1. Why was DVB-H developed by DVB now?
2. Is it true that DVB-H receivers use more power
than receivers used for the Korean T-DMB system?
3. Is it true that DVB-H offers only a limited frame
rate compared to other systems?
4. Will spectrum be available for mobile TV services?
5. Is it true that a proprietary system developed
in the USA – MediaFLO – is largely based on DVB-H,
but delivers a better performance?
6. Is it true that DVB-H services will suffer from
unacceptably long channel change times?
7. Don't UMTS and 3G technologies already provide
mobile television services?
8. In the context of T-DMB services having already
been launched in Korea with multi-vendor support, how far are
we from seeing a launch of DVB-H services?
9. Can DVB-H services be delivered over a pre-existing
10. Can DVB-H be used to deliver mobile TV in countries
that don't use DVB-T for digital terrestrial television?
11. Will anyone really want to watch television
on a mobile phone?
12. Will mobile TV be available free-to-air?
13. Why do the telecommunications network operators
need to be involved with mobile TV services at all? Couldn't broadcasters
just launch DVB-H services independently?
Why was DVB-H developed by DVB now?
DVB-H is the product of DVB’s process of
analysing commercial requirements and producing an open standard
to meet these. Based on DVB-T, but operating in the IP environment
and with special features for the battery-powered, handheld market,
DVB-H is flexible and future-proof.
In the past, DVB-S, DVB-C and DVB-T services have driven the market
for compression technologies, and DVB’s advanced new systems
(DVB-S2, DVB-H) are now at the forefront of the applications which
will use the MPEG-4 Part 10 (H.264) video codecs. Thus the innovations
that gave birth to DVB-H are taking place hand-in-hand with the
developments in these new coding schemes.
In the past, it would have been reasonable to
expert proprietary technologies to dominate the early stages of
a new market. DVB-H has changed this – not only does it
present an ideal solution for the mobile TV market, but it is
Is it true that DVB-H receivers
use more power than receivers used for the Korean T-DMB system?
No. At the outset, DVB recognised that power consumption
in the receiver would be the most important factor in determining
technical decisions concerning the DVB-H standard. It was this
that gave rise to the time-slicing technique in DVB-H. There are
no effective power saving techniques in T-DMB (other than "micro-time-slicing”,
which is not an effective power-saving technique). Rather T-DMB
relies on the fact that it operates in a 1.5MHz channel bandwidth,
rather than the 5, 6, 7 or 8MHz channel bandwidths that DVB-H
can operate in. The lower channel bandwidth for T-DMB means less
data throughput, but also should mean less power. Thus, if you
were to remove DVB-H time-slicing, T-DMB would have lower power
consumption than DVB-H. It does not.
The target power consumption for the DVB-H
tuner and front end was less than 100mW, and the current state-of-the-art
is around 50mW. Our enquiries indicate that the power consumption
of the T-DMB system is about 250mW - that's five times HIGHER
(not lower) than for a DVB-H frontend. And the data throughput
for DVB-H is upwards of 4 times that of T-DMB.
Is it true that DVB-H offers only a limited frame
rate compared to other systems? [up]
Frame rate is a function of the coding technology
you choose and the parameters you choose at your encoder. These
choices are based on the content you are trying to encode, the
size of your target receiver screen, and how much processing power/memory
is available in the receiver. For example, you are naturally going
to choose a different set of parameters for HDTV on a 50"
plasma display than those you would use for a small mobile phone
screen. One of the factors that should be taken into account,
particularly for low-definition small-screened displays, is frame-rate.
It will clearly take less processing power to decode a sequence
at 15fps (frames per second) than it does an equivalent sequence
at 25fps. Other parameters you can play with are resolution, audio
It should be noted that this has nothing
to do with the transmission technology you use, for example DVB-H
or T-DMB. In many of the trials conducted so far using DVB-H,
the receiver used was a Nokia 7710 with a prototype SU-22 DVB-H
streamer. The Nokia 7710 is able to handle about 250-300kbit/s
of video at about 12fps. This is a function of the phone, its
processor and memory - choices made by the manufacturer to suit
the device's screen. But DVB-H and its IP datacast technology
can be used to deliver pictures to screens in buses/cars/laptops
as well as mobile phones, or any other mobile/portable application
you can think of. The overall data throughput in DVB-H is sufficient
to support the resolutions any of these applications require.
