China writes its own digital TV standard
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 ******** 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.
"In COFDM," said Xingjun Wang, a Tsinghua University professor who led the developers of DMB-T, "there is nothing in the guard interval. So by using that part for channel estimation, it saves capacity from the carrier part by about 10 percent. Also, in the time-domain timing recovery, the accuracy and response time will be much shorter than in COFDM technology, which uses a frequency domain. Generally speaking, we can increase 3-dB sensitivity compared to DVB-T."
Usually, OFDM approaches—the basis of DVB-T/H, ISDB-T, T-DMB and Media-Flo—are favored in broadcasting. Trials for Tsinghua's DMB-T are under way in about 30 cities, handily eclipsing the trials for Jiaotong's ADTB-T.
What remains unclear, though, is whether all of China's digital TVs—fixed and mobile—will have to support both the TDS-OFDM and VSB schemes.
Tsinghua University's Wang said demodulators should support both specs, even in handhelds. Rather than just sticking two demodulators on one chip, he said, his team used new techniques to enable the dual-mode demodulation. Details of the new techniques were not immediately available.
On the other hand, Legend Silicon's Yang, said, "Maybe the government will ask the market to make a decision," by giving broadcasters an option on modulation schemes. Yang added, however, that the intent of the new Chinese DTV standard is "to make the single carrier and multicarrier adhere as closely as possible."
Originally, China planned to release a draft for terrestrial digital TV in 2003 and to start the transition in 2004, but industry and government officials brokered a compromise between the two university efforts that emerged as leading contenders. The rivalry, insiders say, was fierce.
At that time, the technologies were quite different, said Legend Silicon's Yang. But the teams have tried for two years to harmonize their efforts.
"It's not an apples-to-oranges comparison anymore," Yang said. "The frame size, the P/N sequence, the synchronization data—everything is the same. The only difference is whether the signal is frequency-domain-defined data or time-domain-defined data."
He called the Chinese standard closer to Japan's ISDB-T than Europe's DVB-T, because China and Japan consider the issue of low power consumption in the main spec. China's DMB-T/H is also unique in that, unlike DVB-H, both terrestrial and handheld devices are designed from the ground up to use the same ********.
Like ISDB-T, the Chinese standard will support HDTV on nomadic devices, while Europe's DVB-T now supports only standard definition. China's new standard also differs from T-DMB, originally developed by South Korea for mobile TV. T-DMB, based on the Eureka-147 Digital Audio Broadcast standard, transmits at lower data rates and is designed for small portable devices like handsets and PDAs.
One key difference between Korea's T-DMB and China's DMB-T/H: The former uses multiple, smaller channels at lower bandwidth, and must use more ******** for channel separation; the latter uses wider channels at higher bandwidth for better ******** efficiency, but the trade-off is a slightly higher receiver cost.
A handful of Chinese companies already have silicon, or are prepping it, for DMB-T/H. Legend's demodulator handles both DMB-T and ADTB-T, and it is working on a low-power version for handheld devices, said Dinesh Venkatachalam, vice president of engineering at Legend.
Shanghai High Definition Digital Technology is working on a second-generation chip that will support both components of the forthcoming standard. Others designing chips include Hangzhou-based Guoxin Technology and Shanghai-based Chinips Electronics. In handhelds, Microtune said it plans to expand its mobile tuner product line, including China's DMB-T/H.
But multinationals in the set-top-box business are more cautious. At STMicroelectronics, "We are watching the standard," said Bob Krysiak, corporate vice president for Greater China, "and we think we understand the combination of the two, but just want to see it written down, and then we will be prepared to implement something as soon as the ink is dry on the spec." Conexant is also taking a wait-and-see approach. "I can't say when we will have a chip out but we are engaged and tracking the spec," said Henry Derovanessian, vice president of marketing for broadband media processing at Conexant.
Set-top-box makers and some TV makers like Haier, Samsung and LG also have prototypes based on DMB-T/H. But Chinese TV and STB makers are mixed over how quickly consumers will adopt DTV services, and that will affect the pace at which TV makers integrate the digital tuners. "Hopefully, the integrated TV will hit the market this year, but it will take at least 10 years to popularize," said Chunguang Wang, a design engineer at TV maker Changhong Electric Co. "It's not easy to change the situation that a large number of families watching digital TV use a complementary STB, and the government is encouraging using STBs as a faster way of popularizing digital TV."
Indeed, the next challenge will be kick-starting the analog-to-digital transition. China had wanted to see 100 million DTV households by 2008, when it plans to air HDTV content from the Summer Olympics in Beijing. A 2015 deadline is in place to end analog broadcasts.
But China is seeing a slow transition. By the end of 2005, only 4.1 million households were using digital TV services, mostly based on cable, according to government figures. That was up considerably from 1 million households the year before, but far short of the government's target, set last year, of 30 million households.
Hurdles include the cost of the STBs and services, and a lack of compelling content that would motivate users to change. The terrestrial transition may face similar challenges, said Mark Natkin, a Beijing-based analyst for Marbridge Consultants.
There are currently 1 users browsing this thread. (0 members and 1 guests)