DVB-T

The standard DVB-T is the application of the standard DVB to the hertzian terrestrial transmissions. In France, this system is used for the Digital terrestrial television.

Principle

This standard takes account of the characteristics of a hertzian transmission:

  1. the band available is reduced: 8 MHz in TV,
  2. strong Attenuation on the level of the receiver, the signal report/ratio with noise (SNR) is limited to 18dB approximately,
  3. Interférence with the adjacent channels,
  4. important Interférence (IIS) Intersymbol related to long multitrajets (distance from important propagation)
  5. Présence of impulsive noise (due to the engines, electrical equipment…).

For a traditional modulation, one would be limited by the SNR to a QPSK -6 or QAM -25 and the IIS would extend on several hundreds from symbols. It is thus preferable to use a modulation of the type OFDM.

In fact, the possible presence of echoes extremely which had with the bad acceptance requirements (not released antennas…) impose COFDM.

Alternatives

SFN makes it possible to save the frequencies but requires a more complex receiver, in particular because it imposes a synchronization in time and frequency. This method is used for the Spanish equivalent of TNT.

DAB uses a temporal interlacing which allows a better correction of fast faindings (fading) and thus a mobile use. On the other hand, the band used is narrower and the reduced spectral effectiveness because of the recourse to a modulation QPSK.

See too

  • Digital terrestrial television
  • DAB Audio DIGITAL Broadcasting
  • DVB Digital Video Broadcasting
  • DVB-H Digital Video Broadcasting - Handheld - Used for the reception by a mobile terminal

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