

[1] Pandharipande, A., “Principles of OFDM,” IEEE Potentials, Volume 21, Issue 2 , 2002.
[2] Schmidl, T.M.; Cox, D.C, “Robust frequency and time synchronization for OFDM,” IEEE Transactions on Communications , Volume 45, Issue 12, 1997.
[3] Luise, M.; Reggiannini, R., “Carrier frequency acquisition and tracking for OFDM systems,” IEEE Transactions on Communications, Volume 44, Issue 11, 1996.
[4] Juha Heiskala, John Terry, OFDM Wireless LANs: A Theoretical and Practical Guide, SAMS, 2002.
[5] Czylwik, A., “Synchronization for single carrier modulation with frequency domain equalization,” IEEE Conference on Vehicular Technology, Volume 3, 1998.
[6] Anuj Batra et al.; Texas Instruments et al., “Multi-band OFDM Physical Layer Proposal for IEEE802.15 Task Group 3a,” 2004.
[7] van de Beek, J.J.; Sandell, M.; Borjesson, P.O., “ML estimation of time and frequency offset in OFDM system,” IEEE Transactions on Signal Processing, Volume 45, Issue 7, 1997.
[8] van de Beek, J.J.; Sandell, M.; Borjesson, P.O., “Low-complex frame synchro-
nization in OFDM system,” IEEE International Conference on Universal Personal Communications, 1995.
[9] Schmidl, T.M.; Cox, D.C, “Low-overhead, low-complexity [burst] synchro-
nization for OFDM,” IEEE International Conference on Communications , Volume 3, 1996.
[10] T. Rappaport, Wireless Communications: Principles and Practice 2/e, Prentice Hill, 2002.
[11] Farrow, C.W., “A continuously variable digital delay element,” 1988., IEEE International Symposium on Circuits and Systems, Volume 3, 1988.
[12] Meng-Han Hsieh; Che-Ho Wei, “A low-complexity frame synchronization and frequency offset compensation scheme for OFDM systems over fading channels,” IEEE Transactions on Vehicular Technology, Volume 48, Issue 5, 1999.