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China Plans Own Digital TV Standard
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Tsinghua
University, China's foremost technology university, has
joined with a Chinese-owned US technology partner in digital
TV development, according to China
Daily.
The alliance is designed to forge a DTV transmission
standard for China that combines spread-spectrum and
orthogonal frequency-division multiplex technologies. With
an eye to future mobile applications, the standard, if
successful, could leapfrog dated US and European specs, some
observers said.
The digital transmission technology is being explored
by researchers at Tsinghua University, based in Beijing,
together with Legend Silicon. The goal of the group is to
develop "a robust and yet very flexible, future-proof
modulation scheme," said Lin Yang, Legend Silicon's
chairman and president.
Borrowing heavily from telecommunications schemes,
the new DTV transmission technology is designed to allow
China to use its DTV spectrum not only for standard- and
high-definition TV broadcasting but also for future data
services and even cellular phone applications.
"If China wants to jump start its information
industry, we need a DTV standard that uses its spectrum
efficiently," Yang said. "We regard this as a
serious natural-resource issue."
Seventy-five percent of China's available spectrum
under 1 GHz is set aside for TV applications. Of the
remainder, 10 to 15 percent is controlled by the military
and the rest is available for existing cell phone
applications. Hence, some engineering executives here said
China needs a DTV standard that allows the sharing of
spectrum reserved for broadcasting with emerging information
delivery services.
- Third way
As a result, Chinese government officials and industry
executives, along with their US-based partners, appear
committed to developing a third way to launch digital TV
broadcasts, based neither on US nor European digital TV
specs. Both US and European camps have waged lobbying
efforts to persuade the Chinese government to adopt
their differing approaches to digital broadcasting. But
beyond trials, neither has received a firm commitment
from Beijing.
China has been carefully monitoring the slow deployment
of digital TV in the United
States and Europe. Persistent DTV transmission
problems, particularly with the US vestigial sideband£¨8-VSB
£© modulation scheme, have "worried us
somewhat," Yang said, "but it also convinced
us that there is an opportunity" for China to
create its own DTV standard.
Observers in China and in the United States agree that
China will go its own way.
"Whatever they adopt will be called a Chinese
standard," said Robert Graves, chairman of the US
Advanced Television Systems Committee. "They do
seem quite intent on putting their own stamp on whatever
standard they pick."
A Chinese DTV standard that incorporates a combination
of broadcast and spread-spectrum technologies "is
going to happen," asserted Ya-Qin Zhang, managing
director of Microsoft Research China, here, and a former
video engineer with US HDTV Grand Alliance member
Sarnoff Corp.
Responding to the Chinese government's plan to roll out
digital TV broadcasts in 2003, three different groups
are expected to submit unique terrestrial DTV
transmission technologies to the Standards Institute of
the State Administration of Radio, Film and TV £¨Sarft
£©¡£ In May, lab testing,
followed by field tests, is scheduled in Beijing, Shanghai
and Shenzhen. The tests will provide side-by-side
comparisons of the homegrown systems with the US
Advanced Television Systems Committee spec, Europe's
Digital Video Broadcast standard and Japan's
Terrestrial Integrated Services Digital Broadcasting£¨ISDB-T£©¡£
The deadline for submitting DTV technology proposals is
April 30.
- Technology teams
Besides the Tsinghua University group, the competing DTV
technology development teams are the HDTV Technical
Expert Executive Group£¨TEEG£©, headed
by Wenjun Zhang, and the Academy of Broadcasting Science
£¨ABS £© team, led by Baichuan Du.
Zhang said his test system has a mobile
telecommunications feature that uses coded orthogonal
frequency-division modulation£¨COFDM
£©¡£ "We own the
intellectual property rights of the technologies,"
he said. "They are based on QAM£¨quadrature
amplitude modulation £©¡£"
TEEG, backed by China's Ministry
of Science and Technology as well as China's State
Planning and Development Committee, has already
developed China's first two prototype DTV systems, based
on 8-VSB and the COFDM multiplex scheme. Some observers
said TEEG may be furthest along in implementing 8-VSB
and COFDM.
