Science Fair Project Encyclopedia
Digital terrestrial television
Digital Terrestrial Television (DTTV or DTT) is an implementation of digital technology to provide a greater number of channels (SDTV) and/or better quality of picture (EDTV, HDTV) and sound (AC3, Dolby Digital) through a conventional aerial instead of a satellite dish or cable connection. The technology used is ATSC in North America, ISDB-T in Japan and DVB-T in Europe; the rest of the world being mostly undecided yet.
DTTV is transmitted on radio frequencies that are similar to 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).
The amount of data that can be transmitted (and therefore the number of channels) is directly affected by the modulation method of the channel. The modulation method is COFDM with either 64 or 16 state Quadrature Amplitude Modulation (QAM). In general a 64QAM channel is capable of transmitting a greater bitrate, but is more susceptible to interference.
The digital data is being compressed lossily, usually with MPEG-2.
DTTV is received via a set-top-box, or integrated receiving device, that decodes the signal received via a standard aerial. However, due to frequency planning issues, an aerial upgrade may be required if the DTTV multiplexes lie outside the bandwidth of the installed aerial (quite common in the UK).
DTT Around the world
The UK leads the world in DTTV uptake by the general population, using the Freeview and Top Up TV platforms. In Germany, on 4th August 2003, Berlin became the first city in the world to switch off its analogue broadcast signal and transfer completely to digital TV.
See also : Digital television
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