Technology development specialist

Julio E Duran Technology Development Specialist julio.duran@intelsat.int Source du document 1.0 INTRODUCTION Following the release of the MPEG overview understanding the DVB standard is important to the development of DTH platform based new services via satellite The commercial potential and diversity of applications have converted the DVB/MPEG-2 to attractive systems for the delivery of different kinds of services and applications via satellite This paper explains in detail what the DVB standard is, its scope, and its technical parameters and characteristics The important Conditional Access System within the DVB is also explained DVB is intended and developed to provide DTH, multiprogram TV services in the BSS (Broadcasting Satellite Services) and FSS (Fixed Satellite Services) bands Additionally, DVB addresses consumer IRDs (Integrated Receiver Decoder) DVB is being used in different applications such as INTERNET, Multimedia Information Broadcasting, Tele-learning, Telemedicine, Tele-shopping, and others The exploitation of the multiplex flexibility allows the use of the transmission capacity for a variety of TV service configurations In the next years, DVB will continue to provide internationally accepted standards for digital broadcasting The most contentious issues at present are the development of "Conditional Access System", "Data Broadcasting" and "Interactive Services" standards 2.1 What is the Digital Video Broadcasting (DVB) Project? The story of the DVB Project began in 1990 Experimental projects such a SPECTRE showed that the digital video compression system known as "Motion Compensated Hybrid Discrete Cosine Transform Coding" was highly effective in reducing the transmission capacity required for digital television Up until then, digital television broadcasting was thought to be impractical to implement commercially In the United States, the first proposals for digital terrestrial HDTV were made In Europe, the Swedish Television suggested that fellow broadcasters should form a pan-European platform to develop digital terrestrial HDTV During 1991, broadcasters and consumer equipment manufacturers discussed how this could be done Broadcasters, consumer electronics manufacturers and radio-regulatory bodies agreed to come together to discuss the formation of a pan-European group that would oversee the development of digital television in Europe - the European Launching Group (ELG) Over the course of about a year, the ELG expanded to include the major European media interest groups, both public and private, the consumer electronics manufacturers and common carriers It drafted a Memorandum of Understanding (MoU) establishing the rules by which this new and exciting game of collective action would be played The MoU was signed by all ELG participants in September 1993, and the Launching Group became the DVB (Digital Video Broadcasting) Project DVB provided the forum for gathering all the major European television interests into one group It promised to develop a complete digital television system based on a unified approach It was now clear that digital satellite and cable television would provide the first broadcast digital television devices Fewer technical problems, and a simpler regulatory climate meant that it could develop more rapidly than terrestrial systems Market priorities meant that digital satellite and cable broadcasting systems would have to be developed rapidly 2.2 Why DVB? Because DVB System provides a complete solution for digital television and data broadcasting across a range of delivery media Careful planning and common sense have been the keys to success From the outset, it was clear that the sound and picture-coding systems of ISO/IEC MPEG-2 should form the audio and image-coding DVB would need to add, to the MPEG transport stream multiplex, the necessary elements to bring digital television to the home through cable, satellite and terrestrial broadcast systems Interactive Television is also an attractive service and DVB might help with the framework for the interactive television services of the future The digital vision and sound-coding systems adopted for DVB use sophisticated compression techniques The MPEG standard specifies a data-stream "syntax" The system designer is given a "tool-box" from which to make up systems incorporating greater or lesser degrees of sophistication In this way, services avoid being over-engineered, yet are able to respond fully to market requirements and are capable of evolution The sound-coding system specified for all DVB systems is the MPEG audio standard The DVB Project suggests, in its current MPEG-2 Guidelines document, that MPEG Layer II (MUSICAM) should be used This is also used for many other audio products and services throughout the world MPEG Layer II is a digital compression system which takes advantage of the fact that a sound element will have a masking effect on lower-level sounds (or on noise) at nearby frequencies This is used to facilitate the coding of the audio with low data rates [3] Sound elements which are present, but would not be heard even if reproduced faithfully, are not coded The MPEG Layer II system can achieve a sound quality which is very close to Compact Disc The system can be used for mono, stereo, or multi-lingual sound, and in future MPEG-2 audio can be used for surround sound [3] 2.3 DVB Standards DVB standards are open and inter-operable Following approval by the Steering Board, DVB specifications are offered for standardization to the relevant standards body (ETSI or CENELEC), through the ETSI/EBU/CENELEC JTC (Joint Technical Committee) and the ITU-R, ITU-T and DAVIC For each delivery system, a set of User Requirements is drawn up by the relevant Commercial Module These are used as constraints on the specification For example, in the case of DVB-T, the