Meanwhile, the Academy of Broadcasting Science group is
working on the modified version of QAM technology for
terrestrial DTV transmission. The group's goal is to use
64 QAM both for cable and terrestrial DTV modulation.
The ABS group is reportedly using a VSB/QAM chip
supplied by Broadcom Corp. It is leveraging a large
number of filter taps built into the Broadcom chip's
equalizer, originally designed for better VSB reception,
to minimize delays associated with QAM-based terrestrial
DTV transmission.
"It is not so clear which technology will be
China's final choice," said Du, vice president of
ABS. "But it's obvious that China needs a
technology of its own.
Up to now, the Tsinghua University group has been
secretive about its DTV work. Of the three efforts,
industry sources said, the Tsinghua team appears to have
the most novel and perhaps the most ambitious solution.
The project is overseen by the State Key Lab for
Microwave and Digital Communication and is led by
Tsinghua professor Ke Gong.
Legend Silicon, cofounded by three Tsinghua University
graduates transplanted to Silicon Valley, is a member of
the National Key Lab's Digital TV Transmission
Technology Development Center. Legend Silicon executives
said they expect to receive transmitter and receiver
chips based on the company's designs from an unnamed fab
outside China by the end of March.
Responding to doubts about China's chip-design
capabilities, Legend Silicon's Yang, also a Tsinghua
professor, said, "We've done solid computer
simulation designs and have a very good design
flow." After completing the design work, "we
got it working last July," Yang said. "We had
no problems in signing off ASIC designs either."
The National Key Lab is also equipped with Cadence
Design tools and serves as a design training center.
Yang is a former director of the wireless group at
Cadence's Design Services Group.
- Leapfrog approach
If China succeeds in developing its own DTV standard,
some experts said it might be able to leapfrog US and
European DTV standards. Political disputes dogging those
standards have made technology upgrades difficult.
Whereas the underlying technologies of the US standard
were developed a decade ago, the Chinese DTV effort aims
to respond to the future needs of the converging
communication, TV and Internet industries. Indeed, when
the U.S industry was developing its DTV spec, there was
no requirement for either mobile or Internet
applications.
"China today is working on a homework
assignment" very different from the one given
earlier to US developers, Yang said.
The core DTV transmission technology, designed by
Tsinghua's Key Lab, is called time-domain synchronous
OFDM£¨TDS-OFDM£©¡£ While
maintaining data rates as high as 32 Mbits/second to
cater to multimedia services, TDS-OFDM is designed for
better synchronization of mobile and burst data
broadcasting.
Using TDS-OFDM, transmission signals are separated into
two parts£º synchronization signals, used
primarily for channel selection, and signals that carry
actual programs. "We use spread-spectrum technology
to send synchronization data, while we depend on OFDM to
send continuous TV broadcast programs," Yang said.
Spread spectrum is used for the synchronized signals,
Yang said, because they need to remain "robust and
easy to detect in a very noisy environment."
- Signals saved
Illustrating the importance of synchronization, Yang
said the biggest DTV problem is the so-called cliff
effect, wherein a digital receiver goes dark if signal
reception is poor. By integrating control signals in the
synchronized data, sent separately with digital
broadcasts using spread-spectrum technology, consumers
could, for example, use such signals to adjust an
antenna to receive pictures.
Tsinghua University has also developed a DTV protocol,
Digital Multimedia Broadcast-Terrestrial£¨DMB-T
£© , that could allow an 8-MHz DTV channel to
be reused for cellular network applications.
"We have 10 million people living in Beijing
alone," Yang said. "If all these people wanted
data services and video-on-demand services at the same
time, we'd have a problem. We need a technology that
supports multiple RF, signal RF and cellular
networks."
Developing its own intellectual property is another goal
of China's DTV effort. Yang described Tsinghua's DMB-T
approach as "a lot of public domain technologies
combined together." But Key Lab has filed for a
patent covering the entire system. Seven others have
been filed for individual transmission technologies.
(people's daily)
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