On the other hand, T-DMB is restricted to operating at about 700kbit/s.
In short, the limiting factor for the mobile environment is the
capability of the receiver to cope with video and audio, not the
Will spectrum be available for mobile TV
Both DAB and DVB-T are already deployed in
countries around Europe. DVB-T has been very successful where
it was launched - DAB less so (outside the UK and parts of Germany).
There is an argument which suggests that because DAB hasn't been
successful, one could use the networks already in place (if such
networks really are still in place) to deploy T-DMB. The difficulty
with this argument is that if the DAB networks are in place, and
there are receivers in the market, you can't simply switch them
off to turn on T-DMB.
The same naturally holds for DVB-H and
DVB-T. Importantly, DVB-H can be included as part of an existing
DVB-T multiplex - naturally there's a compromise to be made on
some of the DVB-H features, but it's certainly possible. Further,
DVB-H trials have successfully found frequencies available for
their services, even in an environment (e.g. Germany) where DVB-T
services are already on air alongside a full analogue PAL service.
Frequency spectrum is a valuable natural
resource and it should be used to deliver maximum benefit to all.
This is one of the motivations behind the move from analogue to
more spectrum-efficient digital technology in the first place.
Such are the demands on this limited resource at present that
frequencies for DVB-H and T-DMB (both new services) will be difficult
to find - but our experience shows that they can be found for
DVB-H. It goes without saying that analogue switch-off will bring
a whole new range of opportunities for spectrum allocation.
It's difficult to predict exactly what's
going to happen when analogue services are switched off. It can
be argued that a demand for spectrum to facilitate terrestrial
HDTV services will reduce the scope for mobile TV. Both DVB-H
and terrestrial DTV use the same basic technologies: DVB-T and
H.264, but the business models are going to be significantly different.
One thing is certain: both DVB-H and DVB-T HDTV will co-exist
following the switch-off of analogue television. Whilst they may
compete for spectrum allocation, their target audiences are going
to be different.
Is it true that a proprietary system developed in the USA –
MediaFLO – is largely based on DVB-H, but delivers a better
MediaFLO® is a technology
which gathers elements from not just DVB-H, but other areas as
well. As it is a proprietary system, little detail is available
about the overall MediaFLO system, but it would appear to use
Turbo Coding (which is used in DVB-RCS and DVB-RCT) and COFDM
(as used in DVB-H and DVB-T). Basically, it uses technical elements
which are quite similar to DVB-H, and one could thus reasonably
expect similar performance. There’s no independent evidence
to support claims that MediaFLO is “better” than DVB-H.
Indeed, DVB-H has more flexibility than MediaFLO in that it provides
more parameters to choose from when designing your network.
Is it true that DVB-H services will suffer from
unacceptably long channel change times? [up]
Channel change time is a
function of many different elements – one is certainly how
the time slicing is implemented in the DVB-H IPDC stream, i.e.
how long does the receiver have to wait before receiving the first
burst of the new service you wish to switch to. However, that
is not all: some early implementations require the receiver to
reload the DVB-H stack and the media player each time a channel
is changed – and this naturally affects channel change time.
The minimum time between bursts is limited by the required power
saving in the receiver front-end. It can be shown that the present
technology will allow burst intervals between 2-4 seconds leading
to average channel switching times of 1-2 seconds whilst retaining
the power-saving benefits of DVB-H. Channel change time will certainly
improve as chip design improves and importantly, the DVB-H set
of standards allows fully flexibility in this area.
For any handheld system, channel change
time must be acceptable to the user, e.g. 0-2s. If it is too long,
consumers will get frustrated with the system. DVB-H proponents
are well aware of this, and have designed a system which meets
Don't UMTS and 3G technologies already provide
mobile television services? [up]
They do, using the MBMS elements in the UMTS
specifications. However, a telecommunications system, even one
implementing a multicast element such as MBMS, is fundamentally
a symmetrical bi-directional system, i.e. one-to-one. Thus, networks
can easily become overloaded when they implement broadcast services
such as video – particularly if they prove popular.
