There are many different systems or transmission standards for digital terrestrial television. Northern America uses ATSC, Japan and Brazil have decided for ISDB-T, China uses DMB-T, Korea uses T-DMB, while Europe, Russia, Australia, India and many other countries are using DVB-T system. DVB-T is one of the standards of the DVB consortium which uses OFDM as a basis for modulation.
Each of these systems has advantages and disadvantages. And once you choose a transmission standard you don't change that decision for quite some time. Transmission standard for digital broadcasting is one of the basic properties that defines the equipment (transmitters and receivers) that can be used in specific country. Changing the transmission standard means replacing receivers and transmitters (at least the modulator) with new devices.
Probably the only reasonable way of introducing new broadcast technology is with new service. You simply offer new, attractive service which, of course, uses new technology. Anybody interested in this new service would need to buy a new set-top-box and, therefore, will never ask questions about technology and standards. A brilliant example of this approach is the introduction of HDTV in the United Kingdom. UK was one of the first countries that started using DVB-T back in 1997. Introduction of HDTV will bring two advanced technologies: DVB-T2 as transmission standard and MPEG-4 as coding standard. This way nobody will care about the price of new technology because it is the new service (HDTV) they will pay for.
Advantages of MPEG-4 over MPEG-2 are pretty obvious. But what advantages brings us DVB-T2? The DVB-T2 standard was finalized in June 2008. It brings us many improvements and features that increase capacity and robustness of the transmission channel. The most important changes comparing to the "old" DVB-T standard are:
Added 256-QAM constellation, each service can have it's own constellation Added 1k, 4k, 16k and 32k modes Added guard intervals 1/128, 19/256, 19/128, (for 32k mode, the maximum is 1/8) Changed Forward Error Correction (FEC) algorithm: Low-density parity-check (LDPC) code + BCH, added code rates 3/5 and 4/5 Fewer pilots (8 different pilot-patterns) and equalization can be based also on the RAI CD3 system Added 1.7 MHz and 10 MHz channel bandwidth Multiple-Input Single-Output (MISO) may be used - Siavash Alamouti scheme
In general, DVB-T2 offers around 50% increase in capacity over DVB-T. DVB-T2 together with MPEG-4 form an advanced system for digital terrestrial television broadcasting. It is very likely that this combination will be widely used in the future and it will not be superseded with some even more advanced technology for years. However, the fact is that we live in a world full of surprises.
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