At 50 kilowatt ERP compared to a typical 10 kilowatts ERP in other countries, Australia used detailed channel plans and an all industry approach to achieve maximum licence area coverage from a single high powered site with limited overspill. Working closely with the regulator the initial power levels offered were proved to be inadequate and was significantly increased as CRA proved that could be achieved by maintaining protection ratios to adjacent television channels.
Radio in Australia is traditionally broadcast at high power in analogue and the industry target was to ensure good indoor and outdoor DAB+ coverage.
Coverage was predicted based on target field strength of 63 dBµV/m at 1.5m for urban indoor coverage. Commercial radio and public service radio have the same power and the same coverage area for digital radio. The digital radio signal is transmitted in Band III from the same location as Australian television signals without causing interference. It is not possible to site high power transmitters elsewhere without causing interference to television services.
The industry was highly motivated to work together to find the best coverage because unlike their analogue services, the digital radio operational costs for the operation of the antenna in four of the five sites are shared by commercial and public broadcasters.
One high powered primary site in each licence area, with lower powered infills has been the successful model in the five state metropolitan capitals covering 60% of the Australian population. Ongoing testing and feedback identified a number of areas where in-building reception could be improved or extended at the boundary of the licence area. The commercial radio industry funded the development and trial of a DAB+ On Channel Repeater (OCR) to fill black spots in coverage from the main DAB+ transmitter.
The OCR has been tested successfully in the Melbourne central business district and has resulted in significant improvement of in-building reception and outdoor coverage in the city.
A total of 16 infill sites across the five metropolitan markets have been identified to address coverage black spots. Low powered on channel repeaters between 300 W – 500 W ERP per ensemble will provide enhanced coverage in these areas.
The costs to all broadcasters were significantly reduced using this model. One high powered DAB+ transmitter, with multiple radio stations transmitting on the same frequency, sharing the cost of the single transmission is both spectrum efficient and cost effective in its savings of infrastructure and operational costs, including the big ticket items of power, connectivity and site leases.
However, it is important in any digital radio policy that broadcasters have the first option to own and operate the multiplex. In Australia, broadcasters set up joint venture companies to hold the spectrum licence and operate the multiplex in each licence area.
Each broadcasting studio has its own DAB+ encoders connected to the multiplexer. Each broadcaster is allocated a proportion of the allocated bandwidth in the ensemble. They provide their own transmission link to the ensemble multiplexer, which is located at the transmission site. Each broadcaster has purchased its own studio equipment and operates and maintains that equipment.
The connection between the service multiplexers at the studio and the ensemble multiplexer is via Internet Protocol on a range of digital links including microwave and Telco circuits.
When developing industry policy, broadcasters must insist on access to Band III spectrum and transmission powers that allow effective coverage across the whole market and incentives to encourage their investment.
One of the key incentives for Australian commercial broadcasters was that each existing commercial analogue station was given 128 kilobits/sec of capacity free as a basic entitlement. If a radio broadcaster had two stations they were given 256 kilobits/sec. The only restriction placed on it was to use it or lose it.
To protect the investment, while broadcasters are carrying two costs of broadcasting – analogue and digital – in Australia no new entrants can come into the digital radio market for six years, to allow time for existing broadcasters to move listeners to digital radio and find new revenue to cover costs.
Australia’s immense geographical size (similar to that of the United States without Alaska but with only 23 million people), coupled with contrasting terrain and weather, requires ongoing planning for digital radio in regional areas. Permanent high powered digital radio services are currently available in five of the 105 Australian radio licence areas. Two low powered trials in Canberra and Darwin are providing valuable technical information about cost effective population and road coverage in regional, less built up terrains and differing climatic conditions.
After a complex channel planning and cost modelling exercise, the radio industry has put forward a funding proposal to the Federal Government for the regional rollout of digital radio based on a high powered approach, with additional repeaters to fill coverage and a shared single ensemble in most areas.
Chief Executive Officer, Commercial Radio Australia
Chairperson of the WorldDMB Asia Pacific Committee