DVB-T2

DVB-T2 is an abbreviation for Digital Video Broadcasting – Second Generation Terrestrial; it is the upcoming extension of the existing standard DVB-T, issued by the European consortium DVB, devised for the broadcast transmission of digital terrestrial television. This system transmits compressed digital audio, video, and other data in "physical layer pipes" (PLPs), using OFDM modulation with concatenated channel coding and interleaving.

History

In March 2006 DVB decided to study options for an upgraded DVB-T standard. In June 2006, a formal study group named TM-T2 (Technical Module on Next Generation DVB-T) was established by the DVB Group to develop an advanced modulation scheme that could be adopted by a second generation digital terrestrial television standard, to be named DVB-T2.^[1]

According to the commercial requirements and call for technologies ^[2] 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. The novel system should provide a minimum 30% increase in payload, under similar channel conditions already used for DVB-T.

The BBC, ITV, Channel 4 and Five have agreed with the regulator Ofcom to convert one UK multiplex (B, or PSB3) to DVB-T2 to increase capacity for HDTV via DTT.^[3] They expect the first TV region to use the new standard will be Granada in November 2009 (with existing switched over regions being changed at the same time). It is expected that over time there will be enough DVB-T2 receivers sold to switch all DTT transmissions to DVB-T2, and H.264.

Ofcom published its final decision on April 3, 2008 for HDTV using DVB-T2 and MPEG-4 AVC ^[4]: BBC HD will have one HD slot after DSO at Granada. ITV and C4 have as expected applied to Ofcom for the 2 additional HD slots available from 2009 to 2012 (C3 + C4 and partners)

Ofcom has indicated that it has found an unused channel covering 3.7 million households in London that can be used to broadcast the DVB-T2 HD multiplex from 2010 i.e. before DSO in London. Ofcom has indicated that they will look for more unused UHF channels in other parts of the UK, that can be used for the DVB-T2 HD multiplex from 2010 until DSO 2.19

The draft standard

The following characteristics have been devised for the T2 standard:

• COFDM modulation with QPSK, 16-QAM, 64-QAM, or 256-QAM (but not 128-QAM) constellations.
• OFDM modes are 1k, 2k, 4k, 8k, 16k, and 32k. The symbol length for 32k mode is about 4 ms.
• Guard intervals are 1/128, 1/32, 1/16, 19/256, 1/8, 19/128, and 1/4. (For 32k mode, the maximum is 1/8.)
• FEC is LDPC and BCH (as in DVB-S2), with rates 1/2, 3/5, 2/3, 3/4, 4/5, and 5/6.
• There are fewer pilots, in 8 different pilot-patterns, and equalization can be based also on the RAI CD3 system.^[5]
• In the 32k mode, a larger part of the standard 8 MHz channel can be used, adding about 2% extra capacity.
• DVB-T2 is specified for 1.7, 5, 6, 7, 8, and 10 MHz channel bandwidth.
• MISO (Multiple-Input Single-Output) may be used (Siavash Alamouti scheme), but MIMO will not be used. Diversity receivers can be used (as they are with DVB-T).
• Bundling of more channels into a SuperMUX (called TFS) is not in the standard, but may be added later.

Comparison of available modes in DVB-T and DVB-T2: ^[6]

For instance, a UK MFN DVB-T profile (64-QAM, 2k mode, coding rate 2/3, guard interval 1/32) and a DVB-T2 equivalent (256-QAM, 32k, coding rate 3/5, guard interval 1/128) allows for an increase in bit rate from 24.13 Mbit/s to 35.4 Mbit/s (+46.5%). Another example, for an Italian SFN DVB-T profile (64-QAM, 8k, coding rate 2/3, guard interval 1/4) and a DVB-T2 equivalent (256-QAM, 32k, coding rate 3/5, guard interval 1/16), achieves an increase in bit rate from 19.91 Mbit/s to 33.3 Mbit/s (+67%).^[7]

Status of the DVB-T2 specification

DVB-T2 test modulator developed by BBC Research & Innovation.

The DVB-T2 draft standard ratified by the DVB Steering Board on June 26, 2008,^[8] and published on the DVB homepage as DVB-T2 standard BlueBook,^[9] has been handed over to the European Telecommunications Standards Institute (ETSI) by DVB.ORG on June 20, 2008.^[10] The ETSI process resulted in the DVB-T2 standard being adopted on September 9th, 2009.^[11]. The ETSI process had several phases, but the only changes were text clarifications. ^[12] DVB-T2 modulators are on the market and receiver chips are under development. Prototype receivers were shown in September IBC 2008 and more recent version at the IBC 2009 in Amsterdam. A number of other manufacturers are demonstrating DVB-T2 at IBC 2009 including Albis Technologies, Arqiva, DekTec, Enensys, Harris, Pace, Rohde & Schwarz, Tandberg, and TeamCast according to BroadbandTVNews.com. It reports that other manufacturers planning DVB-T2 equipment launches include CellMetric, Cisco, Digital TV Labs, Humax, NXP Semiconductors, Panasonic, ProTelevision Technologies, Screen Service, SIDSA, Sony, ST Microelectronics and T-VIPS.^[13]

Since the DVB-T2 physical layer specification is complete, and there will be no further technical enhancements, receiver VLSI chip design has been started with confidence in stability of specification. A draft PSI/SI (program and system information) specification document has been agreed with the DVB-TM-GBS group.

Tests

The first test from a real TV-transmitter was performed by the BBC Research & Innovation in the last weeks of June 2008^[14] using channel 53 from the Guildford transmitter, southwest of London: BBC had developed and built the modulator/demodulator prototype in parallel with the DVB-T2 standard being drafted.

NORDIG published a DVB-T2 receiver specification and performance requirement on the 1 July 2009.^[15]

Notes

References

• DVB document A122, Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2) ,
• DVB document A133 Implementation guidelines for a second generation digital terrestrial television broadcasting system (DVB-T2) and
• DVB document A136 Modulator Interface (T2-MI) for a second generation digital terrestrial television broadcasting system (DVB-T2) are available at the dvb.org website.
• DVB-T2 Fact Sheet, April 2009

External links

• Website of the DVB Project
• OFCOM DTT future
• OFCOM Pilots
• General Overview of DVB-T2