Video for Mobile Phones
- an overview of mobile TV and video for cellular handsets and the
technologies including T-DMB, DVB-H, ISDB-T and MediaFLO that can be used to
provide it.
Mobile video for cell phones promises to be a major force in
the broadcasting and cellular industries over the coming years. With the
functionality in phones increasing, along with people's expectations, placing
mobile video or TV into a phone enables its use to be maximized.
Advantages of broadcast
The concept of broadcasting offers many advantages for mobile video
applications. Using the mobile phone infrastructure has many advantages it is
what may be termed a one to one communications system. However the costs of
downloading videos will need to be paid by the user, and therefore may be large.
If a broadcast style model is used, which may be thought of as a one to many
communications link, then the delivery costs are much lower. The disadvantage is
that the level of choice is reduced to what is being broadcast and there is no
interactive operation. Nevertheless it is this business model that looks the
more attractive and the one that will succeed for video and general mobile
content. The high data rates of 3G being reserved for content such as data
downloads, data communications, video conferencing and the like.
Business models
The exact way in which mobile video will be implemented as far as revenue is
concerned will depend on the operators. There may be subscription services and
there may also be services that are supported by advertising. The huge advantage
that placing video onto mobile phones is that they are an accessory that is
already in people's pockets. It is then possible to extend their functionality
to include video, and this means that another unit is not required for this
functionality. Additionally the billing infrastructure is already in place, so
this too can be extended without the need to start again.
It is possible that the mobile video transmissions could also
be used for other services. These could include traffic and weather reports that
could be broadcast in the background and brought up as required on the mobile.
Additionally they could be used for software upgrades. In this way mobiles could
be upgraded online, and new features added if necessary.
Spectrum considerations
One of the big issues surrounding the mobile video transmissions is that of
radio spectrum. As these transmissions will not utilize the bands already
allocated for cellular communications, further bandwidth will be needed. This is
likely to delay the introduction of mobile video services in some countries.
In an ideal world it would be advantageous to allocate the
same bands for mobile video broadcasting worldwide. In reality this is unlikely
to happen totally, although there will undoubtedly be a large degree of
commonality, although it is likely that not all countries will be able to adopt
the same bands. In addition to this there are no bands set aside for DVB-H
broadcasting, although for DMB, the technology is sufficiently similar to
utilize the bands allocated for broadcasting using DAB.
For the long term it is anticipated that as the UHF analogue
transmissions are closed this will release vast amounts of valuable spectrum and
some of this could be allocated to mobile video broadcasts and in particular for
DVB-H that ahs no allocations that can currently be used.
Main systems
As might be expected, there are several systems being developed. Around the
world there are four major standards that are appearing, two of which appear to
be open international standards.
- T-DMB Terrestrial Digital Multimedia Broadcasting
- DVB-H Digitla Multimedia Broadcasting Handheld
- ISDB-T Integrated Services Digital Broadcasting Terrestrial
- MediaFLO
Of these T-DMB is based on the DAB system that is currently
gaining significant support in the UK and other countries around the world for
audio broadcasting. DVB-H is based upon the DVB-T terrestrial television
broadcasting system that is used in the UK and many other countries. ISDB-T is a
standard that is only being used in Japan, and finally Mediaflow is a scheme
that is being developed by Qualcomm. Mediaflow is a registered trade name of
Qualcomm
System comparisons
It is worth looking at the comparisons between the various systems that are
being trialled and utilized for downloading video.
| |
System |
Strengths |
Weaknesses |
|
| |
Streaming video over cellular network |
- No significant added complexity for handset
- Return path provided for interactivity
|
- System not designed to provide broadcast content
- Provides significant extra load on network structure
- Significant increase in network signaling traffic
- Bandwidth is limited, even for 3G
|
|
| |
DMB
(DAB) |
- DAB is established, open standard
- Infrastucture exists in several countries
- Spectrum already available in some countries
- DAB originally designed for a mobile environment
- Only decodes part of transmission at a time, and this way it its
use of memory and current is efficient
- Only requires a small antenna
|
- In some countries (UK) the licence restrictions restrict 20% of
available capacity for data services
- Frequency allocations vary according to country and this may
restrict roaming
- Alternative Satellite based - S-DMB services are expensive to
build and run
- Will increase size, weight and power consumptions in phones
- No return path for interactive operation
|
|
| |
DVB-H |
- Established standard based on terrestrial DVB-T broadcast
standard
- Spectral efficiency greater than DMB
- Uses advanced codecs
- Has considerable industry support e.g. Nokia
- Content can be broadcast in its original format
- Only requires a small antenna
|
- Entire transmission must be decoded before a particular channel
can be extracted
- Higher power consumption than DMB
- Requires more transmitter sites than the number needed for DVB-T,
but less than the number needed for cellular communications
- Spectrum not allocated or available yet
- No return path for interactive operation
- High chip costs
- Will increase size, weight and power consumptions in phones
|
|
Summary
A number of trials of both DMB and DVB-H have taken place in a number of
countries around the globe. It appears that in the future both systems may be
used, and additionally a variety of different frequency bands may be used. To
combat this and enable phones to provide mobile video roaming, some
manufacturers are developing multi-band multi-standard chipsets. Although the
risk is that these will consume more battery power, careful design has ensured
that this may not be the case.
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