Digital terrestrial

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.

Various systems of digital terrestrial broadcast television systems have been developed:

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.

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