數位電視廣播接收機之高速環境下同步問題之設計

Abstract

近年來，正交分頻多工系統(OFDM)在寛頻通訊應用上愈來愈普及。然而，相較於單載波系統，OFDM系統對於同步問題相當敏感。由於傳送端與接收端振盪器的不完全相同，因此會有取樣頻率偏移的現象，進而導致ICI與ISI的問題。此外，若考慮無線傳輸中，接收端與傳輸端的相對速度不為零，此時會產生都卜勒效應，而使得同步的維持更為困難。本論文中，我們主要探討OFDM系統同步的問題，並以數位電視廣播系統(DVB-T)為討論的平台。DVB-T同步問題的解決方法，已在很多文獻中提出過。然而，大部份都是針對無相對速度或低相對速度下的同步的解決方法。在本篇論文中，為了克服在高速移動下，都卜勒效應所帶來的問題，我們提出了一個新的同步問題的解決方法。之後，我們也將藉由電腦模擬，證明我們提出的方法在高速移動下，仍有很好的效能。

In recent years, OFDM becomes popular for broadband communications. However, compared to single carrier systems, OFDM system is very sensitive to the synchronization problem. The mismatch of crystal oscillators between the transmitter and the receiver circuitry causes the sampling clock frequency offset and will introduce ICI and ISI. Furthermore, if the mobile wireless transmission is considered, the synchronization maintenance will become more difficult because of the Doppler effect. The main topic of this thesis is to discuss the synchronization problems of OFDM systems. DVB-T is selected as the system platform for discuss here. Many synchronization algorithms had been proposed and are applied successfully in DVB-T demodulators. However, most of them can operate properly for stationary wireless and low-mobility receiving. To combat the severe Doppler effect in high-mobility environment, effective synchronization algorithms are necessary. Therefore, the synchronization algorithm in high-mobility environment is mainly concerned in this thesis. We propose an innovative synchronization algorithm, which is shown almost not to be affected by the effect caused by high mobility.