Introduction to Cable TV (CATV): Systems, Services, Operation, and Technology by Lawrence Harte

Author:Lawrence Harte [Harte, Lawrence]
Language: eng
Format: azw3
Publisher: UNKNOWN
Published: 2017-03-17T04:00:00+00:00

Headend

A headend is the master distribution center of a CATV system by which incoming television signals from video sources (e.g., DBS satellites, local studios, video players) are received, amplified, and re-modulated onto TV channels for transmission down the CATV system.

Receivers The incoming signals for headend systems include satellite receivers, off-air receivers and other types of transmission links. The signals are received (selected) and processed using channel decoders. Headends commonly use integrated receiver devices that combine multiple receiver, decoding and decryption functions into one assembly.

Media Processors After the headend receives, separates and converts incoming signals into new formats, the signals are selected and encoded so they can be retransmitted (or stored) in the CATV network.

Transmitters

These signals are modulated, amplified and combined so they can be sent on the CATV distribution system. Figure 1.33 shows a diagram of a simple head-end system. This diagram shows that the head-end gathers programming sources, decodes, selects and retransmits video programming to the distribution network. The video sources to the headend typically include satellite signals, off air receivers, microwave connections and other video feed signals. The video sources are scrambled to prevent unauthorized viewing before being sent to the cable distribution system. The headend receives, decodes and decrypts these channels. This example shows that the programs that will be broadcasted are supplied to encoders and modulators to produce television channels on multiple frequencies. These channels are combined onto a single transmission line by a channel combiner.

Figure 1.33, Head-end System A CATV system may be expanded over a large geographic area to include multiple local headend locations. Local headends may be connected to regional headends and regional headends may be connected to a super headend. To reduce the cost of a CATV system, headend systems can be shared by several distribution systems.

Integrated Receiver Decoder (IRD) An integrated receiver and decoder is a device that can receive, decode, and decrypt broadcast signals (such as from a satellite system) into a form that can be retransmitted on the cable distribution system. In headend systems, IRDs are used to select and process channels from a multi-program transport stream (MPTS) received from a satellite antenna.

The inputs to an IRD (the front end) can include a satellite receiver or a data connection (such as an ATM or IP data connection). The types of processing that an IRD performs can vary from creating analog video signals to creating high definition video digital formats. The outputs of an IRD range from simple video outputs to high-speed IP data connections. Companies that produce IRDs commonly offer variations of IRD (such as analog and digital outputs) that meet the specific needs of the CATV system operator.

Tuner

The IRD has a receiver (tuner) that can select and demodulate a specific RF channel.

Decode

The decoder divides an incoming channel into its component parts.

Decrypt A decryptor can convert the encrypted information into a form that can be used by the system. Network distribution systems may encrypt program channels so only authorized receivers (paying broadcasters) can decode the content.

Media Processing

IRDs may also change the format (transcode) of the media so that it can be used by other devices.

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