Multimedia convergence
In the digital world, a ‘bit’ is a ‘bit’ whether it represents audio, video, data, software, etc. Consequently, in principle, there is no reason for sepa- rate networks for broadcasting and telecommunications. Of course, the reality is slightly more complex. In practice, there are some fundamental distinctions between broadcasting and telecommunications. Broadcasting essentially delivers one-way, one-to-many services, whereas telecom oper- ators provide two-way, one-to-one services. Nevertheless, the boundaries between broadcasting and telecom have become increasingly blurred since the early 1980s; some analogue TV services have been used to deliver limited ‘telecom-like’ services, such as delivery of encrypted teletext serv- ices for individuals or closed groups of users. The introduction of digital radio and TV networks opens up new opportunities for data services, par- ticularly for delivery to portable or handheld devices. Demand for short 30-s video clip (e.g. a football goal) on mobile phones is increasing. Large- scale on-demand video services via Universal Mobile Telecommunication System (UMTS) proved to be uneconomic. Instead, attention has turned to the benefits of one-to-many services: rather than sending individual video streams to each consumer, it would be much more efficient to transmit the same material simultaneously to all those interested. Of course, this ‘new idea’ is actually ‘broadcasting’!
The over-used concept of convergence can apply to incorporating inter- net services onto a broadcasting platform, known as Digital Multimedia Broadcasting, or conversely, incorporating broadcasting services onto the internet platform, known as on-line convergence, or a mixture of the two.
Digital multimedia broadcasting
Arising from the hype surrounding the Internet, there has been increasing interest in offering multimedia services to mobiles. First, there was the big bang of selling frequencies for UMTS all over Europe, but it turned out that UMTS will not offer the huge bandwidth that modern streaming internet applications, such as TV, require. This means that, apart from point-to-point applications, there is an increasing requirement for point- to-multipoint, wireless, internet access technologies. Hence the terrestrial broadcast systems coming into focus, as a means of streaming multimedia content to mobile, portable and handheld receivers.
508 Newnes Guide to Television and Video Technology
There are two different technical solutions that could meet these requirements:
● DVB-H (H for handheld), the latest terrestrial standard from DVB.
● Digital audio broadcasting (DAB), adapted for multimedia delivery.
A third solution, ISDB-T from Japan is not to be deployed in Europe.
Although the fact that all three components: audio, video and data are presented in digital form makes it possible for them to share the same transmission medium, it is not sufficient for piratical convergence. What makes the whole enterprise a practical possibility is their adherence to a standard network communication model, the open system interconnect (OSI) model (refer to Appendix A5).
DVB-H
The terrestrial version of the DVB system (DVB-T) was fully described in Chapter 8. Developed in the mid-1990s, it was primarily intended for portable and stationary reception using roof-top antennas. The design of the system was strongly influenced by the cost of the receiver.
To make the receivers cheaper, time interleaving—which would have benefited mobile reception—was not implemented; instead, the same error correction as the satellite system, DVB-S, was used. DVB-T can effectively be used for mobile and portable reception provided the multi-antenna diver- sity receiver is available to enable high-speed mobile reception of DVB-T. However fast, such varying channels are error prone. The situation is wors- ened by the fact that antennas built into handheld devices have limited dimensions and cannot be continuously pointed at the transmitter if the handheld terminal is in motion. This is just one of the problems of using DVB-T. The stumbling block for the use of straight forward DVB-T for mobile devices is however, the very practical problem of battery life. Power consumption of DVB-T front ends is too high to support handheld receivers that are expected to last from one to several days on a single battery charge.
To make DVB-T suitable for mobile multimedia services, a dedicated standard for handhelds, based on DVB-T, was necessary. It is called DVB- H (DVB-Handhelds). The aim is to provide an efficient way of carrying multimedia services over digital terrestrial broadcasting networks to handheld terminals.
DVB-H specifications were drawn up with the following objectives:
● To power off some part of the reception chain to increase the battery useful lifetime.
● EASY access to services and seamless transition from one service to another;
● Sufficient flexibility/scalability to allow reception of services at various speeds, while optimising transmitter coverage.
● To mitigate against the effects of high levels of man-made noise such as car ignitions interference.
● To provide a generic way to serve handheld terminals in various trans- mission bands and channel bandwidths in various part of the world.
● To receive multimedia services using a single antenna in the portable, mobile and indoor environments.
● To maintain maximum compatibility with existing DVB-T networks and systems.
These requirements were drawn up after much debate and with an eye on the emerging convergence devices providing video services and other broadcast data services to third generation, 3G handheld devices.