General overview of DVB-T2 standard
DVB-T2 tutorial
The European-based DVB consortium elaborated the DVB-T2 specification as an extension of the existing standard DVB-T, in order to allow a better use of the spectral resources by integrating the latest signal processing technologies. The expected gains give up to 50% additional bitrate in the same frequency bandwidth.
DVB-T2 baseline features
The specification is designed primarily for fixed reception to roof-top antennas and has the same frequency spectrum channel characteristics as DVB-T allowing a backward compatibility with the transmission infrastructure currently in place..
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Like DVB-T, DVB-T2 uses OFDM (orthogonal frequency division multiplex) modulation and provides a toolkit with different numbers of carriers (1k, 2k, 4k, 8k, 16k, 32k, 16k extended, 32k extended) and modulation constellations (QPSK, 16 QAM, 64 QAM, 256QAM). For error protection, DVB-T2 uses LDPC (low density parity check) and BCH (Bose-Chaudhuri-Hocquengham) coding. A new technique, known as Rotated Constellations, has been introduced to provide additional robustness in certain conditions. DVB-T2 standard takes also care of transmitter equipments. In 32k particularly, high power peaks are generated and thus minimize the amplifier efficiency (or even endamage it). A special feature called PAPR (Peak Average Power Ratio) reduction has been included in the standard specifications to limit these peaks power without losing information. |
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DVB-T2 vs DVB-T comparison |
DVB-T2 |
DVB-T |
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| FEC | LDPC + BCH | CC + RS |
| Code rate | 1/2, 3/5, 2/3, 3/4, 4/5 | 5/6 1/2, 2/3, 3/4, 5/6, 7/8 |
| Constellation | QPSK, 16QAM, 64QAM, 256QAM | QPSK, 16QAM, 64QAM |
| Guard Interval | 1/4, 19/256, 1/8, 19/128, 1/16, 1/32, 1/128 | 1/4, 1/8, 1/16, 1/32 |
| FFT size | 1K, 2K, 4K, 8K, 16K, 16K ext., 32K, 32K ext. |
2K, 8K |
| Scattered pilots | 1%, 2%, 4%, 8% of total | 8% of total |
| Continual pilots | 0,35 of total | 2,6 % of total |
| Bandwidth | 1.7, 5, 6, 7, 8, 10 MHz | 5, 6, 7, 8 Mhz |
| Max. Bandwidth | 50,34 Mb/s | 31,66 Mb/s |
DVB-T2 system architecture
The main differences between a DVB-T and DVB-T2 system is that the multiplexer shall be connected to a T2 gateway. This T2 gateway receives one or several multiplex e.g one per PLP from the multiplexer and encapsulates these datas into BaseBand Frames. The T2 gateway send the content to DVB-T2 modulators via the T2 Modulator Interface protocol.
DVB-T2 Frame structure
DVB-T2 reuse the PLP or Physical Layer Pipe concept introduced in the DVB-S2 specification. A PLP is a logical channel that may carry one or multiple services. Each PLP can have a different bit rate and error protection parameters. For example, it's possible to split SD and HD services to different PLPs.
The DVB-T2 standard define several profiles:
Type A : single stream input ie. mono PLP
Type B : multi stream input i.e multi PLP. In multi PLP mode the PLPs are time sliced. The multi PLP mode is subdivised in several modes:
- Type 1 : PLP having one slice per T2 frame.
- Type 2 : PLP having two or more sub-slices per T2 frame.
-Time Frequency Slicing (TFS), creates a large multiplex by combining radio-frequency channels (up to 6 frequencies) to make a single 'virtual' channel to allow efficient statistical multiplexing. The TFS is optional in the current DVB-T2 specification.
It's possible to define the type 1 or 2 for each PLP and then to mix in a T2 frame PLPs of type 1 and PLPs of type 2.
