The brazilian system for digital television

Introduction

Digital Television has been a hot topic in the world scenario for the past few years. In Brazil, terrestrial television broadcasting is one of the most ubiquitous and important mass communications media for delivering news, information, cultural programs, and entertainment free of charge.

Nine months ago the Brazilian government has made its selection for a digital television system, the ISDTV, International System for digital Television. Lessons learned from the world experience were used to delineate alternatives for exploration and deployment models that best fitted the needs and singularities of the Brazilian scenario. Brazilian system points toward the opening of new opportunities, high definition television, multiple simultaneous programs, data delivery, interactive communication and high quality mobile and portable services.

Brazilian DTV Milestone

After thorough testing and careful studies, the Brazilian Government issued Decree No. 5.820 of June 29, 2006, which provides regulations for the implementation of a series of technological standards for the transmission and reception of digital terrestrial television signals, guaranteeing the general public unrestricted and free access to these signals.

For the adequate delivery of digital television service in Brazil without the interruption of analog signal transmission, in order to facilitate the transition to digital technology, for each station that is operating, a radio channel with a six megahertz broadband is being allocated to permit the simultaneous transmission of programming in analog and digital technologies.

Brazilian Digital TV Forum established according to the Decree has been working from the end of 2006 and comprises, among others, of representatives of the radio broadcasting sector, the industrial sector, and the scientific or technological community, with common interests for the development of the digital terrestrial TV platform. The work aims the establishment of the technical, regulatory and industrial basis for the digital television implementation in Brazil. Thus, it is coordinating the definition of the specification premises, preparation of the technical standards and the outline of an industrial development plan.

ISDTV specifications are almost finalized and are expected to be released soon. ISDTV is the national response for turning the revolutionary improvement in the information infrastructure into creation of jobs and economic development.

Standardization Task Force

Standardization activities are divided among seven subgroups of specialist volunteer members from the broadcasters, consumer electronics, transmitters and software industries and universities. Task force is organized according to the following figure:

Figure 1: Brazilian standardization structure

 Table 1: ISDTV Technical Overview

 Standards Technical Outline

The Brazilian digital transmission system is completely adherent to the ISDB-T standard. ISDTV allows hierarchical transmission, which is the simultaneous transmission of signals with multiple transmission parameters. A total of 13 segment might be grouped in up to 3 transmission layers using the same scheme of error correction coding, interleaving, guard interval and modulation options as of the Japanese ISDB-T system.  Brazilian standard will incorporate specificities of the Brazilian frequency planning studies such as a critical and a non-critical emission mask.

On source coding relies one of the most significant innovations, which is the adoption of the ITU-T Recommendation H.264 (MPEG-4 AVC, Advanced Video Coding), as the basic compression tool for the system. The high profile is used for the compression of SDTV and HDTV video whilst the baseline profile was selected for the portable applications. Although it is based on the same profile as the Japanese standard, Brazil has selected a higher level (Level 1.3) capable of displaying up to 30 fps.

As per the audio compression, specialists have indicated their preference for the MPEG-4 AAC at the high efficiency profile

 Table 2: Source Coding specification

One or more transport streams defined in MPEG-2 systems are re-multiplexed to create a single transport stream, named broadcast-TS. The aggregated transport stream is subjected to multiple channel coding steps in accordance with the intentions of the service. The transport layer is the structure of the program specific information and service information was kept but descriptors have received a different interpretation. The proposed syntax allows random access to programs and includes information about which programs are transmitted so as to provide a form of TV guide.

The service information was specified under the preconditions of international compatibility in data structures, flexibility in accommodating various program configurations from different broadcasters, and extendibility with respect to future broadcast services.

Brazil will have a unique joint implementation of declarative and procedural middleware and the bridge between them. The Brazilian data coding system is called Ginga and comprises the language specification used by the NCL (Nested Context Language) presentation engine and GEM compliant Java execution engine.

The standard encloses monomedia and multimedia coding system and the data transmission system used for data broadcasting and all the details for data structures, descriptors and protocols. The Brazilian standard specifies NCL for representing multimedia and includes two types of data transmission systems: data carousel and object carousel.

Technical specification of tools to prevent the widespread indiscriminate redistribution of high value broadcast content, i.e., programming, over the Internet are also under the scope of the standardization in course. The proposed system manages content until final consumption in accordance with the particular usage rules. It is intended for protection all types of content – audio, video, associated applications and data by implementing protection protocols at all output interfaces.

