Networks in Evolution Making changes to the digital terrestrial television platform T
Digitalwww.digitag.org Terrestrial Television Action Group
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DigiTAG Report DTT Networks in Evolution Making changes to the digital terrestrial television platform May 2008
Preface This report has been prepared by Jan Doeven on behalf of DigTAG in the period between November 2007 and April 2008. In preparing the report, the following persons have been consulted: Rein Simonse and Senada Alagic, KPN ,The Netherlands Rolf Møkleby, Norkring, Norway Seppo Nieminen, Digita, Finland Aljo van Dijken, chairman CEPT/ ECC Task Group 4 Peter Johnsson, Boxer, Sweden Philippe Debreux, TDF, France Elena Puigrefagut, EBU The advice and feedback from the DigiTAG chairman, Daniel Sauvet‐Goichon, the DigiTAG Steering Committee consisting of Robert Cloudt (Philips), Alex Mestre (Abertis telecom), Neil Robinson (LG) and Bernard Pauchon (TDF) and from Natalie Mouyal and Ed Wilson of the DigiTAG Project Office have been very much appreciated. The photo on the front cover is courtesy of Norkring. Published by DigiTAG – The Digital Terrestrial Television Action Group 17 A, L’Ancienne Route, CH‐1218 Grand‐Saconnex, Geneva – Switzerland Tel : +41 22 717 2735 Fax : +41 22 747 4735 www.digitag.org ©copyright 2008 DigiTAG all rights reserved Version 1.01
Content Executive summary 1. Introduction 2. Services 2.1. Introduction 2.2. Service requirements 2.3. TV for rooftop and portable indoor and outdoor reception 2.4. HDTV 2.5. Mobile TV 2.6. Interactive TV and data services 2.7. Summary 3. Regulatory environment 3.1. Introduction 3.2. Service allocations in the Radio Regulations 3.3. Frequency plans 3.4. Digital switch‐over 3.5. Summary 4. Digital Dividend 4.1. Introduction 4.2. Implementation of GE06 Plan entries 4.3. Implementation of mobile TV in a dedicated sub‐band 4.4. Implementation of 3G mobile services in a dedicated sub‐band 4.5. Use of “white spaces” 4.6. Summary 5. Networks 5.1. Introduction 5.2. Radiation characteristics 5.3. DVB‐T system 5.4. Transmitting sites 5.5. Multiplexes 5.6. Summary 6. Practical cases 6.1. Introduction 6.2. Digital switch‐over 6.3. Roll‐out of a DVB‐H network 6.4. Preparing for HDTV 7. Viewer concerns 7.1. Introduction 7.2. Means to improve reception 7.3. Retuning receivers 7.4. Replacement of receiving equipment 7.5. Communication 8. Conclusions and recommendations List of references
Executive summary Introduction Evolution of digital terrestrial television (DTT) networks will take place resulting from the introduction of new services, regulatory obligations or technology changes. The market will determine the services offered to the viewers. Market conditions are different from country to country, hence the service offer is also likely to be different in each country. Regulations give the framework for development of services and reflect political priorities which may also be different from country to country. Technology, transmitting and receiving equipment will facilitate the introduction of services, but have their limitations. Therefore it is important to make the right choices depending on the service requirements and the regulatory environment. For a successful introduction of services, market players and regulators should cooperate in the development of services. All market players (broadcasters and content providers, multiplex and network operators, consumer electronics manufacturers, consumers) have a great interest in digital terrestrial television and should support the choices made for evolution of the network. Services In the context of this Handbook, DTT services include: − Standard definition TV with rooftop, indoor and outdoor reception, − High definition television (HDTV), − Mobile TV using a broadcast standard (e.g. DVB‐H, DMB) − Interactive and data services. Radio services (T‐DAB) and mobile communication services (UMTS) are not included in the term DTT. However, it should be noted that DTT multiplexes may carry radio services and mobile TV services may be transmitted via the UMTS system. In planning digital terrestrial television a compromise has to be found between multiplex capacity, coverage quality and radiation characteristics. Multiplex capacity is of interest for the service quality. The net bit rate of the multiplex and the number of services in the multiplex determine the bit rate per programme. Coverage quality is important for the number of people able to receive the service. It is expressed as the probability to receive the wanted signal at a location in the presence of noise and interference. All locations with the required reception probability form together the coverage area. Radiation characteristics are related to transmission costs. Transmitter power and antenna specifications, either from a single transmitting station or from a Single Frequency Network (SFN), determine the field strength generated at a receiving location. The trade‐off between service quality, number of potential viewers and transmission costs is a commercial choice. The choice is limited for operational, regulatory and technical reasons. For each type of service the compromise may be different, resulting in different radiation characteristics, different choices regarding compression and transmission system, different number of transmitting sites and different number of multiplexes. Regulatory environment A market based approach is increasingly applied to frequency management. This approach could lead to less spectrum made available for broadcasting and potentially resulting in interference.
Digital terrestrial television transmissions make use of the frequency bands III (174‐230 MHz) and IV/V (470‐862 MHz). In addition mobile television could also make use of part of L‐band (1452‐1479.5 MHz). These bands are also allocated to non‐broadcasting services. Of particular importance is that the upper part of Band V (790‐862 MHz) has been allocated, under certain conditions, to mobile communication servcies (UMTS). In 22 European countries UMTS servies are allowed as of 2007, in other countries from 2015. Detailed frequency plans are in force for each of the above mentioned frequency bands; Bands III and IV/ V are regulated by the Geneva 2006 Agreement (GE06) . These frequency plans allow implementation of broadcasting tranmission with characteristics that are different from those specified in the plan as long as no more interference is caused. Modifications of the plan are possible subject to agreement of neighbouring countries. Digital switch‐over is the national process of transition from analogue to digital television. In the European Union (EU), it is recommended that member‐states switch off analogue television before 2012. The released spectrum will in the first place be used for digital television services that were formerly transmitted in analogue format. Furthermore new services, broadcasting or non‐ broadcasting, will be licensed in the remaining spectrum, the so‐called “Digital Dividend”. Table 1 summarises the main regulatory provisions in relation to the evolution of DTT networks. Regulatory provisions
Radio Regulations
Frequency Plans
Digital Switchover policies
Main issues
Remarks
ITU - WRC07 decided to: − Allocate, in addition to broadcasting , mobile services in 790-862 MHz from 2015 − Perform compatibility studies − Protect broadcasting services in GE06 from mobile services. GE06 Agreement contains provision for: − “Reference Planning Conditions” (RPC) − Flexible implementation of Plan entries − Modifications subject to agreement of affected countries National digital switch-over process includes: − Transition plans − Analogue TV switch-off date − Policy for use of “Digital Dividend”.
22 European countries claimed the right to introduce mobile services from 2007 onwards in 790-862 MHz (channels 61 to 69), or parts of it. Most European countries decided to use portable indoor or outdoor reception as “RPC” for their Plan entries. In EU member-states analogue TV switch-off is recommend before 2012.
Table 1 Main regulatory provisions
Digital Dividend The digital dividend is generally understood as the spectrum that is available above that required to accommodate the analogue television services in a digital format in Band III and IV/V. The digital dividend can be used for broadcasting services, such as digital terrestrial television with rooftop, indoor or outdoor reception, mobile TV, HDTV and interactive television. But mobile communication services may also be implemented in the upper part of the band (790‐862 MHz) and certain low power application could be allowed to make use of so‐called white spaces in the spectrum on a non‐interference and non‐protection basis. For digital terrestrial television services, transmitting station characteristics should be in accordance with the GE06 Frequency Plan. Once implemented, it may be necessary to change the station
characteristics when the service requirements change. Depending on required station changes and the characteristics of the GE06 Plan entry, a modification of the GE06 Plan may be needed, subject to agreement with neighbouring countries. Changes to transmitting stations could relate to: − Radiation characteristics to achieve better coverage; − A different DVB‐T variant to achieve either better coverage or more capacity; − Improved encoders, an enhanced compression system (MPEG4), installation of additional multiplexes or a different DVB system (DVB‐H) and in future a more advanced DVB‐T system (DVB‐T2), to achieve more capacity or a better coverage; − Additional sites to improve or extend coverage. Partitioning of Band IV/V for different kind of services (digital television for large area coverage, mobile TV and mobile communications) is under discussion. Establishment of sub‐bands reduces the spectrum capacity for digital television broadcasting and will require a revision of the GE06 Plan for digital television in Band IV/ V. The loss of spectrum capacity restricts future developments and may require modifications to the networks of existing services. These modifications could involve: − Frequency change as a result of replanning; − A DVB‐T variant with higher capacity, improved compression system (MPEG4) or, in the future, a more advanced DVB‐T system (DVB‐T2), to compensate for loss of capacity; − Change of radiation characteristics and installation of additional sites to compensate for loss of coverage. Implementation of mobile communication services in part of Band IV/V may cause interference to digital broadcasting services. Low power applications that may be allowed on a non‐interference and non‐protection basis in the so‐called white spaces of the spectrum have no direct impact on digital terrestrial television services, provided that in practice the non‐interference conditions can be guaranteed under all circumstances. Table 2 summarises the regulatory measures for implementing digital dividend. Regulatory measure Implementation of GE06 Plan entries Sub-band for mobile TV Sub-band for mobile services Use of “white spaces”
Impact on DTT networks
Remarks
− −
Some modifications of GE06 Plan entries may be needed, subject to agreement by neighbouring countries Revision of GE06 Plan will be needed Revision of GE06 Plan will be needed Specification of applications requires careful attention to avoid interference
− − − −
Introduction of various broadcasting services Limitations in multiplex capacity, coverage or radiation characteristics possible, due to “RPC” Intended for dense networks Limitations to other kind of broadcasting services In channels 61-69 Reduction of number of DTT networks
−
No direct impact on DTT networks
Table 2 Regulatory measures for implementation of Digital Dividend
Networks Changes to digital terrestrial television networks may be necessary due to the introduction of new services, regulatory obligations or technology changes. Some of the changes are costly while others may need some equipment adjustments. Many changes have an impact on coverage.
Radiation characteristics Frequency and maximum radiated power per bearing are specified in the GE06 Agreement. Antenna characteristics are frequency dependent. Coverage for different frequencies transmitted from the same site may therefore be different. Close to the transmitting site, coverage problems may occur due to “nulls” in the vertical radiation pattern. Compression and transmission system A choice has to be made out of sixty DVB‐T variants. Depending on the choices made for the service trade‐off, a variant can be chosen that enables a relatively large multiplex capacity, but high required field strength. Alternatively a choice can be made for a robust variant, with a relative low required field strength, but a more limited multiplex capacity. The quality of the encoders of the compression system improves over time until the technology is mature. By updating encoder software or replacement of encoders, a more efficient use of multiplex capacity can be made. An enhanced compression system (MPEG4) is available on the market, although receiver are initially more expensive compared with MPEG‐2 receivers. It is expected that in a few years the encoders will have significant efficiency gains compared with MPEG‐2. DVB‐H and T‐DMB are transmission systems adapted to the needs of mobile television with handheld receivers. DVB‐T2 is expected by the end of 2009 and will give a higher multiplex capacity which is of particular importance for HDTV. Change of compression or transmission system has no direct impact on coverage. Sites Additional sites in the same network are used to improve or extend coverage. Power distribution over several sites (Single Frequency Network) improves frequency spectrum efficiency. SFN planning is complex and in some cases coverage problems arise due to internal network interference. Multiplexes Additional multiplexes provide extra transmission capacity. Additional multiplexes could be installed on existing sites, but could also form a partly or completely new network. In case of non co‐sited transmissions interference could occur around the transmitter sites. Practical cases Practical cases show that: − DVB‐T transmissions may be subject to restrictions as long as analogue TV has not been switched off (in the home country and in neighbouring countries) and frequency changes to SFNs may be complex and require careful preparations. − DVB‐H may need dense transmitter networks. − HDTV requires MPEG4 compression and, in the future, possibly the newDVB‐T2 transmission system. National decisions, made in collaboration with the receiver manufactures, on the availability of adequate receivers need to made. Consumer concerns Network changes as a result of introduction of new services or implementing regulatory measures may require actions by the viewer in order to receive the new services or continue to receive existing services.
A frequency change, installation of additional sites and additional multiplexes make it necessary for the consumer to retune his receiver. A change of frequency, transmitting antenna, DVB‐T variant and changes to an SFN, as well as non co‐sited transmissions could result in coverage problems in some areas. The consumer may have to install an improved antenna installation in order to receive one or more multiplexes. A change of compression system (MPEG4) and transmission system (DVB‐H) and in future DVB‐T2 requires the purchase of a new receiver in order to receive the services transmitted in this way. However, after a certain transition period, all receivers will be able to receive the old and the new system. In cases where new sites are installed the best signal may arrive from a different bearing and receiving antenna, making adjustments may be necessary. Communications to consumers about network changes and help and information regarding necessary consumer action is essential. Telephone helpdesks and websites can provide detailed information and advice based on accurate coverage predictions. In addition, advertisements, an information channel in the multiplex and teletext can help viewers. Local dealers can provide information and refer the public to websites or telephone helpdesks.
