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Digital terrestrial television (DTTV or DTT) is a technological evolution of broadcast television and an advancement over analog television. DTTV broadcasts land-based (terrestrial) signals. The advantages of ''digital'' terrestrial television, are similar to digital versus analog in platforms such as cable, satellite, and all telecommunications; the efficient use of spectrum and provision of more capacity than analog, better quality images, and lower operating costs for broadcast and transmission (after the initial upgrade costs). A terrestrial implementation of digital television (DTV) technology uses an aerial to broadcast to a conventional television antenna (or aerial) instead of a satellite dish or cable television connection. Competing variants of broadcast television systems are being used around the world. Advanced Television Standards Committee created the ATSC standards that use an ATSC tuner in North America and South Korea—an evolution from the analog National Television System Committee (NTSC) standard. Integrated Services Digital Broadcasting (ISDB-T) is used in Japan, with a variation of it being used in most of South America. DVB-T is the most prevalent, covering Europe, Australia, New Zealand, Colombia and some countries of Africa. DMB-T/H is China's own standard (including Hong Kong and Cuba, though Hong Kong's cable operators use DVB); the rest of the world remains mostly undecided, many evaluating multiple standards. ISDB-T is very similar to DVB-T and can share front-end receiver and demodulator components. Several European countries have switched from analog to digital terrestrial television. ==Transmission== DTTV is transmitted on radio frequencies through terrestrial space in the same way as standard analog television, with the primary difference being the use of multiplex transmitters to allow reception of multiple channels on a single frequency range (such as a UHF or VHF channel) known as subchannels. The amount of data that can be transmitted (and therefore the number of channels) is directly affected by channel capacity and the modulation method of the channel. The modulation method in DVB-T is COFDM with either 64 or 16-state Quadrature Amplitude Modulation (QAM). In general, a 64QAM channel is capable of transmitting a greater bit rate, but is more susceptible to interference. 16 and 64QAM constellations can be combined in a single multiplex, providing a controllable degradation for more important program streams. This is called hierarchical modulation. New developments in video compression have resulted in the H.264/MPEG-4 AVC standard which enable three high-definition television services to be coded into a 24 Mbit/s European terrestrial transmission channel.〔 The DVB-T standard is not used for terrestrial digital television in North America. Instead, the ATSC standard calls for 8VSB modulation, which has similar characteristics to the vestigial sideband modulation used for analogue television. This provides considerably more immunity to interference, but is not immune — as DVB-T is — to multipath distortion and also does not provide for single-frequency network operation (which is in any case not relevant in the United States). Both systems use the MPEG transport stream and H.262/MPEG-2 Part 2 video codec specified in MPEG-2; they differ significantly in how related services (such as multichannel audio, captions, and program guides) are encoded. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「digital terrestrial television」の詳細全文を読む スポンサード リンク
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