Activities among the groups are harmonized so that receivers will correctly respond to source coding, and data coding and will preserve and give effect to the implemented DRM mechanism.

DTV receivers should reflect that digital television is more than just a set of traditional TV channels but also a tool to build new services. The decoding of closed caption and audio description is mandatory. The minimum set of mandatory functions is described in the receiver specification. However it relies on product policy of each manufactures whether or not to install functions beyond those specified in the ISDTV standard.

Transition Timetable

The basic transition plan for Brazil require to implement DTV first, while allowing more time for stations in smaller cities and television translator stations to make the transition. The initial plan applied to approximately stations

The allocation of the digital transmission channels shall be given time-limits of up to seven years and guarantees that translators will not be granted a channel prior to the main station. DTV shall begin in the city of São Paulo, the largest and most important city. First transmissions are expected on December 3^rd, 2007.

Other state capitals such as Rio de Janeiro, Belo Horizonte, Brasília, Fortaleza, and Salvador will follow the initial launch in São Paulo. Smaller cities might only request the authorization for digital transmission after March, 31^st, 2008.

Maximum time-limits for the installation and functioning of the digital transmission station are also defined. Broadcasters interested in signing the allocation document of the digital channel shall comply with the following timetable:

I – six months, after the signing of the channel allocation contract, for presentation of the digital installation project; and

II – 18 months, after approval of the project of installing the digital station, for the digital transmissions start up.

Key technical advantages

The Brazilian standard offers the best reception coverage allows broadcasters to provide more services to their viewers.  Due to the technical robustness and performance it provides lower acquisition and operation costs for broadcasters and good service capability for the viewers.

Transmission specification assures the possibility of delivering programs and applications to hand-held devices. The system is configurable in such a way that the broadcaster may trade capacity against coverage and within a given capacity define which service are to be received, at a given quality level, with stationary, mobile and portable reception respectively.

Viewer will benefit from enhanced image, sharper sound and exciting new applications. H.264 is currently the most powerful and state-of-the-art standard, its design provides the most current balance between coding efficiency, implementation complexity and cost, based on the current state of VLSI design technology. It will be used for the transport of HDTV program material in a virtually transparent fashion using a reduced bit rate.

Sharp images and attractive content have a high potential for a rapid adoption this technology. ISDTV also offers time interleaving to provide powerful channel coding for mobile reception in which variations in field are inevitable.

Key Business Advantages

Flexibility to offer the adequate blend of content that is most appealing to the local audience is the best description of the ISDTV system. HDTV, multiple SDTV services, mobile and portable services and a limitless variety of information services are all harmonized in Brazil under a technical and regulatory umbrella.

Digital television system platform was developed to maximize its unique capacity for offering mobile and portable services and has been actively developed for portable and mobile applications thus providing an alternative to in-house wireless solutions as a means of overcoming the problem of second and third television sets in the home and providing new broadcast entertainment and information services to people on the move.

ISTDV is an effective means of providing increased access to information services to viewers of all socio-economic segments. Reaching the poorer segments of the society is of particular relevance since the vast majority of the Brazilian population relies on free-to-air television as the only means to have access to information and entertainment.

The proposed system ensures a more efficient and cost-effective use of the spectrum when compared to analogue transmission. The specification guarantees the use of SFN, on-channel repeaters and several other techniques for optimizing the coverage and filling shadow areas

Conclusion

The terrestrial digital television implementation is not only a technical and business challenge but also represents an effective means of giving access of the digital technology to all socio-economic segments of society. Flexible business models and mobile and portable reception applications are the key to the digital television platform future viability.

Brazilian digital television is in its early stages of development and implementation with a very promising future. Most of the component standards are existing international standards, but used in an innovative and unique combination. The Brazilian DTTB system uses state-of-the-art technologies with no prejudice whatsoever to time-to-market of receivers in the one year range.

ISDTV system is being developed to provide new applications that facilitate access to culture, information, and entertainment. It will promote the social inclusion, cultural diversity of the country, and the official language through access to digital technology, aiming at democratizing the information.

Economical aspects related to investments in broadcast equipment are also being carefully addressed. The implementation of DTTB in Brazil includes financing and special industrial policies that match the Latin America reality.

The ultimate goal of the whole process is to promote a smooth introduction of the free-to-air terrestrial digital television service with adequate levels of knowledge and confidence throughout the whole productive chain, with an ultimate positive impact to the Brazilian society.

Ana Eliza Faria e Silva
Engineer
TV Globo