Wednesday, January 25, 2006

Korea's DMB Techology

Korea's telecommunications is seen as cutting edge. I often have difficulty explaining some of Korea's recent advancements. This Chosun Ilbo article does a great job on detailing DMB. DMB is technology that can provide digital video and audio content from various services connected to the mobile network.

Chosun Ilbo

Digital multimedia broadcasting or DMB, of both the terrestrial and satellite kind, is bringing television into the palm of consumers’ hands on the move. But how does it work, and what is the difference between the two? The Chosun Ilbo has the answers.

The predecessor of DMB was digital audio broadcasting or DAB, first developed to transfer higher-quality audio to portable devices. As far back as 1987, European countries set up a project group named Eureka-147, and by 1995 they were ready to start the service. Korea began discussion about bringing in the technology in 1997, but by 2003 Korea undertook the development of its own improved version of DAB that would be capable of transmitting multimedia content. That became terrestrial DMB.

Satellite DMB is based on the Japanese System E, which uses a technology called code division multiplexing or CDM that also allows multiple signals to be transmitted over the same bandwidth simultaneously, for the convenience of Korean and Japanese companies.

The main difference between the two DMBs is how they transfer the signal. Satellite DMB uses a signal from the joint Korean-Japanese satellite Han-byeol. It works on a bandwidth of 2.6 GHz, which is low for a satellite yet still higher than terrestrial signals. As a result, satellite DMB requires extra gap fillers for reception in locations such as subways or buildings.

Terrestrial DMB uses transmitting towers, relying on VHF channels used for television signals. The service splits one channel into three blocks and contains a number of video/audio channels in each block. The number of channels is more limited than for satellite DMB but more efficient. Terrestrial DMB uses a low broadband frequency of 200 MHz that can get around obstacles and thus reach users easily wherever they are, although longer antennas are required.

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