DAB vs DVB-H

Digital Multimedia Broadcasting (DMB) is a digital radio transmission system for sending multimedia (radio, TV, and datacasting) to mobile devices such as mobile phones. This technology is an offshoot of Digital Audio Broadcasting which was originally developed as a research project for the European Union (Eureka project number EU147). DMB was developed in South Korea under the national IT project. And the world's first official mobile TV service started in South Korea in May 2005, although trials were available much earlier. It can operate via satellite (S-DMB) or terrestrial (T-DMB) transmission. DMB is based on the Eureka 147 Digital Audio Broadcasting (DAB) standard, and has some similarities with the main competing mobile TV standard, DVB-H. [1]

Like DAB, T-DMB is made for transmissions on radio frequency bands band III (VHF) and L (UHF), for terrestrial. Because the United States and Canada still allocate the first band as for television broadcasting (VHF channels 7 to 13) and the United States reserves the L band for military applications, DMB is still unavailable in North America. Qualcomm's MediaFLO is a proprietary system used there instead. In Japan, 1seg is the standard, using ISDB.

T-DMB uses MPEG-4 Part 10 (H.264) for the video and MPEG-4 Part 3 BSAC or HE-AAC V2 for the audio. The audio and video is encapsulated in MPEG-2 TS. The stream is RS encoding and the parity word is 16 bytes length. There is convolutional interleaving made on this stream, then the stream is broadcast in data stream mode on DAB. In order to diminish the channel effects such as fading and shadowing, DMB modem uses OFDM-DQPSK modulation. A single-chip T-DMB receiver is also provided by an MPEG-2 transport stream demultiplexer. DMB has several applicable devices such as mobile phone, portable TV, PDA and telematics devices for automobiles.

T-DMB is an ETSI standard (TS 102 427 and TS 102 428). As of December 14, 2007, ITU formally approved T-DMB as the global standard, along with three other standards,like DVB-H, OneSeg, and MediaFLO.[2]

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DVB-H (Digital Video Broadcasting - Handheld) is one of three prevalent mobile TV formats. In other words, it is a technical specification for bringing broadcast services to mobile handsets. DVB-H was formally adopted as ETSI standard EN 302 304 in November 2004. The DVB-H specification (EN 302 304) can be downloaded from the official DVB-H website.[1] DVB-H is officially endorsed by the European Union.[2][3][4] The major competitor of this technology is Digital Multimedia Broadcasting (DMB). DVB-SH (Satellite services to Handhelds) now and DVB-H2 in the future are possible enhancements to this technology, providing improved spectral efficiency and better modulation flexibility.

Technical explanation

DVB-H Frame structureDVB-H technology is a superset of the very successful DVB-T (Digital Video Broadcasting - Terrestrial) system for digital terrestrial television, with additional features to meet the specific requirements of handheld, battery-powered receivers.

DVB-H can offer a downstream channel at high data rates which can be used as standalone or as an enhancement of mobile telecommunication networks which many typical handheld terminals are able to access anyway.

Time slicing technology is employed to reduce power consumption for small handheld terminals. IP datagrams are transmitted as data bursts in small time slots. Each burst may contain up to two megabits of data (including parity bits). There are 64 parity bits for each 191 data bits, protected by Reed-Solomon codes. The front end of the receiver switches on only for the time interval when the data burst of a selected service is on air. Within this short period of time a high data rate is received which can be stored in a buffer. This buffer can either store the downloaded applications or playout live streams.

The achievable power saving depends on the relation of the on/off-time. If there are approximately ten or more bursted services in a DVB-H stream, the rate of the power saving for the front end could be up to 90%. DVB-H is a technical system which was carefully tested by the DVB-H Validation Task Force in the course of 2004 (see ETSI Technical Report TR 102 401). DVB-SH recently improved radio performances and can be seen as an evolution of DVB-H.

DVB-H is designed to work in the following bands:

VHF-III (170-230 MHz, or a portion of it)
UHF-IV/V (470-862 MHz, or a portion of it)
L (1.452-1.492 GHz)
DVB-SH now and DVB-H2 in the near future are expected to expand the supported bands.

DVB-H can coexist with DVB-T in the same multiplex.

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Wireless: Carving up big market for tiny televisions
Eric Sylvers International Herald Tribune
TUESDAY, MARCH 21, 2006
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Datamonitor forecasts that in 2009, 90 million DVB-H phones will be shipped, compared with 28 million DMB, 30 million MediaFLO and 18 million with the Japanese standard.
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Some favor DVB-H because it can be used while a viewer is in motion in cars and trains. Like DMB, it makes use of existing TV infrastructure, holding down costs. But most important, DVB-H uses less battery power than DMB and can handle higher bandwidth and thus potentially more channels - about 50, compared with about five on DMB.

"DMB is likely to have problems competing with DVB-H because DMB uses much lower bandwidth," said Eino Kivisaari, a researcher with the Helsinki University of Technology.

DVB-H saves power by sending transmissions in bursts, which lets the tuner switch off between bursts. This cuts power consumption by as much as 95 percent, Datamonitor says. But DVB-H takes longer to change channels, almost 20 seconds in some trials. That will improve, but analysts say it will not go much below five seconds.

DMB can change channels in a few seconds, and it has the advantage that it can be broadcast on frequencies that have already been allocated by most governments, according to the Datamonitor report. But this advantage will be disappear as DVB-H frequencies are allocated.
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