數位電視系統與場測

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，並在1998年成立了數位電視的發射站台來進行各種測試，其中一項測試重點為室內量測，即為本篇論文的重點所在。 數位電視的室內接收效能，其優劣主要乃由量測點的室內環境、建築物的架構、接收天線的種類、以及信號和干擾間的關係所決定。在本篇論文中，我們設計四種不同的接收系統，包含3種天線，並搭配Pre-amplifier的有無，分別量測數位電視與類比電視信號，比較其接收效能的差異。其目的主要在了解於各種不同的接收環境下，例如：穿透物質，樓層高低，與有無車輛或人員移動的差異下，數位的接收效果。 由分析量測結果可知，數位電視的接收效能和電場強度、信號雜訊比以及多重路徑干擾有關。當使用方向性高且低雜訊的天線會有較好的接收，但是，當我們以一般市售的主動式天線進行量測時，其接收效果並不佳。這可能是因為帶通濾波器頻寬太寬或Pre-amplifier的noise 太大，造成其接收效能大為降低。此外，在DTV與NTSC比較上，位於穿透損失大的環境，NTSC略優於DTV；但若在穿透損失小的環境，DTV則遠優於NTSC。

Taiwan formally adopted the ATSC Digital Television (DTV) system as its digital terrestrial broadcasting standard in May 1998. A simple DTV transmission station was set up in 1998 for conducting various tests. One important test item is the DTV indoor reception capability, which is the focus of this study. For a given receiver, the indoor DTV reception, in general, depends on the test site building structure, its surrounding outdoor environment and the receiver antenna system. In this thesis, four antenna systems, consisting three types of antennas with or without pre-amplifier, have been tested. We conducted both DTV and NTSC receiving tests for comparison. We like to find out the impact of various environmental factors on DTV reception such as penetration loss due to different building material, indoor furniture, floor level, and the indoor and outdoor traffic. Therefore, thirty-five test sites were carefully selected, examined, and test data recorded. From the communications system viewpoint, the DTV reception is decided by the field strength, signal-to-noise ratio (S/N), and multipath interference. A receiver system with low noise pre-amplifier and high-directional antenna is shown to have the best reception. In contrast, a typical (low-priced) commercial active antenna has an inferior performance, which may be due to its poor antenna directionality and wide-bandwidth amplifier with high internal noise. Our test data indicate that the DTV reception is typically better than that of NTSC on the same site when the penetration loss is low. However, in the high penetration loss cases, NTSC is somewhat superior to DTV although its CCIR picture quality rating is no better than 3. 2. ATSC DTV SYSTEM OVERVIEW 2.1 ATSC VIDEDO CODING 2.1.1 Video Profile and Level 2.1.2 The Video Representation 2.1.3 Temporal Redundancy Removal 2.1.4 Spatial Redundancy Removal 2.1.5 Quantizing and Run-length coding 2.1.6 Channel Buffer and Decoder 2.2 ATSC AUDIO CODING 2.2.1 The Overview of AC-3 Audio Compression 2.2.2 The Bit stream of AC-3 2.2.3 The Services of AC-3 2.3 TRANSPORT SYSTEMS 2.4 RF/TRANSMISSION SYSTEMS 2.4.1 VSB Transmission Overview 2.4.2 Data Structure 2.4.3 The 8-VSB Spectrum 3. INDOOR FIELD TEST SYSTEMS 3.1 TRANSMISSION SYSTEM 3.1.1 Transmitter Configuration 3.1.2 Signal Characteristics 3.2 RECEIVING SYSTEMS 3.2.1 DTV Receiver 3.2.2 NTSC Receiver 4. INDOOR FIELD TEST PLAN 4.1 TEST SITE SELECTION 4.2 DTV INDOOR FIELD TEST PROCEDURES 4.3 NTSC INDOOR FIELD TEST PROCEDURES 5. TEST SITES AND RESULTS 5.1 THE DIRECTORATE GENERAL OF TELECOMMUNICATION BUILDING 5.2 THE CHINA TELEVISION CORPORATION BUILDING 5.3 THE NATIONAL CENTRAL UNIVERSITY BUILDING 6. TEST DATA ANALYSIS 6.1 ESTIMATES OF PENETRATION LOSS 6.2 STATISTICS OF THE RECEPTION 6.3 ANALYSIS OF THRESHOLD C/N 6.4 RELATIONSHIP BETWEEN TAP ENERGY AND THRESHOLD C/N 6.5 SITE MARGIN AND FIELD STRENGTH 6.6 INDOOR RECEPTION FOR DTV AND NTSC 6.7 INDOOR AND OUTDOOR 6.8 THE DISCUSSION ABOUT THE FAILURE SITES 7. CONCLUSION BIBLIOGRAPHY APPENDIX A