OFDM系統具有抵抗多重路徑干擾及頻譜使用效率高等優異特性，其中抵抗多重路徑干 擾是藉由前置循環字首(Cyclic Prefix,CP) 及多載波之特性以達到免除符碼間干擾(Inter Symbol Interference,ISI)，而頻譜使用效率高則是運用多載波正交特性達到的。在高速 移動環境下，OFDM 訊號經過時變的通道，接收到的訊號會有都普勒擴展(Doppler Spread) 的現象，破壞了子載波間的正交性，而引起載波間干擾(ICI)，降低通道估測準確 度，並使得最高容許的接收速度下降。本論文參考DVB-T/T2 系統，結合傳送端分集技 術並改良通道估測方式。更進一步修改規格使其更適合高速移動下的環境。 OFDM systems exhibit advantageous characteristics in combating multi-path transmission and spectral efficiency, which use cyclic-prefix to overcome the inter-symbol interference (ISI) effect caused in multi-path transmission and multi-carriers with orthogonality to achieve high spectral efficiency. In high mobility environment, when the orthogonal multi-carrier signal passes through time-varying channel, inter-carrier interference (ICI) is resulted due to the loss of orthogonality of subcarriers. The degradation of the system performance due ICI is proportional to the Doppler spread, and thus a limitation in the velocity of the mobile receiver is inferred in OFDM systems. In this thesis we study on using transmitter diversity to improve the performance of OFDM systems in high mobility environment. We propose a modification of the transmitter diversity technique in DVB-T2 standard, which is designed originally for fixed reception, to make it more suitable for high mobility reception. vi
