[opendtv] China comes up with own DTV standard
- From: Steve Wilson <stevenjwilson@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 28 Jul 2006 08:46:26 -0700
FYI...
http://www.eetasia.com/ART_8800423182_590626_82328af9200606.HTM[1]
Posted : 28 Jun 2006
After years of rivalry and numerous delays, China is poised to roll out a
long-awaited standard for terrestrial DTV.
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/Handheld. DMB-T/H[2] 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[3] 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 OFDM and
Jiaotong's vestigial sideband (VSB) modulation.
"Like 802.16, China's new DTV[4] standard has both a single-carrier and a
multicarrier option," said Lin Yang, president of Legend Silicon, a company
closely affiliated with Tsinghua University.
China will deploy DTV over VHFIII and UHF spectrum ranges, using 8MHz
channelbandwidth. Jiaotong's portion of the standard is called ADTB-T, for
Advanced Digital Television[5] 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
lesspower, 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
atASIC 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.
InShanghai, 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
terminalsbut 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 32Mbps 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 3dB 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 DTVs—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 DTV 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 spectrum.
Like ISDB-T, the Chinese standard will support HDTV on nomadic devices,
whileEurope'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
likehandsets and PDAs.
One key difference between Korea's T-DMB and China's DMB-T/H: The former
usesmultiple, smaller channels at lower bandwidth, and must use more
spectrumfor channel separation; the latter uses wider channels at higher
bandwidth for better spectrum 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-generationchip that will support both components of the forthcoming
standard. Others designing chips include Hangzhou-based Guoxin Technology
andShanghai-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 (STB) 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.
STB makers and some TV makers like Haier, Samsung and LG also have
prototypesbased 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 DTV use a complementary STB, and the government is
encouraging using STBs as a faster way of popularizing DTV."
Slow transition
Indeed, the next challenge will be kick-starting the A/D 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
placeto end analog broadcasts.
But China is seeing a slow transition. By the end of 2005, only 4.1 million
households were using DTV 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
--- Links ---
1 http://www.eetasia.com/ART_8800423182_590626_82328af9200606.HTM
2
http://www.eetasia.com/search/keyword.php?keywords=DMB-T%2FH&ACTION_TYPE=SEARCH&operation=PHRASE&search_mod=advanced&section=ALL&encode=1&sub_form=quickform
3
http://www.eetasia.com/search/keyword.php?keywords=Tsinghua+University&ACTION_TYPE=SEARCH&operation=PHRASE&search_mod=advanced&section=ALL&encode=1&sub_form=quickform
4
http://www.eetasia.com/search/keyword.php?keywords=DTV&ACTION_TYPE=SEARCH&operation=PHRASE&search_mod=advanced&section=ALL&encode=1&sub_form=quickform
5
http://www.eetasia.com/search/keyword.php?keywords=Digital+Television&ACTION_TYPE=SEARCH&operation=PHRASE&search_mod=advanced&section=ALL&encode=1&sub_form=quickform
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