General Overview of DVB-T2
The European-based DVB consortium defined within only 2 years an extension of the existing standard DVB-T called DVB-T2, devised for the broadcast transmission of DTTV. According to the commercial requirements issued in April 2007, the first phase of DVB-T2 will be devoted to provide optimum reception for stationary (fixed) and portable receivers (i.e., units which can be nomadic, but not fully mobile) using existing aerials, whereas a second and third phase will study methods to deliver higher payloads (with new aerials) and the mobile reception issue.
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 for compatibility with the Geneva 2006 Agreement.
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, 256 QAM). 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.
The DVB-T2 standard takes also care of transmitter equipment. In 32k particularly, high power peaks are generated and thus minimize the amplifier efficiency (or even damage it). A special feature called PAPR (Peak Average Power Ratio) reduction has been included in the standard specifications to limit these power peaks without losing information.
Diagram ©DVB Scene 2008. All rights reserved. Material is reproduced with the permission of DVB.
Another innovative feature proposed for the DVB-T2 specification, Time Frequency Slicing (TFS), creates a large multiplex by combining radio-frequency channels to make a single 'virtual' channel to allow for efficient statistical multiplexing. However, because not all details of TFS had been confirmed in time for the completion of the specification, 'hooks' have been put in place to allow for its introduction at a later stage.
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 the IBC show in 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 saw 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 Mbits/second 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.
Adopting the new DVB-T2 standard
At this stage, only the British communications regulator Ofcom has presented official plans to launch national DVB-T2 services. Ofcom would like to use DVB-T2 to provide 4-5 high-definition television services from a single multiplex. No other country in Europe has yet issued clear plans for the introduction of DVB-T2 services although there is clearly growing interest.
UK DVB-T2 technical pilot
The BBC and Ofcom are now working to implement the various changes required to upgrade the first multiplex located in the Grenada region. Part of this implementation program 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. Ofcom will then consult on and adopt the selected transmission mode via the DTT Reference Parameters. The pilot, which will involve both laboratory testing and over the air transmissions, is also intended to provide a signal that those developing DVB-T2 receiver equipment will be able to test equipment against.
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.
DVB-T2 deployment phasing
The UK Government recently decided to upgrade one DTT multiplex (Multiplex B) to operate using the DVB-T2 and MPEG-4 standards. The upgraded multiplex will be capable of carrying the BBC HD service and two other HD services – which Ofcom is in the process of allocating. It is expected that carriage of a 4th HD service will be possible in time. The initial services will be launched at digital switchover (DSO), with the Granada region targeted as the first launch region (earlier DSO regions would be retrofitted), after which services will be launched alongside DSO.