[BC] DAB+ - Digital Radio Down Under

[Peter Smerdon]

Perhaps you saw the Radio Magazine piece on Digital Radio rollout in 
Australia -
http://radiomagonline.com/digital_radio/australia-dab-rollout-1021/index.html
It appears to be largely sourced from a story in The Australian newspaper
http://www.theaustralian.news.com.au/business/story/0,28124,26227693-7582,00.html

Maybe I can flesh this out a bit from my perspective....
It's been six months since the official launch in the five biggest metro 
markets (Sydney, Melbourne,Brisbane, Adelaide, Perth), and digital radio 
has got, and is still getting, quite good coverage in the mainstream 
press - mostly in the form of reviews of new radios as they are 
released. Digital Radio is treated like any other entertainment 
technology for review purposes. Product is on display, and available 
from most major retailers who normally stock several types of radios.

The consumer has dozens of brands/models to choose from in most 
categories, but unfortunately one missing product seems to be car radios.
We're waiting to hear about next year's models from the auto makers.

DAB+ supports Electronic Program Guide (EPG) and graphics/animation via 
SlideShow (eg Album Art, extra text info).
At launch in May there were no radios which supported EPG or SlideShow, 
but the second generation models are now starting to appear which do 
support at least SlideShow (Pure Sensia, iRiver B30). EPG is still under 
discussion.

Most (all?) DAB+ radios are DAB/FM models (no AM band) - and DAB+ is 
"new band" technology so it is critical for AM broadcasters to have a 
simulcast presence on the DAB platform.
All existing commercial licensees were allocated 128kbps per license (AM 
or FM), which is being used (typically) to put up a simulcast of their 
AM or FM program (at 64 to 90kbps incl embedded data) plus a second 
"new" program which is either mostly or fully automated.
The full coverage community radio stations (i.e. not "suburban") also 
have a total allocation of (from memory) 512kbps to carve up between them.
The largely Govt-funded ABC and SBS have an ensemble of their own.

There is a moratorium on licenses being issued to new players for six 
years, so the existing players get time to establish the medium without 
extra competition.

Coverage black-spots were mentioned in the newspaper article, and this 
is indeed a real problem - exacerbated by digital's unforgiving nature - 
a signal too low causes a mute.
There is no graceful degradation like analog. Because it's new-band not 
IBOC there's also no blend to analog.

DAB+ has Single Frequency Network capability, so it can have a 
cell-based architecture with strategically located "filler" transmitters.
That's the plan of attack for black-spots.
We can't just throw more power at the problem for several reasons..
    - The ensembles are located in VHF Ch 9A with analog TV services on 
Ch 9 and Ch 10. The analog TV won't be shut down here until 2013, and 
they are nervous of interference.
    - The services have clearly defined License Areas (identical to the 
analog AM and FM License Areas), and the regulators have specified the 
power levels with an eye to this.
    - Licensees in adjacent License Areas are particularly vocal to 
ensure the signal overspill is minimised.
To address this third point a system called the Coverage Management 
System was theorised, whereby lower-power "interferers" would be located 
in the area to be protected to disrupt the encroaching signal. The 
listener's radio would lock to the local transmitter (broadcasting 
silence) preventing reception of the distant signal.
This could be used to justify relaxing the onerous nulls towards the 
adjacent License Area.
At the last minute the regulator ACMA decided (post DAB startup) against 
the use of the Coverage Management System
http://www.acma.gov.au/WEB/STANDARD/pc=PC_311461

So now the nulls remain - more black-spots.
Antennas are directional and powers can vary in the horizontal and 
vertical planes from 50kW down to 1.6kW ERP.
Vertical radiation patterns are used to try to broadly reduce signal 
levels at the License Area boundary.

Given the multiplex/ensemble nature of DAB/DAB+ we have multiple 
broadcasters on the one transmitter.
In the allocated Ch 9A RF space there are 3 separate transmissions, 
confusing called 9A, 9B and 9C.
The commercial broadcasters share 9A and 9B with some community radio 
broadcasters (not yet on air).
The public sector broadcasters (ABC and SBS) have been assigned 9C.

The commercial stations, facilitated by their industry body Commercial 
Radio Australia (CRA), have formed separate Joint Venture Consortia 
(JVC's) in each city to own and operate the transmission equipment.
The JVC holds the spectrum license, and is required to provide access to 
other content licensees (eg: community radio) at a fair and arbitrated 
price.
The equipment is located at existing TV/FM transmission sites on a site 
rental basis, and maintenance is outsourced to a third-party who also 
has maintenance contracts for some other radio and TV services in the area.

This "hands-off" transmission model presents its own challenges, with 
engineers having to come to grips with not being able to deal with 
issues directly themselves, but having to work through third parties - 
sometimes causing frustration.
It's an unavoidable consequence of the multiplex nature of DAB/DAB+.
ISTR that the idea of a multiplex was one of the (the main?) objections 
to DAB in the US (way back when).

I should mention that I had some small involvement with the planning and 
implementation of Digital Radio before I retired from SEN/3MP in 
Melbourne last year.
I participated in CRA's Digital Technical Advisory Committee (DTAC), as 
well as post-retirement consulting for SEN/3MP on implementation up to 
and past launch date.

DTAC is still functioning, and black-spot coverage via SFNs is now their 
top priority.

I probably should stop this opus now.
If any locals can see any errors, feel free to holler.

Regards,

-- 

Peter Smerdon.
Melbourne, Australia.