The future of multimedia

Developments in linear modulation and video compression will enable the development of next generation, spectrum-efficient multimedia radio systems, according to speakers at a recent wireless multimedia conference.

Linear modulation, in which both amplitude and phase are coded and transmitted, will be key to creating systems that can simultaneously transport multiple types of information, said Joe McGheehan, head of the department of electrical and electronic engineering at the U.K.'s University of Bristol. McGheehan was a keynote speaker at the IBC-sponsored "Mobile Multimedia" event, held in London earlier this month.

"Linear modulation system components are going to play a crucial part whenever a network is implemented in the future," McGheehan said. "If we can actually make the system linear enough - and that's the problem - then we've got a transmitter system that can handle any type of information you want to send, whether it be speech, data or video information, in one handset.

Achieving the appropriate degree of linearity may be a bit of a stretch, but McGheehan noted that the technology is starting to become established.

Linear modulation will allow the evolution from today's digital networks to tomorrow's generation of wireless phones in which characteristics such as modulation format, data rate, and voice and channel coding can be defined in a digital signal processor. In this view of the future, multimode software radios would be activated over the air by software appropriate to the particular location in which they were being used.

Nearer to the here and now is the emerging MPEG 4 video compression standard, the subject of a presentation by Dirk Lappe, project manager of a number of EU-sponsored mobile multimedia projects and group leader of the mobile multimedia systems group at Germany's Robert Bosch GmbH.

MPEG 4 segments a video signal into its component parts, codes them separately as objects and transmits the objects to a receiver. MPEG 4 then drops extraneous elements of the signal, retaining those appropriate to the particular application and the speed of the link.

For example, a mobile multimedia terminal user might not have the link bit rate to support the background of a video signal, so a background could be generated locally by the terminal, said Lappe. As such, MPEG 4 should play an important role in overcoming the residual speed limitations of mobile and cellular terminals used for multimedia applications.

MPEG 4, which is backwards-compatible with MPEG 2, is scheduled to be standardized by 1998.

"It will be very important to include the MPEG 4 protocols within the UMTS protocol stack," Lappe said.

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