Annex A

OFDM

Orthogonal Frequency Division Multiplex: A modulation technique

 

used for digital TV transmission in Europe, Japan and Australia;

 

more spectrally efficient than FDM. In OFDM, data is distributed

 

over a large number of carriers spaced apart at precise frequencies.

 

The carriers are arranged with overlapping sidebands in such a way

 

that the signals can be received without adjacent channel

 

interference.

OPPV

Order ahead Pay Per View: An advance purchase of encrypted one-

 

time events with an expiry date.

OSD

On-screen display: Messages and graphics, typically originating

 

from the SMS, and displayed on the subscriber’s TV screen by the

 

IRD, to inform the subscriber of problems or instruct the subscriber

 

to contact the SMS.

Packet

A unit of data transmitted over a packet switching network. A packet

 

consists of a header followed by a number of contiguous bytes from

 

an elementary data stream.

PAL

Phase Alternating Line: A colour TV broadcasting system where the

 

phase of the R-Y colour-difference signal is inverted on every

 

alternate line to average out errors providing consistent colour

 

reproduction.

PAT

Program Association Table: Part of the MPEG-2 Program Specific

 

Information (PSI) data and is mandatory for MPEG-2 compliance.

 

The PAT points (maps) to the PMT.

PCM

Pulse Code Modulation: A process in which a signal is sampled,

 

each sample is quantized independently of other samples, and the

 

resulting succession of quantized values is encoded into a digital

 

signal.

PCR

Program Clock Reference: A time stamp in the transport stream

 

from which the Decoder timing is derived.

PDC

Program Delivery Control: A Teletext service allowing simple

 

programming (i.e. VideoPlus) of VCR recording times. If the desired

 

program is rescheduled, PDC updates the programming information

 

in the VCR.

Pel

Picture Element: Also known as a pixel. The smallest resolvable

 

rectangular area of an image either on a screen or stored in

 

memory. On-screen, pixels are made up of one or more dots of

 

colour. Monochrome and grey-scale systems use one dot per pixel.

 

For grey-scale, the pixel is energized with different intensities,

 

creating a range from dark to light (a scale of 0-255 for an eight-bit

 

pixel). Colour systems use a red, green and blue dot per pixel, each

 

of which is energized to different intensities, creating a range of

 

colours perceived as the mixture of these dots. If all three dots are

 

dark, the result is black. If all three dots are bright, the result is

 

white.

EN/LZT 790 0005 R1A

A-13