On 31 August 2012, the ACMA undertook an informal consultation process on the proposed approach for the digital television (DTV) broadcast coverage area, which closed on 28 September 2012.
In this response, the ACMA addresses technical issues raised by the respondents about the proposed methodology of generating maps under certain parts of the Radiocommunications Advisory Guidelines (Managing Interference from Transmitters - 700 MHz Band) 2012.
Two stakeholders questioned whether maps produced under part 3.2 of the Radiocommunications Advisory Guidelines (Managing Interference from Transmitters - 700 MHz Band) 2012 would be published as final maps or whether the ACMA intends to provide ongoing updates to any published maps as a result of future variation to DTV station transmission parameters.
The ACMA does not intend to provide ongoing updates to the published maps once they are finalised. This provides certainty to all stakeholders, especially spectrum licensees who will need to implement measures to comply with the conditions of their licence.
Variations to existing DTV services are not expected to have a significant effect on the maps. In the highest population growth areas, where variations (if any) would be most likely, buffers have already been applied to DTV coverage edges, through the use of horizontal radiation pattern (HRP) envelopes and the expansion of the maps to aggregate any partially covered populated centres (see below). New DTV services will need to be planned to be able to operate in the new spectrum environment. This applies to any future retransmission services, which will be planned so that the received signal is strong enough to overcome any interference due to out-of-band emissions.
The ACMA confirms that 'coverage' areas of in-band links (IBLs) have not been included, since their purpose is to provide an off-air input feed to another television broadcasting transmission site. At such sites there are generally access restrictions and out-of-band emissions from ubiquitous handsets are not expected to be an issue.
The exception is Bowen Environs IBL which, at the time of its introduction, was also intended to provide coverage to populations at the foot of Mt Pring, in addition to providing off-air input feeds to Collinsville North IBL and Bowen Town. Unlike other IBLs, Bowen Environs is able to cover areas once covered by discontinued sites, namely Bowen (Sprole Castle). Despite significant terrain shielding to the north of Summer Hill, there are very few people living north of Mt Pring and Mt Roundback.
One stakeholder questioned the use of the term 'maximum server' when describing the analysis used by the ACMA to determine DTV coverage areas. The 'maximum server' analysis identifies a particular transmission site (transmitting a suite of DTV services) as the 'maximum server' in the areas in which that site provides higher signal field strengths than any other site. Therefore, for any particular site, the 'maximum server' coverage area is the area in which that site provides higher signal field strengths than any other site.
One stakeholder sought clarification from the ACMA on whether the minimum median field strength (@ 10 m) of 54 dBµV/m applied to alternative services in the 'maximum server' analysis. The ACMA confirms that all services in the 'maximum server' analysis have coverage boundaries at the minimum median field strength of 54 dBµV/m. A limitation of the signal prediction software is that a single minimum median field strength value must be used for the maximum server analysis. Different values cannot be used for each individual site involved in the analysis.
One stakeholder stated that 'actual clutter in a service area often is a determining factor that causes degradation of DTV signal quality whereby viewers orientate their receive antennas toward their desired transmitter which may not necessarily be the highest field strength as determined by the maximum server prediction analysis'.
For this reason, the ACMA has stated in the coverage area methodology paper that 'in [densely populated] areas it may not be reasonable to assume that there is a boundary-on one side of which viewers receive signals from a 'Block E' site and on the other side of which viewers receive signals from another site.
Therefore, the ACMA concluded that, on a case-by-case basis, certain adjoining urban centres and localities (UCLs) should be aggregated to the Block E maximum server coverage area'. This measure addresses most of the situations where building clutter causes a viewer to orientate their receive antenna towards a site which does not provide the highest field strength as predicted by the 'maximum server' analysis.
An exception would be dense vegetation in rural areas, but this would apply to far fewer viewers. Note that the the 'example maps' document on the ACMA engage post provides a detailed list of the coverage areas to which UCLs or state suburbs (SSCs) have been aggregated to 'maximum server' coverage areas.
One stakeholder proposed the addition of small areas to the Block E coverage areas, in which reception is claimed to be problematic from main (that is, non-Block E) stations. The ACMA agrees with these suggestions and will include:
- Kurrimine Beach to the Mission Beach coverage
- Mount St John, Bohle and Garbutt to the Townsville North coverage
- Hunter Street West and Wulguru South to the Stuart coverage
- The river valley south of Maclean to the Maclean/Ashby coverage
- The area between Mullaway and Arrawarra Headland to the Woolgoolga coverage
- The area between Mount Kembla and Cordeax Heights to the Mount Kembla coverage
- Glen Ayr to the Mudgee Town coverage
- Areas south-west of the Colac transmitter site to the Colac coverage
- Deviot, Swan Point and Gravelly Point to the Hillwood coverage.
One respondent suggested that measures to protect DTV reception should be incorporated into Australian Standard AS1417-2012, and made compulsory under the Broadcasting Act 1992. The suggested measures included:
- the standardisation of antennas tuned to receive particular channel blocks
- the standardisation of masthead amplifiers that include filters cutting off frequencies above 694 MHz, due to the increased susceptibility to receiver overload when masthead amplifiers are connected.
The use of in-line filters, along with frequency-selective masthead amplifiers and antennas tuned to particular channel blocks, are all potential mitigation measures that may be available to viewers in the unexpected event of interference between spectrum-licensed 700 MHz band transmitters and DTV receivers. The ACMA appreciates the suggestions made, and notes that such mitigation measures fall outside the scope of the development of the technical conditions that need to be met by spectrum licensees.
The ACMA wishes to thank all respondents for their comments, and has taken all comments into consideration in finalising the methodology for production of Block E digital television coverage maps and the 700 MHz band exclusion zone maps. The final Block E coverage maps are available here.