Comparison of two restack planning approaches
Engineering Report TPS 2011/01
FEBRUARY 2011
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acma | iii
Contents (Continued)
Executive summary i
1 Introduction 1
2 Channel planning and assignment assumptions 2
2.1 Channel planning assumptions 2
2.2 Channel assignment assumptions 3
2.3 General observations on channel planning 4
3 Comparison Process 13
3.1 Process and metrics for comparing digital channel plans 13
3.2 Other issues that are less able to be quantified 13
4 Analysis/Discussion 14
4.1 Sites requiring changes 14
4.2 VHF ↔ UHF band changes 17
4.3 Channel changes 17
4.4 Size of channel moves 23
4.5 Use of Band IV channels at sites that do not have Band IV services 27
4.6 Use of channel 51 28
4.7 Changes to off-air input channels 29
4.8 Adjacent channel off-air feeds 31
4.9 Combiners 33
4.10 UHF channel span 35
4.11 Services transmitted from significantly different sites or antennas 36
5 Summary 38
APPENDIX A – INDICATIVE “MINIMUM MOVES” PLAN 40
APPENDIX B – INDICATIVE “BLOCK” PLAN 47
ANNEX 1 – Derived antenna data for digital television services 55
ANNEX 2 – Location of transmitter sites in each switchover area 82
ANNEX 3 – Assumed input arrangements for digital television services 89
acma | 55Executive summary
This report[1] presents two indicative restacked digital channel plans for the Regional Queensland and Brisbane Licence Areas. Those plans provide examples of the “6 channel block” (Appendix A) and a “minimum moves” (Appendix B) planning approaches that were developed using common assumptions and which can be subjected to comparative analysis. Comparisons of basic characteristics of the two indicative plans are detailed in section 4 of the report and are summarised in section 5.
Cost and sequencing/implementation time comparisons are considered in separate reports.
Initial observations, in terms of the basic parameters evaluated, are that the scale of the differences is relatively small in comparison to the scale of the changes required to clear channels 52-69. This is borne out by the fact that the indicative minimum moves plan leads to 69.3% of services changing channels, which is approximately 10% less than the 79.8% of services that would change under the block plan approach. These changes affect nearly all of the 102 broadcaster, retransmission conversion and gap-filler transmission sites evaluated in this report. Eleven sites are unchanged under the minimum moves plan whereas four are unchanged under the block plan.
Changes at high power sites (of which there are 9 evaluated in this report) are expected to be particularly significant as the costs incurred at these sites are likely to be high. Under the minimum moves channel plan, three of these high power sites are unchanged, but all sites are changed under the block plan. Furthermore, five high power services at two sites change bands (VHF-to-UHF or UHF-to-VHF) under the minimum moves plan compared with the 11 high power services at five sites which change bands under the block plan.
One area where moderately large differences have been identified is the affect on off-air inputs. Off-air inputs are often used at repeater sites to receive the signal to be transmitted[2]. Under the block plan approximately 24% more sites would require changes to at least one off-air input channel.
A further issue with off-air inputs is that it may be more difficult to implement an off-air feed arrangement when the repeater output channel is adjacent to a channel that is carrying a weak, distant input signal. Such situations would occur more often under a minimum moves plan than under a block plan. The indicative channel plans show this adjacent channel off-air input issue arises for 8 broadcaster services under the minimum moves plan compared with 3 broadcaster services under the block plan. Analysis of 27 additional sites for proposed gap fillers and broadcaster funded retransmission conversions found that a further 6 services under the minimum moves plan and 2 services under the block plan respectively would have adjacent channel off-air inputs.
The observations made above and throughout this report provide a quantitative measure of the differences between practical implementations of the two planning approaches. The differences in the number of transmitter, combiner replacements and retunes and other changes have been used as inputs to derive estimates of cost and timing differences between the two planning approaches. Those derivations and analyses are the subject of separate companion reports.
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1 Introduction
This report provides two indicative restacked digital channel plans for broadcast sites within the Regional Queensland and Brisbane Licence Areas for the purpose of allowing case study comparisons to be performed on each indicative plan. In developing those plans adjacent parts of northern New South Wales were taken into account due to their influence on channel availability at sites in Queensland, but sites in more remote parts of Queensland were not included. The Regional Queensland and Brisbane region was chosen for this comparison study because it is large enough to yield statistics that will allow useful comparisons to be made between the two planning approaches. In addition at ACMA/industry meetings, it was accepted that the south-east Queensland area presents the most difficult planning task in Australia.
The purpose of the report is to present the two indicative example digital channel plans that are representative of the “6 channel block” and a “minimum moves” planning approaches and to present a range of initial comparisons of the plans. They do not however discuss cost and time-to-implement comparisons between the plans as those issues are covered in separate reports.