Terrestrial Commercial Module proposed user requirements that outline broad market parameters for a DVB-T system (price-band, user functions, etc.) The Technical Module then developed the specification, following the user requirements The approval process within DVB requires that the relevant Commercial Module support the specification before it is finally approved by the Steering Board In addition DVB has developed DVB Receiver Guidelines, suggestions for Interfaces for the domestic receiver, and a Common Interface specification intended for conditional access applications Both interface documents were agreed by the DVB Steering Board in March 1995 and are now with CENELEC for standardization [5] DVB-S has been acknowledged by the ITU in a Recommendation for the broadcast transmission of digital television for 11/12 GHz satellites DVB-C is also included in an ITU Recommendation Technical specifications in the areas of subtitling, MVDS (Multipoint Video Distribution System) and interactive television are being submitted to the appropriate standards body Copies of the Standards are available from ETSI and the EBU (see Table 1): Specification Reference Title (ETSI) DVB-S ETS 300 421 DVB Status Digital Broadcasting System for television, sound and data services; Framing Structure, Channel Coding and modulation for 11/12 GHz satellite services SB 3(93)9 approved DVB-C DVB-SI ETS 300 429 ETS 300 468 Digital Broadcasting System for television, sound and data services; Framing Structure, Channel Coding and modulation for cable systems Digital Broadcasting System for television, sound and data services; for Service Information (SI) SB approved SB 5(94)20 approved DVB-T ETS 300 744 Digital Broadcasting System for television, sound and data services; for Digital Terrestrial Television SB 12(95)7 approved DVB-MS ETS 300 748 Digital Broadcasting System for television, sound and data services; for Multipoint Video Distribution System at 10 GHz and above SB 12(95)15 approved DVB-MC ETS 300 749 Digital Broadcasting System for television, sound and data services; for Multipoint Video Distribution System below 10 GHz SB 14(96)43 approved DVB-SMATV ETS 300 473 Digital Broadcasting System for television, sound and data services; Satellite Master Antenna Television (SMATV) distribution systems SB 7(94)26 Rev DVB-NIP ETS 300 802 Digital Video Broadcasting (DVB); Network Independent Protocols for DVB Interactive services SB 14(96)44 approved DVB-RCC ETS 300 800 Digital Video Broadcasting (DVB); DVB interaction channel for Cable TV distribution system (CATV) SB 14(96)45 approved DVB-RCT ETS 300 801 Digital Video Broadcasting (DVB); DVB interaction channel through PSTN/ISDN SB 14(96)10 approved Table DVB Specifications Status Specification Reference Title (ETSI) DVB-PDH ETS 300 813 DVB Status DVB Interfaces to PDH network SB 14(96)5 approved DVB-SDH ETS 300 814 DVB interfaces to SDH networks SB 15(96)4 approved DVB-CS ETR 289 Digital Video Broadcasting (DVB); The Common Scrambling system description SB 14(96)9 approved DVB-CI ETR 289 Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications SB approved DVB-Data prTS 101 192 Digital Video Broadcasting (DVB); Specification for the transmission of data services in DVB bitstreams SI-DAT drafting Table (continue) DVB Specifications Status 2.3.1 DVB-S Baseline System for modulation and channel coding for satellite digital multi-programme TV/HDTV services to be used for satellite digital TV for primary and secondary distribution in FSS and BSS bands[9] The Baseline System is intended to provide Direct-to-Home (DTH) services for consumer Integrated Receiver Decoders (IRDs) as well as collective antenna systems (SMATV) and cable television head-end stations The Baseline System uses QPSK modulation and concatenated error protection strategy based on a convolutional code and a shortened Reed-Solomon code The Baseline System is suitable for use on different satellite transponder bandwidths Compatibility with MPEG-2 coded TV services, with a transmission structure synchronous with the packet multiplex, is provided The multiplex flexibility allows the use of transmission capacity for a variety of TV service configurations, including sound and data services All service components are time multiplexed (TDM) on a single digital carrier 2.3.2 DVB-C Baseline System for a Digital multi-programme Television by Cable (DTVC) [10] Harmonized transmission standard for cable and satellite, based on the MPEG-2 System Layer, with the addition of Forward Error Correction (FEC) technique It is compatible with the modulation/ channel coding system used for digital multiprogramme television by satellite (DE/JTC-DVB-6) The System allows for further evolution as technology advances and is capable of starting a reliable service as of now The Baseline System is based on QAM modulation scheme It allows for 16, 32 or 64-QAM constellations and permits future extension to higher constellation such as 128 and 256-QAM 2.3.3 DVB-SI (Specification for Service Information (SI) in DVB systems) The provision of a solution for the "Seamless Transition Networks" with respect to the "Network Identification Table" in the case of SMATV and some CATV networks was not covered by the ETS 300 468 (SI) Ed As a consequence HISPASAT, RAI, DTI, SAT/Sagem, Sharp and the Spanish Administration proposed revision EWP items on ETS 300 468 and ETR 211 Specification of Service Information (SI) data which forms part of DVB/MPEG-2 bitstreams is defined, in order that the user can be provided with information to assist in the selection of services and/or events within the bitstream, so that the Integrated Receiver Decoder (IRD) can automatically configure itself for the selected service SI is specified in ISO/IEC 13818-1 as Programme Specific Information (PSI)[6] This specification complements the PSI by providing data to