1. Introduction Digital terrestrial television network are likely to change in the coming years. Broadcasters and/or network operators will introduce new services and improve existing service. Changes to digital TV networks may also be necessary for regulatory reasons. Furthermore, changes to networks may be necessary to restore coverage quality or multiplex capacity due to introduction of other (nonbroadcasting) services or because some parts of the frequency band are no longer available due to the introduction of sub-bands or guard-bands. The Geneva Agreement (GE06) is the regulatory framework for the use of frequencies for broadcasting and other services in Bands III and IV/V. The frequencies are only fully available after a transition period which ends in 2015. Based on the current availability of television services on the analogue platform, it could be assumed that a digital dividend exists to launch new services. Many applications for the digital dividend are under discussion, planned or already implemented. These applications may include: 1. Improvement of terrestrial broadcasting services: e.g. services with higher technical quality (notably HDTV) or an increased number of programmes; 2. “Converged” broadcasting services which are expected to be primarily “hybrids” of traditional broadcast and mobile communication services; 3. Services which do not belong to the broadcasting family of applications: e.g. future services and applications which are not yet marketed or existing ones which do not operate yet in these frequencies (e.g. extensions of 3G services, short-range radio applications). The European Commission’s (EC) proposal that EU member states should finalise analogue television switch-off by 2012 has accelerated the implementation of digital terrestrial television. In almost all European countries (in and outside the EU) digital terrestrial television transmissions have started and in a number of countries analogue switch-off is in progress or has been completed. The coming years will show a further evolution of terrestrial television networks in the framework of GE06 due to the implementation of the digital dividend applications. These developments create challenges and opportunities for broadcasters and network operators who will be able to implement the applications in the first and second categories listed above. However, when new companies are licensed to operate (broadcasting or non-broadcasting) services in Band III, IV or V, or when even non-licensed services are allowed, there are also threats. Not only is less spectrum available for the development of new services by existing market players, but the new transmissions may have an impact on the costs or quality of existing services. The report describes the evolution of terrestrial television networks and the impact it may have on: Coverage Transmitters and antennas Network operation With the report, DigiTAG members will be better equipped in their discussions with other market players and national regulators about the changes that need to made to terrestrial television networks in the coming years.
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2. Services 2.1 Introduction Section 2 deals with services and applications that will drive digital terrestrial television network evolution in Band III, IV/V and the 1.5 GHz band. Network evolution depends on: −
− −
The market, which will determine the services offered to viewers. Market conditions are different from country to country, hence the service offer is likely to be different in each country. Regulations, which will give the framework for the development of services. Regulations reflect political priorities which may also differ between countries. Technology, and transmitting and receiving equipment will facilitate the introduction of services, but have their limitations. Therefore it is important to make the right choices taking into account the service requirements and the regulatory environment.
For a successful introduction of services market players and regulators should cooperate in the development of services. All market players (broadcasters and content providers, multiplex and network operators, consumer electronics manufacturers) have a great interest in digital terrestrial television and should support the choices made for the evolution of the network. Digital terrestrial television services can be categorised by type of reception and type of content as in Table 2.1: Types of reception − − −
Rooftop Indoor or outdoor portable Mobile and handheld
Types of content − − − −
Standard definition TV (SDTV) High Definition TV (HDTV) Interactive TV Data services
Table 2.1 Services that drive network evolution
DigiTAG has published a number of handbooks and reports where more information can be found on digital terrestrial television services, including: − Building bridges between decision makers and frequency planning experts (2003); − Digital Terrestrial Television in Eastern and Central Europe (December 2006); − Analogue Switch‐off; strategies to end analogue terrestrial television in Europe (2006); − HD on DTT, key issues for broadcasters, regulators and viewers (2007); − Television on a handheld receiver‐broadcasting with DVB‐H (2007); − DVB‐SSU, implementing system software updates on the terrestrial television platform (2007); − Mobile Broadcast Television in Europe (January 2008). The DigiTAG website (www.digitag.com) provides detailed information on the progress in implementing digital terrestrial television for countries using the DVB‐T standard. The following subsections describe the choices, regarding technology and transmitting and receiving facilities that need to be considered when introducing new services. 3
2.2 Service requirements In planning digital terrestrial television, a compromise has to be found between: − Multiplex capacity; − Coverage quality; − Radiation characteristics. The compromise determines to a great extent the type of terrestrial television network and the evolution the network may undergo. Multiplex capacity is of interest for the service quality. The net bit rate of the multiplex and the number of services in the multiplex determine the bit rate per programme. Multiplex capacity is limited by the technology of the compression and transmission system and the choice of the DVB‐T variant. Coverage quality is important for the number of potential viewers and is expressed as the probability to receive the wanted signal at a location in the presence of noise and interference. All locations with acceptable reception probability form together the coverage area. Coverage quality also depends on the choice of the DVB‐T variant, and on the characteristics of the receiving installation, in particular the receiving antenna and the specified reception conditions in the GE06 Agreement. Radiation characteristics are related to the transmission costs. Transmitter power and antenna specifications, either from a single transmitting station or from a Single Frequency Network (SFN), determine the field strength generated at a receiving location. Radiation characteristics are limited by the GE06 Agreement, but also by the practical limitations of transmitting equipment and transmitting station facilities. The trade‐off between service quality, number of potential viewers and transmission costs is a commercial choice.
2.3 Rooftop and portable indoor and outdoor reception 2.3.1 General Rooftop reception, also called fixed reception, is characterised by a fixed directional receiving antenna mounted on the roof of a house. Rooftop reception can be seen as the basic requirement for digital terrestrial television. In most countries it is required that nearly full coverage is provided for rooftop reception, at least for public broadcasting services. In areas where cable television has been established, rooftop antennas have often disappeared. Local communities have sometimes even mandated the dismantling of rooftop antennas. Indoor or outdoor reception with simple antennas is an important feature of digital terrestrial broadcasting. This way of reception is called portable reception. Different types of indoor or portable receiving antennas and portable receiving devices have appeared on the market, including active indoor antennas and digital terrestrial television receivers for use with PCs. The minimum field strength requirements for portable reception are much more demanding than for rooftop reception because of the low receiving height, screening of the building and no or moderate directivity of the receiving antenna. In a number of countries, networks are designed in such a way that indoor reception in areas with high population density has been optimised. 4
2.3.2 Multiplex capacity In order to motivate consumers to buy a digital receiver for terrestrial TV services, an attractive broadcast package needs to contain 20 to 30 popular services. Such a number is also needed to provide better competition with the satellite and cable delivery media. A large number of services of high individual interest to only a few people can best be delivered by means of on‐demand services via broadband TV. The EBU recommends that in order to provide an acceptable video quality in conventional displays, the average data capacity allocated to each service should range from 3 to 4 Mbit/s depending on the DVB‐T variant and on the statistical multiplexing, if used [1]. In practice the balance between the number of services in a multiplex and bit rate per service is often to the advantage of the number of services. It should, however, be noted that quality requirements need to be increased with the advent of flat panel screens. EBU research has shown that flat screens are more sensitive to artefacts and require about two times higher bit rate for a high‐quality picture than the conventional Cathode Ray Tubes (CRT) [2]. Furthermore, current trends show that consumers are purchasing increasingly larger screens compared with their old television sets. Therefore, the subjective decrease in picture quality becomes even more apparent with large screen sizes as encoding and decoding artefacts are more visible. 2.3.3 Coverage quality Most planning criteria are recommended by ITU [3], but for coverage assessment network operators often adapt certain criteria to the national situation. An important criterion to be defined is the coverage quality that is considered acceptable. In general, a location probability of 95% is taken as acceptable coverage for rooftop reception. In case of portable reception, percentages ranging from 70 to 95 are taken. It should be noted that location probabilities of less than 95% may well lead to complaints. For assessing coverage quality, sophisticated network planning software is needed as well as an accurate transmitter database and terrain and clutter databases. Shape, terrain and the size of the areas to be covered depend very much on the country. As part of the service requirements, the areas to be covered with a certain programme package should be defined together with the required reception probability and, as far as needed, areas or conditions where a lower probability is considered acceptable. 2.3.4 Radiation characteristics The required minimum field strength for portable reception and in particular indoor reception (normalized at a reception height of 10 m) is much higher than for rooftop reception. The (rounded) differences, based on the minimum median field strength values given in annex 3.2 of the GE‐06 Agreement, are indicated in Table 2.2. Band III IV/V
Difference indoor‐rooftop 31 dB 37 dB
Power factor 1200 5000
Difference outdoor‐rooftop 21 dB 25 dB
Power factor 125 300
Table 2.2 Difference in required minimum field strength for rooftop and portable reception
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The differences shown in table 2.2 represent the maximum difference between rooftop and portable (indoor and outdoor) reception. The radiation characteristics related to outdoor and in particular indoor reception are such that coverage over a large area can in practice only be achieved by means of power distribution and use of Single Frequency Networks.
2.4 HDTV 2.4.1 General High‐definition television (HDTV) services provide viewers with a significantly enhanced television experience. The demand for HD services is driven by such factors as [4]: − The growing number of households with HD‐ready displays; − The apparent decrease in quality of standard‐definition services on flat‐panel displays; − The emergence of new HD‐capable technologies; − The desire to watch high‐profile sporting events in HD quality. The number of households purchasing flat‐panel displays is increasing rapidly. It is estimated that by 2008, almost 50% of European households will have a flat‐panel displays, with penetration expected to increase to 87% by 2010. Since the launch of the HD‐ready logo in January 2005, nearly all available flat‐panel displays sized at 28 inches or higher are HD‐ready. As more households become equipped with HD‐ready television sets, they will expect to be able to access high‐definition services. Criteria for coverage quality and radiation characteristics for HDTV are similar as for rooftop and portable reception. The considerations contained in Sections 2.2.3 and 2.2.4 are also relevant in case of HDTV. HDTV is particularly attractive for large screens. While large screens can also receive the signal via simple indoor antennas, in many cases, indoor reception is used for second sets, usually with smaller screen sizes. 2.4.2 Multiplex capacity In the case of HDTV, picture quality is the main objective and, consequently, the number of services in a multiplex is limited. Initially, a limited number of HDTV programmes is likely to be acceptable to viewers. However, future demands, to convert all current services in HD quality without extending the number of multiplexes will be a great challenge. The capacity requirement for HDTV is such that the MPEG2 compression format is not seen as a viable option, although it is technically possible to transmit one HD service in MPEG2 in a multiplex as has been the case in Australia (and the United States using ATSC). For HDTV, a new HD capable receiver is needed and this opportunity can be taken to implement a more efficient compression system. The following aspects are of particular importance for HDTV: − Investigations in the EBU show that HDTV using MPEG4 compression may require 10‐12 MB/s for a good picture quality; − It will be necessary to carry at least two HDTV services per multiplex to justify the use of spectrum and make an economically viable offering; − 720p is more frequency efficient than 1080i; 1080i would need 10‐20% higher transmission capacity, depending on type of content; − The DVB Project is currently developing a second generation standard for digital terrestrial broadcasting, the so‐called DVB‐T2 standard [5].
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The main objectives of the DVB‐T2 system are: − At least 30% more net capacity than DVB‐T under similar reception circumstances; − Improved robustness against interference from other transmitters resulting in better frequency reuse; − Better SFN performance, distance between adjacent transmitters at least 30% larger − Focus on fixed reception using existing antennas; − Backwards compatibility with DVB‐T signal not required; − Compatible with GE06 Agreement; − Early consumer products available by the end of 2009. Mass market quantities of DVB‐T2 receivers are expected from 2012.
2.5 Mobile TV 2.5.1 General Mobile television has different meanings. It could be mobile reception of digital television signals of networks set up primarily for rooftop or indoor reception. It could also mean reception of television on handheld devices such as mobile telephones. The latter has received considerable attention, although concerns have been raised. Is it a mobile communication service with the network owned by telecommunication operators, or is it a broadcasting service with the network owned by broadcast network operators? Or is it a combination of both? There are several systems for mobile television as shown in table 2.3. Mobile TV systems DVB‐T
DVB‐H T‐DMB DAB‐IP DVB‐SH MediaFlo UMTS
Comment − − − − − − − − − − − − − −
For use in Band III in a 7 or 8 MHz channel and Band IV/V in a 8 MHz channel in Europe (6 MHz channel in Latin America) Some limitations in battery consumption and reception at higher speeds For use in Band III, IV, V and the 1.5 GHz band in a 5, 6, 7 or 8 MHz channel Designed for use in handheld devices For use in Band III and 1.5 GHz in a 1.7 MHz channel Designed for use in handheld devices For use in Band III and 1.5 GHz in a 1.7 MHz channel Designed for use in handheld devices For use in a hybrid satellite and terrestrial network in the 2 GHz range Designed for use in handheld devices In use in the USA in the UHF television bands Designed for use in handheld devices For use in the 2 GHz (and possibly other frequency range) As part of the telecommunication service offerings
Table 2.3 Mobile TV systems
This report will only focus on DVB‐T, DVB‐H and T‐DMB. From the network planning point of view there is no difference between T‐DMB and DAB‐IP. The considerations of Section 2.3 can also be applied for mobile reception of transmissions using the DVB‐T system. DVB‐H and T‐DMB have both advantages and disadvantages. The main difference is the bandwidth and the frequency bands for which the system is specified. In order to transmit in T‐ 7
DMB the same number of services as in DVB‐H, more DMB multiplexes will be necessary. The choice between the systems will be mainly a matter of available frequency bands and channel raster adapted for that band. The European Commission supports the introduction of mobile television and mandating the DVB‐H system has been considered. However mandating has been resisted but DVB‐H is seen by the Commission as the favoured mobile television system. To this effect DVB‐H has been added to the EU List of Standards, which serves as a basis for encouraging the harmonised provision of telecommunications across the EU. Handheld devices can be used at indoor and outdoor locations, in stationary position and a high speeds in cars and trains. The receiving antenna has small dimensions, compared with the wave length and many devices use built‐in antennas. These circumstances are responsible for very high minimum field strength requirements. 2.5.2 Multiplex capacity Handheld devices have very small screens and both DVB‐H and T‐DMB use advanced compression systems (MPEG4). Therefore the bit rate per programme can be relatively low. As the reception conditions are very demanding, most operators tend to choose a robust system variant with the consequence of a limited net bit rate. In that case, 10 to 15 programmes may be accommodated in a DVB‐H multiplex. The number of TV services in a T‐DMB multiplex is in practice 5 to 6. 2.5.3 Coverage quality For mobile and handheld reception, a high coverage quality is required. The location probability is often taken as 95% for handheld portable reception and 99% for handheld reception inside a moving vehicle. 2.5.4 Radiation characteristics Even with a robust system variant, the field strength requirements are high because of the poor receiving antenna performance and the reception conditions (indoor, outdoor, in a vehicle with or without external antenna). The most demanding reception conditions are: − In Band III; 16QAM and handheld reception inside a moving vehicle without connection of the receiver to an external antenna; − In Band IV and 1.5 GHZ; 16QAM and handheld indoor reception. Table 2.4 EBU report on planning parameters for handheld reception indicates examples of ranges for the minimum required field strength at a receiving height of 1.5 m [6] for various types of mobile and handheld reception. System DVB‐H T‐DMB
Band III Band IV Band V 1.5 GHz 57 to 76 dB µV/m 61 to 82 dB µV/m 60 to 81 dB µV/m 60 to 81 dB µV/m 56 to 68 dB µV/m ‐ ‐ 60 to 75 dB µV/m
Table 2.4 Examples of minimum required field strength for handheld reception at 1.5 m
In practice network roll‐out will start with high power transmitters near towns for coverage of urban areas. As far as required, Single Frequency Networks with a dense transmitter raster will be installed to improve coverage. More information on network aspects for DVB‐H and T‐DMB can be found in a report published by the EBU [7]. 8
2.6 Interactive TV and data services 2.6.1 General Multiplex capacity is generally used for video and related sound services. Sometimes a package of radio programmes is also included. In addition, the multiplex may contain data for a variety of services including: − Electronic Programme Guide − Service Information − Interactive services − Teletext − System Software Update (SSU) The amount of data allocated to the above mentioned services varies considerably from case to case. Figures 2.1 show examples of the composition of a multiplex of respectively a 14.7 Mbit/s and 20.1 Mbit/s [1].
