Figure 1. Technology bit rates and mobility. Source: “The Convergence of Broadcast & Telecommunications Platforms,” ad hoc Group DVB-UMTS, Report No. 1 (Full), 6.2.2002 Edi- tor: Rainer Lueder. Click here to see an enlarged diagram.
The promise of mobile TV has brought the worlds of public wireless telecom and broadcasting into close collaboration and imminent competition.
Since the late 1990s when digital terrestrial TV entered public life, mobile TV has been an application area of interest. It has been associated with an increasing variety of new advanced transmission and compression technologies, business models and service concepts.
In this article, mobile TV refers to AV transmission or signal distribution, point-to-point and point-to-multipoint, and moving receivers. Mobile TV in its general form also appears to be rolling out in three distinct, if converging, areas: telecom, as an extension of phones (smart-phones); the IT industry, notebook receivers and rich media PDAs; and as an extension of television, out of the home.
Figure 1 illustrates the different technologies that offer potential of mobile multimedia, and gives a rough sense of bit rate versus mobility.
The history of modern, digital mobile TV effectively began in 1996 and 1997, when German broadcaster RTL conducted trials of a DVB-T service on slow moving trams in downtown Cologne and on the German autobahn in a yellow Bugatti at speeds up to 300km/h.
In 1998, the Japanese Digital Broadcast Experts Group approved ISDB-T, a digital terrestrial standard that supports mobile terminals accessing more rugged segments of the transmitted signal to receive video, radio and other data services. Pilots and trial services are already up and running.
In 1999, the Singapore Broadcast Corporation (SBC) introduced TV Mobile — the world's first public transport broadcast TV service — on buses and trams and mass transit services. Mercedes is introducing DVB-T reception as an option in its cars sold in Europe.
The power consumption of DVB-T front ends, however, is too high to support handheld devices for one to several days on a single charge. Since 1999, DVB has been working on how to complement UMTS, the European 3G standard, with broadcast services. The pieces of the technical puzzle are basically a power-efficient tuner-demodulator design, the use of IP-datacasting as a video and data delivery layer and a more efficient video compression solution than MPEG-2. This standard came to be called DVB-H (for handheld). And the basic reason why it exists is power consumption.
Last November, the European Telecommunications Standards Institute (ETSI) approved DVB-H for delivery of mobile television to handheld devices like cell phones.
The commercial appeal of digital television could be summarized as having a choice between improved picture and sound, or more rugged signals. Having more rugged signals means worse images; better images means less robust signals. New advanced video coding systems promise to make low bit rates achievable. However, new codecs require more hardware and memory resources, and eat power, and thus, battery life. With the new systems, a new trade-off is introduced: video coding efficiency versus complexity.
All of the more robust transmission and reception methods, for DVB-T and DVB-H, and even enhanced VSB from the ATSC, find the available data rate reduces as robustness increases. Next-generation video and audio codecs such as MPEG-4 AVC (H.264) and Microsoft Windows Media Video (VC-1) appear to solve this problem.
The 3G partnership project (3GPP) has standardized on MPEG-4 (Part 2: simple visual profile) coding. Late last November, DVB approved new guidelines for low bit-rate applications (such as DVB-H) adopting MPEG-4 AVC Video.
The Nokia DTB-T Mediascreen (left) has a battery life of 20 minutes, while the Nokia 7700 DVB-H Mediatermi-nal (right) has a battery life of two hours.
Does a new codec really help? In compression, the most efficient coding scheme takes the most amount of work — the decode needs more muscle to do more tasks in less or the same amount of time. So, we are back to Moore's law: Soon, we will have the processing power, BUT now there is more work to be done. Anyone who has ever really used an advanced mobile communication device that is video-capable will know the impact these features have on battery life.
In South Korea, a novel strategy has been attempted, where mobile broadcast TV services are offered using the Korean Digital Multimedia Broadcasting (DMB) standard. DMB comes in flavors: T-DMB, using terrestrial airwaves, and S-DMB, which provides a direct satellite-to-mobile phone feed.
South Korea is also forging ahead with a new Broadband Wireless Access standard called “WiBro,” an example of the new “4G” Wireless LAN-based system, specified in the IEEE as 802.16. Based on the same physical layer (OFDM) as 16d, 802.16e is tailored for the high mobility environment, including handover and roaming.
WiMax is integrated and IP-based, and potentially goes beyond the hybrid DVB-T/UMTS approach. Many people believe this direction is the most promising way to implement broadband connectivity with mobility. With IPTV and voice over IP, this can complement (or compete) with 3G telephone systems.
It is clear that a hybrid broadcast/cellular approach, even if that is 3G, is an interim phase. WiMax may hold the promise of being a unifying generation of converged technology, supporting as it does full duplex IP.
DVB-H trials in Berlin and Helsinki are using existing terrestrial TV masts to broadcast compressed signals to handsets with add-on receivers.
In the UK, the mobile network O2 will start using DVB-H in 2005. The UK's NTL, a clear competitor to U.S.-owned transmission services company Crown Castle, is active in TV network operation in the UK. Crown Castle will broadcast 16 channels on a spare TV frequency. O2 plans to give 500 Nokia TV phones to subscribers to test a service, which could cost around $22 per month for a bouquet of news and entertainment channels.
Last October, Crown Castle began operating pilot DVB-H services from three transmitters near Pittsburgh, PA, viewed on prototype Nokia mobile TV phones and DIBcom mobile receivers.
Whether it is a mobile phone with AV capability or a PDA-based mini video jukebox, or some other kind of mobile TV device, the “killer” device of choice for consumers is not entirely clear, as lifestyles still evolve.
Whatever technology is used, it is clear broadcasters will need to drop some of the precepts of traditional programming. The Singapore TV mobile service found programs could not be longer than 10 minutes, the length of an average Singapore bus ride.
People are free to watch TV on their mobiles only in a certain rhythm. Broadcasters need to think differently about making the right kind of programs and making sure people can afford the time to watch them. That is a subject for another article.
Martin Jacklin is a technical author and consultant based in Geneva, and is a member of Broadcast Projects, (www.broadcastprojects.com) an alliance of independent consultants working in the digital media industry.