Digital Terrestrial Televisión (DTTV or DTT)

Digital Terrestrial Television (DTTV or DTT) is the technological evolution and advance from analogue terrestrial television, which broadcasts land based (terrestrial) signals. The purpose of digital terrestrial television, similar to digital versus analogue in other platforms such as cable, satellite, telecoms, is characterised by reduced use of spectrum and more capacity than analogue, better-quality picture, and lower operating costs for broadcast and transmission after the initial upgrade costs. A terrestrial implementation of digital television technology uses aerial broadcasts to a conventional antenna (or aerial) instead of a satellite dish or cable connection.

Competing variants of digital terrestrial television technology are used around the world. Advanced Television Standards Committee ATSC is the one used in North America and South Korea, an evolution from the analogue National Television Standards Committee standard NTSC. ISDB-T is used in Japan, with a variation of it used in Brazil, Argentina, Peru, Chile^[1] and most recently Venezuela, while DVB-T is the most prevalent, covering Europe, Australia, New Zealand, Colombia, Uruguay and some countries of Africa.DMB-T/H is China's own standard (including Hong Kong, 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. The United States of America has switched from Analogue to Digital terrestrial television, while Europe is hoping to have completed its switchover mostly by 2012.

Transmission

DTTV is transmitted on radio frequencies through the airwaves that are similar to standard analogue 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.^[2] 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 bitrate, but is more susceptible to interference. 16 and 64QAM constellations can be combined in a single multiplex, providing a controllable degradation for more important programme streams. This is called hierarchical modulation.ref

New developments in compression have resulted in the MPEG-4/AVC standard which enable three high definition services to be coded into a 24 Mbit/s European terrestrial transmission channel.^[2]

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.

Advantages and disadvantages

Advantages:

• Digital reception tends to be better overall, particularly with a good signal. With a weaker signal there is little perceptible difference, in fact analogue can be better.^{[citation needed]}
• It is easier to obtain the optimum digital picture than the optimum analogue picture.
• Many more channels can fit on the digital transmission.
• Interactive (red button) services can be provided.

Disadvantages:

• New equipment (Set-top box) may be required.
• Increased electricity consumption by the digital receiving equipment.^{[citation needed]}
• An upgraded antenna installation may be required.
• Analogue requires lower signal strength to get a viewable picture. By extension, digital does not degrade as gracefully as analogue. For example, with low signal strength an analogue picture gets fuzzy (but is still viewable) while a digital picture freezes and stops updating.
• Switching channels is slower because of the time delays in decoding digital signals.

Reception

DTTV is received via a digital set-top box, or integrated receiving device, that decodes the signal received via a standard aerial antenna. However, due to frequency planning issues, an aerial with a different group (usually a wideband) may be required if the DTTV multiplexes lie outside the bandwidth of the originally installed aerial.^{[clarification needed]} This is quite common in the UK, see external links.