aid automatic tuning of IRDs, and additional information intended for display to the user, mainly in text form The form of presentation of the information is not specified, and IRD manufacturers have freedom to choose appropriate presentation methods It is expected that Electronic Programme Guides (EPG) will be a feature of Digital TV transmissions The definition of EPG is outside the scope of the SI specification, but the data contained within the SI specified here could be used as basis for an EPG The present specification describes Service Information (SI) for use in broadcast MPEG-2 bitstreams The MPEG-2 System layer specifies SI which is referred to as Programme Specific Information (PSI) The PSI data provides information to enable automatic configuration of the receiver to demultiplex and decode the various streams of programme within the multiplex The basic building blocks which are part of the DVB System are the MPEG-2 data packets These are fixedlength containers with 188 bytes of data MPEG includes Program Specific Information (PSI) so that the MPEG-2 decoder can capture and decode the packet structure This data, transmitted with the pictures and sound, automatically configures the decoder and provides the synchronization information necessary for the decoder to produce a complete video signal at its output [6] MPEG-2 also allows a separate Service Information system to be used to complement the PSI DVB has prepared an open Service Information system to accompany DVB signals It can be used by the decoder and the user, to navigate through the array of services offered Key data, necessary for the DVB IRD (Integrated Receiver Decoder) to automatically configure itself, is available in the MPEG-2 PSI DVB-SI adds information that enables DVB IRDs to automatically tune to particular services and allows services to be grouped into categories with relevant schedule information In a DVB environment, the viewer of tomorrow will be receiving a multitude (perhaps hundreds) of channels with his IRD These services could range from interactive television, to near video-on-demand, to specialized programming The viewer will need help DVB-SI provides the elements necessary for the development of the Electronic Programme Guides (EPG) that are likely to become a feature of the new digital television services More elaborate EPGs may also be provided, perhaps as additional elements via a receiver interface DVB-SI is based on four tables, plus a series of optional tables Each table contains descriptors outlining the characteristics of the services/event being described The four tables are: NIT The Network Information Table groups together services belonging to a particular network provider It contains all the tuning information that might be used during the set-up of an IRD It is also used to signal a change in the tuning information SDT The Service Description Table lists the names and other parameters associated with each service in a particular MPEG multiplex EIT The Event Information Table is used to transmit information relating to all the events that occur or will occur in the MPEG multiplex The EIT contains information about the current transport, and optionally covers other transport streams that the IRD can receive TDT The Time and Date Table is used to update the internal clock of the IRD In addition there are three optional SI tables: BAT The Bouquet Association Table provides a means of grouping services that might be used as a way an IRD presents the available services to the viewer A particular service can belong to one or more bouquets RST The sections of the Running Status Table are used to rapidly update the running status of one or more events The Running Status sections are sent out only once, at the time the status of an event changes, unlike the other SI tables which are normally repetitively transmitted ST Stuffing Tables may be used to replace or invalidate either sub-tables or complete SI tables With these tools, DVB-SI covers the range of practical scenarios Seamless transition between satellite and cable networks, near video-on-demand, and all operational configurations, are possible 2.3.4 DVB-T Digital terrestrial broadcasting is one of the cornerstones of DVB The DVB-T system specification, for the terrestrial broadcasting of digital television signal, was approved by ETSI in February 1997 [4] The Coded Orthogonal Frequency Division Multiplexing (COFDM)-based system, proposed in DVB-T, allows the use of either 1705 carriers or 6817 carriers Reed-Solomon outer coding and outer convolutional interleaving are used, in common with the other DVB standards The inner coding is the same used for DVB-S The data carriers in the COFDM frame can use QPSK and different levels of QAM modulation The modulation system combines OFDM with QPSK/QAM 2.3.5 DVB-MS Modulation and channel coding system for the distribution of digital multi-programme Television (TV)/High Definition Television (HDTV) by Multipoint Video Distribution Systems (MVDS) in the 40 GHz band The System described in this ETS is based on that described in ETS 300 421 for 11/12 GHz satellite services It allows the same consumer Integrated Receiver Decoder (IRD) to be used for either service, when used with a Low Noise Block (LNB) down-converter for the appropriate frequency band The frequency band 40,5 to 42,5 GHz has been harmonized within CEPT under Recommendation T/R 52-01 The System however, is applicable to other frequency bands above 10 GHz The System uses Quaternary Phase Shift Keying (QPSK) modulation and concatenated error protection strategy based on a convolutional code and shortened Reed-Solomon (RS) code The System is suitable for use on different MVDS transmitter bandwidths Compatibility with Moving Pictures Experts Group-2 (MPEG-2) coded TV services (see ISO/IEC IS 13818-1), with a transmission structure synchronous