High-density SFNs the future of TV?


The phenomenal growth of mobile wireless broadband services will propel digital broadcasting into a new era, says network specialist Broadcast Australia. Driven largely by popular consumer devices such as the Apple iPhone, consumer expectation for next-generation services—including television—on portable and mobile devices will prompt savvy broadcasters to re-examine network design and operation.

“Our experience suggests that the future of television viewing will incorporate an increasing range of portable and mobile devices, such as netbooks, high-tech phones and the new breed of low cost portable TVs,” says Chris Jaeger, Managing Director Broadcast Australia International Business.

“Almost every country in the world is experiencing the same massive uptake of mobile wireless broadband services. This is setting the precedent for portable and mobile connectivity; the average consumer will expect to have access to all multimedia and entertainment services just about anywhere. It also has the potential to introduce TV to a whole new range of viewers—particularly those in less advantaged communities who can afford the new range of receivers, but also by virtue of exciting new digital content.”


Network coverage

Jaeger warns, however, that if digital television service providers want to leverage this opportunity, they need to ensure there is adequate network coverage. “Mobile wireless broadband services are designed to penetrate into buildings, and are moreover often carried by dedicated infrastructure indoors,” he says. “Conventional broadcast television networks, on the other hand, are typically designed for fixed reception by an external antenna. If reception on a mobile or portable device is achieved in this environment it is simply fortuitous.”

Broadcasting to portable and mobile devices injects additional complexity into network planning, as devices are likely to have low-performance receive antennas at variable orientation. In order to address challenges such as reduced antenna height, building penetration, reduced receive antenna gain, and higher required location availability, mobile TV trials have shown that field strengths need to be in excess of 30dB higher than in a fixed-reception environment.



According to Broadcast Australia, the most practical means of achieving such a high grade of coverage is to deploy a high-density distributed transmission network—essentially a single-frequency network (SFN) comprising multiple low-power transmission sites that together provide a consistently high signal level across the entire coverage area. Such a network also delivers signals from multiple directions, thereby improving location availability and reducing the impact of building clutter.

“We have done a lot of work on using high-density SFNs for mobile TV, but there is also a very real argument for deploying standard and high-definition television broadcast networks based on the same architecture,” Jaeger says. “This would allow anyone with an appropriate device to receive television on their portable computers or other portable TV devices now becoming widely available at very low prices.”

Jaeger adds that a high-density distributed transmission network would also address numerous other digital television reception challenges, most notably reception in high-density living environments. Multilevel residential condominiums in cities such as Singapore and Hong Kong are typically serviced by master antenna TV systems, which need to be re-engineered to carry digital TV signals. In some cases they need to be replaced at not inconsequential cost.


Cost implications

If residents could receive digital television via a simple indoor ‘rabbit ear’ antenna or USB type receiver, there would be no need to undertake the significant cost of upgrading the vast number of master antenna systems. A study by Broadcast Australia subsidiary, Singapore Digital, found that the cost to deploy a distributed transmission network in Singapore was less than a quarter of that of upgrading master antenna TV systems across the city state.

“We are entering a new era of terrestrial broadcasting—an era when the variety of ways in which television is experienced is escalating dramatically,” Jaeger says. “Viewing habits are changing and it makes sense to plan for a ‘next-generation’ transmission network that will satisfy all demands simultaneously.”

A distributed transmission network can provide a common network infrastructure for broadcasting HD and SDTV signals for fixed, portable and mobile reception, without the need for external receive antennas. This, says Jaeger, not only paves the way for portable and mobile TV, but will assist the television broadcasting industry to keep pace with the exciting and dynamic services supported by mobile wireless broadband networks. “The extraordinary success of the iPhone is an indication of habits and expectations to come,” Jaeger says. “Television broadcasters have the opportunity to adapt their thinking now and be ready to catch the wave.”

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