[opendtv] China writes its own digital TV standard
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 26 Jun 2006 12:19:05 -0400
Very interesting.
I thought ADTB-T was the orthogonal AM scheme described some time ago,
which was almost identical to 8-VSB except that it used a two-phase AM
approach instead of chopping off a sideband of AM. But here they
actually mention that it's VSB. So something must have changed.
China seems to have liked Sinclair's idea. Accept both.
Bert
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China writes its own digital TV standard
Mike Clendenin
(06/26/2006 9:00 AM EDT)
URL: http://www.eetimes.com/showArticle.jhtml?articleID=3D189601091
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.
"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 spectrum.
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
spectrum for 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-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."
Slow transition
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.
All material on this site Copyright 2006 CMP Media LLC. All rights
reserved.
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