with the packet multiplex, is provided Exploitation of the multiplex flexibility allows the use of the transmission capacity for a variety of TV service configurations, including sound and data services All service components are Time Division Multiplexed (TDM) on a single digital carrier 2.3.6 DVB-MC Modulation and channel coding system for the distribution of digital multi-programme Television (TV)/High Definition Television (HDTV) by Multipoint Video Distribution Systems (MVDS) below 10 GHz The System described in this ETS is based on that described in ETS 300 429 on framing structure, channel coding and modulation for cable systems The frequency band may/will be harmonized within CEPT The System is suitable for use on different MVDS transmitter bandwidths Compatibility with Moving Pictures Experts Group-2 (MPEG-2) coded TV services (see ISO/IEC IS 13818-1), with a transmission structure synchronous with the packet multiplex, is provided Exploitation of the multiplex flexibility allows the use of the transmission capacity for a variety of TV service configurations, including sound and data services All service components are Time Division Multiplexed (TDM) on a single digital carrier 2.3.7 DVB-SMATV Transmission System proposal for Digital multi-programme Television by suitable for distribution in Satellite Master Antenna Television (SMATV) systems [12] This ETS is complementary to ETS 300 429 (Cable) and it is aligned with ETS 300 421 (Satellite) The system described in this ETS is compatible with the modulation and channel coding systems used for digital multi-programme television by cable and satellite transmission The system is based on the MPEG-2 System Layer, with the addition of appropriate Forward Error Correction (FEC) technique The system allows for further evolution as technology advances and is capable of starting a reliable service as of now 2.3.8 DVB-I (Interactive Systems) DVB has worked in developing a set coherent practical specifications for an Interactive TV System This system is divided in two standards: 2.3.8.1 DVB-NIP Covers the core DVB requirements to enable interactive services supporting broadcasting to the home with narrowband return channels The system defined in this ETS provides a generic solution for a variety of future interactive services, through the adoption of DSM-CC User-to-User, Download and Object Carousel protocols, as specified in MPEG-2 The interactive services are provided on systems consisting of a high bit rate downstream channel (up to the maximum bit rate of the Broadcast channel) from the Service Providers to Service consumers and low bit rate interaction channels (up to 150 kbit/s) The Broadcast Service Provider and the Interactive Service Provider need not operate from the same location The services are primarily digital video broadcast enhanced with interactivity At the simplest level the Interactive channel allows the consumer to react by voting, to order articles displayed in the broadcast programme, to select certain programme bouquets or to choose movies in near-video-on-demand systems It is also possible to deliver text, graphics, audio and still pictures (including e-mail) on-demand , although this may require an interactive channel with higher bit rates There are many possible network configurations covering the currently specified DVB broadcast options including satellite, terrestrial, cable, SMATV and MMDS [12] conjunction with PSTN, ISDN, cable and other Interactive channel options The network dependent protocols are specified in ETS 300 800/801 & ETS 300 803 The implications for interactive services via these types of networks are described in a separate guidelines document DTR/JTC-00DVB-44 "Guidelines for the use of the DVB network-independent protocols for interactive services" which will also summarize the functionality of the protocols identified in this ETS This ETS is the baseline specification for the provision of interaction channel for CATV It is noted that the DVB project does not intend to specify a return channel solution associated to each broadcast system because the Interoperability of different delivery media to transport the return channel is desirable The solutions here provided for interaction channel for CATV networks are a part of a wider set of alternatives to implement interactive services for DVB broadcasting systems 2.3.8.2 DVB-RCT This ETS is the baseline specification for the provision of return channel based on PSTN and ISDN to DVB Systems It is noted that the DVB project does not intend to specify a return channel solution associated to each broadcast system because the Interoperability of different delivery media to transport the return channel is desirable Therefore the PSTN/ISDN solutions for the return channel apply to satellite, cable, SMATV, terrestrial, MMDS or any future DVB broadcasting system The solutions here provided for return channel through PSTN/ISDN are a part of a wider set of alternatives to implement interactive services for DVB broadcasting systems 2.3.9 DVB-Data DVB-Data is seen as one of the new applications for DVB Data broadcasting involves file downloading, data carousels, and protocol tunneling for a wide range of applications including INTERNET delivery and the broadcast of secure private data [19] This standard is in drafting status This specification is designed to be used in conjunction with the DVB-SI 2.3.10 DVB-CS (Common Scrambling) Support for use of scrambling and Conditional Access (CA) within digital broadcasting systems [14], meant as a marketing tool to attract interested parties for applying/receiving the "CS system specification", which will be released to qualified applicants on receipt of a non-disclosure agreement This ETR does not include "Security" issues The Common Scrambling Algorithm was designed to minimize the likelihood of piracy attack