ITU-R REPORT BT.1225 PDF

Introduction

The broadcasting of services using new television systems described in CCIR Recommendation 650 and of HDTV systems described in CCIR Report 1.075 will encourage the build-up of a receiver base of high resolution and wide aspect ratio display equipment. Such equipment will offer an attractive prospect for the enhancement of existing data broadcasting services such as teletext, and for the development of entirely new services.

CCIR Recommendation 653 provides information about teletext systems developed for use with television systems of CCIR Recommendation 470 i.e. with NTSC, SECAM and PAL. This report is intended to be the basis on which a new draft recommendation, appropriate to the data broadcasting systems associated with the TV systems of Recommendation 650 and the HDTV systems of Report 1075, will be prepared during the study period 1990-1994.

The transition from conventional television to HDTV will offer the possibility of developing data broadcasting within a balanced distribution of maintaining compatibility between existing and new services. The introduction of HDTV services opens new possibilities for the broadcasting of data and accelerates the evolution of present teletext services towards the use of more sophisticated presentation features (e.g. DRCS, geometric, photographic, etc.) and completely new applications.

High resolution and wide aspect ratio displays make attractive the introduction of a variety of new teletext display formats, from computer-like 80 Latin alphabet characters per row, through to studio quality caption generator font styles and colour palette options.

Development of data broadcasting also acts in favour of the existing trend towards the integration at the technical and service levels between interactive and broadcast digital networks. In this process it is extremely important to maintain close cooperation with the CMTT, the appropriate CCITT Study Groups, the IEC and the ISO.

Emissions in digital format in an HDTV environment include integral parts of the programme such as sound and digital television components, primary programme related services such as subtitles and access control messages, and secondary digital components for non-TV-related services such as teletext, telesoftware and other data broadcasting services, which occupy capacity not used by the TV related services or freed by the removal of the TV service outside of broadcast hours.

At the present stage of development of HDTV in satellite broadcasting, two systems have been developed for use in the 12 GHz band i.e. MUSE and HD-MAC. Both systems require extensive signal processing to insert the HDTV signal into the relatively "narrow RF-band" channels (24 - 27 MHz). It is currently believed that not only will the channel bandwidth available in the 12 GHz band prevent the achievement of the full quality potential of the HDTV studio standard, but will also restrict the available capacity for data broadcasting services [CCIR, 1986-90a, b].

The CCIR has therefore envisaged the need for a further BSS band carrying HDTV in "wide RF-band" channels and offering received picture quality approaching that of the studio originated standard (see CCIR Report 1075).

To this end the WARC-ORB(88) has identified the frequency range for world-wide allocation to HDTV from 12.7 to 23 GHz. Preliminary proposals for "wide RF-band" HDTV systems, which use both analogue FM and fully digital solutions, consume from about 54 to 105 MHz depending on the system. In developing these proposals the necessary capacity for sound and data services must be adequately taken into account. The best prospect of achieving this is likely to be obtained from the fully digital approach to "wide RF-band" HDTV.