高速移動環境下DVB-T數位電視廣播之通道估測與等化

Channel Estimation and Equalization for DVB-T in High-mobility Environment

施寶鎮(Pao-chen Shih)

指導教授 ： 陳逸民

國立中央大學/資訊電機學院/通訊工程學系/碩士(2007年)

摘要

DVB-T是採用正交分頻多工（OFDM）的技術來傳送，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）及多載波之特性以達到免除碼字間干擾（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，DVB-T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)，使得最高容許的接收速度下降。為了克服高速移動所引起的載波間干擾(ICI)，本論文將前人方法加以改良，介紹了一套適合高速移動接收的通道估測與等化的方法。
過去文獻中，有人採用一階線性的方式來近似通道的變化，估測出ICI的值；本論文中比較了三種不同ICI估測的結果，兩種採用一階線性近似的方法，另一個為二階近似。並利用反覆式ICI消除的方法提升接收機的效能。DVB-T在8K模式、16QAM、編碼率為1/2的條件下，利用此套改良的方法可以使系統的最高容許歸一化都普勒頻率(Normalized Doppler Frequency)由原本的0.086提升到0.13。

關鍵字

高速移動 ； 載波間干擾 ； 歐規數位電視地面廣播

並列摘要

DVB-T is an OFDM system, which exhibits outstanding characteristics in terms of simplicity in combating multi-path transmission and efficiency in spectral utilization. The ISI effect results from the multi-path interference could be successfully eliminated by the insertion of cyclic-prefix and the use of multi-carriers. In high-mobility environment, DVB-T signals pass the time-varying channel, and a loss of sub-carrier orthogonality due to Doppler spread of received signals leads to inter-carrier interference (ICI).This ICI effect degrades the maximum allowed velocity of reception. For eliminating this ICI effect due to high-mobility reception, this thesis modifies other’s methods and introduces a method about channel estimation and equalization, which is suitable high-mobility reception.
Some ICI estimation schemes, which using first order linear model to approximate the channel variations, have been developed. This thesis compares three different schemes of ICI estimation, which two is first order model and the other is second order model, and iteratively repeats ICI cancellation to improve the maximum allowed velocity of reception. This modified method improves the normalized Doppler frequency from 8.6% to 13% for DVB-T signals in 8K mode、16QAM、code-rate=1/2.

並列關鍵字

High-mobility ； DVB-T ； ICI

參考文獻

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