over a long period of time The specification, prepared by the Conditional Access Specialists' Group, is lodged with the European Telecommunication Standards Institute (ETSI) as custodian The technical details are distributed, and the technology licensed, by the custodian to appropriate organizations upon signature of a license agreement By using the Common Scrambling Algorithm system in conjunction with the standard MPEG data transport and selection mechanisms it is possible to incorporate in a DVB transmission the means to carry multiple messages which all enable control of the same scrambled broadcast but are generated by a number of different CA systems This 'Simulcrypt' technique allows both the delivery of one Programme to a number of different decoder populations that contain different CA systems, and also for the transition between different CA systems in any decoder population, for example to recover from piracy The 'Multicrypt' option is also available, facilitated by the Common Interface (DVB-CI) specification proposed for standardization by CENELEC (European Committee for Electrotechnical Standardization) 2.3.11 DVB-CI (Common Interface) The Common Interface operates at the MPEG Transport Stream level, and although specifically intended for conditional access, it may also prove useful in other applications, such as for Electronic Program Guides The CA functions of decryption and descrambling take place in a small plug-in module, similar in size and appearance to a PCMCIA card as popularly used with lap-top PCs This CA Module may operate in conjunction with a smartcard through an associated smart-card reader [14] The DVB Project has agreed to an Important procedure, or Code of Conduct, which should help service providers gain access to markets where decryption systems other than their own are in use The DVB Project has also adopted a series of Recommendations on Antipiracy Legislation, which it has submitted to the European Commission and other European bodies These most notably call for criminal penalties for the commercialization and use of pirated decoder devices The area of Conditional Access has received particular attention within DVB Discussions have prove to be difficult and lengthy, but common consensus has yielded a package of measures 3.0 DVB Transmission System The DVB systems Cable (DVB-C), Microwave (DVB/MVDS) and Satellite (DVB-S) are very similar, using the same parameters, little changes at the RF transmission system and in the Error Correction System [7] A model of digital satellite system is shown in the Figure "DVB-S Transmission System" In this example, the system translates the output of the MPEG-2 transport stream multiplexer (see Section 3.1) to a signal appropriate for a satellite channel Although the following system description, based on European Telecommunication Standards, assumes a single carrier per Transponder with multiple services carried as packetized data in the time-division multiplex (TDM) of the transport data stream, multicarrier systems using frequency-division multiple access (FDMA) techniques, each carrying a transport data stream, are also possible This technique was also used for the Skyplex system but added some changes in the ground stations Figure DVB-S Transmission System (Ku-band) 3.1 Transport Stream Multiplexer [6] The PES packets are organized into a one or various Transport Packet in the Transport Stream Multiplexer (see Figure 2) A transport packet is always 188 bytes (1504 bits) long The content of each transport packet (see Figure 3) is a 4-bytes Header followed by an Adaptation Header (used to fill the 188 bytes of the transport packet, if is necessary) and a Payload (184 Bytes without Adaptation Header) time beyond which the system will not be usable Disable messages may have an indefinite lifetime whereas enable messages may have a lifetime of a month or so For security reasons, communication between the SMS and the SAS can be encrypted although this may not be necessary if all systems are in a secure environment 4.7 Common Interface The European DVB Project has designed a Common Interface for use between the Integrated Receiver Decoder (IRD) and the CA system As shown in Figure 16, the IRD contains only those elements that are needed to receive clear broadcasts The CA system is contained in a low-priced, proprietary module which communicates with the IRD via the Common Interface No secret conditional access data passes across the interface [15,16] The Common Interface allows broadcasters to use CA modules which contain solutions from different suppliers, thus increasing their choice and anti-piracy options Figure 16 DVB Common Interface 4.8 Simulcrypt In the case of SimulCrypt, each service is transmitted with the entitlement messages for a number of different proprietary systems, so that decoders using different conditional access systems (in different geographic areas) can decode the service SimulCrypt requires a common framework for signalling the different Entitlement Message streams Access to the system is controlled by the system operators Operation of the system requires commercial negotiations between broadcasters and conditional access operators A code of conduct has been drawn up for the operation of SimulCrypt The philosophy behind the system is that in one geographical area, it will only be necessary to have a single smart card or CA module and a single decoder to receive the local service If one wanted to descramble the service of a neighboring area, one could subscribe to, and use the smart card/module for that service Consequently, it is only necessary to have a single Subscriber Management System for a given area When a viewer wants to watch services from two neighboring areas, it is necessary for both services to carry the entitlement messages for that viewer Therefore it is necessary to have secure