A second point is that the revenue that you can
generate per minute per subscriber is gong to be less than the
core voice and data services offered over 3G networks. This would
suggest that operators would be better off using their telecoms
network for the delivery voice/data services, and another one
(with a lower cost per bit) for the delivery of video and other
broadcast services, e.g. DVB-H.
In the context of T-DMB services having
already been launched in Korea with multi-vendor support, how
far are we from seeing a launch of DVB-H services? [up]
Interestingly, the T-DMB profile which is
being used in Korea is only one of the T-DMB systems being standardised
by ETSI, there is another profile (which better matches the European
DAB networks and operators’ requirements) which is also
being standardised. A further important point about T-DMB services
in Korea is that they require a broadcaster to maintain a separate
network (a T-DMB one), but regulatory requirements prevent the
delivery of anything other than free-to-air services over this
network. This raises the issue of how such a network could be
For this reason, DVB-H is an attractive proposition
in Korea, especially when combined with DVB-T. However, the Korean
insistence on ATSC for terrestrial DTV (and we know that ATSC
can’t do mobile, let alone handheld broadcasting) means
that such a DVB-T/DVB-H network will have to wait until spectrum
is freed in the context of analogue switch-off, a process which
is suffering from delays due to lacklustre sales of ATSC receivers.
Can DVB-H services be delivered over a
pre-existing DVB-T network? [up]
Certainly – this is the way the system
was designed. Indeed, trials done in Germany have shown that a
DVB-H time-sliced multiplex processed by a DVB-T statistical multiplexer
creates a unique “dual services” transport stream,
usable without impacting the existing receivers in the market.
Moreover, two DVB-H multiplexes operated by different
entities can share the same transmission network, as is being
demonstrated on the Paris
pilot network in France.
Can DVB-H be used to deliver mobile TV in
countries that don't use DVB-T for digital terrestrial television?
DVB-H is designed to be combined with DVB-T
networks should this be desired, but it is certainly not a requirement.
In the early stages, we are likely to see networks delivering
DVB-H exclusively. DVB-H makes technical and economic sense whether
on its own, or combined with DVB-T.
Some countries, e.g. US, South Korea, have chosen
DTV transmission systems which are limited to the delivery of
DTV to fixed receivers with a roof-top antenna. These countries
have consumers interested in receiving DTV in a mobile handheld
environment, and DVB-H is ideally suited to servicing this market.
Will anyone really want to watch television
on a mobile phone? [up]
trial has shown that about 60% of the viewers of the trial felt
that the service would become popular. Further, 40% of viewers
felt that they would either acquire a DVB-H capable phone at the
time of purchase of the next phone, or when usage has become more
common. A further 47% felt that they could well subscribe to the
service and acquire a DVB-H phone in the future. In short, the
trials so far show that people like watching TV on mobile phones.
Will mobile TV be available free-to-air?
Korean and Japanese broadcasters are required
to deliver mobile TV free-to-air. This is quite limiting in respect
of generating revenue from such a service. For this reason, DVB-H
has built in the Service Purchase and Protection from the outset.
Generating revenue from subscriptions or pay-per-view is a useful
means of helping pay for the service. Advertising could well work,
but an advertising model on a mobile phone raises a number of
It is reasonable to presume, that for regulatory
reasons DVB-H could be available free-to-air, as in Korea and
Why do the telecommunications network operators
need to be involved with mobile TV services at all? Couldn't broadcasters
just launch DVB-H services independently? [up]
Mobile TV doesn’t NEED to involve anyone
other than the broadcast network operator, and the service provider.
However, there are many reasons why a co-operative approach may
be judicious. For example, many countries have mobile phone models
which see the phones being subsidised by the operators, and to
have mobile TV on such phones would require some co-operation
between the mobile TV operator and the telco. Billing is going
to be a key element to the success of mobile TV, and telecoms
operators typically have sophisticated billing infrastructures
in place – and a subscription model is that favoured by
viewers according to the DVB-H trials underway.
On the other hand, there are countries where the
regulatory model prevents free-to-air broadcasters from becoming
involved in pay-TV services on terrestrial networks. In such an
environment, DVB-H could be considered for broadcasting to handhelds,
e.g. suitably equipped mobile phones, PDAs, etc. And in this environment,
the co-operative approach may have less benefits.
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