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Glossary
Reference Guide: TT128x High Definition Professional Receiver/Decoder Page A-3
ST.RE.E10141.5
COFDM
Coded OFDM: COFDM adds forward error correction to the OFDM transmission consisting of Reed-Solomon
(RS) coding followed by convolutional coding to add extra bits to the transmitted signal. This allows a large number
of errors at the receive end to be corrected by convolutional (Viterbi) decoding followed by RS decoding.
Compression
Reduction in the number of bits used to represent the same information. For the purposes of a broadcast system,
it is the process of reducing digital picture information by discarding redundant portions of information that are not
required when reconstituting the picture to produce viewing clarity. Compression allows a higher bite-rate to be
transmitted through a given bandwidth.
Compression System
Responsible for compressing and multiplexing the video / audio / data bit-streams, together with the authorisation
stream. The multiplexed data stream is then ready for transmission.
C
R
C
B
Digital Colour difference signals. These signals, in combination with the luminance signal (Y), define the colour
and brightness of each picture element (pixel) on a TV line. See: Chrominance
CRC
Cyclic Redundancy Check: A mathematical algorithm that computes a numerical value based on the bits in a
block of data. This number is transmitted with the data and the receiver uses this information and the same
algorithm to ensure the accurate delivery of data by comparing the results of algorithm and the number received. If
a mismatch occurs, an error in transmission is presumed.
CVCT Cable Virtual Channel Table (ATSC).
dB
Decibels: A ratio of one quantity to another using logarithmic scales to give results related to human aural or
visual perception. dB is a ratio whereas dBm, for example, is an absolute value, quoted as a ratio to a fixed point
of 0 dBm. 0 dBm is 1 mW at 1 kHz terminated in 600Ω. 0 dBmV is 1 mV terminated in 75Ω.
DCE
Data Communications Equipment: Typically a modem. It establishes, maintains and terminates a session on a
network but in itself is not the source (originator) or destination (end receiving unit) of signals (e.g. a computer, see
DTE). A DCE device may also convert signals to comply with the transmission path (network) format.
DCT
Discrete Cosine Transform: A technique for expressing a waveform as a weighted sum of cosines. Raw video
data is not readily compressible. DCT is not in itself a compression technique but is used to process the video data
so that it is compressible by an encoder. DCT processes the picture on an 8x8-pixel block basis, converting the
data from an uncompressible X Y form (as displayed by an oscilloscope) to a compressible frequency domain form
(as displayed by a spectrum analyser). Can be forward DCT or inverse DCT.
DDS Direct Digital Synthesiser.
Decoder
The unit containing the electronic circuitry necessary to decode encrypted signals. Some Decoders are separate
from the receiver but in satellite TV broadcasting, the term is often used interchangeably as a name for an
Integrated Receiver Decoder (IRD). The term IRD, or IRD / Decoder, is usually associated with satellite TV
broadcasting while Cable systems are based on Converters or on Set-Top Boxes / Converters.
Decoding Time-stamp
A field that may be present in a PES packet header that indicates the time that an access unit is to be decoded in
the system target Decoder.
DID Data Identifier.
Differential Coding Method of coding using the difference between the value of a sample and a predicted value.
DIL
Dual In Line: The most common type of package for small and medium scale integrated circuit
s. The pins hang
vertically from the two long sides of the rectangular package, spaced at intervals of 0.1 inch.
DIN Deutsches Institut für Normung: German Standards Institute.
Dolby Digital Formerly AC-3. An audio coding system based on transform coding techniques and psychoacoustic principles.
Downlink The part of the satellite communications circuit that extends from the satellite to an Earth station.
Downconvert The process by which the frequency of a broadcast transport stream is shifted to a lower frequency range.
DPCM
Differential Pulse Code Modulation: An audio digitisation technique that codes the difference between samples
rather than coding an absolute measurement at each sample point.
DSNG Digital Satellite News-Gathering.
DSP Digital Signal Processor.
DTE
Data circuit Terminating Equipment: A communications device that originates (is the source) or is the end
receiving unit (destination) of signals on a network. It is typically a terminal or computer.
DTH
Direct To Home. The term used to describe uninterrupted transmission from the satellite directly to the subscriber,
that is, no intermediary cable or terrestrial network utilised.
DTS Digital Theater Systems: A motion picture digital sound system.
DVB
Digital Video Broadcasting: A European project which has defined transmission standards for digital
broadcasting systems using satellite (DVB-S), cable (DVB-C) and terrestrial (DVB-T) medium, created by the
EP-DVB group and approved by the ITU. Specifies modulation, error correction, etc. (see EN 300 421 for satellite,
EN 300 429 for cable and EN 300 744 for terrestrial).