The transition from analogue to digital television

By Alfredo Magenta

One of the most important inventions of the twentieth century was broadcasting with analogue radio and television systems. The last few years, however, have seen the birth of digital broadcasting. Migration from analogue to digital techniques has started. There are a number of migration paths to choose from. Each country will follow its own switch-over path, often influenced by its broadcasting legacy. But much more than a technical migration will be involved. Considering the role of television and radio in modern society, the switchover can be a complex process with economic, social and political implications.

Changing from analogue to digital affects all links in the broadcasting value chain — content, production, transmission and reception — all of which require technical upgrading to support digital broadcasting. It is important to remember that, as in many other industries, changes are brought through the emergence and exploitation of new technologies, based on business demand. Market forces and consumer demand will eventually drive the digitization of broadcasting. With this in mind, it is worth first briefly examining the benefits that digitization offers.

Technical benefits of digitization

The primary benefit of digital television is greater control over channel performance. The overall performance of an analogue communications channel is dictated largely by the characteristics of the channel itself. The overall performance of digital systems is largely a factor of the quality of the conversion processes (analogue to digital and vice-versa), provided that the capabilities of the channel are not exceeded. As a result, the performance of analogue systems tends to deteriorate as the channel performance deteriorates, while digital systems remain as defined by the conversion process until they fail completely. Unfortunately, though, this means that the subjective effects of channel performance on digital systems are much more obtrusive when working close to the ultimate channel capacity.

The ability of digital systems to compress data into a smaller space is another relevant factor. In the broadcasting context, this means the use of compression coding techniques which allow relatively high sound and picture quality to be accommodated in a much smaller channel bandwidth. A related benefit is the ability to trade between quality (the degree of compression) and spectral occupancy, more or less at will.

Taking the two factors together, under certain conditions, approximately five digital terrestrial television channels (plus ancillary data) occupy the same amount of spectrum as one analogue channel. In addition, the transmitter power per channel is — in round figures — a tenth of that for an analogue channel.

Furthermore, digital systems facilitate the addition of ancillary data services, allowing such features as automatic or semi-automatic tuning, conditional access, and the inclusion of supplementary (or even completely unrelated) data streams. Single-frequency networks and error correction are two other important features.

The choice of digital technology can be affected by the lack of compatibility between digital and analogue broadcast transmission systems. While this can cause some transition problems, it is generally advantageous, because the digital systems have been optimized against their own technical and financial considerations and are not compromised by having to be compatible with less advanced existing technologies.

Considering that any technical transition strategy must work within certain commercial and regulatory imperatives, a simple solution can be to allocate a new band of spectrum to accommodate the new digital programmes. In the fullness of time, as migration takes place, the old spectrum can be given up. If necessary, and with careful equipment design, it would eventually be possible to transfer the digital services back to the original band. Eureka 147 DAB has been introduced in Europe in this way. The technical characteristics of the system even allow different frequency bands to be used in different countries.

Given the lower demands of digital systems in both bandwidth and power, there is scope for digital transmissions to fit into bands that are already occupied by other services. Where a digital transmission can be made to occupy the same amount of spectrum and have the same interference impact as an analogue channel, it might be possible simply to replace an existing analogue service with a digital one, or to use an existing but unused frequency allocation.

Commercial considerations

The major commercial advantage of digital services is the ability to offer a greater range and diversity of services at lower transmitter power, and without the need for additional spectrum. This capability is likely to be the most attractive aspect of digital television from the broadcaster’s perspective.

New commercial opportunities will exist. However, there could also be commercial drawbacks. For any individual broadcaster, there is, for example, the cost of replacing equipment and it is unlikely that this will be offset by increased revenue (either through advertising or subsidies). It is also necessary to persuade the audience to invest in new receivers, or set-top boxes, at acceptable prices. To do this, it is necessary either to offer a wider range of high quality programming and improved formats, such as wide screen and high definition television. Warning consumers that the analogue service will disappear also stimulates demand. In certain cases the intervention of governments can be crucial. In some environments, spectral allocations are traded between broadcasters, including new entrants. The availability of more channels in such an environment will, in the short term at least, depress the value of the existing allocations.

Any commercial transition strategy will probably require that analogue versions of existing programme streams remain available until a high level of market penetration of digital receivers is achieved. Typically, this will mean that digital and analogue versions of the same programmes are present simultaneously during the transition period. Various technical strategies can be, and have been, deployed to achieve this.

The market forces and consumer demand that are driving the switchover to digital pose a major challenge to industry. It is also crucial to inform consumers about their options so that they know when to migrate to the new system. A successful switchover will be facilitated by coordinated action from the numerous players involved, including broadcasters, equipment manufacturers, retailers and governments.

Regulatory matters

The three ITU Sectors, each within its own sphere of competence, are responsible for activities and studies relating to broadcasting. In the first half of the twentieth century, these activities included standardization work for analogue television systems, and for digital systems in the latter part of the century.

ITU will continue to play a pivotal role in the regulation of spectrum usage and broadcasting technologies. A debate on spectrum aspects of the switchover to digital has already been launched among some administrations within their spectrum policy frameworks. The prime objective is to encourage efficient and flexible spectrum usage, while preserving the service mission of broadcasting. Among other things, the debate will address the economic value of spectrum allocated to terrestrial and satellite broadcasting services, and the transparency needed in setting this value.

ITU’s broadcasting planning conferences are good examples of how system development is encouraged when flexibility is introduced into the international regulatory framework. For instance, the agreement forged at Stockholm in 1961 (ST61) has been accommodating the needs of analogue broadcasting in Europe successfully for almost four decades. And the Regional Radiocommunication Conference (RRC-04/06) is planning the transition from analogue to digital broadcasting for 119 countries.

It is not envisaged that ITU should be involved at the level of, for example, setting common switch-off dates or prohibiting sales of analogue receivers. However, national digital broadcasting markets and policies will continue to be monitored. Policy interventions by ITU Member States should be transparent, justified, proportionate, and timely, so as to minimize the risks of market distortion. They should also be formulated according to clearly defined and specific policy goals, and be non-discriminatory and technologically neutral. Achieving these aims requires careful assessment of the impact of policy changes, as well as monitoring of policy implementation and market evolution.

Consumers will decide

It is now becoming possible for just one device in the home to cover all broadcasting bands and all systems, at an acceptable price. And the more devices are sold, the lower the price will get. This will also encourage the expansion of services and applications, opening the door to the creation of a Universal Mobile Telecommunication System (UMTS) — or IMT-2000 — that is integrated with other services. Through technological convergence, truly new types of media will have been achieved.

Alfredo Magenta, Chairman, ITU Radiocommunication Study Group 6 (Broadcasting services)

There are many players during transition periods between one dominant technology and another, but the past has shown that the principal actors are the final users of new services. They will be the driving force behind the change from analogue to digital broadcasting, even while they are influenced by the policies of administrations, service providers and manufacturers. What is very important and urgent, however, is coordination among all these stakeholders. If consumers are ready to buy new equipment that manufacturers have produced, it is very important for administrations to have in place a frequency planning programme, and for broadcasters to have prepared attractive content. Coordination of these efforts will determine how fast the transition will be made, and will lead to wider consumer choice and enhanced competition.

When (through economies of scale) digital receivers become cheap enough to replace all their analogue predecessors around the world, then the real convergence between services will have come to fruition. That will be the basis for the complete development of UMTS (IMT-2000). People everywhere will be able to send and receive information anywhere, in any language, while at work, at home or on the move. The global information society will truly have arrived.