What is DVB-T2?

- an overview, information or tutorial about the basics of what is DVB-T2, the second generation standard for Terrestrial Digital Video Broadcasting being adopted around the globe.

DVB-T2 is the next development of the Digital Video Broadcasting - Terrestrial standards. It builds on the technology and on the success of DVB-T to provide additional facilities and features in line with the developing DTT or Digital Terrestrial television market.

Although some may see DVB-T2 as a competitor to the existing DVB-T standard, this is not the case,. It is planned that the two standards will co-exist for many years, with DVB-T2 allowing additional features and services.

DVB-T2 basics

The DVB-T2 standard uses Orthogonal Frequency Division Multiplex as the basic radio transmission medium. This form of transmission is particularly robust and allows for the reception of data signals (in this case television data) in the presence of some interference or missing channels as a result of effects like multipath.

Note on OFDM: Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each another there is no mutual interference. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. This means that when the signals are demodulated they will have a whole number of cycles in the symbol period and their contribution will sum to zero - in other words there is no interference contribution. The data to be transmitted is split across all the carriers and this means that by using error correction techniques, if some of the carriers are lost due to multi-path effects, then the data can be reconstructed. Additionally having data carried at a low rate across all the carriers means that the effects of reflections and inter-symbol interference can be overcome. It also means that single frequency networks, where all transmitters can transmit on the same channel can be implemented. For more information on OFDM click here

The new DVB-T2 specification provides the facility to select a variety of different options to match the requirements of the network operator.

For error correction technology, that used for DVB-S2 has been incorporated. This comprises LDPC (Low Density Parity Check) coding combined with BCH (Bose-Chaudhuri-Hocquengham) coding. The combination of these two techniques has been proved to provide excellent performance in the presence of high noise levels and interference.

As before, several options are available in areas such as the number of carriers, guard interval sizes and pilot signals, so that the overheads can be minimised for any given transmission channel.

DVB-T2 specification highlights

Parameter	DVB-T	DVB-T2
Number of carriers in signal	2k, 8k	1k, 2k, 4k, 8k, 16k, 32k
Modulation formats	QPSK, 16QAM, 64 QAM	QPSK, 16QAM, 64 QAM, 256QAM
Scattered pilots	8% of total	1%, 2%, 4%, 8% of total
Continual pilots	2.6% of total	0.35% of total
Error correction	Convolutional Coding + Reed Solomon 1/2, 2/3, 3/4, 5/6, 7/8	LPDC + BCH 1/2, 3/5, 2/3, 3/4, 4/5, 5/6
Guard interval	1/4, 1/8, 1/16, 1/32	1/4, 19/128, 1/8, 19/256, 1/16, 1/32, 1/128

DVB-T2 summary

While DVB-T2 represents the next evolution for digital terrestrial television, it is planned to operate it alongside the current DVB-T standard for many years and evolve the changeover to DVB-T2. This evolution should occur in much the same way that has occurred between DVB-S and DVB-S2.

As DVB-T2 offers additional facilities, it will enable the broadcasters the possibility of offering new and captivating services to ensure that they are able to keep their viewers. Building on the success of the existing digital television services, DVB-T2 is bound to see a significant level of take-up over the coming years.