Editing DVB-C (section)

=== DVB-C transmitter ===
[[File:dvbc tx scheme.svg|thumb|350px|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 program stream]] (MPEG-PS). One or more MPEG-PSs are joined together into an [[MPEG transport stream]] (MPEG-TS). This is the basic digital stream which is being transmitted and received by home [[set top box]]es (STB) or relevant integrable decoder (e.g. Conax) module. Allowed [[bit rate]]s 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-TS is identified as a sequence of [[Packet (information technology)|data packets]], of fixed length (188 bytes). With a technique called [[Scrambler (randomizer)|energy dispersal]], the byte sequence is [[correlation|decorrelated]].
* External encoder: a first level of protection is applied to the transmitted data, using a nonbinary [[block code]], a [[Reed–Solomon error correction|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: In order to get a rotation-invariant constellation, this unit shall apply a differential encoding of the two Most Significant Bits (MSBs) of each symbol.
* 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 and back-end|front-end]].

{| class="wikitable"
|+ Available bit rates for a DVB-C system (Mbit/s)
|-
! rowspan="2" | Modulation !! colspan="5" | Bandwidth (MHz)
|-
! 2 !! 4 !! 6 !! 8 !! 10
|-
! 16-QAM
| align="right" | 6.41
| align="right" | 12.82
| align="right" | 19.23
| align="right" | 25.64
| align="right" | 32.05
|-
! 32-QAM
| align="right" | 8.01
| align="right" | 16.03
| align="right" | 24.04
| align="right" | 32.05
| align="right" | 40.07
|-
! 64-QAM
| align="right" | 9.62
| align="right" | 19.23
| align="right" | 28.85
| align="right" | 38.47
| align="right" | 48.08
|-
! 128-QAM
| align="right" | 11.22
| align="right" | 22.44
| align="right" | 33.66
| align="right" | 44.88
| align="right" | 56.10
|-
! 256-QAM
| align="right" | 12.82
| align="right" | 25.64
| align="right" | 38.47
| align="right" | 51.29
| align="right" | 64.11
|}