DMB-T數位電視廣播採用時域同步正交分頻多工(TDS-OFDM)調變技術，利用PN序列取代傳統CP-OFDM系統的循環字首做為保護間隔，並同時作為系統同步與通道估測。因此訊號在頻域上沒有放置導引信號，比典型CP-OFDM系統具有更高的頻譜效率。 對於OFDM系統而言，接收機系統同步是一個重要的課題，如果發生符元時間誤差、載波頻率誤差以及取樣率誤差，將造成載波間干擾與符元間干擾現象，對系統效能影響甚大。本論文目的是針對DMB-T系統設計一套內接收機同步機制，包括時間同步、載波頻率同步與取樣率同步，另外也包括系統通道估測與等化。同步動作主要依賴PN序列之循環擴展結構與相關性並結合掃頻、延遲相關器和再取樣器進行估測；通道估測依賴在時域上與本地端PN序列進行線性相關得到，若PN序列相位為已知，提出時域之LS通道估測。最後給出內接收機之完整架構與系統效能，證實設計之架構適合DMB-T系統。 The digital multimedia broadcasting – terrestrial (DMB-T) adopt the time domain synchronization-orthogonal frequency division multiplexing (TDS-OFDM). Instead of cyclic prefix scheme in traditional CP-OFDM systems, PN sequence has been proposed for guard interval, system synchronization and channel estimation in DMB-T system. TDS-OFDM provides higher spectrum efficiency than CP-OFDM due to no pilot in the transmitted signal. OFDM systems are deeply affected by synchronization errors including timing offset, carrier frequency offset and sampling frequency offset, which cause inter-carrier-interference and inter-symbol-interference. Hence the synchronization system is essential in receiver. In this thesis, a whole synchronization scheme including symbol synchronization, carrier frequency synchronization and sampling frequency synchronization for DMB-T system is presented. Synchronization errors are estimated by frequency-scan, delay correlator and re-sampler based on the correlation and cyclic-extend architecture of PN sequence. In addition, Channel estimation and equalization are discussed. In time domain, channel estimation is based on the correlation between the received signals and the locally generated PN sequence. If the phase of PN sequence is known, channel can be estimated by time domain least-square. Finally, the architecture design of inner receiver is suitable for DMB-T system.