The PLPs are combined into T2 Frames. A T2 Frame starts with preambule P1 and P2. The T2 framing structure is described are after
DVB-T2 Modulator Interface
The T2 gateway encapsulates data into BaseBand frame. These BB frames are send to the DVB-T2 modulator over a specific DVB-T2 Modulator Interface protocol described hare after.
DVB-T2 testing
Testing of the specification has begun in the United Kingdom. in June 2008. The BBC, together with the broadcast network operators Arqiva and National Grid Wireless, made the first DVB-T2 test transmission. In September 2008 at IBC show (Amsterdam), the DVB stand presented a number of milestone technology demonstrations that highlighted the recent advancements that have been made by DVB in the area of Digital Terrestrial Television (DTT). Visitors to the stand have seen for the first time H.264 encoded HD content delivered over a live end-to-end terrestrial transmission system using DVB-T2 technology.
In the first DVB-T2 demo, three HD channels were broadcasted in one multiplex, each coded at 11 Mbit/sec with the latest H.264 encoders. The signal was decoded using a newly developed BBC demodulator and an H.264 decoder, and then shown on an HD display.
| In a second presentation, ENENSYS Technologies, NXP Semiconductors and Pace have highlighted the robust characteristics of DVB-T2. The purpose of this end-to-end demonstration was to show how the standard enables the handling of the injection of noise and interference and the successful functioning of the DVB-T2 signal in such environments to provide excellent reception. |  |
UK DVB-T2 technical pilot
The BBC and Ofcom worked to implement the various changes required to upgrade the first multiplex located in Grenada region. Part of this implementation programme involves a DVB-T2 technical pilot that is aimed at validating the DVB-T2 standard and identifying a preferred transmission mode for adoption within the UK. The pilot, which involved both laboratory testing and over the air transmissions is also intended to provide a signal that those developing DVB-T2 receiver equipment was able to test equipment.
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For this purpose, a transmitter has recently been installed at the Crystal Palace broadcast tower to carry-out DVB-T2 test transmissions. This follows successful end-to-end lab tests from source to receiver display, and has been made possible thanks to the close collaboration between Arqiva and ENENSYS. ENENSYS has provided the real-time and hardware based DVB-T2 modulator, which has been connected to the Arqiva transmission equipment. This ambitious program will also support the DVB-T2 manufacturing community by providing an open on-air test transmission to enable product testing and development. Prototype DVB-T2 receivers are to become available soon and will be ready for use in the technical pilot project over the coming weeks and months. |
Adopting the new DVB-T2 standard
The British communications regulator Ofcom decided to upgrade one DTT multiplex (Multiplex B) to operate Freeview HD service using the DVB-T2 and MPEG-4 standards. The upgraded multiplex will be capable of carrying the BBC, ITV and Channel4 HD service. It is expected that carriage of a 6th HD services will be possible in time. The initial services was launched at digital switchover (DSO) December 2nd of 2009, with the Granada region targeted as the first launch region (earlier DSO regions would be retrofitted), after which services will be launched alongside DSO.
In Finland, DNA Oy got license to operate two DVB-T2 multiplexes. The launch is expected to take place by the end of 2010. A trial was launched in December 2009 in the Lahti city.
Some countries in Europe such as Italy, Turkey, Serbia, has already made some announcement about deployment of DVB-T2 network.
Some trials should also take place in Germany, Spain, Sweden and Austria.
DVB-T2 Glossary
| BB |
BaseBand |
| FEC | Forward Error Correction |
| FEF |
Future Extension Frame |
| MISO |
Multiple Input Single Output |
| PAPR |
Peak to Average Power Ratio |
| PLP |
Physical Layer Pipe |
| T2-MI | T2 Modulator Interface |
| TI Block |
Time Interleaving Block |
| TFS | Time Frequency Slicing |
| LDPC | Low Density Parity Check |
| BCH | Bose Chaudhuri Hocquengham |
References:
- DVB website : http://www.dvb.org/technology/standards/
- Wikipedia : http://en.wikipedia.org/wiki/DVB-T2