links between the different Subscriber Management Systems of the different operators to allow transfer of the entitlement messages between operators 4.9 Multicrypt MultiCrypt (receiver equipped with more than one CA system) is an open system which allows competition between conditional access system providers and Subscriber Management System operators MultiCrypt uses common receiver/decoder elements which could be built into television sets The Common Conditional Access Interface can be used to implement MultiCrypt Conditional access modules from different system operators can be plugged into different slots in the common receiver/decoder, using the common interface 4.10 Return Link For most home installations, a return path could be set up between the set-top decoder and the Subscriber Management System using different delivery media return (Cable, Microwave, Satellite, etc ) For example, calls could be initiated by the customer using a remote control unit which auto-dials a number delivered overair Also, the broadcaster may want the customer's decoder box to contact the SMS This process could be initiated by commands sent over-air or (less likely) the SMS could dial up the customer's decoder box and interrogate it directly There are a number of reasons for using a return link: a) Enhanced security; The return path establishes a one-to-one link between the broadcaster and each decoder box Communication via the return path should be encrypted b) Payment billing; Pre-booked Pay-Per-View (PPV) and impulse PPV could be registered using the return path c) Interactive TV; The return path could be used for audience participation (for example voting, games playing, teleshopping and telebanking) d) Transmission of entitlement messages; For large shared networks, the capacity for transmission of entitlement messages may be inadequate and additional capacity may be achieved by using the telephone network The return path could also be used to check that the decoder is tuned to the correct channel when giving authorization over-air This could reduce the number of over-air signals that have to be repeated perpetually e) Interactive Services; The return path could be used for internet services, tele-medicine, tele-education, videoconferencing and others DVB has standardized return channel system for PSTN/ISDN (DVB-RCT) and cable TV system (DVB-RCC) The DVB-RCC brings together many elements from the DAVIC 1.x specifications The return link via Satellite is being reviewed by the DVB Project and DAVIC for standardization, but they don't have decided yet, what is going to be the access protocol and the open achictecture DIGITAL SATELLITE SYSTEM (DSS) DSS makes use of several standards, but is not fully compliant with the European Digital Video Broadcasting (DVB) satellite convention DSS was designed before the ratification of DVB However, DSS should be compliant with the most difficult Interoperability aspect of DVB: video and audio representation In fact, the video and audio bitstreams are unaffected by the transport layer protocol An MPEG-2 video bitstream transported over DSS packets will demultiplex identically to a bitstream transported by DVB means The DSS system utilizes a concatenated encoding scheme The first section is a Reed-Solomon encoder, followed by an interleaver, a Convolutional encoder, and a QPSK modulator No randomization function is performed [13] Each DSS packet consists of various data fields Inner error correction (6/7 viterbi): 24.5 bytes Packet length: 147.0 bytes Outer error correction (RS): 16.0 bytes Synchronization Byte; One added to 146 byte interleaving (see Figure 17) Header length: 3.0 bytes Payload: 127.0 bytes Total (6/7): block after ~171.5 bytes (~1372 bits or ~686 symbols/sec for QPSK) Expressed from a hierarchical perspective: Layer Rate Analog Waveform Bandlimited to 24 MHz Symbol Stream 20 Million 4-QPSK symbols/sec Bitstream 40 Mbit/sec (2 bit/symbol * 20 MHz) Packet Stream 34 Mbit/sec (after convolutional code) Payload Stream 30 Mbit/sec (after packet header and FEC) Each data packet is 146 bytes (before interleaving) A byte is made up of bits The first two bytes in the data packet contain the Service Channel Identification (SCID) and Flags The SCID is a 12 bit number, to 4095, that identifies the data channel to which the packer belongs Each Flag is bits long The Flag controls whether the packet is encrypted, and if so, which key decodes it The third byte of information is a 4-bit Packet Type indicator and a 4-bit Continuity Counter The Packet Type identifies the packet's data types When combined with the SCID, the Packet Type determines how the packet should be used The Continuity Counter increments once for each Packet Type and SCID The next 127 bytes of information consists of the payload data which is the actual usable information sent from the program provider, as shown in figure 16 Figure 16 Data Packet (before Interleaving) Figure 17 Data Packet (After Interleaving) Physical Layer (L Band Interface, 12 GHz satellite link) DSS IRDs receive the satellite signal after amplification and block down conversion at the receive antenna The signal is transmitted via coaxial cable to the IRD at L band Either polarization may be selected by changing the level of the block downconverter supply voltage This power is supplied to the downconverter by the IRD via the coaxial cable Receive Frequency 950 to 1450 MHz Transponders per polarization 16 Transponder Bandwidth 24 MHz Transponder Spacing 29.16 MHz Polarization Selection Voltage RHCP: 11.5 to 14.0 volts LHCP: 16.0 to 19.0 volts 5.1 DSS decoder system To illustrate the makeup of the DSS System, a block diagram of the video Signal path is provided below Note: this diagram is generic enough to apply to many other set top-box designs [Dish/LNB] > [Tuner/IF demodulator] > [A/D] > [QPSK demodulator] > [Viterbi