The main contenders for the mobile multimedia broadcast platforms and the areas where they are being first deployed are:

DAB-IP in UK
DVB-H in Europe and USA
T- and S-DMB in Korea
ISDB-T in Japan
FLO in USA
TDtv in UK
DVB-SSP in Europe
DMB-TH in China

Most of these technologies are based on the robust modulation scheme of coded orthogonal frequency division multiplexing (C-OFDM), with certain implementational, technical and political differences. The main advantage of C-OFDM is its resilience to transmission errors by virtue of the data being spread across a large number of independent carriers. The main exception to using C-OFDM modulation is TDtv, which uses a time division/code division multiple access (TD-CDMA) system, more in line with the operators’ existing mobile telecoms modulation schemes.

The technologies are described briefly below:
DAB-IP: The Digital Audio Broadcast (DAB) standard (EU-147) is designed to provide approximately 1 Mb/s of multiplexed audio programme data in an RF bandwidth of approximately 1.7 MHz, to mobile and portable devices. Some countries’ regulatory rules allow part of the DAB multiplex to be used for non-programme data (e.g. 20% in the UK). Thus in Packet Mode, DAB-IP can provide a broadcast platform of some 100’s of kb/s of Internet and multimedia data. DAB radio receiver technology is relatively mature and well-integrated and prototype DAB mobile ‘phone handsets have existed for some years.

DVB-H: The Digital Video Broadcast standard for Handheld devices is based on the existing DVB-T standard for fixed and in-car reception of digital TV. The main additional elements are in what is called the 'link layer (ie, the details and link specifications above the actual physical modulation), and involve the sequential turning on and off of the decoding circuitry (time slicing) to save battery power, and additional forward error correction for the encapsulated data packets. The system can provide up to around 5 Mb/s of content payload, according to transmission mode used and exhibits good spectral efficiency in its higher modulation modes.

T-DMB: The Digital Multimedia Broadcast service has been developed as a platform for mobile television services based on the format of the Digital Audio Broadcast (DAB) Standard, but with additional forward error correction for the video content. Terrestrial DMB (T-DMB) uses VHF Band III spectrum (around 200 MHz), while satellite DMB (S-DMB) uses S-Band frequencies around 2.5 GHz). The system uses the complete DAB multiplex with a payload for programmes of around 1 Mb/s. Large networks may be configured in practice using a mix of satellite S-DMB for distribution and T-DMB within urban areas.

ISDB-T: The Integrated Services Digital Broadcasting Standard has been used in Japan for satellite and terrestrial broadcasting of standard and high definition TV for some years. The flexibility of the ISDB standard allows individual segments of the 13-segment payload multiplex to be grouped and allocated as required to different services and coding formats. The government has allocated 1/13th (one segment) of the terrestrial digital TV multiplex to mobile television services, with a payload of around 1 Mb/s and the requirements that it will be a free-to-air service, with a number of manufacturers offering compatible equipment.

FLO: The Forward Link Only Standard is based on C-OFDM and coding principles similar to DVB-H. However, it uses different coding (turbo-coding) as part of its data compression processes, and a layered (hierarchical) mode of modulation for transmission. This produces a robust base service level that all subscribers can decode, plus an enhancement layer for improved pictures/details where the receiver carrier to noise level allows. Like DVB-H the service is designed primarily for operation in the UHF broadcast spectrum (450 – 860 MHz) with similar payload (up to 5 Mb/s) and modes.

TDtv: Time Division television is a newly-developed system that takes advantage of unused spectrum originally reserved for time division multiplexed 3G mobile ‘phone services. The system offers a spectrally and cost efficient technology, enabling mobile operators to deliver up to 50 channels of video to standard cell phone screens, in 5MHz of unpaired spectrum. Unlike unicast mobile TV services which take additional network bandwidth for every subscriber download, TDtv leverages MBMS to allow an unlimited number of customers to watch the same channel or use the same network bandwidth.

DVB-SSP: DVB Satellite Service to portable Devices is a developing hybrid system that has proposed the high power uplinking of C-OFDM mobile multimedia broadcast signals to a geo-stationary satellite for re-transmission direct to mobile terminals in rural areas, and via terrestrial repeaters in urban and difficult coverage areas. Because of the problems of amplifying high peak-to-mean ratio C-OFDM signals especially at very high frequencies, there are likely to be two versions of SSP – one for systems below 3GHz and one for systems above 3 GHz using different modulation and coding.

DMB-TH: After years of delay, the Chinese Government announced their compulsory standard for all digital terrestrial TV service operators in China. The standard will be known (rather confusingly) as DMB-TH (Digital Multimedia Broadcasting – for Terrestrial and Handheld). Previously, there were three candidate standards in experimental use in various Chinese cities; DMB-TH is a C-OFDM based standard containing a combination of parameters from these three, and targeted for UHF broadcast spectrum. Similar to ISDB-T, the multiplex can cater for fixed-location, mobile and handheld terminals.

All of these platforms are still developing in terms of their applications (digital rights’ management, authorisation, service information, billing etc.), human factors (handset design, electronic program guide, convergence with other 3G services etc) and network planning for reliable service coverage. This last factor is critical to the investment and financing of the mobile multimedia networks. Network planning needs to take into account many complicated issues including variable in-building transmission losses, urban street canyon effects, and reception for high and low mobile handset speeds.