What is DVB-T2 system?

DVB-T2 is a digital terrestrial transmission system developed by the DVB project. It introduces the latest modulation and coding techniques to enable the highly efficient use of the valuable terrestrial spectrum for the delivery of audio, video and data services to fixed, portable and mobile devices.

DVB-T2 uses OFDM modulation, with a large number of subcarriers delivering a robust signal. Also like DVB-T, DVB-T2 offers a range of different modes, making it a very flexible standard. To perform error correction, DVB-T2 uses the same coding that was selected for DVB-S2. The combination of low density parity check (LDPC) coding and Bose-Chaudhuri-Hocquengham (BCH) coding delivers excellent performance in an environment with high noise levels and interference, yielding a very robust signal.

Several options are available with regard to aspects such as number of carriers, guard interval size and pilot signals. Overhead can therefore be minimized for any target transmission channel. A new technique named "rotated constellations" provides significant additional robustness in difficult channels. A mechanism for separately adjusting the robustness of each delivered service within a channel is provided in order to achieve the required reception conditions (e.g. indoor antenna/roof-top antenna). This same mechanism allows transmissions to be tailored to enable a receiver to save power by decoding only a single program rather than an entire multiplex of programs.

Key performance features of DVB-T2:

* At least 30 to 50 % higher transmission capacity and improved SFN performance as compared to DVB-T
* Service-specific transmission robustness
* Program transmission for mobile and stationary receivers
* Extensive re-use of DVB-T infrastructure
* Reduction of peak-to-average power ratio and therefore of operating costs at the transmitter end
* Enhancements provided by DVB-T2
* OFDM modulation with additional IFFT modes
* Efficient error protection by means of LDPC coding
* Transfer and integration of the DVB-S2 baseband frame concept
* Q-delayed rotated constellations
* MISO transmission
* Reduction of crest factor


What is the difference between DVB-T and DVB-T2?

DVB-T and DVB-T2 are both standards for transmitting bits from one (or a few) ground based transmitters to very many receivers i.e. both are broadcast standards. They are both designed to have the capacity to transmit live digital television. 

Both can accept a MPEG2-TS - an MPEG-2 Transport (bit)Stream - and deliver the same bit-steam at the receiver - error free. The bits that form the payload of the transport stream can be interpreted as MPEG2/MPEG4 video, as audio encoded with different codecs - MEPG1 level 2 (MP2), HE-AAC, Digital Dolby .etc..., as teletext or subtitles, as EPG program guides, as firmware downloads for receivers etc..... 

Note MPEG2-TS has no relation to MPEG2 video compression, but was named in the 1990's where MPEG2 was a common prefix for everything related to digital video. 

Nor has the DVB transmission standards any direct relation to MPEG-2 or MPEG-4 video compression - DVB-T can carry MPEG-4 and DVB-T2 can carry MPEG-2 - it is even likely it will at some stage. 

DVB-T2 allows a more general form - the Generic Stream Encapsulation or GSE - which is designed for general use including for IP data (TCP/IP) and it adds less overhead. For TV broadcast MPEG2-TS is currently used by both standards - as this is a more well known format to broadcasters. But GSE is part of DVB-S2 now and will be part of the new cable standard DVB-C2 as well. 

While the MPEG2-TS is unchanged - almost everything about cutting the bit-stream into pieces converting these pieces into radio waves and assemble everything correctly at the receiver - is new and/or used differently with DVB-T2. 

Some parts of the transmission system are unchanged: 

The UHF frequency channels can be the same 8 MHz channels used by analogue TV or by DVB-T in Europe. 7 MHz VHF III channels and 6 MHz US/Asian channels are likewise supported. 5 MHz channels are specified in both standards. 

New with DVB-T2 standard is the 1.7 MHz channel that will fit directly into a T-DAB channel allocation. 

The RF power amplifiers, TX antennas and the TX mast/tower are all unchanged. 

The specifications for RX aerials/antennas and masthead amps are unchanged. 

Most of the SI signalling is unchanged - except for a few new codes that only will be present in DVB-T2 transmissions. 

Some of the main differences are: 
Transport streams - that each can carry more multiplexed bit-streams - can be allocated to Physical Layer Pipes or PLP's. Each PLP can be encoded with its own QAM modulation and FEC protection - some can be highly protected, but have low useful bit-rate while another PLP can have less protection and a high bit-rate - all on the same DVB-T2 multiplex. 

DVB-T2 uses a very much stronger Forward Error Correcting code - the LDPC/BCH code. DVB-T uses the rather weak Viterbi algorithm followed by a ReedSolomon code. The RS code itself uses 8% of the bit-rate, while the BCH code used with DVB-T2 just uses 0.2-0.3%. 

DVB-T2 allows many more FFT modes 1k, 2k, 4k, 8k, 16k, 32k (DVB-T is only using the 8k mode except for the 2k mode at pre-DSO UK transmitters and maybe 4k with DVB-H). Larger FFT modes lowers the overhead with SFN's very significantly. But Doppler effects will make the larger FFT modes of little use in a true mobile environment. 
Note all PLP's within a DVB-T2 multiplex must all use the same FFT mode. 

DVB-T2 enables 256-QAM modulation. This will allow 8 bits to be encoded at each constellation/frequency slot. 

DVB-T has a fixed and large overhead (8%) from 'pilot-tones' that are used for synchronisation and channel estimation. DVB-T2 has 8 different 'pilot-patterns' - some with very low overhead. 

DVB-T2 uses something called 'Rotated Constellations' that divides each constellation into two parts, which both contains all the information (2,4,6 or 8 bits). One half is then swapped with the same half of a another constellation/frequency slot before transmission. Assume aA is the two parts of one frequency slot and bB is another. Then these two are transmitted as aB and bA at different frequencies. If say aB is lost due to noise or fading then all bits can be recovered from the bA frequency slot. This increases very significantly the chance of error free reception in difficult situations. This will also enable the code-rates 4/5 and 5/6 to be used in real system (the DVB-T code-rates 5/6 and 7/8 are rather fragile and useless) 
(In practice 'a' is moved to 'B', 'b' to 'C', 'c' to 'D', 'd' to 'E' .... and 'z' to A' before the frequency interleave) 

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