[LINK] Digital radio

[David Boxall]

On Thu, 28 May 2009 at 17:00:18 +1000 I wrote:
> For the time being, I reckon I'll stick to my lash-up (SD set-top box - 
> $59, plus 7" LCD monitor - $48, and ancient speakers - $?). The sound 
> could be better, but it receives the Band III test transmissions from 
> Sydney OK.

To satisfy my own curiosity, I looked into what's planned for digital 
radio. Some of it might be of interest to Link.

Apparently, test transmissions were DAB, but the industry intends using 
DAB+. My cheap lash-up probably won't work.

Broadcasts will be in VHF Band III and L-Band (just below 1.5 GHz). I 
haven't found anything for my local area, but the frequencies allocated 
in Sydney are between analogue TV channels 9 & 10 (in the area occupied 
by digital TV channel 9A).

For regional areas, Digital Radio Mondiale (DRM) and L-Band satellite 
are mentioned. They seem to be talking DRM on Band III, but 
<http://www.drm.org/> indicates that it is more suited to lower 
frequencies: "While DRM currently covers the broadcasting bands below 30 
MHz, the DRM consortium voted in March 2005 to begin the process of 
extending the system to the broadcasting bands up to 174 MHz. The 
design, development and testing phases are expected to be completed by 
2009". The satellite option offers some hope to remote & regional areas. 
I wonder what the battery drain would be like (for a portable radio 
without a dish antenna)?

For the time being, there are no plans to discontinue AM and FM 
transmissions. I wonder about the impact if (when) that eventually 
happens. For example, what happens to "In disaster situations, listen to 
your local ABC radio" if the signal comes via satellite and it's the 
same for the whole continent?

DAB, DAB+, T-DAB, S-DAB, DRM, DRM Plus: help! Every technology comes 
with a plethora of initialisms/acronyms, but here we have TLAs Plus.

Interesting times.

<http://www.abc.net.au/radio/digital/>
... most DAB receivers will not be able to receive the DAB+ broadcasts 
that the industry will use when digital radio officially launches.
...
The ABC has had a long-standing commitment to the development of digital 
radio in Australia. New digital-only radio services are being developed 
that will complement existing services.
...

<http://www.dbcde.gov.au/broadcasting/radio/digital_radio>
...
Commercial broadcasters will commence test transmissions of digital 
radio services in the five mainland state capitals during May 2009. It 
is expected that the national broadcasters will commence their digital 
radio services in these markets by 1 July 2009.

The legislation is premised on digital radio as a supplement to existing 
radio services in Australia, rather than a replacement technology. ...

<http://www.acma.gov.au/webwr/_assets/main/lib100535/digital_radio_task_group_report-01%20july.pdf>

This report responds to the Minister’s Direction of 18 December 2004 on 
the question of spectrum availability for digital radio in bands 
corresponding to those used for the T-DAB (Eureka 147) standard.

Executive Summary

*Spectrum available in the short-term*
Subject to necessary regulatory aspects being addressed, three VHF Band 
III and three L-Band frequency blocks can be provided in each of the 
five major metropolitan centres.

*VHF coverage*
The VHF services may not fully cover their respective metropolitan 
licence areas. For the Sydney case, which was studied in some detail, 
information received from a current T-DAB trial indicates that VHF 
coverage will be patchy at locations beyond Parramatta and other 
locations at similar distances from the transmitter site. In addition 
there could be some areas of deficient coverage due to shadowing by CBD 
buildings.

*VHF transmitter deployment constraints*
Transmitters using the VHF frequency blocks must be effectively co-sited 
with operating channel 9 and channel 10 analog television transmitters 
in order to avoid causing adjacent channel interference to viewers of 
those television services. This will generally prevent the deployment of 
a VHF single frequency network (SFN), although there may be scope to
implement low power VHF SFN transmitters at some television translator 
sites, subject to a strategy being developed and implemented to manage 
and remedy any interference to television reception.

*L-Band repeater requirements*
To address these VHF coverage deficiencies a network of L-Band repeaters 
would be required to in-fill and extend the coverage achieved by the VHF 
transmitter. Depending on the prediction model used and the amount of 
coverage of the licence area about 5 to 11 such L-Band translators might 
be required. Although it was not studied, it is expected that in cities 
other than Sydney a smaller number of L-Band in-fill/coverage extenders 
would be required.

Due to the requirement for in-fill transmitters the available VHF Band 
III and L-Band frequency blocks would need to be allocated as pairs so 
that broadcasters could be given the capability to fully cover their 
radio licence area. The regulatory aspects of such an arrangement have 
not been explored in this report. The use of L-Band to in-fill VHF 
services is not ideal as there will be short interruptions to reception 
when receivers switch between the different bands. The
preferred VHF SFN approach where all transmitters are on the same 
frequency will not possible until switch-off of analog television. 
Re-arrangement of digital television channels after analog switch-off 
may also be necessary.

