| DVB-T2 |
| DVB-T2 is Second Generation Terrestrial; it is the extension of the television standard DVB-T, issued by the 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. It is currently broadcasting in parts of the UK under the brand name Freeview HD.
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| History of DVB-T2 |
| 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. |
According to the commercial requirements and call for technologies issued in April 2007, the first phase of DVB-T2 would 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 would 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 agreed with the regulator Ofcom to convert one UK multiplex (B, or PSB3) to DVB-T2 to increase capacity for HDTV via DTT. |
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| They expected the first TV region to use the new standard would be Granada in November 2009 (with existing switched over regions being changed at the same time). It was expected that over time there would 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 H.264: BBC HD would have one HD slot after DSO at Granada. ITV and C4 had, as expected, applied to Ofcom for the 2 additional HD slots available from 2009 to 2012. |
| Ofcom indicated that it found an unused channel covering 3.7 million households in London, which could be used to broadcast the DVB-T2 HD multiplex from 2010, i.e., before DSO in London. Ofcom indicated that they would 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. |
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| The DVB-T2 specification |
| The DVB-T2 draft standard was ratified by the DVB Steering Board on June 26, 2008, and published on the DVB homepage as DVB-T2 standard BlueBook,. It was handed over to the European Telecommunications Standards Institute (ETSI) by DVB.ORG on June 20, 2008. The ETSI process resulted in the DVB-T2 standard being adopted on September 9, 2009. The ETSI process had several phases, but the only changes were text clarifications. Since the DVB-T2 physical layer specification was complete, and there would be no further technical enhancements, receiver VLSI chip design started with confidence in stability of specification. A draft PSI/SI (program and system information) specification document was also agreed with the DVB-TM-GBS group. |
| Tests of DVB-T2 |
| Prototype receivers were shown in September IBC 2008 and more recent version at the IBC 2009 in Amsterdam. A number of other manufacturers demonstrated DVB-T2 at IBC 2009 including Albis Technologies, Arqiva, DekTec, Enensys, Harris, Pace, Rohde & Schwarz, Tandberg, and TeamCast. 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. The first test from a real TV transmitter was performed by the BBC Research & Innovation in the last weeks of June 2008 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. In March 2009 the Digital TV Group (DTG), the industry association for digital TV in the UK, published the technical specification for high definition services on digital terrestrial television (Freeview) using the new DVB-T2 standard. The DTG's test house: DTG Testing are testing Freeview HD products against this specification. |
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| The DVB-T2 Standard |
| The following characteristics have been devised for the T2 standard: |
COFDM modulation with QPSK, 16-QAM, 64-QAM, or 256-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 concatenated LDPC and BCH codes (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.
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 (Alamouti scheme), though 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. |
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DVB-T |
DVB-T2 |
| FEC |
Convolutional Coding + Reed Solomon 1/2, 2/3, 3/4, 5/6, 7/8 |
LDPC + BCH 1/2, 3/5, 2/3, 3/4, 4/5, 5/6 |
| Modes |
QPSK, 16QAM, 64QAM |
QPSK, 16QAM, 64QAM, 256QAM |
| Guard Interval |
1/4, 1/8, 1/16, 1/32 |
1/4, 19/256, 1/8, 19/128, 1/16, 1/32, 1/128 |
| FFT size |
2k, 8k |
1k, 2k, 4k, 8k, 16k, 32k |
| Scattered Pilots |
8% of total |
1%, 2%, 4%, 8% of total |
| Continual Pilots |
2.6% of total |
0.35% of total |
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| 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%). |
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| Technical Details |
| The processing workflow is as follows: |
Input pre-processing
Physical Layer Pipe (PLP) creation: adaptation of Transport Stream (TS), Generic Stream Encapsulation (GSE), Generic Continuous Stream (GCS), or Generic Fixed-length Packetized Stream (GFPS)
Input processing
Mode adaptation
Single PLP (mode 'A'): data are assembled in groups called BaseBand Frames (BBFRAMEs), with lengths of Kbch bits, defined by modulation and coding (MODCOD) parameters, in a 'normal' length or 'short' length version
Input interface
CRC-8 encoding
BaseBand (BB) header insertion
Multiple PLPs (mode 'B')
Input interface
Input stream synchronization
Delay compensation
Null packets deletion
CRC-8 encoding
BB header insertion
Stream adaptation
Single PLP (mode 'A')
Padding insertion
BB scrambling: a Pseudo Random Binary Sequence (PRBS) with generator 1 + x14 + x15 is used to scramble completely every BBFRAME
Multiple PLPs (mode 'B')
PLP scheduling
Frame delay
In-band signaling or padding insertion
BB scrambling
Bit Interleaved Coding and Modulation (BICM)
Forward Error Correction (FEC) encoding: each BBFRAME is converted into a FECFRAME of Nldpc bits, by adding parity data. Normal FECFRAMEs are 64,800 bits long, whereas short FECFRAMEs are 16,200 bits long. The effective code rates are 32,208/64,800 (1/2), 38,688/64,800 (3/5), 43,040/64,800 (2/3), 48,408/64,800 (3/4), 51,648/64,800 (4/5), 53,840/64,800 (5/6)
Outer encoding: a BCH code, capable to correct 10 or 12 errors per FECFRAME, is used to compute parity data for the information data field. The BCH generator polynomial is of the 160th, 168th, or 192nd grade
Inner encoding: a Low Density Parity Check (LDPC) code is cascaded to the BCH
Bit interleaving
Parity bits block interleaving
Twist column interleaving
Bit interleaving
Parity bits block interleaving
Twist column interleaving
Bit demultiplexing to cell words
Gray mapping of cell words to constellations: either QPSK (4-QAM), 16-QAM, 64-QAM, or 256-QAM maps are used
Constellation rotation and cyclic quadrature (Q) delay: optionally, the constellations may be tilted counterclockwise by an amount of up to 30 degrees. Furthermore, the quadrature (imaginary) part of the cells is cyclically shifted by one cell
Cell interleaving
Time interleaving
Frame building
Cell mapping
Frequency interleaving
OFDM generation
Multiple-Input Single-Output (MISO) processing
Pilot insertion and dummy tone reservation
Inverse Fast Fourier Transform (IFFT)
Peak-to-Average-Power-Ratio (PAPR) reduction
Guard interval insertion
P1 symbol insertion
Digital-to-Analog Conversion (DAC) |
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| Framing structure of DVB-T2 |
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| DVB-T2 Links |
| DVB.org DVB-T2 |
| Freeview Freeview is the digital terrestrial platform in the UK, it currently has one DVB-T2 multiplex. |
| Overview of DVB-T2 by Enensys |
| Understanding DVB-T2 DigiTAG Handbook on DVB-T2. (PDF) |
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