數位電視場測與結果分析

Abstract

我國在1998年5月正式確定採用美國ATSC DTV標準作為台灣數位電視地面廣播系統之標準，並且擬定了數位電視開播時程。為了確定數位電視的服務區域和制定傳輸參數，我們必須了解到數位電視信號在地面傳輸之各種特性、可能受到的干擾以及信號和畫面品質之間的關係。 在這篇論文當中包含了兩階段的量測。第一階段量測是調查類比電視信號在VHF/UHF頻道的傳播特性，其主要目的是確定這兩者不同之處。在第二階段，我們則量測數位電視信號，並針對數位電視與類比電視的服務效能作一比較。在類比電視量測中，我們選擇了45個量測點；數位電視量測則有88個量測點，量測範圍涵蓋了整個大台北地區(包括台北、桃園及新竹等地)。量測點的地理環境則包含了都會區、鄉鎮區及郊區。所有的信號是由台北的竹子山發射站所發射的。 一般而言，數位電視的畫面品質和電場強度以及信號雜訊比有關。此外，嚴重的多重路徑干擾可能會導致傳輸錯誤。在45個重複量測類比電視信號和數位電視信號的量測點上，就畫面品質和服務效能而言，數位電視系統遠比類比電視系統還要好。

In May 1998, Taiwan announced a formal decision on adopting the ATSC Digital Television (DTV) Standard as its local digital terrestrial broadcasting standard. An aggressive DTV broadcasting schedule was also being set. In order to define the DTV service area and specify the transmission parameters, we need to know the characteristics of the DTV signal over the irregular terrain, the impact of interference, and the relationship between the signal power and video quality. There were two phases in this study. In phase I, we investigated the NTSC broadcasting signal characteristics over the VHF and the UHF channels. The objective is to identify their differences. In phase II, we measured the broadcasting DTV signal and compared the DTV service availability against the NTSC service availability. We selected 45 test sites for NTSC measurements and 88 test sites for DTV measurements, covering Taipei city and its vicinity (including Taipei, Tao-Yuan and Hsin-Chu). Test sites were chosen to include three types of environment: urban suburban and rural areas. The transmitter was located on the Chu-Zue Mountain in Taipei. In general, the video quality of DTV is related to the field strength and the S/N. In addition, multipath impairments may result in transmission errors. Among the 45 test sites that both NTSC and DTV tested, DTV system is obviously much better than the NTSC system on video quality and service availability.