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 family digital audio/video stream, using a QAM modulation with channel coding.

1 Technical description of the transmitter
2 Technical description of the receiver
3 References
4 See also
5 External links

[edit] Technical description of the transmitter

Scheme of a DVB-C transmission system

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

Source coding and MPEG-2 multiplexing (MUX): video, audio, and data streams are multiplexed into an MPEG-2 PS (MPEG-2 Programme Stream). One or more PSs are joined together into a MPEG-2 TS (MPEG-2 Transport Stream); this is the basic digital stream which is being transmitted and received by home Set Top Boxes (STB). Allowed bitrates for the transported MPEG-2 depend on a number of modulation parameters: it can range from about 6 to about 64 Mbit/s (see the bottom figure for a complete listing).

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.

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.

DAC and front-end: the digital signal is transformed into an analog signal, with a digital-to-analog converter (DAC), and then modulated to radio frequency by the RF front-end.

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

[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.