- DVB-C2
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List of digital television broadcast standards DVB standards (Europe) DVB-S (satellite) DVB-T (terrestrial) DVB-C (cable) DVB-H (handheld) - DVB-SH (satellite)
ATSC standards (North America/Korea) ATSC (terrestrial/cable) ATSC-M/H (mobile/handheld) ISDB standards (Japan/Latin America) ISDB-S (satellite) ISDB-T (terrestrial) ISDB-C (cable) SBTVD/ISDB-Tb (Brazil) DTMB standards (China) DTMB-T/H (terrestrial/handheld) CMMB (handheld) DMB standards (Korean handheld) T-DMB (terrestrial) S-DMB (satellite) MediaFLO Codecs Video Audio Frequency bands VHF UHF SHF DVB-C2 is a digital cable transmission system developed by the DVB Project. It uses the latest modulation and coding techniques to enable highly efficient use of cable networks where, up to now, in many cases downstream transmission capacity is already being used to its limit. DVB-C2 will initially be used for the delivery of innovative new services, such as video-on-demand (VOD) and high definition television (HDTV), helping digital operators to remain competitive and also to meet retransmission requirements; in the longer term the migration of current DVB-C services to DVB-C2 is also foreseen.
Contents
History
DVB-C was first published by ETSI in December 1994, subsequently becoming the most widely used transmission system for digital cable television. The standard is deployed worldwide in systems ranging from the larger cable television networks (CATV) down to smaller satellite master antenna TV (SMATV) systems.
A range of factors have combined to create the demand for DVB to create a second generation cable transmission standard, as has been the case with DVB-S2 and DVB-T2 for satellite and terrestrial transmission.
- Many CATV networks are already full to capacity.
- Operators with high digital penetration need the flexibility to keep their offering competitive
- CATV networks retransmitting content from other networks, e.g. satellite, must keep pace with their evolution
- New tools are needed to address both private and business customers, particularly with IP-based content
- Performance improvements, e.g. zapping time, are needed to increase digital penetration in some markets
As with all DVB standards, the specification is based on a set of Commercial Requirements. Key requirements include an increase in capacity (at least 30%), support of different input protocols, and improved error performance. DVB-C2 reuses some of the building blocks of other second generation DVB transmission systems - the “DVB Family” approach. The new standard was not required to be backwards compatible with DVB-C, although DVB-C2 receivers will be able to also handle DVB-C services.
April 2010 saw the publication of the DVB-C2 specification (EN302769. An updated version is already available as DVB BlueBook A138 and the Implementation Guidelines Document (DVB BlueBook A147). In the same month, the Technical University of Braunschweig performed the first live DVB-C2 transmission, which validated the strong expected performance boost of the new system.
The first DVB-C2 tuners are expected mid-2011.
System differences with DVB-C
As with its predecessor, DVB-C2 offers a range of modes and options that can be optimised for the different network characteristics and the requirements of the different services planned for delivery to cable customers.
Table comparing available modes and features in DVB-C and DVB-C2
DVB-C DVB-C2 Input Interface Single Transport Stream (TS)Multiple Transport Stream and Generic Stream Encapsulation (GSE)Modes Constant coding and modulationVariable Coding & Modulation and Adaptive Coding & ModulationFEC [[Reed-Solomon error correcion|Reed Solomon (RS)]]LDPC + BCHInterleaving Bit-InterleavingBit- Time- and Frequency-InterleavingModulation Single Carrier QAMCOFDMPilots NOScattered and Continual PilotsGuard Interval NO1/64 or 1/128Modulation Schemes 16 to 256-QAM16 to 4096-QAM
By using state of the art coding and modulation techniques it offers greater than 30% higher spectrum efficiency under the same conditions as today’s DVB-C deployments. After analogue switch-off the gains in downstream capacity will be greater than 60% for optimized HFC networks.DVB-C2 system overview
The generic C2 System model is represented in figure 1. The system input(s) may be one or more MPEG-2 Transport Stream(s) and/or one or more Generic Stream(s). The Input pre-processor, which is not part of the C2 System, may include a service splitter or a demultiplexer for Transport Streams (TS) used to separate the services into the C2 System inputs, which are one or more logical data streams. These are then carried in individual Physical Layer Pipes (PLPs).
The system output is a single signal to be transmitted on a single RF channel.
DVB-C2 system architecture
Figure 2: DVB-C2 modulator block diagram
Input pre-processor
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
The mode adaptation modules, which operate separately on the contents of each PLP, slice the input data stream into data fields which, after stream adaptation, will form baseband frames (BBFrame). The mode adaptation module comprises the input interface, followed by three optional sub-systems (the input stream synchronizer, the Null Packet deletion unit and the CRC-8 encoder) and then finishes by slicing the incoming data stream into data fields and inserting the baseband header (BBHeader) at the start of each data field.
Stream adaptation
Stream adaptation provides:
- Scheduling: The scheduler shall decide together with the Data Slice builder which Data Slices of the final C2 System will carry data belonging to which PLPs
- Padding: Padding may be applied in circumstances when the user data available for transmission is not sufficient to completely fill a BBFrame, or when an integer number of UPs has to be allocated in a BBFrame.
- BB Scrambling: The complete BBFrame shall be randomized. The randomization sequence shall be synchronous with the BBFrame, starting from the MSB and ending after Kbch bits.
Bit Interleaved Coding & Modulation
FEC encoding
This sub-system shall perform outer coding (BCH), inner coding (LDPC) and bit interleaving. The input stream shall be composed of BBFrames and the output stream of FECFrames. Finally, the LDPC output, go through a bit interleaver.
Mapping bits onto constellations
The bit-stream from the bit interleaver is demultiplexed into N sub-streams. The number of sub-streams depends on the modulation (QPSK, 16QAM, 64QAM, 256QAM, 1024QAM, 4096QAM). These sub-streams are split into two parallel cell words. Each cell word from the demultiplexer shall be modulated using either QPSK, 16QAM, 64QAM, 256QAM, 1024QAM, 4096QAM
Data Slice Packets Generation
The complex cells of one or two FECFrame shall form a Data Slice Packet. The Data Slice Packets for Data Slice Type 1 only transmit the FECFrame data and rely on a pointer within the Level 1 Signaling Part 2 to detect their start. The Data Slice Packets for Data Slice Type 2 carry a FECFrame header that allows for synchronization to the Data Slice Packets without any additional information.
Frame Builder
The function of the frame builder is to assemble the cells of the Preamble Symbols(s) as well as the cells produced for each of the Data Slices into arrays of active OFDM Cells corresponding to the preamble structure and each of the Data Slices and OFDM Symbols which make up the overall frame structure. The frame builder operates according to the dynamic information produced by the scheduler and the configuration of the frame structure.
OFDM Generation
The function of the OFDM generation module is to take the cells produced by the frame builder, as frequency domain coefficients and to transform them into the frequency domain.
See Also
References
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