FEC] > [Reed-Solomon FEC] > [Systems demultiplexor] > [Video decoder ] > [NTSC modulator] > [D/A] > [RF modulator] > [TV] Dish/LNB: Low Noise Block converter maps 500 MHz of the Ku band (BSS) (RF carrier around 12 GHz) onto coax cable (RF carrier in the more friendly neighborhood of GHz) In the dual-LNB deluxe DSS receiver system, both polarities (set of 16 transponders) are mapped onto the same coax cable (total ~1 GHz) Tuner/IF Demodulator: essentially isolates one data carrier out of the total 16 carriers contained within the 500 MHz spectrum A/D: samples the IF analog Baseband signal for processing by the QPSK decoder QPSK Demodulator: converts the sampled modulated signal into a stream of discrete bits Viterbi decoder: performs deconvolution of the bitstream Reed-Solomon FEC: performs error correction using the supplied redundant 16 bytes per packet Systems Demultiplexor: separates audio, video, VBI (vertical blanking information data such as closed caption and teletext), program guide, and conditional access information into separate bitstreams Video Decoder: decodes video bitstreams into raw 4:2:0 YCbCr pictures These pictures (whether coded as fields or frames) are output one field at a time at a sample rate of 13.5 MHz for Y (luminance) and 6.75 MHz for each of the color channels (Cb and Cr) NTSC Modulator: converts the "CCIR 601" YCbCr format stream into a composite video stream D/A: separately converts the composite digital video stream and component Y/C digital video stream into analog Baseband signals The Y/C signal is compatible with the S-Video format conveyed on the round, MiniDin 4-pin connector The composite analog signal is additionally provided on the RCA phono-style connector The video composite signal is also modulated on an RF carrier RF Modulator: modulates the analog composite video signal onto an RF carrier (channel or 4), along with a (mono) analog audio subcarrier 5.2 DSS vs DVB-S DVB-S specifies conformance at several levels, including channel coding (e.g symbol rate, QPSK modulation, Reed-Solomon forward error correction, Viterbi convolution for outer error correction, packet interleaving), transport layer (MPEG-2 Systems Transport bitstreams), and elementary stream layers (MPEG-2 Video, MPEG-1 Audio) [18] DSS elements are nearly identical to DVB Subtle differences exist such as packet length (DSS packets are 147 bytes long whereas MPEG-2 Transport streams packets are 188 bytes long), but the more expensive implementation items are the same (modulation, error correction) The differences between the two standards are shown in Table below: Demodulation and Channel Decoding Function DVB-S DSS Randomization for energy dispersal PRBS: 1+X14+ X15 NONE Synchronous randomization YES N.A Loading sequence into PRBS reg 100101010000000 N.A Reed-Solomon Outer code 204,188, T=8 146, 130, T=8 Forney: I=12, M=17 Ramsey II: N1=13, N2=146 RS code generator polynomial RS field generator polynomial Convolutional Interleaving Inner Coding Convolutional Code constraint length K=7 Basic Code 1/2 Generator Polynomial 171, 133 (octal) Forward Error Correction (FEC) 1/2, 2/3, 3/4, 5/6, and 7/8 Signal Modulation 1/2, 2/3, and 6/7 QPSK , no differential coding Symbol Rate Variable Fixed Not specified 20 Mbaud Occupied Bandwidth (at -3dB) Variable 20 MHz Allocated Bandwidth (at -25dB) Variable 25.1 MHz Symbol Rate Range Baseband Shaping Roll-off 0.35 (square root raised cos.) 0.20 (square root raised cos.) Table Differences between DSS and DVB-S Transport and Demultiplexing Transport Layer MPEG-2 (ISO/IEC 13818-1) Proprietary Packet size (bytes) 188 130 Identification ID (bit) 13 (PID) 12 (SCID) Continuity Counter (bit) Adaptation Flag (bit) CC (AD) Scrambling Flag Priority (bit) (Aux) (Scrm.) (P) Bundle Boundary (bit) None (PE) Error Indicating (bit) (E) byte Media Error Field Payload (byte) 184 127 Sync word byte 47HEX None (after Interleaving) Sync byte inversion From 47HEX to B8HEX None (every transport packet) Statistical multiplexing Master Reference Clock Method of Sync for Video & Audio Not restricted Capable 27 MHz Time Sampling Table (continue) Differences between DSS and DVB-S Source Decoding Function DVB-S DSS Video source decoding Syntax MPEG-2 Video source decoding Levels at least main level Video source decoding Profiles at least main profile Audio source decoding MPEG-2 Layers I and Layer II MPEG-1 Layer II Others Characteristics Typical Transponder bandwidth (MHz) Satellite downlink frequency range Compatibility with SMATV Not specified 24/27 MHz Originally designed for 11/12 GHz, not excluding other satellite frequency ranges YES Some processing is required at the Head-end when transmodulating to QAM Compatibility with existing telecommunications hierarchies The transport stream could be defined to be accommodated within the existing hierarchies Selectable Conditional Access YES Service Information ETS 300 468 Proprietary EPG ETS 300 707 Proprietary Supported Not specified Teletext Subtitling Supported Close Caption Not specified YES Delivery TV standards Not specified NTSC and PAL M 4:3 4:3 16:9 16:9 Aspect Ratios (2.21:1 optionally) Video resolutions formats Not restricted, recommended: 720x480 720x576 704x480 704x576 544x480 544x576 480x480 480x576 352x480 352x576 352x240 352x288 Frames rates Compatibility with ATM Compatibility with other MPEG-2 Not specified 29.97 [ATM-V Audio Visual Multimedia Systems (AVMMS)] To be determined ISO/IEC 13818-1 Some processing required delivery systems Table (continue) Differences between DSS and DVB-S WORKING WITH DAVIC Since the inception of DAVIC (the Digital Audio-Visual Council created in 1994), DVB members have understood the importance of working closely with it DAVIC covers an extremely wide field, generally extending well outside the area of broadcasting, and DAVIC seeks to provide end-to-end Interoperability for the use of