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Glossary
Page A-8 Reference Guide: TT128x High Definition Professional Receiver/Decoder
ST.RE.E10141.5
P-picture/P-frame
A picture / frame produced using forward prediction. It contains predictions from either previous I frames or
previous P frames. The P frame is used as a reference for future P or B frames.
ppm Parts per million.
PPV
Pay Per View: A system of payment for viewing services based on a usage / event basis rather than on on-going
subscription. Subscribers must purchase viewing rights for each PPV event that they wish to view. PPV events
may be purchased as IPPV or OPPV.
Program
PC - A sequence of instructions for a computer.
TV - A concept having a precise definition within ISO 13818-1 (MPEG-2). For a transport stream, the timebase is
defined by the PCR. The use of the PCR for timing information creates a virtual channel within the stream.
Programme
A linking of one or more events under the control of a broadcaster. For example, football match, news, film show.
In the MPEG-2 concept, the collection of elementary streams comprising the programme, have a common start
and end time. A series of programmes are referred to as events.
P
R
P
B
Analogue Colour difference signals. Refer to C
R
C
B
for an explanation.
PROM
Programmable Read-Only Memory: A device, which may be written once with data for permanent storage, and
then read whenever required. Special types of PROM permit the erasure of all data by Ultraviolet light (EPROM) or
by application of an electronic signal (EEPROM).
PS Program Stream: A combination of one or more PESs with a common timebase.
PSI
Program Specific Information: Consists of normative data, which is necessary for the demultiplexing of transport
streams and the successful regeneration of programs. (See also: SI).
PSIP Program System Information Protocol: The ATSC equivalent of SI for DVB.
PSK Phase Shift Keying: A method of modulating digital signals particularly suited to satellite transmission.
PSR Professional Satellite Receiver: See also: IRD.
PSU Power Supply Unit.
PTS Presentation Time Stamp (ATSC).
QAM
Quadrature Amplitude Modulation: A method of modulating digital signals, which uses combined techniques of
phase modulation and amplitude modulation. It is particularly suited to cable networks.
QPSK Quadrature Phase Shift Keying: A form of phase shift keying modulation using four states.
QSIF Quarter Screen Image Format.
Quantise
A process of converting analogue waveforms to digital information. 8-bit quantisation as set out in ITU-R Rec. 601.
uses 256 levels in the range 0 – 255 to determine the analogue waveform value at any given point. The value is
then converted to a digital number for processing in the digital domain.
RAM
Random Access Memory: A volatile storage device for digital data. Data may be written to, or read from, the
device as often as required. When power is removed, the data it contains is lost.
RAS
Remote Authorization System: A TANDBERG TV proprietary public-key encryption system used to prevent
unauthorized viewing of a TV programme or programmes.
RF Radio Frequency.
ROM
Read Only Memory: A non-volatile storage device for digital data. Data has been stored permanently in this
device. No further information may be stored (written) there and the data it holds cannot be erased. Data may be
read as often as required.
RS
Reed-Solomon coding: An error detection and correction, coding system. 16 bytes of Reed-Solomon Forward
Error Correction code are appended to the packet before transmission, bringing the packet length to 204 bytes.
The 16 bytes are used at the receiving end to correct any errors. Up to eight corrupted bytes can be corrected.
RLC
Run Length Coding: Minimisation of the length of a bit-stream by replacing repeated characters with an
instruction of the form ‘repeat character x y times’.
SCPC Single Channel Per Carrier.
Spectral Scrambling
A process (in digital transmission) used to combine a digital signal with a pseudo-random sequence, producing a
randomised digital signal that conveys the original information in a form optimised for a broadcast channel.
Scrambling
Alteration of the characteristics of a television signal in order to prevent unauthorised reception of the information
in clear form.
SDI Serial Digital Interface.
SDT
Service Description Table: Provides information in the SI stream about the services in the system; for example,
the name of the service, the service provider, etc.
SELV Safety Extra Low Voltage (EN 60950).