2 Channel planning and assignment assumptions
2.1 Channel planning assumptions
Appendix A and Appendix B present indicative, example channel plans using two different planning approaches, viz. “six channel block” and “minimum moves”, that were developed using the following common planning assumptions:
Clear all currently operating and planned services from the 694-820 MHz range;
Reserve 2 VHF Band III channels for future regional digital radio deployment (assumed for this comparison study to be channels 9 and 9A);
Identify 6 services at all sites in the Brisbane and Regional Queensland licence areas that have at least one broadcast service, except licence area overlap sites on the Gold and Sunshine Coasts where 9 services are to be identified;
Channels were identified at 75 broadcast (or hybrid[3]) sites and at an additional 27 retransmission conversion or gap filler sites;
Notional channels were also identified for sites in northern NSW that may affect channel selection at sites in Queensland;
Shift Brisbane high power SBS and one unassigned channel to VHF Band III (so that all Brisbane high power services are in Band III);
Consequential to making Brisbane a VHF Band III only site, VHF digital -to- VHF digital pairings between Brisbane and Wide Bay should be avoided (see section 2.3.3);
In choosing UHF channels at Wide Bay choose the lowest practical channels. (The current highest operating analog service is RTQ39);
Separate the current Gold Coast (Mount Tamborine) – Currumbin - Gold Coast Southern Hinterland (Mt Springbrook) Single Frequency Network (SFN) into two separate groups;
Separate the Sunshine Coast (Bald Knob) – Nambour - Noosa/Tewantin - Gympie (Black Mountain) - Gympie Town (Tozer Hill) SFN into two separate groups;
Set up co-channelling arrangements between Gold Coast and Sunshine Coast sites that avoid direct co-channelling between Mt Tamborine and Bald Knob national or Brisbane commercial services. (Co-channelling between regional commercial services may be acceptable since the patterns of each service point away from the other licence area);
Cairns region repeaters have been organised into three groups but with some (relatively minor) differences to the current DCP groupings. Notably Babinda was moved to a group that includes Herberton, Atherton and Mossman;
Proserpine area feed arrangements have been changed so that Proserpine feeds the current Flametree & Jubilee Pocket retransmission site via an on-channel repeater. Airlie Beach and Shute Harbour can then be fed by the Flametree & Jubilee Pocket site. (These changes mirror a proposal made by regional commercial broadcasters during discussions on Regional Queensland gap fillers and retransmission site conversions);
Further, the arrangement for feeding commercial (and unassigned) services in the Bowen and Collinsville area has been assumed to be revised. Bowen Town would be fed from a new link-fed Bowen (Summer Hill) site. Collinsville would be fed by a chain comprising Bowen (Summer Hill) - Collinsville North - Collinsville.
Continue current UHF planning practice which, wherever possible, attempts to place higher power services on lower UHF channels. This will tend to place low/moderate power services on the upper channels including channel 51;
Wherever practical Band IV channels were used at sites that currently have Band IV services, and conversely use of Band IV channels was avoided as far as possible at sites that currently only have Band V channels. (In particular use of Band IV channels at sites with no Band IV pedigree should be avoided at high population sites);
VHF channels should not be proposed at sites that do not have currently operating VHF services;
For the minimum moves approach changes between VHF and UHF bands were avoided. (For the block approach single band VHF only or UHF only channel selection is implicit in the definition of the planning approach).
2.2 Channel assignment assumptions
2.2.1 Block Plan
It is understood that an important principle of the block plan approach is to avoid first adjacent channel filtering for off-air fed commercial services. This assumes that national services do not require off-air feeds and/or are more able to accept satellite feeds, together with any associated higher costs or logistical issues. Therefore ABC and SBS services are placed on each edge of the block.
However, considerations about block edges and adjacent channel off-air inputs do not apply for VHF Band III channels, so current VHF assignments have been maintained (except where they fell on channels 9 or 9A which have been notionally identified for digital radio) . It is understood that there is no intention to “block convert” 6 channels (arguably 8 for Band III) in a single amplifier at broadcast repeater sites.
General rules
1/ Channel assignment for blocks B, C, D is: ABC, STQ, TNQ, RTQ, UA, SBS.
2/ Channel assignment for block E is: ABC46, STQ47, TNQ48, RTQ49, SBS50, UA51.
3/ For block A don’t change any currently operating services (unless they are on channels 9 or 9A) but, if possible, group national services together and, if possible, group commercial services together.
However minor changes to the assignment order were made in some cases to: maintain currently operating services on current channels except where this led to concerns about adjacent channel off-air feeds; or to optimise the plan for sequencing purposes[4].
2.2.2 Minimum moves plan
Avoid changing the assignments of any operating services (unless they are on channels 9 or 9A) that fall within the chosen channel set;
If channel 51 is used (unless used by an operating service) put the unassigned service on channel 51;
If common channels are being used at nearby sites maintain those relationships;
Where practical, make channel selections that avoid adjacent channel off-air feed situations[5];
Where necessary make assignments that would assist in improving the sequencing plan4.; and,
If no other guidelines apply, follow the order of current digital channels at the site.
2.3 General observations on channel planning
2.3.1 Brisbane/Gold Coast/Sunshine Coast SFNs
As noted earlier existing Sunshine Coast and Gold Coast region SFNs were broken into smaller groups of sites. Channel selections for those groups were arranged so that co-channelling of Mount Tamborine and Bald Knob services was limited to regional commercial services.
In pairing Mount Tamborine or Bald Knob channels with adjacent regional services attention was also paid to the different antenna patterns of different services at both Mount Tamborine and Bald Knob as this provides opportunities to achieve a more efficient re-use of channels.
2.3.2 Co-channel pairing of high power services around Brisbane
Compatibility studies of major services surrounding Brisbane were performed. The key outcome was that due to geographic adjacencies, or near adjacencies, many of the areas around Brisbane cannot operate with the same channels. From the viewpoint of channel re-use however the most important observations were that Richmond/Tweed and Darling Downs services can co-channel and Wide Bay and Southern Downs can co-channel. This is illustrated in Figure 2.1 through the use of common colours for major sites that are able to be co-channelled.
Figure 2.1: Map showing indicative coverage of major broadcast sites around Brisbane
To make best use of the observation that channels can be re-used at certain pairs of sites, channels at one or other, or both, sites in the pair need to be changed to bring them into alignment. Under the block plan completely new channels are used for all channels of the Southern Downs-Wide Bay pair and for the Darling Downs-Richmond/Tweed pair only two Richmond/Tweed channels are retained without change. By contrast under the minimum moves plan existing co-channel pairings between Darling Downs and Richmond/Tweed are retained and two channel moves are made at Darling Downs to align other channels. For the Southern Downs-Wide Bay pairing only one existing Wide Bay channel was retained without change.