digital images and sound across countries and between applications and services DAVIC liaison officers have been appointed in DVB to co-ordinate the efforts of both groups Harmonization with DAVIC has been achieved in many areas The DVB Cable and Satellite Systems have been adopted by DAVIC The DVB subtitling group has also reached broad agreement with DAVIC, after a good deal of discussion and a willingness to change its own draft specification Other harmonization agreements have been reached in areas including interactive services, receiver interfaces, and Service Information, and work will continue to ensure the greatest possible commonality 7.0 Conclusions Although DVB began as a European project, its membership has now spread around the globe, and, reflecting this, the project members now aim at achieving world standards Liaison takes place regularly with the ITU-R and the ITU-T on the world standardization of systems developed under the DVB project, and many DVB members are long-standing members of ITU-R and ITU-T technical committees The DVB-C cable system specification is currently being considered by ITU-T Working Party 1/9, the DVB-S satellite system specification is being considered by ITU-R Working Party 10-ll/S, and the terrestrial digital specification has been submitted to ITU-R Task Group 11/3 The DVB Steering Board has now established a Promotion and Communications Module charged with responding to the many requests being received from all parts of the world for information on the DVB systems Consumers worldwide paid a high price for the diversity of analogue broadcasting standards The division of the television services worldwide between NTSC, PAL,SECAM and MAC built substantial barriers between continents and within Europe Digital television broadcasting can change this INTELSAT can use DVB-S standard to give to its Signatories better alternatives to non-standard systems that exist at present This document focuses on describing the DVB-S standard The DVB-S standard is optimized for single carrier per transponder TDMA (Time Division Multiple Access) in order to operate the satellite TWTA close to saturation, thus optimizing the satellite power efficiency However it could be used also for multi-carrier FDMA (Frequency Division Multiple Access) type applications, allowing better operational flexibility, by originating and uplinking the signals from different locations, but at the expense of reduced performance in terms of power and spectrum efficiency A follow on activity will study the new applications and standards that are being used to delivery data on top of the MPEG-2 based DVB transmission standards (Data Broadcasting specification) such as Data Piping, Data Streaming, Multiprotocol Encapsulation, Data Carousels, and Object Carousels The most useful of these applications is the DSM-CC download protocol because this is an open protocol These protocols will be covered in the next IOM about " Data Broadcasting" References: [1] S N Baron, M I Krivocheev "Digital Image and Audio Communications", Van Nostrand Reinhold 1996 [2] J L Mitchell, W B Pennebaker, C E Fogg, D J LeGall "MPEG Video Compression Standard", Chapman & Hall 1997 [3] J B Rault, Y F Dehery, M Lever "The ISO/MPEG Audio Musicam Family", IEE Conference held at the IEE, Savoy Place, January 1995 [4] http://www.ebu.ch/dvb_contents.htm [5] http://www.ebu.ch/dvb_standards/dvb_world.htm [6] J Duran "MPEG-2 Overview", INTELSAT IOM, August 1997 [7] ITU-R 217/11 "Document" 10-11S/28-E22, March 1996 [8] C Elia and E Colzi "Skyplex: Distributed Up-link for Digital Television via Satellite", IEEE Transactions on Broadcasting, Vol.42, No 4, December 1996 [9] ETSI "Digital Broadcasting System for Television, sound and Data services; Framming structure, channel coding and modulation for 11/12 GHz satellite services", ETS 300421, june 1994 [10] ETSI "Digital Broadcasting System for Television, sound and Data services; Framming structure, channel coding and modulation for Cable Systems", ETS 300429, December 1994 [11] ETSI "Digital Video Broadcasting (DVB) Specification for conveying ITU-R System B Teletext in DVB bitstreams", ETS 300472, Octuber 1996 [12] ETSI "Digital Broadcasting System for Television, sound and Data services; Satellite Master Antenna Television (SMATV) distribution systems", ETS 300473, May 1995 [13] K Birdwell "Self-Installer Manual DSS", 1995 [14] ITU "Functional Model of a Conditional Access System" 11-3/66-E, 28 October 1996 [15] M Buer, J Wallace "Integrated Security for Digital Video Broadcast", IEEE Transactions on Consumer Electronics, Vol.42, No 3, August 1996 [16] J Giachetti, V Lenoir, A Codet, D Cutts, J Sager "A Common Conditional Access Interface for Digital Video Broadcasting Decoders", IEEE Transactions on Consumer Electronics, Vol.41, No 3, August 1995 [17] M Cominetti, V Mignone, A Morello, M Visintin "The European System for Digital Multi- Programme Television by Satellite", IEEE Transactions on Broadcasting, Vol.41, No 2, June 1995 [18] ITU "Feasibility of Common Functional Requirements for Satellite Multiprogramme TV Reception Archictecture and Cost Estimations", 10-11S/TEMP/40-E, October 1996 [19] DVB Project "Specification for Data Broadcasting & Commercial Requirements", DVB Document A027, May 1997 ... Conditional Access Specialists' Group, is lodged with the European Telecommunication Standards Institute (ETSI) as custodian The technical details are distributed, and the technology licensed,... specialized programming The viewer will need help DVB-SI provides the elements necessary for the development of the Electronic Programme Guides (EPG) that are likely to become a feature of the... appropriate Forward Error Correction (FEC) technique The system allows for further evolution as technology advances and is capable of starting a reliable service as of now 2.3.8 DVB-I (Interactive