Fracarro SIG7120 Instrucciones De Uso página 35

ATTACHMENT - GLOSSARY
ASI - Asynchronous Serial Interface - The DVB Asynchronous Serial Interface (ASI) is a very popular standard
interface for conveying MPEG-2 transport streams between professional equipment.
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.
• MPEG-1 is the audio and video optimized compression to be used for low quality applications.
• MPEG-2 is used for high quality television applications.
• 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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