基於多載波/多碼下一代數位電視廣播系統之研究

Abstract

由於DVB-T是以正交分頻多工傳輸技術為架構，而正交分頻多工傳輸系統效能會受限於多路徑通道干擾。針對這個問題，本論文提到一種使用完美正交性的華氏碼作為展頻碼，也就是將正交分頻多工傳輸技術結合分碼多重存取傳輸技術，使訊號分散在各個次載波上傳送，並在系統接收端使用軟性多路徑干擾消除技術，以消除通道對傳送訊號造成的多路徑干擾，來提升系統效能。另外介紹了一種編碼增益直逼雪儂極限的編碼方式，低密度同位檢查碼，以期能取代DVB-T兩層編碼。並在系統接收端使用包含軟性多路徑干擾消除器之渦輪等化技術，利用等化器和編碼器互相傳遞軟性資訊，來更一步提升系統效能。最後經由電腦模擬驗證上述所有技術在多徑衰減通道中可有效的提高效能。

DVB-T system is based on OFDM system, but the performance of OFDM system is limited by the interference of multi-path channel. To solve this problem, in this thesis we combine the OFDM and CDMA transmission techniques with walsh codes which has perfect orthogonality for data spreading. And we also use the iterative soft multi-path interference cancellation to improve the performance of the system. In addition, we use LDPC code, which can be close in the Shannon limit, to replace two codes which are used by DVB-T system. And we also propose a turbo equalization to improve the performance of the multi-path interference cancellation and the channel decoder by using the iterative pass of soft information between equalizer and decoder. Finally, the performances of these techniques mentioned above were evaluated by computer simulation in multi-path fading channels and from the simulation results, the performances are improved effectively.