*Number of services that can be provided in the short-term*
Between 5 and 9 services can be provided per multiplex or frequency 
block with trade-off between audio quality and/or potential data 
capacity and the number of services. Depending upon this choice, the 
three VHF Band III and three L-Band frequency block pairs could provide 
between 15 and 27 wide-coverage services in each major metropolitan market.

*Regional spectrum availability*
In many regional licence areas, especially those that are geographically 
adjacent to major metropolitan areas, there will be little or no readily 
available VHF Band III spectrum. Even where there may be apparently 
“unused” VHF Band III spectrum in an area, its use may need to be 
restricted to very low power levels due to the need to avoid 
interference to co-channel
adjacent area television services.

*Regional coverage and alternative technologies*
Although L-Band terrestrial transmitters could in theory be used to 
provide digital radio coverage in regional areas (if enough transmitter 
sites could be established) serious questions about the economic 
practicality of such an approach remain. For that reason it is 
recommended that alternative technologies that may be better suited to 
the needs of regional Australia should be further studied. Those 
alternatives include L-Band satellite and Digital Radio Mondiale (DRM) 
technology (at this stage neither of these is sufficiently available to 
be recommended as a solution for adoption).

*L-Band satellite spectrum*
It is recommended that 12 MHz of L-Band spectrum should be reserved to 
preserve options for the introduction of a satellite digital radio 
system until such time as decisions can be taken on the need or 
otherwise for such a solution. The band between 1461 and 1473 MHz is 
proposed as being the most suitable.

*Spectrum availability in the medium term*
Unless alternative technologies prove viable, services that cannot be 
accommodated with the readily available three VHF Band III and three 
L-Band frequency blocks would need to be accommodated using either: 
additional VHF Band III spectrum; or, additional L-Band spectrum.

Additional VHF Band III spectrum could be provided by: (i) a 1 MHz shift 
of channel 10, or; (ii) closure of analog television services. The 1 MHz 
shift would provide a relatively small capacity increment (though it 
could cater to all current Sydney and Melbourne wide-coverage area 
services with 7 services-per-multiplex). The closure of analog 
television services is subject to current government policy 
consideration and the timing for this is uncertain.

The availability of additional L-Band spectrum is subject to varying 
degrees of incumbency by licensed radiocommunication services that 
provide point-to-point fixed link services, Defence services and 
point-to-multipoint Universal Service Obligation telecommunication 
services in regional and remote areas. The report proposes a strategy 
that would maximise the ability of incumbent radiocommunications 
licensees to continue to use L-Band while providing necessary 
opportunities for introduction of broadcasting services.

Clearance of incumbent L-Band services to allow the 
replication/migration of broadcasting services into L-Band will impose 
costs on incumbent licensees and is likely to be resisted. The 
transition process will need to be supported by appropriate regulatory 
arrangements (including a revision of the 1.5 GHz Band Plan). Suggested 
L-Band arrangements have been described in the report that would allow a 
staged introduction of T-DAB while minimising the impact on incumbent 
services and preserving the policy option to consider an L-Band 
satellite system. An issue that will need careful consideration is the 
time-frames within which clearance of incumbent radiocommunication 
services would be required. In particular the clearance of some of the 
incumbent Defence licences may not be simple or straight-forward.

*Possible strategy for digital radio introduction*
These considerations suggest that a multi-stage process for introduction 
of digital radio services may be appropriate.

The first stage involving access to three frequency blocks at VHF Band 
III (complimented by infill/coverage extender capacity at L-Band) in 
major metropolitan areas could be introduced as soon as appropriate 
legislation is passed and necessary regulatory instruments are made or 
varied.

Depending on the number of services-per-multiplex adopted, those 
frequency blocks could provide 15 to 27 wide-coverage services in a 
radio licence area. Currently there are 28 and 29 wide-coverage services 
operating in the Sydney and Melbourne radio licence areas respectively. 
Of those, 18 wide-coverage area services are provided by commercial or 
national broadcasters in each radio licence area.

It is clear that at the “first stage”, digital radio capacity cannot be 
provided for all currently operating wide coverage and local area 
services in Sydney and Melbourne. Capacity could however be provided for 
all currently operating wide coverage commercial and national services, 
if 6 (or more) services were assigned to each multiplex.

There are more options, and more uncertainty, for the following 
stage(s). Key considerations on options for the second (and potentially 
subsequent) stages are:
• Availability of additional VHF Band III spectrum depends on closure of 
analog VHF Band III television services.
• Clearance of L-Band spectrum will take time and will impose costs on 
incumbents. If fixed links within 200 km of metropolitan areas need to 
be relocated to other bands the estimated cost could be up to $32 
million. Additional costs will be also imposed on non-fixed link licensees.
• Development of alternative technologies (eg. DRM or L-Band satellite) 
could shift the planning paradigm (especially in regional areas) toward 
L-Band satellite or DRM.

-- 
David Boxall | Any given program,
| when running correctly,
| is obsolete.
| --Arthur C. Clarke