DVB Mobile TV : FAQ

1. Why was DVB-H developed by the DVB Project?

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 DVB-H services will suffer from unacceptably long channel change times?

6 . Don't UMTS and 3G technologies already provide mobile television services?

7 . Can DVB-H services be delivered over a pre-existing DVB-T network?

8 . Can DVB-H be used to deliver mobile TV in countries that don't use DVB-T for digital terrestrial television?

9 . Will anyone really want to watch television on a mobile phone?

10 . Is mobile TV available free-to-air?

11 . 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?

12. Can DVB-H be combined with CDMA in services and handsets?

13. Is Statistical Multiplexing possible with DVB-H?

14. What is IP Datacast / DVB-IPDC?

15. What is the difference between the two SPP (Service Purchase and Protection) solutions proposed in the DVB-IPDC specification TS 102 474?

16. What is the difference between OMA BCAST and DVB-IPDC?

17. Is DVB-IPDC "bearer independent"?

Why was DVB-H developed by the DVB Project? [up]

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.
Acting as a complement to existing broadcasting technologies such as DVB-S, DVB-C and DVB-T, DVB-H uses advanced audio and video coding technologies such as H.264 to expand the reach of standard broadcasting services. MobileTV is seen as a key driver for new and more complex mobile services and handsets and DVB-H is a key enabling technology..

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 completely open.

Is it true that DVB-H receivers use more power than receivers used for the Korean T-DMB system? [up]

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 less than 40mW. Our enquiries indicate that the power consumption of the T-DMB system is about 150mW - that's four times higher than for a DVB-H frontend. And the data throughput for DVB-H is upwards of 4 times that of T-DMB. For a full comparison of DVB-H and T-DMB, please visit the Technology section.

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 compression, etc.

It should be noted that video frame rate 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 transmission system.

Will spectrum be available for mobile TV services? [up]

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 (no matter how few), 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 - 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 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.

Opportunities also exist in frequency bands other than UHF. For example, such opportunties for S-band (2-3GHz) led to the development of the DVB-SH specification adapted to the hybrid terrestrial satellite environment.

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 full 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 these requirements.

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.

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? [up]

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. Towards the end of 2006 we are likely to see the launch of at least one commercial DVB-H service in the USA.

Will anyone really want to watch television on a mobile phone? [up]

The FinPilot 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. Similar results were reported in the interim report on the Oxford Trial.

Will mobile TV be available free-to-air? [up]

There are free-to-air mobile TV services using DVB-H on air in Finland, India and the Philippines. Using T-DMB and ISDB-T respectively, Korean and Japanese broadcasters are also delivering delivering mobile TV free-to-air. The difference is that Japanese and Korean requires mobile TV in the broadcasting bands to be free-to-air - and the systems used for this are geared to such a scenario. To increase the revenue-generating potential of mobile TV, a Service Purchase and Protection specification has been made available for use with DVB-H 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 questions.

It is reasonable to presume, that for regulatory reasons DVB-H could be available free-to-air, as in Korea and Japan.

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.

Can DVB-H be combined with CDMA in services and handsets? [up]

Yes. DVB-H is designed to have an independent of set of protocols coving service purchase and protection, electronic services guides and content delivery. There is no reason why DVB-H cannot be combined with CDMA just as easily as with GSM.

Is Statistical Multiplexing possible with DVB-H? [up]

Yes, there are several ways this can be achieved. Most hinge on the implementation of the IP encapsulator, which takes the encoded video and audio and drops this into time slices. The enabling factor here is that the time slices can be of variable length, so as the data in them is adapted by a statistical multiplexer, then so is their size.

Another means of implementing statistical multiplexing is where there may be more than one service contained in each time-slice. Whilst this will have a negative impact on battery consumption, stastical multieplxing is possible within the time slice itself and between the services contained in it.

What is IP Datacast / DVB-IPDC? [up]

IP Datacast is a set of technologies optimised for delivering any kind of content to mobile devices over IP, with the help of broadcast networks dimensioned for mobile reception. The main elements of the DVB IP Datacast specifications are:
- an Electronic Service Guide, to describe the services available to end devices;
- Content Delivery Protocols, to transport any kind of content over a broadcast bearer;
- Service Purchase and Protection, to enable over-the-air protection of delivered content and subsequent purchase mechanisms.
IP Datacast has been primarily specified to in conjunction with DVB-H bearer technology but it can adapt to any bearer able to deliver IP datagrams. For more information: DVB-IPDC Fact Sheet

What is the difference between the two SPP (Service Purchase and Protection) solutions proposed in the DVB-IPDC specification TS 102 474? [up]

DVB-IPDC includes two Service Purchase and Protection profiles building on different principles. The "18Crypt" profile makes use of device-based security mechanisms derived from OMA DRM 2.0, while "Open Security Framework" (OSF) is a framework enabling multiple key management systems based on smartcards.

What is the difference between OMA BCAST and DVB-IPDC? [up]

OMA BCAST and DVB-IPDC are two sets of specifications fulfilling similar market needs but with different emphases. OMA BCAST looks at integrating deeply with mobile network infrastructures. On the other hand, DVB-IPDC is built consistent with broadcast operator and content provider infrastructures while adopting tools developed by the mobile community.

Is DVB-IPDC "bearer independent"? [up]

DVB-IPDC has been designed to be bearer independent. The Internet Protocol (IP) layer is the chosen bearer abstraction layer.