Figure 2.1 Examples of multiplex composition
The following subsection deals in more detail with interactive services. 2.6.2 Interactive services There are two types of interactive television services: − Local interactive services, where the information is stored in the receiver ( teletext is an example); − Remote interactive services, where information is sent to the programme provider via a return channel, this information can include a reaction to a programme (e.g. voting) or a demand for certain programmes (video on demand or pay per view). Remote interactive TV has long been seen as an important feature of digital television. However remote interactive TV applications are limited in many countries. Remote Interactive services require a return path. If the return path is provided by wired or mobile telecommunication systems, interactive services have no direct impact on the terrestrial digital television network. A system for an in‐band return path has been specified, the so‐called DVB‐RCT, but no commercial applications exist at the moment. Local interactivity, however, is popular. Teletext was standardised in 1974 and is still an important part of the digital television service offer. 9
Basic interactive services, like teletext, can be used with standard DVB‐T receivers. For more advanced interactive services, receivers should be equipped with the MHP or MHEG systems. In a number of countries, combined DVB‐T/ IPTV boxes with hard disks are offered to consumers. The most popular programmes can be received off‐air via digital terrestrial television networks, while IPTV networks provide additional information, on‐demand programmes and special interest programmes. Programmes of choice can be automatically downloaded on the hard disk. In this way wide band remote interactive services are obtained. In order to show and select the stored programmes, each programme should be accompanied by metadata. In the future, a further integration of (multi) media services in and around the house will be achieved through the “Home Network”. A Home Network is an IP‐based (wireless) network interconnecting the various terminals in a home to each other as well as to broadcast and other access networks. It is expected that the Home Network will change the way in which consumers make use of television services.
2.7 Summary 2.7.1 Service developments The market will ultimately decide which digital terrestrial television services are provided to viewers. In general, it can be observed that digital terrestrial television as Free‐To‐Air (FTA) offer, or FTA in combination with a pay TV offer, is very popular. Due to presence of flat panels screens in an increasing number of European households, there is a need for high quality video. HDTV is expected to become the future norm for TV viewing in the living room. A number of countries have already begun HDTV transmissions. Cable TV, satellite TV and IPTV are less restricted in capacity than digital terrestrial networks and may therefore be more suitable for HDTV transmissions. In some markets digital terrestrial networks will also offer HDTV, in other markets terrestrial television networks will be mainly used for second sets, recreational homes and handheld devices. In the latter case, the main TV set(s) will be connected to cable, satellite or IPTV for HDTV reception. Consumer demand for mobile TV still needs to be proven. However, it is expected that at least one or two multiplexes will be used for TV with mobile telephones in a number of countries. Interactive TV and, in particular, use of on‐demand and time‐shifted services via PVRs or IPTV networks (TV Anytime) is expected to be of increasing importance. With the development of Home Networks, consumer demand for integrated media devices and interactive data services is expected to increase even more. This may lead to a decreasing need for linear broadcasting, and an increasing need for content that can be downloaded. Digital terrestrial networks will face increasing competition due to the service offerings on digital cable TV, IPTV and satellite TV platforms. Digital terrestrial television is, however, a cost effective way to distribute (a relative limited) package of popular programmes and to achieve near universal coverage. Additional information and special interest programmes may be supplemented using IPTV networks, where available. 10
2.7.2 Service and network evolution For each type of service in a digital terrestrial television network basic choices have be made between three interdependent parameters: multiplex capacity, coverage quality and radiation characteristics. The choice will have a major impact on the transmitter network. Television services aimed at reception with rooftop antennas require moderate field strength levels. The choice is often made for high coverage probability over large areas and a relative high net bitrate of the multiplex. Television services aimed at reception with small antennas at indoor and outdoor locations require considerably higher field strength levels than rooftop reception. Choices are often made for a more robust DVB‐T system variant and as consequence a lower net bit rate of the multiplex, a moderate to high coverage probability and a more dense transmitter network than for rooftop reception. Services generally target urban areas. Because HDTV requires a high net bit rate per multiplex, MPEG4 compression is used to make efficient use of the spectrum. An advanced transmission system DVB‐T2 is under development with the first receivers expected to be on the market by the end of 2009. Mobile TV requires very high field strength levels and a very robust DVB‐T variant is likely to be chosen and hence a limited net bit rate per multiplex. Mobile TV systems like DVB‐H and T‐DMB make use of MPEG4 compression. A high coverage probability is needed. The network generally consists of high power transmitters near towns complemented by transmitters in SFN. Interactive television could use a significant part of the multiplex capacity. For remote interactivity a return path is needed using fixed or mobile telecommunication systems.
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3. Regulatory environment 3.1 Introduction Regulatory decisions regarding the use of the frequency spectrum are taken by national regulatory bodies, on the basis of international treaties and recommendations. To this purpose, national administrations work together in international forums such as the International Telecommunication Union (ITU) and the European Conference of Postal and Telecommunications (CEPT). Within the European Union (EU), the spectrum policies of the European Commission (EC) are of great importance to national administrations. Digital terrestrial television transmissions make use of the frequency bands III (174-230 MHz) and IV/V (470-862 MHz). In addition mobile television can also make use of part of the L-band (14521479.5 MHz). This Section deals with the main regulatory provisions for use of these bands, such as: Service allocation in the Radio Regulations; Frequency Plans; Digital switch-over. Regulatory measures for implementing digital terrestrial television and other services in Band III, IV and V and the impact these measures may have on digital terrestrial networks in these bands is described in Section 4 (Digital Dividend).
3.2 Service allocations in the Radio Regulations 3.2.1 General The ITU Radio Regulations form a treaty between ITU member states and are reviewed at regular intervals by World Radio Conferences (WRC). The last WRC (WRC-07) was held in 2007 and the next one is planned in 2011. The Radio Regulations prescribe the use of frequency bands and give procedures for managing the use of these bands. A recent tendency, particularly in the EU, has been to regulate spectrum on a service and technology neutral basis. In its proposed "Telecom Package" issued on 13 November 2007, the EC advocates the principle of "service neutrality" in which the type of service provided within a given frequency band is not established by policy but rather by the market. This approach to frequency management may lead to several types of services allocated frequencies bands and to a need to review of the existing ITU definitions of e.g. broadcasting, mobile and fixed services. The market based approach in spectrum management is of great concern for services that are not only based on economic values, but also on cultural values, such as broadcasting [8]. This approach may also lead to the use of the same frequency band by services with very different technical characteristics. Avoiding interference needs careful considerations. 3.2.2 Band allocations In Europe and Africa, band III (174-230 MHz) is allocated to broadcasting services and, in some countries, to mobile services. Contrary to one or two decades ago, there is little interest for mobile communication services in band III.
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In Europe and Africa, Band IV/V (470-862 MHz) is allocated to broadcasting services and, as a result of decisions made at WRC-07, for mobile services in the frequency range 790-862 MHz (TV channels 61 to 69) from 17 June 2015. This date corresponds to the end of the analogue / digital broadcast transition period as established in the GE-06 Agreement. However, in 65 countries, including 22 European countries (see figure 3.1), mobile services are allowed immediately after WRC-07, under the condition that broadcasting services (or other services using the band in accordance with the Radio Regulations) in neighbouring countries will be protected. Figure 3.1 Access to mobile services from 2007 light grey: 790-862 MHz dark grey: 830-862 MHz
It should be noted that within the mobile service allocation, international mobile telecommunication (IMT) services have been identified as one of the possible uses. IMT services include both IMT 2000 (3G technologies, UMTS, CDMA 2000, WiMAX) as well as IMT advanced services (4G). At the WRC-07, national administrations decided to merge IMT 2000 and IMT advanced services into a single category. WRC-07 agreed that broadcasting services in GE06 should be protected from mobile services and that countries planning to implement mobile services in the frequencies between 790-862 MHz must coordinate with neighbouring countries prior to implementation. Furthermore, WRC-07 calls on the ITU to study compatibility between mobile and broadcasting services in the frequency range 790-862 MHz. The results of these studies will be presented at WRC-11. In addition Band IV/V is allocated to the following other services: Radio astronomy (channel 36), in some countries; Radio navigations services (645-862 MHz), in some eastern European countries; Fixed communication services in 790-862 MHz; Services ancillary to broadcasting (such as radio microphones) provided that broadcasting and mobile services are protected, in some countries. The band 1452-1492 MHz is allocated to broadcasting and satellite broadcasting and the use is, according to the Radio Regulations, limited to digital audio broadcasting. However in Europe the band is partly planned for terrestrial services and partly allocated to satellite services (see also 3.3.3).
3.3 Frequency Plans 3.3.1 General For most broadcasting bands international a-priori frequency plans have been established, such as the GE-06 Agreement. The main conditions for a successful frequency plan are: Equitable access to the frequency band for all countries concerned; Avoidance of unacceptable interference; Flexibility for future developments.
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Frequency plans provide: The rights of the participating countries for use of transmissions of which the technical characteristics are described in detail; Procedures for the execution of the agreement; Procedures for modifications of the frequency plan; Procedures for notification of operational transmissions. 3.3.2 Band III, and IV/ V The use of Band III and IV/ V for broadcasting and non-broadcasting services is regulated by the GE06 Agreement. Band III has been planned for digital radio (T-DAB) and digital television (DVB-T). Results of GE06 are often expressed in the number of “layers”. “Layers” are not defined in GE06, but are in general understood as the number of channels that can be received in an area. Most countries achieved three T-DAB and one DVB-T “layer” in Band III. Almost all European countries have adapted a 7 MHz channel raster in Band III. Band IV/V has been planned for DVB-T in a 8 MHz channel. Most countries achieved seven or eight DVB-T “layers” in Band IV/V. The procedures of the GE06 Agreement make a flexible implementation of the Plan possible. The main provisions in this respect are: Plan entries can be used for broadcasting transmissions with different characteristics than specified in the Plan entry, provided that the interfering field strength of the Plan entry, calculated at a great number of points, is not exceeded; the so-called conformity check ; Plan entries can be used for different applications of broadcasting or mobile services provided that the band is allocated to the relevant service in the Radio Regulations and that the power density limit of the Plan entry is not exceeded (see Figure 3.2);
Figure 3.2 Power density of an alternative application not exceeding the power density of a Plan entry
Plan entries can be modified after agreement of countries that are potentially affected by the change. It should be noted that the modification procedure can take a considerable time before all agreements have been reached. If after about 2 ¼ years the necessary agreements have not been reached, the proposed modification will lapse. The GE06 Agreements contains two frequency plans, an analogue TV plan and a digital broadcasting plan. These two plans are not mutually compatible. After a transition period, the analogue TV plan will cease to exist and analogue television transmissions are no longer protected. The transition period ends on 17 June 2015. However in a number of African countries, including northern Africa, analogue television in Band III needs to be protected until 17 June 2020. More information about the GE06 Agreement can be found in two EBU documents [9] and [10]. 15
3.3.3 1.5 GHz band In Europe, it has been agreed to use the lower part of the band 1452-1492 MHz for terrestrial broadcasting and the upper part for satellite broadcasting with digital radio (see figure 3.3).
Figure 3.3 L band division
Under the auspices of the CEPT, the band 1452-1479.5 MHz has been planned for digital radio services (T-DAB) as per the Special Arrangement of Maastricht 2002 (MA02). Initiated by the EC, the application of this band has been made more flexible. Following a revision to MA02 in Constanta in 2007 (MA02revCO07), it is now possible for band 1452-1479.5 to offer mobile multimedia services using, for example, the DMB or DVB-H systems. Although the procedures of MA02revCO07 Agreement allow the use of digital systems with various bandwidths, the Plan is designed for a bandwidth of 1.7 MHz. If e.g. DVB-H with a 5 MHz bandwidth is implemented, three channels need to be combined in the same location, subject to agreement of neighbouring countries.
