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DVB-C (cable transmission) is the Digital Video Broadcasting (DVB) system used for distribution of digital television over cable networks. DVB-C uses the same 8 (or 7 or 6) MHz channels as used for the distribution of the old analogue TV. This channel is filled with a data container which can carry MPEG-2 compressed video, audio and data services. In this way, the distribution of digital television channels can be introduced without the need to cease the distribution of analogue television.
DVB-C uses Quadrature Amplitude Modulation (QAM) for the modulation of the data on the carrier. Normally 64-QAM is used but lower level modulation schemes, such as 16-QAM and 32-QAM, and higher level modulation schemes such as 128-QAM and 256-QAM can also be used. The data capacity increase with higher level modulation schemes but the data will be less robust against noise and interference.
An 8 MHz channel can carry a payload capacity of 38.5 Mbps if 64-QAM is used. This payload is enough for 4-6 television programs.
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