By spreading the transmission across a greater number of lower- powered sites, HDNs effectively overcome the problems traditionally associated with reception for mobile and portable devices.

Market indications clearly demonstrate that the future of TV viewing will incorporate an increasing range of portable and mobile devices including high-tech phones and low-cost personal media players (PMPs). As the price of these devices has fallen in recent times, their numbers in the marketplace have grown. This, in conjunction with the recent growth of mobile wireless broadband services, is leading to a corresponding escalation in user demand for a full range of broadcast services to match the capabilities of this new breed of mobile and portable devices.

Customers are naturally disappointed if they buy a device that has been marketed as capable of receiving digital TV (DTV), only to find they are restricted to using the device in specific areas, or that the networks are not providing the services they want to enjoy. Consequently, broadcasters are coming under increasing pressure from viewers to improve the network infrastructure to accommodate changing viewing habits. The general expectation is for TV reception to be available wherever there is mobile-phone coverage; an achievement just not possible through existing terrestrial DTV networks.

One innovative way DTV service providers can potentially address this demand is through the adoption of emerging high-density networks (HDNs). HDNs are essentially single-frequency networks comprising multiple low-power transmission sites that together provide a consistently high signal intensity level across the entire coverage area.

The HDN advantage

A HDN differs from a classic TV transmission network in both its make-up and its purpose. Conventional broadcasting networks rely on relatively few high-powered transmission sites, the signals from which are designed to be received by comparatively sophisticated antennas, placed in elevated outdoor locations (rooftops, for example), and correctly oriented towards the transmission site.

On the other hand, with their low-performance receive antennas positioned at variable orientations and low elevation, reception for hand-held or portable devices tends to be fortuitous at best from these existing networks.

By spreading the transmission across a greater number of lower- powered sites, HDNs effectively overcome the problems traditionally associated with reception for mobile and portable devices. HDNs also permit conventional TVs to receive the broadcast signals via indoor antennas, rather than relying on properly oriented large external antennas.

While this is a minimal consideration for viewers living in relatively low-density residential environments, it can become a major benefit for audiences in high-density apartment complexes, which rely on master antenna TV systems (MATVs).

MATVs typically comprise a single antenna on the roof of the building that splits and boosts the signal for individual apartment feeds. With the migration from analogue to digital broadcasting, many of these MATVs are incapable of supporting digital signals, and so need to be upgraded. Offering viewers the ability to receive broadcast signals directly in their apartments using a local indoor antenna, HDNs can provide a cost-effective alternative to the costly and disruptive process of replacing each MATV system in every building. While this latter driver puts the responsibility for the cost of upgrades with the broadcaster, rather than the consumer, studies in high-density areas, such as Singapore, have shown that the overall cost of providing a HDN would be substantially less than that of upgrading the MATV systems.

Reaching the masses

The capability of HDNs to address the challenge of broadcasting to mobile and portable devices, as well as conventional TV sets without external antennas, is indicative of the markets for which HDNs are likely to provide a good fit. These include cities or countries where high-density living prevails, and areas where there are likely to be a significant number of portable devices.

For countries yet to take the digital plunge, especially in the South-east Asian region, there are many advantages to considering the HDN concept as a viable entry move into the DTV marketplace. Following the Australian model of establishing a more conventional DTV infrastructure would not necessarily best meet the requirements of many of these countries. HDNs would work well for Singapore and Hong Kong, where the majority of the population lives in high-density residential apartment buildings.

Similarly, there is a compelling argument for HDN deployment in countries like India, which historically has suffered a low incidence of TV ownership. Here, many people cannot afford to buy conventional TV sets and are more likely to buy cheaper portable devices that are now flooding the market. HDNs provide the opportunity to reach a hitherto virtually untapped audience, and could even present an innovative alternative resolution to the country's limited Internet access by means of infocasting/ datacasting services.

HDNs can also be used to improve the reception performance of existing digital networks in many markets where spectrum may be limited, and where multiplex payloads can be varied to provide more content across part or all of the market.

Network design is critical to ensure that the right coverage is achieved to adequately address such reception challenges presented by lower antenna height, reduced receive antenna gain, and building penetration. Here, a graded signal intensity is crucial for areas where there is a high degree of 'clutter' interference from topography and man-made structures.

Mobile-TV trials have shown that field strengths need to be in excess of 3OdB higher than in a fixed-reception environment, if good-quality reception is to be enjoyed on mobile or portable devices. While a classic network cannot deliver this uniformly across a service area, a HDN can do so.

The broad picture

A further challenge to HDN service providers is to offer the right customer proposition, both in terms of content and pricing. It is anticipated that content packages will vary widely between markets, and be very dependent on the specific interests of the viewers in each area. Content can include highly popular material, as well as narrow-casting of niche-interest programming, such as ethnic community services and some sports coverage. Free-to-air networks can also contemplate the HDN advantage of being able to provide good and uniform coverage to portable devices and PC dongles.

The HDN model should be viewed as a complementary alternative, rather than competition to IPTV and TV-over-3C services. With broadcast platforms it does not matter if there is one viewer, or a million viewers, as it is a one-way transmission effectively without an audience limitation. The capacity constraints of 3G unicast or multicast, by comparison, make them less suitable for high-demand programmes.

It makes sense, therefore, to utilize IPTV, 3C and streaming to provide services for specialist low-demand content often referred to as 'long tail' programming and video-on-demand. By allocating these niche programmes to a more suitable delivery platform, spectrum can be freed up on the HDN networks for broadcasting more popular content, thereby providing a better overall service to the viewer.

HDNs offer the promise of TV reception in a wide variety of locations on a broad range of portable, mobile and large-screen devices, and as such they will play an increasing role in the future of DTV. With a multitude of platforms accessible, it is inevitable that market forces will ensure that the content provided will be made available through the most suitable medium for the target audience. HDNs are set to occupy a prime part of this broad picture, helping to provide an enhanced TV-viewing experience to a wider audience across the globe.

(Courtesy: APB)