3.4 Digital switch-over 3.4.1 General Digital switch-over is a complex process that takes many years. National governments need to adopt a clear strategy for the transition from analogue to digital television that is supported by all organisations concerned. A number of elements that should be included in the strategy are: Date for analogue switch-off; Coordination of frequencies with neighbouring countries for digital television during the transition period; Licensing process for digital terrestrial television; Agreements regarding termination of analogue television licenses; Provisions for simulcasting; Agreements with consumer equipment manufactures to ensure that a sufficient number of adequate digital receiving equipment is available in time; Provisions to enable low income households to buy digital receiving equipment; Communication campaigns to inform the public. The manner in which digital television is introduced and the time period necessary to complete the process depends on the market and differs very much from country to country. The simulcast period, when broadcast services are transmitted in both digital and analogue formats in a given area, depends very much on the market and the switch-over strategies adopted. In practice, simulcast periods ranging from zero to fourteen years can be observed. After analogue television has been switched-off, spectrum becomes available for new services. The released spectrum is often called the “Digital Dividend” (see Section 4).
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3.4.2 Analogue switch-off As indicated in Section 3.3.2, analogue television will no longer be protected after 17 June 2015 (and an additional five years for Band III in a number of African countries). However, the European Commission proposes that member-states complete digital switch-over by 2012 [11]. Some national governments have promoted digital switchover through loans or grants, subsidised set top boxes, or temporary reductions in license fees paid by broadcasters. The EC has opened enquiries into digital switch-over funding in a number of member-states where it believes that EC state aid rules have been violated. In general, EU member-states can make funding available on condition that it does not favour one specific delivery platform. 3.4.3 Licensing National administrations prepare legislation taking into account ITU, CEPT agreements and, among EU member-states, EC policies and directives. On the basis of national legislation licenses for digital television are granted. Throughout Europe, the licensing processes for digital terrestrial television vary considerably. In some countries, network operators are granted licenses, in others, multiplex operators or content providers. Selection of applicants is sometimes done on the basis of auctions, in other cases by means of comparative tests (“beauty contests”). In most cases, public broadcasting transmissions are licensed by priority. License costs differ considerably, in some cases a fee is required that covers the costs of the licensing process by the regulator, in other cases “administrative pricing” of spectrum is used where the fee is related to the market value of the part of spectrum concerned.
3.5 Summary The use of the frequency spectrum is regulated at the international level by the Radio Regulations. Digital terrestrial television can make use of Band III, IV & V and the L-band. These bands can, to a certain extent, also be used by other non-broadcasting services (see table 3.1) Band 174-230 MHz Band III 470-862 MHz Band IV/V
14952-1492 MHz L-band
Services Broadcasting Mobile communication services in some countries Broadcasting Mobile communication services in 790-862 MHz from 2015 and in 22 European countries from 2007 Radio navigation and Radio astronomy in some countries Audio broadcasting and audio satellite broadcasting Mobile and fixed services
Table 3.1 Frequency band allocations
Increasingly, a market based approach is applied to frequency spectrum management. This approach could lead to the introduction of non-broadcasting services in these bands causing fewer frequencies to be available for broadcast services and increasing the risk for interference. Detailed frequency plans are in force for Bands III, IV/V (GE06) and the L-band (MA02revCO07). The main features of the GE06 Agreement are: Analogue TV Plan valid until 2015; Digital broadcasting Plan in Band III based on T-DAB and DVB-T system; 17
Digital broadcasting Plan in Band IV/V based on DVB-T system; Use of other broadcasting applications is possible if causing no more interference than a Plan entry; Rules for introduction of non-broadcasting services; Modifications subject to agreement of potentially effected administrations. The Special Arrangement MA02revCO07 contains a frequency plan for T-DAB in the range 14521479.5 MHz. It has similar provisions as GE06 with regard to use of other broadcasting applications and modifications of the Plan. Digital switch-over is the national process of transition from analogue to digital television. In the EU, member-states are encouraged to switch off analogue television by 2012. The released spectrum will, as a priority, be used for digital television services that were formerly transmitted in analogue format. The remaining spectrum, the so-called “Digital Dividend” can be licensed for new services, both broadcasting and non-broadcasting (see Section 4).
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4. Digital dividend 4.1. Introduction Many interpretations exist for the term “Digital Dividend”. However, for the countries in the European Union, the definition used by the European Commission and its advisory body the Radio Spectrum Policy Group (RSPG) is most relevant. The Digital Dividend is, according to the RSPG, to be understood as the spectrum made available over and above that required to accommodate the existing analogue television services in a digital form in VHF (Band III: 174‐230 MHz) and UHF (Bands IV and V: 470–862 MHz). In its Communication on “EU spectrum policy priorities for the digital switchover in the context of the upcoming ITU Regional Radiocommunication Conference 2006 (RRC‐06)”, the European Commission identified three categories: 1) Spectrum needed for the improvement of terrestrial broadcasting services: e.g. services with higher technical quality (notably HDTV), increased number of programmes and/or enhancement of TV experience (e.g. multi‐camera angles for sports, individual news streams and other quasi‐interactive options); 2) Radio resources needed for “converged” broadcasting services which are expected to be primarily “hybrids” of traditional broadcast and mobile communication services; 3) Frequencies to be allocated for new “uses” which do not belong to the broadcasting family of applications. Some of these potential new “uses” of the spectrum dividend are future services and applications which are not yet marketed and others are existing ones which do not yet operate in these frequencies (e.g. extensions of 3G services, short range radio applications). In most countries, the analogue TV services can be accommodated into one DVB‐T multiplex. However, countries with five or more analogue TV services and using DVB‐T with a robust modulation may need two DVB‐T multiplexes for broadcasting their existing analogue TV services in digital format. For a successful introduction of DVB‐T, more multiplexes are needed than the ones containing the current analogue TV programmes (see Section 2 Services). However, according to the RSPG definition, the multiplexes not needed to transmit the analogue services in digital format, will be seen as a digital dividend (see Figure 4.1). More information on the digital dividend is given in article [12].
Figure 4.1 Band III, IV & V spectrum
This section deals with the regulatory measures for implementing the digital dividend and the impact these measures may have on digital terrestrial networks.
The regulatory measures relate to: 19
1. 2. 3. 4.
Implementation of GE06 Plan entries; Implementation of mobile TV in a dedicated sub‐band; Implementation of 3G services in dedicated sub‐band; Use of “white spaces”
It should be noted that in all cases the procedures of the GE06 Agreement must be fulfilled (see Section 3.3.2). Cases 1 to 3 may require modifications to the GE06 Plan in an increasing order of complexity. The EC proposes to establish sub‐bands of Band IV/V for three types of applications [13]. Its proposals are summarised in Table 4.1. Type of service per sub‐band
Spectrum management
− −
Unidirectional high power networks − Mainly broadcasting services −
National management Progressively moving of necessary channels inside the sub‐band through GE06 modifications
−
Unidirectional medium to low power networks Mainly mobile multimedia services
−
National management, combined with optional EU coordination Sub‐band available on a non‐exclusive basis
− − −
Bi‐directional low power networks Mainly fixed and mobile communication services
− − −
EU harmonisation on flexible basis Gradual implementation to cope with national constraints
Table 4.1 EC proposals for partition of Band IV/V
Proposals for use of Band III, IV and V by non‐broadcasting services have raised the concern of the broadcasting community [14]. It is feared that less spectrum will be available for the development of broadcasting services and that interference might occur, particularly between broadcasting and two‐ way mobile services.
4.2 Implementation of GE06 Plan entries 4.2.1 Band usage GE06 has DVB‐T Plan entries in Bands III and IV/V. Band III has also been planned for T‐DAB. Some countries have the intention to convert their DVB‐T Plan entries in Band III into four T‐DAB blocks and use Band III exclusively for DAB related systems, including DMB or DAB‐IP for mobile television. More information on the use of DVB‐T plan entries for T‐DAB can be found in CEPT report [15]. Currently there are not many digital terrestrial television networks in operation in Band III. The main advantages and disadvantages of Band III compared to Band IV/V are: Advantage Disadvantage − Frequency Plan for T‐DAB or DMB − Limited spectrum capacity − Less propagation loss − Higher man made noise levels − Lower minimum field strength − Larger antenna dimensions For the implementation of digital dividend the emphasis is mainly on Band IV/V as the EC proposals mentioned in Section 4.1 illustrate.
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4.2.2 Network planning conditions The majority of the Plan entries in GE06 are specified with so‐called “Reference Planning Conditions”. Most used for digital TV are a set of characteristics for rooftop or portable outdoor reception. The latter term stands also for portable indoor or mobile reception at a lower coverage quality. Figure 4.2 shows the specified DVB‐T reception mode in the GE06 Agreement in Europe. Most used basic characteristics of DVB‐T reception modes in Band IV/V are: Reception Capacity Minimum mode field strength Rooftop ≤ 24 Mb/s 56 dBμV/m Portable ≤ 16 Mb/s 78 dBμV/m Table 4.2 Basic characteristics of reception modes
Figure 4.2 Reception modes specified in GE06
As long as no additional interference is caused or no greater protection is demanded than that defined in the Plan, it is not necessary to modify a Plan entry. However, the more the “Reference Planning Conditions” of the GE06 Plan entry deviate from the wanted specifications, the more difficult it will be to achieve a satisfactory coverage with the given power limitations of the Plan entry or with the interference levels resulting from the GE06 implementation. Table 4.3 indicates possible limitations in implementing GE06 Plan entries for different kind of services. Service DTT indoor or outdoor DTT rooftop and HDTV Mobile (handheld) TV
Limitations in applying GE06 reception mode Rooftop Portable Power limitations ‐ ‐ High interference levels Power limitations Some power limitations
Table 4.3 Possible limitations in implementing GE06 Plan entries
When digital television services with indoor, mobile or handheld reception need to be implemented in Plan entries for rooftop reception and full coverage is required, it may be necessary to agree with neighbouring countries on an increase in power of the Plan entry and to use distributed power by means of a more dense SFN. Plan entries for portable reception generally have much higher interference levels than Plan entries for rooftop reception. If digital television services with rooftop reception need to be implemented in Plan entries for portable reception, the power requirements are therefore considerably higher than would be necessary in case the Plan entry was specified for rooftop reception. However, the power associated with a Plan entry for portable reception is in general (more than) sufficient to cover the area for rooftop reception. 21
Use of GE06 Plan entries for mobile TV or HDTV limits the number of services for Standard Definition television. This can, to a certain extent, be compensated by the application of more efficient compression or transmission systems (see Section 5.4). 4.2.3 Network configuration GE06 Plan allocates frequency rights as assignments and allotments. An assignment gives the right to use a frequency with station characteristics such as coordinates, radiated power, antenna height and antenna pattern. An allotment gives the right to use a frequency in a defined area. The interference potential of an allotment is characterised by a defined transmitter network structure that represents a real network, the so‐called Reference Network. For digital television the GE06 Agreement contains four types of Reference Networks. In principle, all Plan entries can be used for all kind of network configurations provided that the “conformity check” (see Section 3.3.2) has been fulfilled. However, allotments are in general implemented by Single Frequency Networks (SFN) and assignments by Multi Frequency Networks (MFN).
4.3 Implementation of mobile TV in a dedicated subband Handheld devices with built‐in antennas have very poor reception sensitivity (see also Section 7.2). Antenna gain can be improved if handheld terminals are designed for a more limited bandwidth than the full Band IV/V (470‐862 MHz). In general, narrowband antennas with an improvement of about 4 dB can be expected over a bandwidth around 10% or less of the centre frequency. For this reason a dedicated sub‐band for mobile (handheld) TV is considered. More efficient planning is another reason to consider a dedicated sub‐band for mobile TV. In this case, so‐called “high power/high tower” applications and “low or medium power/low tower” applications make use of different parts of the band. However, mobile TV requires higher power compared with all other broadcasting applications. The implementation of mobile TV differs very much in practice, ranging from “high power/high tower” to dense networks with lower power. When Plan entries are specified for portable reception, it may be more efficient not to subdivide Band IV/V. The frequencies of Plan entries forming a network are generally scattered over Band IV/V. In case of a sub band it will be more difficult to compose one or more networks for mobile TV out of the suitable GE06 Plan entries in a dedicated sub‐band and at the same time obtain full coverage for the other digital TV networks in Band IV/V. The frequency range for mobile TV in Band IV/V is limited to channels below 56 (750 MHz) if simultaneous operation in the handset is required with GSM in the 900 MHz band, due to interoperability problems within the handset. In the future, GSM services in the 900 MHz band may be replaced by UMTS and interoperability problems in the handset may less. Consequently, there may be less constraints on the channels that can be used for mobile TV. However, when UMTS is implemented in the frequency range 790‐862 MHz and the relevant handsets are also equipped for mobile TV with the DVB‐H system, channels limitations will need to be reconsidered. A sub‐band for mobile TV could in principle be created by re‐planning Band IV/V. This is, however, a very time consuming exercise and will result in frequency changes and possibly changes in power and antenna patterns of many Plan entries. Use of a dedicated sub‐band for mobile services limits the number of services for HDTV and Standard Definition television. This can, to a certain extent be compensated by the application of more efficient compression or transmission systems (see Section 5.4). 22
4.4 Implementation of 3G mobile services in a dedicated subband 4.4.1 General If part of the digital dividend is used for 3G mobile services in Band IV/V, including uplink services, part of Band IV/V should be made free from broadcasting and planned for 3G mobile services. The upper part of Band IV/V has been identified for 3G services at WRC‐07 (see Section 3.2). If a country decides to implement 3G mobile services in Band IV/V, it will therefore be most likely in the TV channels 61 to 69. Clearing a part of band V from broadcasting clearly has consequences on current and future digital television services. Also In addition, compatibility between mobile and television services, even if applied in different sub‐bands, requires careful attention. 4.4.2 Impact on broadcasting services The impact of a sub‐band for 3G mobile services on digital terrestrial television differs between countries depending on the frequencies used for digital television. In some countries, the frequencies of whole digital television networks are concentrated in channels 61 to 69, whereas in others this band is not (yet) used for broadcasting. In most countries, frequencies for multiplexes are scattered in band IV/V. The channels 61 to 69 represent the frequency recourse of about one network for national coverage. The adoption of a sub‐band for 3G mobile services, and thereby deleting GE06 Plan entries in that frequency range, would create coverage holes in several multiplexes. The GE06 Agreement was agreed following six and a half years of preparations, intensive bi‐and multilateral negotiations and two ITU Conference, RRC‐04 (3 weeks) and RRC‐06 (5 weeks). An acceptable frequency plan was only possible after a considerable reduction of country input requirements and by means of a few millions of administrative agreements to overcome potential incompatibilities. This resulted in an interference limited plan in many areas, with interference levels much higher than the agreed planning assumptions. It is not realistic to assume that holes in coverage due to the establishment of a sub‐band can be cured by adapting characteristics of transmitters in the remaining 41 channels or by accepting limited loss of coverage. In general, one multiplex needs to be given up and re‐planning will be required in order to obtain satisfactory coverage for the remaining multiplexes. This will result in frequency changes and possibly changes in power and antenna patterns for many Plan entries. A transition from the original GE06 plan to a modified plan will be needed. The loss of one multiplex clearly limits the introduction of new digital television services and can, to a certain extent, be compensated by the application of more efficient compression or transmission systems (see Section 5.4). 4.4.3 Compatibility issues between 3G and television services The following compatibility problems require attention: − Adjacent channel interference around non co‐sited transmissions; − Transient interference from mobile terminals; − Interference from a broadcast transmitter into base station reception; − Overloading of the digital broadcasting receiver.
