Fracarro KSTT Instrucciones De Funcionamiento página 31

ATTACHMENT - GLOSSARY
BITRATE
The bitrate is the measurement of signal's transmission rate; it is calculated according to the bit per second
(bps). The multiples are Kbps (1.024 bps), Mbps (1.024 Kbps) and Gbps (1.024 Mbps).
COFDM (Coded Orthogonal Frequency Division Multiplexing)
A modulation diagram that shares the digital signals on more simultaneous carriers. Then the signals are
orthogonally sent, one to another, in order to avoid interferences. It is used in Europe by the DVB-T standard.
CONSTELLATION
Representation with the I/Q coordinates of the phase and amplitude status that a QAM or QPSK modulated
digital carrier can take.
FEC - Forward Error Correction
A technique to correct the errors during the reception phase. It is obtained by adding a known redundancy
during transmission. The code rate is indicated like a ratio between the signal part used for services and the
total part of the available signal. For example, a FEC of 2/3 indicates that 2/3 is the available part for services
whilst 1/3 of the signal is devoted to the correction code.
GUARD INTERVAL
To avoid echoes generated by the transmitter itself, or echoes coming from other transmitters belonging to the
same network, a guard interval is inserted between two consecutive symbols.
MPEG (Motion Picture Experts Group)
International committee for the standardization of the codification, compression, transmission and recording
of images and sound. The compression consists of the elimination of a few data coming from the signal
digitalization; the compression is not perceived by human eyes and ears.
o MPEG-1 is the audio and video optimized compression to be used for low quality applications.
o MPEG-2 is used for high quality television applications.
o MPEG-4 uses a more efficient compression algorithm and allows, differently from a MPEG-2, a higher
reduction of the bitrate without significant losses in quality.
OVERFLOW
It is used when a digital memory (for example a buffer) is loaded over its capacity to keep data. The excess
data are lost or, even worse, affect the functioning.
PES - Packetized Elementary Stream
It is the digital data packet relevant to a program's audio-video-data information.
PID - Packet Identifier
Number of 13 bits contained in the TS (Transport Stream) that allows one to identify if a TS packet belongs to
a PES. The choice of program is carried out by the insertion of the relevant video and audio PIDs; a specific
information flow is associated to each PID.
PILOT CARRIER
In the COFDM modulation, besides the data carriers that transport the information, the OFDM frames contain
other carriers, called pilots, which are used for auxiliary functions, such as the synchronization of the frame,
frequency, time, channel estimate, identification of the transmission mode and the detection of the phase
noise.
PS (Program Stream)
group of PES that transports audio, video and data signals relevant to only one service with a common time
base.
SYMBOL RATE
The symbol rate is the measurement of the rate of a signal calculated in a number of symbols per second. For
example, in the QAM modulation, each symbol is formed by a number of bits equal to the exponent of the
power of 2 that indicated the type of used modulation.
TS (Transport Stream)
The Transport Stream is the result of multiplexing all the PESs relevant to audio, video and data of the various
transmitted channels. Each DVB flow is made up by a Transport Stream; a Transport Packet sequence is 188
bytes.
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