Australian DTV Delivers ‘Digital Difference’


Australian DTV Delivers ‘Digital Difference’


Mike Dallimore Broadcast Australia


For around a decade, Broadcast Australia has been deploying a nationwide digital broadcast network for DTT services in Australia. Mike Dallimore, Broadcast Australia Vice President, International Business Development, explores the challenges of the massive project, providing insight into key lessons learnt and what constitutes the ‘digital difference’.


Comprising in excess of 500 services, Broadcast Australia’s nationwide digital broadcast network provides fully managed television transmission services to Australia’s two national broadcasters and several regional commercial stations. The decade-long deployment has been a digital journey of untold challenge and engineering effort, demanding technologies to be pioneered and new skills accumulated.


Catalysed by a federal government mandate to commence DTV broadcasting by 01/01/01, Australia was one of the first countries in the world to deploy DVB-T services. Field trials of the fledgling DVB-T standard were carried out in Sydney and Canberra in the late 1990s, around the time of the standard’s adoption by the national communications regulator, the Australian Communications and Media Authority (ACMA). Now, some ten years later, nearly 100 per cent of the widely dispersed Australian population has access to DTTB services and a great deal has been learnt about the planning, design, deployment and ongoing management of digital broadcast networks.


Start with Spectrum


As a starting point, spectrum was assigned for DTTB services in both the VHF and UHF bands, which are also used for analogue television services in Australia. There followed an important period of network coverage planning and system design. ACMA had stipulated that digital coverage must equal that of existing analogue services, and that analogue and digital services would be simulcast in the years before analogue was switched off.


Sophisticated software tools were used to model coverage, accommodating the well-documented ‘cliff effect’ in digital systems, where the picture quality abruptly deteriorates to become unwatchable. It was also necessary to protect the


existing analogue channels from interference by the digital services. In many cases adjacent channels were being used; therefore where necessary the digital signal was power limited to prevent interference. To help control interference further and streamline infrastructure requirements, it was assumed that multiple digital and analogue channels would be broadcast via a combined antenna system.


In addition, the spectrum plan identified around 20 areas nationally to be covered using single-frequency networks (SFNs), where multiple transmission sites operate on the same frequency. Here, the content, frequency and timing of the signal at the receiver are critical. Again, software modelling tools were used to design these sophisticated systems, where the location of transmission sites, ERP levels and signal modulation schemes were predominantly fixed, leaving site launch timing as the main variable for tuning the performance of the SFN.


Digital Difference


It soon became clear that digital technology is vastly different from analogue, particularly from a system design and integration point of view. The program signal undergoes several digital processing steps before it is broadcast, including encoding and multiplexing. Achieving interoperability between the different electronic elements of the digital system demanded extensive equipment evaluation and trial integration. In the early days of DTTB, such equipment wasn’t necessarily provided by the same vendor, making integration more complex.


This difficulty was raised another degree by the shift towards IT-based technology and systems. For an industry accustomed to relatively simple analogue instruments that had been in place for up to 20 years, the transition to highly sophisticated digital ‘black boxes’ required a


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