Digital TV StandardstMyn1 Digital TV Standards All digital TV variants can carry both standard- definition television (SDTV) and high-definition television (HDTV). SDTV digital television systems derive much of their structure from the need to be compatible with analog television. In particular, the interlaced scan is a legacy of analog television.

Digital TV StandardstMyn2 Attempts were made during the development of digital television to prevent a repeat of the fragmentation of the global market into different standards (that is, PAL, SECAM, NTSC). However, once again, the world could not agree on a single standard, and, hence, there are three major standards in existence: the European DVB system and the U.S. ATSC system, plus the Japanese system ISDB. In addition, for example Korea has adopted S-DMB for satellite mobile broadcasting and China has announced DMB-T/H.

Digital TV StandardstMyn3 DVB, short for Digital Video Broadcasting, is a suite of internationally accepted open standards for digital television. DVB standards are maintained by the DVB Project, an industry consortium with more than 270 members, and they are published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union (EBU).

Digital TV StandardstMyn4 DVB systems distribute data using a variety approaches, including by satellite (DVB-S, DVB-S2), cable (DVB-C), terrestrial television (DVB-T) and terrestrial television for handhelds (DVB-H). These standards define the physical layer and data link layer of the distribution system. Devices interact with the physical layer via a synchronous parallel interface (SPI), synchronous serial interface (SSI), or asynchronous serial interface (ASI). All data is transmitted in MPEG-2 transport streams with some additional constraints.

Digital TV StandardstMyn5 These distribution systems differ mainly in the modulation schemes used, due to the different technical constraints. DVB-S uses QPSK, 8PSK or 16-QAM. DVB-S2 uses QPSK, 8PSK, 16APSK or 32APSK, at the broadcasters decision. QPSK and 8PSK are the only versions regularly used. DVB-C (VHF/UHF) uses QAM: 16-QAM, 32-QAM, 64- QAM, 128-QAM or 256-QAM. Lastly, DVB-T (VHF/UHF) uses 16-QAM or 64-QAM (or QPSK) in combination with COFDM and hierarchical modulation.

Digital TV StandardstMyn6 The DVB Multimedia Home Platform (DVB-MHP) defines a Java-based platform for the development of consumer video system applications. In addition to providing abstractions for many DVB and MPEG-2 concepts, it provides interfaces for other features like network card control, application download, and layered graphics.

Digital TV StandardstMyn7 The Advanced Television Systems Committee (ATSC) is the group that developed the ATSC digital television standard for the United States, and some other countries have also adopted it. The ATSC standards are intended to replace the NTSC system used mostly in North America. Many aspects of ATSC are patented, including elements of the MPEG video coding, the AC-3 audio coding, and the 8-VSB modulation. As with other systems, ATSC depends on numerous interwoven standards.

Digital TV StandardstMyn8 For transport, ATSC uses the MPEG-2 Systems specification, known as Transport stream, to encapsulate data, subject to certain constraints. ATSC uses 188-byte MPEG transport stream packets to carry data. Before decoding of audio and video takes place, the receiver must demodulate and apply error correction to signal. Then, the transport stream may be demultiplexed into its constituent streams.

Digital TV StandardstMyn9 Dolby Digital AC-3 is used as the audio codec, though it was officially standardized as A/52 by the ATSC. It allows the transport of up to five channels of sound with sixth channel for low-frequency effects (the so- called 5.1 configuration). ATSC signals are designed to use the same 6 MHz bandwidth as NTSC television channels. Once the video and audio signals have been compressed and multiplexed, the transport stream can be modulated in different ways depending on the method of transmission.

Digital TV StandardstMyn10 Terrestrial broadcasters use 8-VSB modulation that can transfer at a maximum rate of Mbits/sec, sufficient to carry several video and audio programs and metadata. Cable television plants generally operate at a higher signal-to-noise ratio and can use 16-VSB or 256- QAM to achieve a throughput of Mbits/sec, using the same 6 MHz channel.

Digital TV StandardstMyn11 Integrated Services Digital Broadcasting (ISDB) is the digital television and digital audio broadcasting format that Japan has created to allow radio and television stations there to convert to digital. ISDB is maintained by the Japanese organisation ARIB. The core standards of ISDB are ISDB-S (satellite television), ISDB-T (terrestrial), ISDB-C (cable) and 2.6 GHz band mobile broadcasting which are all based on MPEG-2 video and audio coding as well as the transport stream described by the MPEG-2 standard, and are capable of high definition television (HDTV).

Digital TV StandardstMyn12 ISDB has adopted the MPEG-2 video and audio compression system. The various flavours of ISDB differ mainly in the modulations used, due to the requirements of different frequency bands. The 12 GHz band ISDB-S uses PSK modulation and ISDB-T (in VHF and/or UHF band) uses COFDM with PSK/QAM. Some comparisons have been made in the Figure 1.

Digital TV StandardstMyn13 Figure 1. Some characteristics of the three DTV systems.