Philips J. Res. 50 (1996) 47-60

PRE-STANDARDIZATION OF DIGITAL MULTIMEDIA SYSTEMS by ALBERT

J. STIENSTRA

Philips Research Laboratories, Prof Holstlann 4, 5656 AA Eindhoven, The Netherlands

Abstract Standardization is essential for successful development of the market for multimedia systems and applications. Due to the novelty of the technologies involved and the fact that the market is as yet very small, but growing fast, the general consensus in industry is that standardization via the formal procedures employed by the existing standards organizations would take too long. The new market opportunities, created by digital audio, video and multimedia systems and applications, have made it possible to organize specification projects in a phase preceding formal standardization. In these specification projects many industry players are taking part with some of their best engineers and managers as delegates. Two clearly visible examples of these projects are the Digital Video Broadcasting project in Europe and the Digital AudioVisual Council with a global approach. In this article a short description of the projects, the goals and the methods is given. Keywords: digital audio, digital video, digital multimedia, digital television broadcasting, standardization, MPEG, DVB, DAVIC.

1. Introduetion Both the Digital Video Broadcasting project (DVB) and the Digital AudioVisual Council (DA VIC) are non-profit organizations, aimed at rapid development of digital system standards. DVB started before DAVIC, as a sequel to the Eureka 95 HDTV project. It was driven commercially by the European broadcasters on cable, satellite and terrestrial networks, to make use of the opportunities created by the source coding standards developed by the Motion Pictures Expert Group (MPEG) in ISO/lEC, especially those known as MPEG-2 [1]. It was felt by industry that the formal path to standardization of this brand new technology, using the procedures of the existing standards

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A.J. Stienstra bodies, would take much longer than necessary. Within two years, a complete digital broadcasting transmission system was specified. However, due to the broadcasting origins of DVB, initially no attention was given to interactivity, apart from offering the viewer a sophisticated system for programme selection. A little more than one year after DVB, DAVIC started, mostly driven by the telecommunications and computer industries. Similar to DVB, the DA VIC members were of the opinion that the initial stages of standardization - specification of the systems involved - would take too long if done in the existing standardization organizations. A major technology driver in DAVIC, next to MPEG, is packet switching, according to what is known as Asynchronous Transfer Mode (ATM). From the beginning, DAVIC has been focused on interactive digital multimedia systems. At the end of 1994, when DVB had realized its core transmission standards, DA VIC had become sufficiently big to be noticed. Many companies participating in DVB were at the time also DAVIC members. The stake in DVB, combined with the global standardization objectives of DAVIC, created a strong urge in those companies to integrate the DVB transmission systems for cable and satellite in the DA VIC specifications, which they succeeded in doing. Some parts of the DVB transmission standards had to be adapted to make them globally applicable, e.g. in the American and Japanese 6MHz wide cable channels. At the same time, DVB had become aware of the potentialof interactive broadcast services. A new module, the Interactive Services Commercial Module, was set up in March 1995, with the mandate to generate commercial requirements. The DVB Technical Module supported this by installing ad-hoc groups for specification of the physical and higher layers of the low speed interaction channel - sometimes called the return channel - between the end user and the broadcaster. However, DVB being very much aware of DAVIC, these technical groups were instructed to follow carefully the technical development in DAVIC and start no activities already taken care of. In DAVIC, meanwhile, it was recognized that the first deployment of interactive multimedia services would most likely take place in the form of broadcast enhanced with interactivity, with high data rates from service provider to user and much lower data rates vice versa. As a result, DVB and DAVIC have now become very much aligned, with DVB playing an important role in DA VIC as the organization of European and Japanese broadcasters and consumer electronics industries, creating a good balance with the American and European telecommunications and computer industries. The DAVIC specifications will be very instrumental in creating a global system for multimedia services, a large playing field for

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new applications in communication and entertainment. In the following two sections DVB and DA VIC each will be explained in some more detail.

2. The Digital Video Broadcasting project 2.1. Aims and progress of the project

The DVB project is aimed at the development of a system specification for digital video, audio and data broadcasting services. The basic concept of the system is that it should operate as a container for the MPEG-2 Transport Stream multiplex. The services making use of the system should be introducible within a short time, with maximum likelihood of commercial success. Because of this, the project is driven by commercial requirements, defined by European broadcasters operating satellite, cable and terrestrial networks. The system specification is developed for final standardization in the European Telecommunication Standards Institute (ETSI). The original DVB scope was formed by unidirectional digital television broadcast services, ultimately to replace the present European analogue services via satellite, cable and terrestrial broadcasting networks. Due to emerging market interest and the activities of DA VIC this scope was widened in 1995 to provide the means for interactive services with low bandwidth interaction channels. Flexible implementation ofthe signal quality levels should be possible. Video quality will range from VHS quality level (MPEG-1) to studio quality (CCIR Rec. 601), conforming to MPEG-2 main profile/main layer. The audio quality level can range from commentary-quality mono to CDquality 5-channel surround sound, conforming to MPEG Layer II (MUS 1CAM). Transmission system flexibility should allow implementation on existing and near future European satellite, cable and terrestrial networks, by permitting a range of effective payload bit- and symbol-rates. In addition to the audio and video signals, the DVB transmission system also provides information on the programme being broadcast. To complete the whole, DVB provides for a Common Scrambling system. In 1995 more than 180 organizations were members of the project. The organizations range from broadcasters, network operators and equipment manufacturers to legislating and regulating authorities. Membership is open to all, provided that the DVB Memorandum of Understanding (MoU) is signed and a yearly membership fee is paid. Together the MoD signatories constitute the DVB General Assembly, which elects a Steering Board for the operational project management. The Technical Module and the three

