DVB-C

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DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television over cable. This system transmits an MPEG-2 or MPEG-4 family digital audio/video stream, using a QAM modulation with channel coding.


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[edit] DVB-C2

On February 18, 2008 it was announced that a new standard - DVB-C2 - would be developed during 2008. The new standard should be ready very early in 2009.

The DVB TM-C2 issued on February 18. 2008 a "Call for Technologies" for DVB-C2. DVB-C2 CfT Proposals including simulation programs and information on patent rights can be submitted until June 16. 2008. The draft standard should be ready very early 2009.

A very core point is the expectation that DVB-C2 will be the last cable standard ever, i.e. there will never be a -C3 standard.

"The results of the DVB-C2 Study Mission already provided clear indications that technologies are available allowing the performance of the second generation DVB cable transmission system to get so close to the theoretical Shannon Limit that any further improvements in the future would most likely not be able to justify the introduction of a disruptive third generation of cable transmission system." (DVB-C2 CfT)

The new standard may be ready for use late 2009 or more likely sometime during 2010 depending on the individual cable companies.

[edit] Technical description of the DVB-C transmitter

Scheme of a DVB-C transmission system
Scheme of a DVB-C transmission system

With reference to the figure, a short description of the single processing blocks follows.

  • MUX adaptation and energy dispersal: the MPEG-2 TS is identified as a sequence of data packets, of fixed length (188 bytes). With a technique called energy dispersal, the byte sequence is decorrelated.
  • External encoder: a first level of protection is applied to the transmitted data, using a nonbinary block code, a Reed-Solomon RS (204, 188) code, allowing the correction of up to a maximum of 8 wrong bytes for each 188-byte packet.
  • External interleaver: convolutional interleaving is used to rearrange the transmitted data sequence, such way it becomes more rugged to long sequences of errors.
  • Byte/m-tuple conversion: data bytes are encoded into bit m-tuples (m = 4, 5, 6, 7, or 8).
  • Differential coding: the two most significant bytes in each m-tuple are encoded in order to give some ruggedness to the signal.[clarify]
  • QAM Mapper: the bit sequence is mapped into a base-band digital sequence of complex symbols. There are 5 allowed modulation modes: 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM.
  • Base-band shaping: the QAM signal is filtered with a raised-cosine shaped filter, in order to remove mutual signal interference at the receiving side.
Available bitrates for a DVB-C system, assuming a ratio of 1.15 between bandwidth and symbol rate. All (decimal) values in Mbit/s.
Available bitrates for a DVB-C system, assuming a ratio of 1.15 between bandwidth and symbol rate. All (decimal) values in Mbit/s.

[edit] Technical description of the receiver

The receiving STB adopts techniques which are dual to those ones used in the transmission.

  • Front-end and ADC: the analog RF signal is converted to base-band and transformed into a digital signal, using an analog-to-digital converter (ADC).
  • QAM Demodulation
  • Equalization
  • Differential decoding
  • Outer deinterleaving
  • Outer decoding
  • MUX adaptation
  • MPEG-2 demultiplexing and source decoding
  • Programmable Transport Stream

[edit] References

  • ETSI Standard: ETSI EN 300 429 V1.2.1 (1998-04), Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for cable systems, download from ETSI.

[edit] See also

[edit] External links