China writes its own digital TV standard

TAIPEI, Taiwan — After years of rivalry and numerous delays, China is poised to roll out a long-awaited standard for terrestrial digital television.

The mandatory standard will cover both fixed and mobile terminals and will eventually serve more than half of China's TV viewers, especially those in suburban and rural areas.

Though its name is not official yet, the standard is being called Digital Multimedia Broadcast-Terrestrial/Hand- held. DMB-T/H signals the beginning of the end for small Chinese trials of Europe's DVB-T standard, and it adds another rival to the mix for mobile-TV services in China—the world's largest market for TVs and mobile phones.

An official announcement of the new standard is imminent, sources in China said, and could come as soon as this week. Its release will end a fierce rivalry between two universities with very different approaches to the terrestrial standard.

DMB-T/H is an outgrowth of work at Tsinghua University in Beijing and Jiaotong University in Shanghai, each of which had hoped to provide the sole technology--but neither of which had the technical or political muscle to achieve that goal.

The result is less a combination of their work than a coexistence of two modulation schemes—Tsinghua's time-domain synchronous orthogonal frequency-division multiplexing (OFDM) and Jiaotong's vestigial sideband (VSB) modulation.

"Like 802.16, China's new digital TV standard has both a single-carrier and a multicarrier option," said Lin Yang, president of Legend Silicon, a Fremont, Calif.-based company closely affiliated with Tsinghua University.

China will deploy digital TV over VHFIII and UHF spectrum ranges, using 8-MHz channel bandwidth. Jiaotong's portion of the standard is called ADTB-T, for Advanced Digital Television Broadcast-Terrestrial. Like the U.S. DTV standard, ATSC 8-VSB, it is based on single-carrier frequency.

Supporters say ADTB-T technology lets signals travel longer distances at less power, with user terminals that are better at detecting weak signals. It has an edge in protecting against adjacent-channel interference and offers better performance at higher bit rates, making the technology a good candidate for HDTV streams to fixed terminals, said Yao Wang, an executive at ASIC designer Shanghai High Definition Digital Technology Industrial Co., which is affiliated with Jiaotong University.

But unlike ATSC, Jiaotong's ADTB-T can provide nomadic TV service as well. In Shanghai, a trial has been under way since 2004 in which five transmitters broadcast to about 2,000 terminals, 1,600 of them in taxis. Nomadic services are also being tested on buses in Weihai, Shandong Province, and trials for fixed TV services are under way in five other cities and counties.

But Tsinghua believes its DMB-T proposal is good not only for fixed terminals but also for video and data broadcasts to portable devices like handsets and PDAs.

DMB-T taps the OFDM modulation scheme of Europe and Japan. Its 4k carriers are modulated with quadrature phase-shift keying or quadrature amplitude modulation. But it differentiates itself by using time-domain synchronous (TDS) OFDM.

With data rates as high as 32 Mbits/second to cater to multimedia services, TDS-OFDM aims to better synchronize mobile and burst data broadcasts.

But TDS-OFDM, unlike coded OFDM, uses the protective guard interval between data blocks by inserting a pseudo-noise sequence to do synchronization and channel estimation.