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A.J. Stienstra Commercial Modules (Cable and Satellite, Terrestrial, and Interactive ,Services Commercial Module) report to the Steering Board, where the decision is made to communicate specification items to the formal standards bodies. In addition to the modules, the Steering Board set up some ad-hoc groups for specific administrative tasks and a special one for Conditional Access. The Technical Module set up a score of sub-groups and ad-hoc groups, to deal with the different technical aspects of DVB. All organizational entities are populated by experts, supplied by the DVB signatories. The DVB project formally started at the end of 1993, with the aim to complete the system specification at the end of 1995. A number of preceding organisations have contributed to the technical work of DVB, such as RACE 2082 (dTTb) and the European Launching Group with its Working Group Digital Television Broadcasting. The main drivers of the project are the Commercial Requirements, which are generated by the Commercial Modules to serve as guidelines for the work in the Technical Module where the technical specifications are developed. The commercial modules are populated by commercial staff from the DVB member companies.

2.2. Results of the DVB project Four core standards specify digital framing, coding and modulation for the different transmission media: 1. DVB-S: the satellite system for use in the 11/12 GHz band, for a wide range of transponder bandwidths. This specification is standardized by ETSI in ETS 300421 [2]. 2. DVB-C: the cable transmission system for 8 MHz channels, compatible with the DVB-S satellite system. The ETSI standard is named ETS 300 429 [3]. 3. DVB-SC: the satellite master antenna TV (SMATV) system, the combination of a satellite headend with a small cable system. The ETSI standard for SMATV is called ETS 300473 [4]. 4. DVB- T: the terrestrial TV transmission system specification, which is currently under development and expected to be finalized at the end of 1995. Additional standards are: •

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DVB-Teletext: ITU-R System B Teletext in DVB bitstreams, standardized by ETSI as ETS 300 472 [5].

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DVB-SI: Service Information, for use in Electronic Programme Guides, etc. This specification is standardized by ETSI as ETS 300 468 [6]. DVB-Subtitling: coding of on-screen graphic objects, for subtitling and similar applications. This specification has been transferred to ETSI for standardization. DVB-IRD: physical interfaces, specification of the interfaces on the DVB Integrated Receiver Decoder. This specification has been given to CENELEC for formal standardization. DVB-PI: professional interfaces, specification of interfaces on equipment for cable and satellite head ends and similar professional environments. CENELEC is dealing with formal standardization. DVB-CI: the Common Interface for conditional access and other applications. This specification has been offered to CENELEC for formal standardization.

In addition to standards, DVB has produced other results such as the Common Scrambling System, a number of guidelines for the implementation and use of the DVB systems and a recommendation for antipiracy legislation in Europe.

2.3. Satellite transmission physical and data link layers The physical and data link layers of the satellite broadcasting system are described in ETS 300421 in the form of framing structure, modulation and channel coding. This European Telecommunication Standard (ETS) is intended to provide Direct-To-Home (DTH) delivery via satellite for reception by a consumer Integrated Receiver Decoder (IRD). It uses Quaternary Phase Shift Keying (QPSK) modulation and a concatenated error proteetion strategy. The standard is designed to provide a Quasi-Error-Free (QEF) demodulated signal quality at the user side, meaning less than one uncorrected error event per transmission hour. The inner code is of convolutional type and can be configured flexibly, allowing optimization of the performance to specific system requirements. The outer code is of Reed-Solomen type and has fixed parameters. The standard is not restricted to any particular transponder bandwidth (i.e. the symbol rate is not specified). A framing structure is used which is synchronous to the MPEG-2 Transport Multiplex structure (see Fig. I).

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A.J. Stienstra 2.4. Cable transmission physical and data link layers The physical and data link layers of the cable broadcasting system are described in ETS 300 429 in the form of framing structure, modulation and channel coding. This standard for cable transmission is, in a similar way as the satellite standard, intended to provide delivery to a consumer Integrated Receiver Decoder (IRD). It uses Quadrature Amplitude Modulation (QAM) and the same forward error proteetion strategy as used in the satellite transmission system. The cable transmission system is also designed to provide quasi-error-free output signal quality at the receiver end. The cable transmission system does not make use of an inner code. The outer code is the same Reed-Solomon code with the same interleaver as used in the satellite transmission system. The cable system is specified for use with channels of 8 MHz bandwidth and allows transparent transcoding of DVB satellite transmission signals (the cable symbol rate is also not specified). The signal processing is specified in detail in ETS 300429, in the following processes to be applied to the MPEG-2 transport multiplex data stream at the cable modulator side (see Fig. 2): • • • • • •

multiplex adaptation and data randomization for energy dispersal (synchronous method); outer coding (shortened Reed-Solomon, of parameter (204, 188, 8)); convolutional interleaving (I = 12); byte to symbol conversion with differential encoding (rotationally invariant); base band shaping for r.f. modulation (square root raised cosine, roll-off factor of 15%); modulation (16 or 64QAM).

3. The Digital Audio-Visual Council 3.1. General aspects of the Council Similar to DVB, but now on a world-wide scale, the purpose of the Digital Audio-Visual Council (DAVIC) is the promotion of the success of emerging digital audio-visual applications and services, in the first instance of the interactive broadcast type. This is accomplished by providing for the rapid availability of internationally agreed specifications of open interfaces and protocols, maximizing interoperability across countries and applications

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