scope:

Introduction

The members of the MAC/packet family

The MAC/packet family of systems consists of the following three members: C-MAC/packet, D-MAC/packet, D2-MAC/packet. These systems incorporate the following common features:

- time-division multiplexing

- MAC picture coding, with the capacity for extended aspect ratio and enhanced picture quality 

- packet multiplexing for sound and data

- digital high and medium quality sound coding and error-protection method

- service identification

- conditional access with video, sound and data scrambling

- full-channel digital mode of operation.

The clock frequencies used in these systems have simple relationships with the sampling frequencies of the digital studio standard defined in CCIR Recommendation 601.

The specification of the three members of the MAC/packet family is given in EBU doc. Tech. 3258, 2nd Issue. The present document is only concerned with the D2-MAC/packet system.

Expected bearers

The D2-MAC/packet system is suitable for satellite broadcasting with frequency modulation and for cable distribution with vestigial-sideband amplitude modulation, with full transparency.

It is expected that in the future, the D2-MAC/packet system could be used for other applications, such as terrestrial broadcasting, point-to-point transmissions, video cassettes, etc.

Sunary description of the system

The particular features of the D2-MAC/packet system are:

- a baseband time-division multiplex in which analogue picture signals are combined with duobinary encoded digital sound, synchronization and data signals

- the capacity of the sound/data multiplex is about 1.5 Mbit/s in the case of normal television transmissions and nearly 10 Mbit/s in the case of full-channel sound and data mode of operation; these figures are respectively equivalent to four and up to 26 high-quality sound channels with 15 kHz bandwidth. with near-instantaneous 14/10-bit companding (protected by one parity bit per sample). The spare data capacity can be used for other services.

can be used with frequency modulation in a satellite channel, or with AM/VSB in a channel of at least 7 MHz bandwidth.

Choice of facilities

The "Rules of operation" reproduced as Part 8 of the present document are the rules applicable for the broadcasting of services using this specification for compatibility with basic receivers.

General organization of the system

The MAC/packet signal is the common bearer for numerous services. Each service is based on the use, possibly combined, of service components which can be classified in three categories:

- picture (analogue broadcasting)

- sound (digitally broadcast)

- data, a general term covering components which do not belong to the two preceding categories.

The following considerations introduce other important points:

- the multiplicity of channels available to the user imposes the need for channel identification to facilitate receiver tuning

- technology allows the design of a system broadcasting analogue and digital components in the same RF channel, and with the possibility to modify the respective parts of each component. For this purpose, a time-division multiplexing technique is used, referred to in this Introduction as TDM multiplex for transmission (time-division multiplex)