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Adjacent channel interference around non co‐sited transmissions is similar to the case described in Section 5.6.3. Table 5.4 shows possible solutions. Mobile terminals of the 3G service can be used everywhere. When mobile services and broadcast services are located in adjacent channels, the use of a mobile terminal near to indoor, outdoor and mobile digital television receiving antennas could cause interference to digital TV reception. Studies in ITU take place for avoiding this kind of interference; the following measures may be needed: − Sufficient guard bands between 3G uplink and broadcast transmissions; − Adequate maximum transmitting power of 3G terminals; − Sufficiently low out of band emissions of 3G terminals. A sub‐band for 3G services is not mandatory. Countries can decide to use the upper part of Band V for digital broadcasting, for 3G services or other non‐broadcasting services as far as allowed by the Radio Regulations. It could therefore happen that on one side of a border digital television transmission take place on one of the channels above 60 and on the other side of the border a 3G base station is installed. The 3G base stations with relative low power will probably not cause interference to the broadcasting reception. However, the receiving part of 3G base stations is very sensitive and the broadcasting transmission could cause interference to the 3G up‐link. Careful planning of the mobile service and geographical separation from the broadcasting transmission may be necessary. Tests with digital broadcasting receivers showed that out of band protection ratios are in general below the specified values under normal operating conditions. However, in case of overloading, either by a wanted or unwanted signal, the out of band protection ratios exceed the specifications. It is expected that digital television receivers interfered by 3G signals show similar behaviour. In particular the image channel (n+9) protection ratio in case of overloading is of concern. Figure 4.3 shows the possible channel configurations in the upper part of Band V. A guard band or duplex gap of one TV channel is assumed between up and down link. In case where 3G services are used as Time Division Duplex (TDD) each 3G frequency block will be used for up‐ and down link. Television reception on channels 53 to 60 could be affected by image channel (n+9) interference on some receivers if overloaded. In the case of Frequency Division Duplex (FDD) and use of the upper four channels for uplink transmissions, the possibility of image channel interference is limited to channels 57 to 60. In order to improve compatibility, the out of band performance of digital television receivers need to be improved.
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Figure 4.3 Channel interactions
4.5 Use of “white spaces” The term “white space” is used to indicate a part of the spectrum, which is available for a radiocommunication application at a given time in a given geographical area on a non‐interfering and non‐protection basis with regard to other services. These so‐called white spaces can be used for services ancillary to broadcasting like wireless microphones and talk‐back links, as is customary in many countries. These kinds of services are also known as “Programme Making and Special Events” (PMSE) services. In addition, several low power short range devices on a license exempt basis are seen as future applications for these white spaces. Of particular interest are new technologies like software defined radio and cognitive radio. With these technologies services search their own frequency on the basis of certain criteria. The feasibility of these kinds of applications, on a non‐inference basis with digital broadcasting, has not yet been proven. It should be noted that even if cognitive radio is tested positively in the United States, it does not necessarily mean that it can be applied in Europe because of the more dense use of the spectrum and the different digital television system. The specification of these kinds of devices requires careful attention in order to guarantee that no interference will be caused to broadcasting applications.
4.6 Summary The digital dividend is generally understood as the spectrum that is available above that required to accommodate the existing analogue television services in a digital form in Band III, IV and V. The digital dividend can be used for broadcasting services, such as digital terrestrial television with rooftop, indoor or outdoor reception, mobile TV, HDTV and interactive television. Mobile communication services can be allocated to the upper part of the band (790‐862 MHz) and certain low power application could be allowed to make use of so‐called white spaces in the spectrum. For digital terrestrial television services, transmitting station characteristics should be in accordance with the GE06 frequency plan. Once implemented it may be necessary to change the station characteristics when the service requirements change. Depending on required station changes and the GE06 Plan entry, a modification of the GE06 plan may be needed, subject to agreement with neighbouring countries. Transmitting stations modifications could relate to: − Change of power or antenna to achieve better coverage; − Change to a different DVB‐T variant to achieve either better coverage or more capacity;
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−
−
Change to improved encoders, an enhanced compression system (MPEG4), installation of additional multiplexes or in future to a more advanced DVB‐T system (DVB‐T2), to achieve more capacity; Installation of additional sites to improve or extend coverage.
More details on the above mentioned network modifications are given in Sections 5.3, 5.4, 5.5 and 5.6. Partitioning Band IV/V for different kinds of services (digital television for large area coverage, mobile TV and mobile communications) is under discussion. The establishment of sub‐bands reduces the spectrum capacity for digital television broadcasting and will require a revision of the GE06 frequency plan for digital television in Band IV and V. The loss of spectrum capacity restricts future developments and may require modifications to the networks of existing services. These modifications could involve: − Frequency change as a result of replanning; − Change to a DVB‐T variant with higher capacity, improved compression system (MPEG4) or in future a more advanced DVB‐T system (DVB‐T2) to compensate for loss of capacity; − Change of station characteristics and installation of additional sites to compensate for loss of coverage. More details on the above mentioned network modifications are given in Sections 5.3, 5.4 and 5.5. Implementation of mobile communication services may give interference to digital broadcasting services. Low power applications in the so‐called white spaces of the spectrum have no direct impact on digital terrestrial television services, provided that, in practice, the non‐interference conditions can be guaranteed under all circumstances. More information on the application of digital dividend can be found several the CEPT reports [16], [17], [18] and [19].
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5 Networks 5.1 Introduction As a consequence of the developments described in Sections 2 (Services), 3 (Regulatory environment) and 4 (Digital dividend), changes to terrestrial television networks may be needed. Network changes can relate to one or more of the following network elements: Radiation characteristics; DVB-T system; Transmitting sites; Multiplexes.
5.2 Transmitting station and network layout Transmitting site Figure 5.1 shows a simplified block diagram of a typical site with transmitting facilities for three multiplexes. The figure shows a reserve transmitter in n+1 configuration which can be used in case of maintenance or transmitter breakdown. The reserve transmitter should then be adjusted to the frequency and the power of the transmitter it replaces. Another often used reserve configuration is formed by installing Figure 5.1 Typical transmitting site reserve units per transmitter such as a double driver stage. The RF power amplifier, in case of solid state transmitters, has a built-in redundancy due to the parallel operation of a number of amplifiers. In some cases, the antenna is split into two parts and each part is fed by an antenna cable. In this way, part of the antenna installation can be switched off while the station is still operational, albeit on reduced radiated power. Transmitter networks Digital terrestrial television transmitter networks consist in general of the following parts: Central multiplex centre; Central monitoring and operations centre; Distribution links (radio relay, fibre optic); Main transmitters; Fill-in transmitters. The transmitters can be operated as Multi Frequency Network (MFN), as Single Frequency Network (SFN) or as a combination of both. The latter can consist of main stations as MFN and a main station 27
and a number of low power stations as SFN. In SFN, coverage is achieved by means of power distribution over several stations. The total power of the stations in the SFN is less than the power of one station that would be needed to coverage a similar area. Moreover, reception probability is improved by simultaneous reception of multiple useful signals. Operation of a SFN is complex, in particular regarding the synchronisation in transmitter timing, and is also more costly. More information on SFN maintenance can be found in the EBU report on Single Frequency Network Maintenance [20]. In a MFN configuration, it is possible to broadcast local programmes per site and with a higher bit rate because a long guard interval is not needed. Fill-in transmitters are usually fed off-air by a main transmitter and the signal is retransmitted at a different frequency (MFN). In a SFN, it is also possible to feed a fill-in transmitter off-air and retransmit at the same frequency, but care must be taken to ensure a sufficient isolation between incoming and outgoing signal. Sufficient isolation is in some cases difficult to achieve and fill-in transmitters in SFN are then fed in the same way as main transmitters by radio relay or fibre optic link.
5.3 Radiation characteristics 5.3.1 Reasons for change Changes to the radiation characteristics of a transmitting station may take place for a variety of reasons such as: Introduction of new services ; Implementation of the GE06 Agreement ; Introduction of sub-bands and guard-bands ; Operational reasons; Coverage improvement. Operational reasons for changing characteristics of digital TV stations could occur when the roll-out of TV networks is realised under time pressure. It is not always possible to acquire the required local planning licenses in time or to have transmitters available at the required power level. Therefore, temporary installations or even stations, with restricted power or antenna height may be necessary. It could also occur that antenna installations cannot handle the power requirements of new digital transmitters and that antennas need to be replaced. It may turn out that the coverage of a station is unsatisfactory or becomes unsatisfactory as a result of an increase in interference due to the roll-out of digital TV stations in neighbouring countries. A more powerful transmitter or improved antenna diagram may then need to be installed. 5.3.2 Frequency A frequency change requires the retuning of the transmitter and antenna filters. In the case of a SFN, all transmitters in the SFN must change frequency and preferably simultaneously. In Section 6.2, an example of a frequency change for a number of SFNs is given. The antenna pattern is frequency dependent and can be different for the new frequency (see Section 5.3.4).
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In addition, the new frequency may require restrictions in other directions than those used by the former frequency as a result of international agreements. In order to comply with these restrictions, the maximum radiated power may need to be reduced. The GE06 Agreement may also cause the interference situation to be different from channel to channel. If the new frequency is in another part of the band, propagation characteristics will be different. A frequency change will therefore most likely result in coverage changes which, in some areas, could result in coverage problems. In these cases, viewers in the areas concerned have to be informed and advised on ways to improve their reception. Figure 5.2 shows the difference in transmission coverage for two different channels (21 and 60), using the same antenna as in the diagram shown in figure 5.4 (see Section 5.3.4). The red coloured locations show a coverage loss after changing from channel 21 to 60. At the grey coloured locations coverage is sufficient on both channel 21 and 60, however, in most places the field strength on channel 60 is less than on 21. A few locations, the blue coloured ones, benefit from the change; coverage is sufficient on channel 60 but not on 21.
Figure 5.2 Example of coverage difference between channel 21 and 60 Coverage plot: Progira
5.3.3 Power Increasing radiated power, as far as allowed by the GE06 Agreement and local planning licenses can be implemented in different ways as indicated in order of complexity in table 5.1.
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Ways to increase power Adjustment of transmitter power level Additional power amplifier units
Comment Within the limits of the power amplifier of a given transmitter
Replacement of transmitter by a more powerful one
Replacement of antenna by one of higher gain (more tiers)
Transmitter cabinets should have sufficient space and be prepared for it. Power of reserve transmitter should be increased or a power reduction accepted in case the reserve transmitter is operational. Cooling installation and power supply may have to be adapted. Transmitter building should have sufficient space. Power of reserve transmitters should be increased or a power reduction accepted in case the reserve transmitter is operational. Antenna mast should have sufficient space and mechanical strength. See also Section 5.3.4
Table 5.1 Ways to increase radiated power
5.3.4 Antenna Horizontal radiation pattern The antenna pattern is influenced by the antenna construction and the frequency. The basic radiating element is a panel with dipole arrangements. In general a transmitting antenna consists of several tiers of panels. The number of panels in a single tier depends on the support structure and the required horizontal radiation pattern. Non-directional antennas located at the top of the mast have often four panels per tier. Figure 5.3 shows a 6-tiers UHF TV antenna as seen from top to bottom. In order to achieve the right input impedance of the antenna, the antenna cable length to the panels of three of the tiers has been adapted. The panels in these three tiers have been placed further outwards to compensate the impact on the pattern.
Figure 5.3 6-tiers antenna seen from the top Photo: Rein Simonse
As example Figure 5.4 shows the pattern of a nondirectional antenna for a channel in the lower end of Band IV and the upper end of Band V.
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Figure 5.4 Horizontal antenna diagram in lower end (left) and upper end (right) of Band IV/V
Newly designed antenna constructions have considerably improved radiation characteristics throughout the frequency band as shown in the example of Figure 5.5.
Figure 5.5 Horizontal antenna diagram in lower end (left) and upper end (right) of Band IV/V of modern designed antenna
Vertical radiation pattern The vertical radiation pattern is of particular interest for coverage close to the transmitter. The more tiers, the more antenna gain, but the more problematic reception close to the transmitting site. Some network operators do not install antennas of more than eight tiers if the site is located in an urban area. With more tiers the necessary null-fill can only be realised at the costs of the additional gain. Figure 5.6 shows the vertical diagram of an eight tiers antenna with extra null fill in the area below 10°.
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Even without changing the number of tiers, the replacement of an antenna almost always changes the angle of the “nulls” in the vertical diagram, resulting in a location shift of areas with lower field strength close to the transmitter. Areas of high field strength near the transmitter are also of concern. In areas where maxima occur in the pattern close to the transmitter, the field strength could be so high that it causes interference to consumer and professional equipment. Very close to the antenna there may be a health danger. There are different regulations per country; field strength limitations and hence limitations in the radiated power may be necessary.
Figure 5.6 Vertical radiation pattern
The main beam of the vertical antenna radiation pattern should be directed towards the coverage area (and not beyond). In particular, in case of high antenna heights or relative small coverage areas a beam tilt will be necessary (see also Figure 5.6). This beam tilt has the additional advantage that less power is radiated towards the horizon and thus less interference towards other transmissions. Polarisation Horizontal polarisation causes less ghost images in reception compared with vertical polarisation Therefore with analogue TV most antennas are horizontally polarised. While ghost images are not a problem in digital TV, most countries have opted for horizontal polarisation because of the existing base of horizontally polarised rooftop antennas and the wish to reuse existing transmission installations as much as possible. If reception at low receiving heights is important and the receiving antennas are mainly vertically polarised, e.g. in case of indoor and mobile TV reception, vertical polarisation may be adopted. Operational aspects Antenna changes are costly if new antennas or antenna combiners need to be installed. Work on antennas needs often to be done at elevated locations. Due to weather conditions, antenna maintenance and construction may be restricted to summertime (see Figure 5.7). There is limited space on antenna masts. For new antennas, compromises may have to be made regarding height and aperture. In some cases, a temporary antenna with smaller aperture (and consequently lower gain) may need to be installed until another antenna has been removed. If the lower gain cannot be compensated by a higher transmitter power a reduced coverage will be the result.
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Figure 5.7 TV station in winter time in Norway. Left iced antenna; right restricted entrance Photo: Norkring
5.3.5 Antenna height Increasing antenna height is generally a frequency efficient way to improve coverage. It allows the coverage area to be enlarged, but, beyond the horizon, the interfering field strength to other service areas is marginal. Increasing antenna height is, however, not a trivial matter and may not be possible in many cases due to practical or regulatory reasons. Furthermore, in many countries existing transmission installations are used mainly for digital TV for reasons of cost savings and the inability to increase antenna height. In some countries, however, more dense digital TV networks are used (as SFN) in order to improve indoor and mobile reception. In these cases, the coverage area per transmitter is smaller than it was with analogue TV, therefore antenna heights could also be lower. In case of high antenna heights and relative small coverage areas, care should be taken with the null-fill in the vertical radiation pattern and an adequate beam tilt will be needed (see also 5.3.4).
5.4 DVB-T system 5.4.1 Reasons for change The choice of DVB-T variant, compression or transmission system depends on the kind of services that need to be provided (See Section 2). These requirements may change over time. It may also be necessary to adopt a more efficient compression or transmission system if the number of multiplexes is reduced or cannot be extended, and the requirements for broadcasting services exceed the capacity of the available frequency band. This is of paramount importance if Band IV/V is partitioned (See Section 3) and the required services have less spectrum available. 5.4.2 DVB-T variant The options The DVB-T system has the choice of 2k or 8k Fast Fourier Transform (FFT) sizes, three types of carrier modulation and five code rates; in total, there are 120 possible variants (see Figure 5.8).
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With a proper choice of modulation and code rate a robust variant can be achieved with low required field strength, but also a low bit rate. Alternatively, a high multiplex capacity can be chosen, but in that case a high field strength is required. The guard interval is important for Single Frequency Networks (see Section 5.5.2). In addition there is a choice for non-hierarchical modulation and hierarchical modulation. In the latter case, a choice also has to be made between three possible modulation parameters.
Figure 5.8 Variants of 8k DVB-T system
Changing DVB-T variant is a simple adjustment in the transmitter. The transmitter with the lowest net bit rate of a network determines the multiplex capacity of that network, therefore all transmitters of a network have generally been adjusted to the same DVB-T variant. The bit rate of the MPEG Transport Stream, the incoming signal to the transmitter, should not exceed the bit rate of the DVB-T variant for which the transmitter has been adjusted. FFT size The 2k and 8k variants refer to the number of OFDM subcarriers in the digital signal. There is a trend to use 8k only. 2k has an advantage for mobile reception because interference due to the Doppler effect occurs at four times higher speeds than with 8k. With 2k, however the guard interval, important for SFN operation, is four times shorter than with 8k. The DVB-H system also has a compromise variant of 4k. Carrier modulation and code rate In the case of portable reception and in particular indoor reception, field strength requirements are very demanding and the trend is to use 16QAM with relative low code rate (2/3 or ½). For rooftop reception 64 QAM and a relative high code rate (2/3 or 3/4) is often chosen. As indicated in Section 2.2, a compromise has to be found between multiplex capacity, coverage quality and wanted field strength. In practice, different compromises are made: 16QAM is also used for networks planned for rooftop reception and 64QAM for networks planned for indoor reception. There are cases known where a very high number of services need to be broadcasted over a small area and 64QAM with a code rate of 7/8 is used providing 31.6 Mb/s. Hierarchical modulation Hierarchical modulation is not used much in practise. It allows for the transmission of two independent multiplexes by one transmitter (one frequency) with different transmission quality at the costs of some overhead capacity. A high priority multiplex can, for instance, be used to broadcast a limited number of main services for indoor reception in a large area. The low priority multiplex can 34
be used to broadcast a larger number of services for indoor reception near the transmitter but for rooftop reception in the country side. 5.4.3 Compression and multiplexing General Encoding and multiplexing takes place at a central point and is a relative expensive part of the transmission chain. Changing or improving compression or the multiplex system has no direct impact on the transmitter stations and on coverage. Statistical multiplexing is often used and compared to a constant bit rate per service, it provides a way to increase multiplex capacity while maintaining picture quality. More information on statistical multiplexing can be found in the EBU report on statistical multiplexing [21]. Upgrading encoders Experience has shown that the efficiency of encoders improves over the years until the technology is mature. Upgrading or replacing encoders of the same compression system will result in more services in a multiplex or the same number of services with a higher quality. The following practical case is an example of improvement made to MPEG2 encoders over a period of seven years: Example of multiplex with MPEG2 encoders First multiplex system installed in 2001 Upgrade of first system in 2003 Replacement of first multiplex system in 2006 Upgrade of second system in January 2008
Result The number of services transmitted in five multiplexes in 2001, are transmitted with similar quality in four multiplexes in January 2008
Table 5.2 Example MPEG2 evolution
Use of MPEG4 MPEG4 is an improved compression system, it is also known as MPEG-AVC, ITU-T H.264 and MPEG-4 Part 10. Compared to MPEG2, MPEG4 should achieve a coding efficiency improvement of at least 1.5 times. This improvement will be achieved when the MPEG4 technology is mature. In cases where MPEG4 is used to provide an increased number of services in a multiplex, an additional advantage is obtained with statistical multiplexing. HDTV services, for which an adequate receiver is needed, started in Europe on the terrestrial networks with MPEG4 in 2008. 5.4.4 Transmission system The process of modulation and error coding takes place in the driver of a digital TV transmitter. A transmitter may already be equipped for different transmission systems. If not, a change of transmission system, for instance replacing DVB-T by DVB-T2 or DVB-H requires a software change or replacement of the driver modules in the transmitter. A change of transmission system has a minor direct impact on the network. However, the service for which the new system has been implemented may have very different requirements (e.g. mobile TV) and adequate receivers are needed. For terrestrial HDTV transmissions, MPEG4 compression is used (see also Section 5.4.3). When HDTV introduction is planned with DVB-T/MPEG4, no more than two HDTV services can be accommodated in a multiplex if it is required to show critical material on large flat screens. With medium size screens and when the viewing distance is more than three times the screen height, three HDTV services in a multiplex may be delivered. It is also expected that MPEG4 encoders will improve over the years (as 35
did MPEG2 encoders). If introduction is foreseen in 2010 or later, use of the improved DVB-T2 system can be considered (see also Section 2.4.2). Introduction of a new transmission system for existing services can only be done, without service interruptions, by means of parallel transmissions of the existing and the new system. When all receivers are equipped with the new system, the transmissions carrying the old system can be closed down and the multiplexes used for new services. This process will be shortened if, after a certain date, only consumer equipment able to receive the new and old system is allowed to be sold. Nevertheless, it is expected that this process will take many years. If no multiplexes are available for parallel operation of a new transmission system such as DVB-T2 , because, for example, spectrum in Band IV/V has been allocated to other non-broadcasting services, one or both of the following ways may be considered: Source new frequencies based on GE06 procedures ; these frequencies may be constrained in certain cases; Free one multiplex by moving the services from this multiplex to other multiplexes, making use of the advantages of more mature MPEG2 technology (see also example in table 5.2) and by using a DVB-T variant with higher capacity (see Figure 5.8) and introduce in the freed multiplex HDTV services in DVB-T2/MPEG4.
5.5 Transmitting sites 5.5.1 Reasons for change In general, television network roll out starts with main stations to cover the majority of the population. In later years, the network is extended to cover less densely populated areas and to improve coverage by means of fill-in stations. A number of analogue fill-in transmitters in mountainous areas and cities were set up in order to resolve reception problems due to ghost images. With digital TV, ghost images are not a problem. Digital terrestrial television networks will therefore in many cases need fewer fill-in stations. 5.5.2 Coverage extension After the main population centres have been covered by relatively few stations, each additional station is expensive in term of costs per inhabitant. Public broadcasters have an obligation for universal coverage and will need to extend coverage of their programmes to nearly the whole country. In some countries the universal coverage obligation is not restricted to terrestrial television and satellite TV is accepted for coverage in rural areas. Commercial broadcasters without a public service mission may not wish to cover a whole country and restrict the terrestrial network to cover main population centres. In general, existing sites will be reused and the investment costs of digital TV may be limited to replacing the analogue transmitter by a digital one (often of lower power) and reusing the antenna originally installed for analogue TV. Depending on the characteristics of the relevant GE06 Plan entry the antenna diagram may not be optimal for digital TV e.g. when power restrictions needed for digital TV are required in other directions than was the case with analogue TV. In the case of a SFN, the distance between transmitters in the SFN requires special attention. If at a reception point the relative delay time between two transmitters in the SFN exceeds the length of 36
the guard interval, self interference of the SFN may occur. Table 5.3 shows a number of ways to resolve self interference: Remedy Increase guard interval
Comment Only possible if the longest guard interval is not yet used To be applied in all transmitters in the SFN Reduction of multiplex capacity
Reduce power of most distant transmitter
Coverage reduction Impact on coverage minimised if power reduction in the direction of the problem area is possible (direction diagram)
Add artificial delay in nearest transmitter Use more robust DVB-T variant (i.e. lower C/I)
Coverage reduction due to self interference caused by artificial delay in other parts of the coverage areas To be applied in all transmitters in the SFN Reduction of multiplex capacity
Use different frequency for one of the related transmitters
Additional frequency should be available in GE06 Plan If transmitter becomes part of adjacent SFN: o New self interference problems may appear o Programme package of other SFN should be relevant Costs of additional transmitter should be acceptable Adequate site should be available
Use fill-in transmitter to cover a small problem area Table 5.3 Resolving self-interference
Figure 5.9 shows as example a self interference area in an SFN network and the solution by means of an artificial delay of 100 s at one of the transmitter sites. More information on SFN planning can be found in the EBU guide on SFN frequency planning and network implementation [22]. Figure 5.9 Self-interference in a SFN (left) and possible solution (right) Coverage plots: Progira
5.5.3 Coverage improvement Inside a coverage area, reception probability could be marginal or below acceptable limits because of terrain, buildings, woods etc. There are limitations in the accuracy of coverage predictions; some of 37
these areas of poor reception are only discovered after complaints from viewers. With detailed terrain and clutter data and well tested propagation prediction methods it may be possible to predict coverage with an accuracy of a few dBs compared to measurements in some situations. Good reception is a statistical feature and depends on many variables including interference field strengths exceeded for 1% of time. An accurate transmitter database with all wanted and potential interfering transmitters is also a prerequisite. Even when predicted coverage meets the standards, complains may be received. In making coverage predictions it is always assumed that viewers use proper receiving equipment that complies with frequency planning standards. Section 7 deals with receiving equipment and how reception can be improved on the receiving site. If indoor reception or mobile reception is required, the power specified in the GE06 Agreement is probably not sufficient to cover a large area with one transmitter, as would be the case with rooftop reception. Power distribution by means of an SFN is necessary. If the SFN becomes dense, the chance increases that at certain locations two or more signals of equal field strength are received, the socalled zero dB-echo. DVB-T receivers show decreased sensitivity in these cases, ranging from about 5 to 10 dB (in case of 64QAM2/3) if the signals have equal strength. If the time difference is small (< 0.5 µs) additional problems may occur with the synchronisation of receivers. Figure 5.10 gives an example of an area affected by zero dB-echo. On the left side, no account is taken of zero dB echo. However, in practice, coverage could be as on the right side, depending of the type of receiver.
Figure 5.10 Example of area affected by a zero dB echo (right) Coverage plots: Progira
Zero dB-echo could affect relatively large areas particularly in open terrain. If a dense SFN is used, it is important that the planning software takes into account the zero dB-echo. With proper network planning, the zero dB-echo area can be minimised or shifted to less populated areas. 38
5.6 Multiplexes 5.6.1 Reasons for change Most countries have rights in the GE06 Agreement for seven or eight DVB-T “layers” in Band IV/V and one in Band III. “Layers” are not defined in GE06, but are generally understood as the number of channels that can be received in an area. In most countries, current licences do not yet cover all layers provided by the GE06 Agreement. More layers may be licensed when: Analogue TV has been switch-off (including in neighbouring countries) and restrictions to layers removed; Decisions have been made about new broadcasting services or other non-broadcasting services; New technology is mature enough to be implemented; Market requirements are clearer. There is a certain tendency to concentrate digital terrestrial television in Band IV/V and to use Band III for radio or multimedia services using a system from the DAB family. 5.6.2 Use of common sites Use of common sites for transmission of existing and new multiplexes has the advantage that existing facilities, like distribution link, transmitter building, mast, antenna and reserve transmitter, can be used. When engineering and installing a broadcasting site, it is advantageous to take into account future extensions. It is often far more expensive to modify links, buildings, masts and antennas at a later date. Use of common sites may be complex when different network operators make use of the site. Priority rules have to be made for use of limited space in buildings and masts. Common use of antenna combiners and antennas also requires clear agreements on responsibilities, costs and maintenance. Common use of antennas may be an advantage for economic and operational reasons; however, it does not always provide optimal coverage (see also Section 5.3.4). When additional multiplexes are intended for a different kind of network, common use of sites is only partially possible. If a dense digital TV network is required additional sites are necessary and antennas at existing sites may be too high, or have the wrong polarisation. 5.6.3 Use of different sites Different network topologies may be necessary if: Several operators make use of the same frequency band; Some multiplexes make use of dense networks.
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The situation is illustrated in Figure 5.11. Adjacent channel interference may occur around non co-sited stations and use of the first, second, or third adjacent channel on both sides of the wanted channel or the image channel. The non co-sited station could be a broadcasting station, but also a mobile base station. Even mobile terminals could cause adjacent channel interference at very short distances.
Figure 5.11 Non co-sited transmitters
Adjacent channel interference is a local problem. Possible solutions are indicated in table 5.4. Remedy Cross polarisation Power adjustment Antenna adjustment Adequate frequency separation Fill-in transmitter
Comment Only effective in case of rooftop reception and in those cases where the other station is situated in the main beam of the receiving antenna Coverage of second station may not be sufficient Provided that frequency, not being 1st, 2nd 3rd adjacent channel or image channel, is available As SFN; relatively expensive
Table 5.4 Solutions for adjacent channel interference
If different network operators are involved, the question will arise as to who will have to pay for these provisions.
5.7 Summary Changes to digital terrestrial television networks may be necessary as a result of introducing new services, regulatory obligations or technology changes. Some of the changes are costly while others may need some equipments adjustments. Many changes have an impact on coverage. The table below lists the changes described in this Section and summarises capital expenditure elements and impact on coverage.
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Change Frequency Power increase Antenna replacement
Antenna height
Capex elements Antenna filters Power modules or new transmitter Antenna tiers
Transmission system
In general, increased reception probability (if higher number of tiers) In some cases, reduced reception probability In some cases, problems with high or low field strength near the antenna In general, increased reception probability (in case of increased height) In some cases, reduced reception probability In some cases, problems with high or low field strength near the antenna
Mast and antenna
DVB-T variant
Compression and multiplexing
Possible consequence for coverage In some cases, reduced reception probability Increased reception probability, but also more interference
-
Or, increased coverage probability and reduced capacity Or, reduced coverage probability and increased capacity No impact on coverage, provided that receivers are able to decode (new) compression system Increased multiplex capacity (more services or increased picture or sound quality)
Upgrade or replacement of multiplex and encoding equipment Replacement by improved compression system (MPEH4) New drivers or software
No direct impact on coverage, provided that receivers are able to demodulate new system
More sites
Building, mast, transmitters, antenna, distribution link
In general, coverage improvement In some cases, reduced reception probability in SFN
More multiplexes
New transmitters Possibly new sites
More services or increased picture or sound quality In some cases, reduced coverage near non cosited transmitters
Table 5.5 Summary network changes
An additional costs factor to be considered relates to the necessary communication with viewers to inform them about the changes and actions they need to take in order to improve reception (see also Section 7). Changing compression or transmission system of existing services requires simulcasting of existing and new system until most of the receiving equipment has been converted to the new system.
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6. Practical cases 6.1 Introduction In this Section three practical cases of network evolutions are described relating to digital switch‐ over, roll‐out of a DVB‐H network and preparing for HDTV.
6.2 Digital switchover Digital switch‐over is a complex process and may, as far as the transmitter network is concerned, include the following steps: − Adapting f digital television stations in accordance with the GE06 Agreement and bilateral agreements, sometimes in several stages (see example in table 6.1); − Setting up of digital stations that will replace analogue ones after analogue switch‐off; − Setting up of digital stations for additional services; − Switching off of analogue TV in accordance with the nationally agreed date(s); − Continuing of the operation of existing services with minimal interruptions. Table 6.1 shows an example of modifications made to a station in the Netherlands. Modifications were necessary in order to bring the characteristics in accordance with the GE06 Agreement and bilateral agreements. Date
Station modifications − First installation 1st Q 2001 − Directional antenna − Reduced antenna height 4th Q 2006 −
Change of frequency
− 2 Q 2007 −
Power increase New non‐directional antenna on top of mast
nd
Reason − DTT launch; use of unused analogue TV frequencies − Restrictions due to bilateral agreements − No space for directional antenna on top of mast − Analogue switch‐off − Frequencies according to GE06 − Bilaterally agreed restrictions remain − Restrictions no longer needed − Analogue TV antenna has been removed − Use of vertical polarisation
Table 6.1 Digital switch‐over stages at a particular station
The following example, also from the Netherlands, shows the case of frequency changes at 19 sites (see Figure 6.1). At each of the 19 sites, five frequencies are in operation in different SFN configurations. Per region, some of the SFNs have to change frequency in order to bring the stations characteristics in accordance to the GE06 Agreement. The frequencies allocated in the GE06 plan made it necessary to modify the SFN configurations and to interchange the multiplex feeds between transmitters in a number of cases. At each site the combiner (the unit that combines the output of the five transmitters into one antenna) had to be modified and a number of transmitters per site had to be retuned. Operational requirements allowed only short interruptions of the services during night time.
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Figure 6.1 Example of frequency change at 19 sites
The project started with the purchase of new combiners with five inputs. The following steps were taken consecutively in each of the five regions (A to E), each region consisting of three to five sites: 1. Tuning new combiner to existing five frequencies; 2. Bringing new combiner into operation in one night for temporary use; old combiner is available for re‐ use; 3. Tuning of old combiner to new frequencies and the remaining unchanged frequencies; 4. Tuning transmitters to new frequencies and bringing into operation of old combiner (on new frequencies) in one night; new combiner is free of use; 5. Transport new combiner to site of next region undertaking change. After the project was finished, the remaining combiners were used in new sites. An additional complication occurred in region A. The agreement with cable operators to provide six weeks of advance warning prior to a frequency change could not be fully respected and a cable operator threatened to take legal action. Therefore one frequency change at one site was postponed and temporary measures taken without affecting the rest of the project. It should be noted that the interruption in the transmission was short and during night time. However, in practice, the viewer experienced a longer interruption because receivers needed to be retuned (see also Section 7.3).
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6.3 Rollout of a DVBH network The main constraints for planning of DVB‐H networks are the availability of channels and the very high required minimum field strength. DVB‐H signals can be part of a DVB‐T multiplex. However, the multiplex capacity for DVB‐T signals is reduced and the DVB‐H signal has much less capacity than if a dedicated channel is available. There are two possible ways of sharing a DVB‐T channel: − DVB‐H and DVB‐T within the same multiplex; the video and audio services which are intended for a service to handheld receivers (DVB‐H) in the form of an IPDC (Internet Protocol DataCast ) is combined in an MPEG Transport Stream with MPEG‐2 or MPEG‐4 services intended for conventional DVB‐T receivers; the DVB‐T modulation mode is unchanged for all signals contained in the Transport Stream and hence, whether the main DVB‐T signal mode is intended for reception on directional roof‐top antennas, or indoor set top antennas, the coverage obtained for handheld receivers is unlikely to be satisfactory; − DVB‐H and DVB‐T in hierarchical modulation (see also Section 5.4.2); in this case two independent MPEG Transport Streams are applied to the hierarchical modulator, the low priority part for DVB‐T, the high priority part for DVB‐H. Different coverage is obtained for the two streams, the cost being an overall reduction in data rate capacity. A dedicated channel has the preference of most network operators, because the full channel capacity is available for DVB‐H services and no sharing agreements are necessary in cases where different operators are involved in the provision of DVB‐T and DVB‐H services. DVB‐H can, in principle, make use of all channels in Band III, IV/ V and the 1.5 GHz band. However DVB‐H terminals for Band III do not exist (at present). In Band IV/V channels below 56 (750 MHz) should be used if simultaneous operation with GSM900 is required. In general T‐DMB or DAB‐IP is used for mobile TV reception in Band III. A very high field strength is needed for DVB‐H because of the poor receiving antenna performance and the difficult reception conditions. (See also Section 2.5). With the power restrictions of the GE06 Agreement and the powers that can practically be achieved, a single station would in most cases not be sufficient to cover a large area. Therefore a more dense transmitter network (Single Frequency Network) could be implemented. In practise, very different configurations for mobile TV networks have been put into place, ranging from a network similar to those used for rooftop or portable TV reception to very dense networks and combinations thereof. Studies in the UK [23] show typical cell radii for handheld reception in very dense networks. For comparison, T‐DMB is also indicated. Cell radii are very dependent on the assumptions and constraints that are found in practice. Frequency range Band III Band IV/V 1.5 GHz
System T‐DMB (1.7 MHz) DVB‐H (8 MHz) DVB‐H (5 MHz)
Antenna height 25 m 25 m 25 m
Table 6.2 Typical cell radii of a dense network
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Radiated power 1kW 2 kW 5 kW
Cell radius Urban Suburban 3.5 km 5.0 km 2.0 km 2.5 km 1.5 km 2.0 km
The number of sites in a dense network for a metropolitan area of about 30 by 30 km of which is 25% urban and 75% rural is shown in table 6.3. Frequency range Band III Band IV/V 1.5 GHz
System T‐DMB (1.7 MHz) DVB‐H (8 MHz) DVB‐H (5 MHz)
Number of sites 20 65 100
Table 6.3 Typical number of sites
In France, the DVB‐H network planned will use existing sites and, if necessary, be complemented by new sites. DVB‐H services are planned in a first phase for 73 main cities representing 35% of the population with extensions to 70 to 80% of the population expected. One DVB‐H multiplex will start in early 2009. New frequencies will be used for the DVB‐H transmitters. These frequency assignments are not in the GE06 Plan and are therefore subject to international coordination.
6.4 Preparing for HDTV Each DVB‐T network can be used for HDTV provided that the multiplex capacity is sufficient to transmit the HDTV services. A change from standard definition to HDTV has no impact on coverage if the DVB‐T variant is unchanged. For the introduction of HDTV services, it is essential that viewers have appropriate receiving equipment. EICTA, in consultation with the EBU and other members of the broadcast industry, have agreed on minimal requirements for HD receivers and displays. Viewers are informed that equipment carrying the logo conforms to these specified requirements. The logo shown on the left hand side of Figure 6.2 is attached to displays, the right hand side logo to set‐top boxes and integrated TV sets.
Figure 6.2 HD logos
HD‐ready screens are present in many homes (see also Section 2.4.1). However, the main challenge will be to ensure that when HDTV services are introduced, sufficient quantities of adequate receivers are available in shops for attractive prices. In Norway for instance, the following measures are taken to ensure a successful HDTV introduction: − MPEG4 transmissions only; − Only HD/SD compatible receivers with HDMI output and down conversion of HD to SD; − Reduction in the number of services in a multiplex when HD starts and re‐arrangement of the other services. In France, DVB‐T services started in standard‐definition using MPEG2 for free‐to‐ air services and MPEG4 for pay‐TV services. HDTV services will start using MPEG4, in spring of 2008 with three free‐ to‐air HD services in currently unused multiplex. A second multiplex with three free‐to‐air HD services will be launched at the end of 2008. In addition, one or two HD pay‐TV services will be introduced by converting an existing SD MPEG4 pay‐TV services into HD MPEG4. In order to stimulate digital terrestrial television, including HD services, the sale of analogue only TV set is prohibited since 46
March 2008 and all new TV set must include MPEG2 decoder for standard definition. All new HDTV sets will have to include MPEG2 and MPEG4 decoder from December 2008. It is expected that HD receivers will become the de facto reference within one or two years and consequently MPEG4 will be widespread. In early 2008 the price of MEG4 receivers was 4 to 5 times higher than MPEG2 receivers, but mass‐market volumes may result in the prices of MPEG4 receivers to decrease.
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7. Viewer concerns 7.1 Introduction It may be necessary for viewers to take action after certain network changes (see table 7.1), in order to receive new or improved services, or to continue to receive existing services. Viewer actions Retuning of receivers
Adjusting receiving antenna Installing improved receiving antenna
Purchasing new receivers
Network change − Frequency change − Fill‐in transmitter in MFN − Additional multiplexes − Fill‐in transmitter − SFN − Frequency change − Transmitting antenna − DVB‐T variant − SFN − Additional multiplexes − Transmission system − Compression system
Table 7.1 Viewer actions that may be needed after network changes
External factors can cause reception quality to deteriorate. These factors include the increase of interference levels when launching new digital TV services and local interference from other services that make use of the same band. It should be noted that viewers may have reception problems should their reception quality decrease despite maintaining reception quality above the agreed standards. In most cases, viewers can take measures to improve reception quality, however the broadcast community must provide information and assistance. This section will deal with: − Means to improve reception; − Retuning receivers; − Replacement of receiving equipment; − Communication with viewers.
7.2 Means to improve reception Elements in the receiving installation important to achieve high‐quality reception are: − Location of the receiving antenna; − Directivity and gain of the receiving antenna; − Antenna cable loss; − Match between antenna and receiver; − Receiver sensitivity ; − Receiver selectivity.
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The receiver characteristics depend on the design and implementation of the receiver. In general receivers comply with the EICTA specifications. Although some characteristics, e.g. selectivity, may be improved in the future (see Section 4.4.3), the viewer cannot improve a given receiver. To improve reception, attention should be directed to the antenna and, in particular, its location, directivity and gain all of which are frequency dependent. Active antennas, antenna amplifiers and diversity reception can also help improve reception. Antenna location The receiving antenna height is a very important factor. In principle rooftop antennas should be placed above local clutter. Indoor reception can be improved by locating the antenna at a high position in the room, on a higher floor or outside. Even antennas of small dimensions, mounted outside at a height of, for example 3 meters, give a considerable improvement to reception probability compared to indoor reception. Field strength distribution can be divided in macro and micro variations. Macro variations relate to a small area of, for example 100 by 100 meters, and the location probability requirements refer to such an area. Micro scale variations relate to the receiving location with dimensions of a few wave lengths and are mainly caused by multipath due to reflections on nearby objects. The receiving antenna should be located at a position where the field strength is maximal. However, micro variations are frequency dependent and it may be difficult to find an optimal position if several frequencies must be received and the average field strength levels are near the minimum required value. For rooftop antennas the position is determined at the time of installation and the choice is limited by the construction of the roof. Portable antennas can, in principle, be placed at an optimum location for each frequency channel. However, it does not contribute to the pleasure of watching television if the antenna position has to be changed each time a different frequency channel is selected. Directivity and gain The effective antenna aperture is a function of the wave length and the gain compared to a half wave dipole. Very small antennas, like built‐in antennas of handheld receiving equipment have very a poor gain. On the other hand, directional rooftop antennas have large dimensions and a considerable gain. For network planning, the receiving antenna gains are assumed as indicated in table 7.2. The antenna gain for rooftop and portable antennas are given in the GE06 Agreement. EBU document [6] indicates antenna gain values for handsets. Antenna type Rooftop (gain minus cable loss) Adapted portable antenna External portable antenna (telescopic or wired headset) Integrated antenna
Band III 5 dB ‐2 dB ‐13 dB ‐17 dB
Band IV 7 dB 0 dB ‐8 dB ‐12 dB
Band V 7 dB 0 dB ‐3 dB ‐7 dB
Table 7.2 Antenna gain relative to a half wave dipole
In practice, rooftop or portable antennas can have poor characteristics, in particular with regard to directivity and gain as a function of frequency. It would be helpful for the public if adequate information on receiving antennas could be provided.
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Reception can be improved by using an antenna with a better gain. In case of rooftop reception this can be realised by an antenna with more elements to achieve better directivity and gain and an antenna amplifier to compensate cable loss. Portable reception can be improved by means of a small directional antenna to obtain more gain or an active antenna to achieve a lower noise figure and better matching with the receiver.
Figure 7.1 Active indoor antenna
Figure 7.1 shows an example of an active indoor antenna. By means of a telescopic antenna, handheld reception can be improved at locations where reception would otherwise be poor. Diversity reception Mobile and portable reception can be considerably improved by the use of antenna diversity. Handheld television devices are too small to include more than one antenna. An antenna diversity system reduces the effect of fast fading and consists of two or more antennas and a dedicated receiver. The outputs of the antennas are combined using certain weight factors and are decoded using the standard decoding algorithm. The application of antenna diversity has the following advantages compared to reception with a single antenna: − Reduced required field strength (6 to 8 dB); − Better reception at higher speeds; − Less reception problems when people are moving around the antenna; − Less problems with receiving several multiplexes; − Easier to find an optimal position for a portable receiving antenna. Despite these advantages, diversity antenna reception equipment is not generally available.
7.3 Retuning receivers After a frequency change or bringing into use of a new frequency, receivers need to be retuned. Some receivers perform background scanning in the standby mode and are therefore automatically adjusted to new frequencies. However, in most receivers retuning is performed by manually activating an automatic frequency search via a menu. Experience shows that retuning is difficult for many viewers who must take the following actions: First step − Go to menu − Select “installation” − Execute “Reset default values”
Second step − Go to menu − Select “installation” − Execute “Automatic transmitter search”
After these steps, it may be necessary to restore the preferred order of services or to delete services that are not appreciated. Good communication is essential for announcing and performing a frequency change.
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7.4 Replacement of receiving equipment New receiving equipment is necessary in case of: − New compression system (e.g. MPEG4); − New transmission system (e.g. DVB‐T2; DVB‐H); − New television system (e.g. HDTV). The replacement cycle of modern electronic devices is rather short, in particular if fashion is involved as is the case with mobile telephones. In general, it is assumed that digital receiving equipment has replacement cycles of three to six years. However, it could be expected, as in analogue television, that a replaced STB or integrated digital TV set continues to be used in other rooms or in recreational premises. Furthermore, digital television reception units are used in several devices such as PVRs and PC‐devices. Receiving equipment incorporating new compression or transmission systems is likely to be more expensive than equipment with mature technology. Forcing viewers to replace receiving equipment may not be appreciated and may only be acceptable if new and attractive services are offered.
7.5 Communication Viewers need to be informed about reception possibilities, network changes and the impact that may have on reception and the actions that have to be taken. The following tools can be used to communication with viewers: − Website; − Telephone help desk; − Advertisements ; − Information via local dealers; − Information channel in multiplex; − Teletext pages.
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Figure 7.2 Example reception advice from Boxer website (www.boxer.se)
Figure 7.2 shows reception advice given on the website of the DTT operator Boxer in Sweden. After entering an address, the map shows if the reception quality is very good, good are weak. In this example, reception at the indicated address is weak and the viewer is advised to use an antenna amplifier. The nearest transmitter (in this case Älvsbyn at 280 degrees) is also indicated. Furthermore, information about the nearest installation companies and the channels that be can be received is available by clicking on the appropriate link.
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8. Conclusion and recommendations Digital terrestrial television network evolution in Band III, IV and V will be driven by a wide choice of services that will include HDTV, mobile TV, interactive and data services, and portable reception. Ultimately, however, the market will determine which of these services are offered to viewers. Service offerings will differ from country to country based on the needs of each market. The broadcast industry must work together For each service it will be necessary to make choices regarding such issues as the type of reception (rooftop, indoor, outdoor, mobile, handheld), the area to be covered and the system to adopt (DVBT, DVB-H, DMB). A trade-off between multiplex capacity, coverage quality and radiation characteristics will be needed; the compromise made is related to service quality, number of potential viewers and transmission costs. In addition a choice needs to be made about the type of network (use of existing sites and/or new or additional sites, SFN, MFN). Broadcasters and/or network operators should discuss these issues and, where appropriate, make agreements with receiver manufactures to ensure that adequate types of receivers are available in sufficient quantities and in time. Regulatory framework needs to be clearly defined The use of Bands III, IV / V is heavily regulated by international agreements such as the ITU Radio Regulations and the GE06 Agreement. The European Commission has put forward distinct policies about the use of Digital Dividend, favouring a market-led approach to its allocation. The possibility exists to use parts of Band IV/V for non-broadcasting services, such as mobile communication systems (UMTS). At the last ITU World Radiocommunications Conference many countries have agreed to open channels 61 to 69 for such services. However, compatibility studies between digital broadcasting and non-broadcasting services are currently underway given the serious concerns about the consequences of mixing broadcast services with two-way transmissions. The results of these studies will be presented at the next ITU World Radiocommunications Conference in 2011. The broadcast community needs to follow developments regarding the application of the “Digital Dividend” carefully Decisions made by national administrations to reserve a sub-band for particular services would require re-planning and result in changes and restrictions to existing and planned services. Such developments should be followed carefully and consequences in costs and coverage should be analysed. Furthermore, as long as no clear national decisions are made about the use of the channels 61 to 69, implementation of digital terrestrial television in these channels should be avoided as far as possible.
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The developments on the use of low power or license-exempt applications in Band IV/V are of considerable concern and should be followed carefully to ensure against interference to digital broadcasting services. Viewers need to be educated about network changes Introduction of new services or modifying networks is complex and requires careful preparation. Changes may be needed to radiation characteristics, system variants and compression or transmission systems and additional transmitting sites and additional multiplexes may have to be installed. Most of these network changes will affect viewers and their ability to receive television services. Furthermore, existing receiving antennas may not be suitable for new services due to the frequency range for which the antenna has been designed or because of its bearing. Excellent communication to the public to prepare them for network changes is essential. Most network changes will have at minimum an impact on a few households and may have an effect on all households. Accurate coverage predictions are important in order to judge the effect of network changes in the area concerned and to inform the public about the opportunities for receiving new services or to retain reception of existing services. Improve reception through enhanced receiving antennas Reception can be improved at a receiving location by use of better receiving antennas, whether for roof-top, indoor or handheld reception. Extendable antennas can improve handheld reception while so-called ‘active’ antennas are best for indoor reception and use of antenna amplifiers and antennas with more directivity and gain can improve rooftop reception. The use of an active antenna is facilitated by the integration of a switchable 5 V power supply on the antenna output connector in DTT receivers. Plan carefully for the future When replacing transmitting antennas, the new antennas should be of a modern design with generally improved frequency dependent characteristics. Single frequency networks (SFNs) are an efficient way to provide coverage for portable (indoor) and mobile reception over large areas. However, SFN planning is complex and great care is needed to avoid self interference and so-called ‘0 dB echo’ interference. If additional multiplexes are expected to be introduced in the future, it is advantageous to take extra space and capacity into account in the design and layout of transmitter buildings, antennas and mains electricity power supply. Later extensions to the network risk generating high costs as existing equipment is made redundant and replaced. Networks will need to evolve in the future to meet the service requirements of each market. It is for the broadcast industry to ensure that it is prepared to meet these challenges.
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References 1. EBU doc. I37-2006: Guidelines for the RRC-06. EBU, Geneva 2. EBU doc. I39-2004: Maximizing the quality of conventional quality broadcasting in the flat panel environment. EBU, Geneva 3. ITU-R Recommendation BT.1368-7 Planning criteria for digital terrestrial television services in the VHF/UHF bands 4. DigiTAG Web Letter October 2007 #64: HD on the terrestrial platform 5. DigiTAG Internal Web Letter, February 2008: Update on the proposed DVB-T2 specification 6. EBU doc. Tech 3317, version 2: Planning parameters for hand-held reception, concerning the use of DVB-H and T-DMB in Bands III, IV, V and 1.5 GHz. EBU, July 2007 7. EBU doc. Tech. 3327, Network aspects for DVB-H and T-DMB. EBU, April 2008 8. The Effects of a Market-Based Approach to Spectrum Management of UHF and the Impact on Digital Terrestrial Broadcasting. Oliver & Ohlbaum Associates Ltd and DotEcon Ltd, 27 February 2008 9.
GE06 – overview of the second session (RRC-06) and the main features for broadcasters; Terry O’Leary, Elena Puigrefagut and Walid Sami. EBU Technical Review No 308, October 2006
10. EBU BPN 083 Broadcasting aspects relating to the procedures for Coordination and Plan Conformity Agreement in the GE06 Agreement, November 2007 11. Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions; on accelerating the transition from analogue to digital broadcasting COM(2005) 204 final, Brussels, 24.05.2005 12. Implementation of the Digital Dividend-technical constraints to be taken into account; Jan Doeven. EBU Technical Review No 309, January 2007 13. Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions. Reaping the full benefits of the digital dividend in Europe: A common approach to the use of the spectrum released by the digital switchover; COM(2007) 700 final, Brussels, 13.11.2007 14. EBU View. How should the digital dividend be used? Long-term public interest versus shortterm profit. 15. ECC Report 116 The possibilities and consequences of converting GE06 DVB-T allotments/assignments in Band III into T-DAB allotments/assignments, Athens, February 2008
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16. Final Report from CEPT to the European Commission in response to the Mandate on: compatibility issues between “cellular / low power transmitter” networks and “larger coverage / high power / tower” type of networks (also referred to as Report A), 30 March 2007 17. Final Report from CEPT to the EC on Technical feasibility of harmonising a sub-band of bands IV and V for Fixed/Mobile applications (including uplinks), minimising the impact on GE06 (also referred to as Report B), 18 January 2008 18. CEPT Supplementary Report (to Report B) to ECC; Technical options for the use of a harmonized sub-band in the band 470-862 MHz for fixed/mobile applications (including uplinks) (also referred to as Supplementary Report to Report B), 20 February 2008 19. A preliminary assessment of the feasibility of fitting new/future applications/services into non-harmonised spectrum of the digital dividend (namely the so-called "white spots" between allotments) (also referred to as Report C), Expected in June 2008 20. EBU BPN 075 Single Frequency Network Maintenance, March 2007 21. EBU BPN 037 Final Report on Statistical Multiplexing, January 2001 22. EBU BPN 066 Guide on SFN Frequency Planning and Network Implementation with regard to T-DAB and DVB-T, July 2005 23. Planning for mobile multimedia networks (VHF, UHF and L-band); Brian Tait (Arqiva)), presentation at EBU Forecast, November 2007
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