Nxtwave chip thwarts ghosts that haunt digital-TV rollout
eetimes.com
By Junko Yoshida
EE Times
(08/19/99, 12:20 p.m. EDT)
NEW TOWN, Pa. — Nxtwave Communications Inc., a small company spun
out of Sarnoff Corp. three years ago, has developed a chip that could simplify
and therefore accelerate the rollout of digital TV, according to information
from numerous industry sources. The new silicon solves the dynamic
multipath problem that has dogged DTV, and will enable consumers to
receive DTV signals via a simple indoor antenna.
Nxtwave (New Town, Pa.), formerly known as Sarnoff Digital
Communications, will announce its single-chip vestigial side-band (VSB)
demodulator next week. The chip, which is equipped with an equalizer
designed to deal with the dynamic behavior of the multipath, is slated for
launch later this year.
The chip's development removes an enormous element of consumer
resistance to DTV — the necessity of installing a costly outdoor antenna to
receive a ghost-free DTV picture. A DTV receiver that integrates
Nxtwave's VSB solution could conceivably receive DTV signals in a ground
floor basement just by using an indoor bow-tie antenna, according to an
industry source familiar with the breakthrough.
When it was formed in 1996, Nxtwave received from Sarnoff Corp.
(Princeton, N.J.) non-exclusive rights to VSB technology developed by
Sarnoff. Meanwhile, Motorola Inc. has a similar non-exclusive arrangement
to use Sarnoff's VSB technology. Motorola is also scheduled to unveil its first
VSB chip early next week.
Nxtwave is said to have developed its own intellectual property in the DTV
signal-reception area in the last three years that allowed it to develop a
unique VSB chip that's resistant to dynamic multipath, based on its own
design and implementations.
An engineering executive at a major DTV system company acknowledged
that DTV reception via indoor antennae remains a "horrendous problem" for
DTV penetration in the U.S. market. "If [the Nxtwave development is] true,
VSB-based DTVs could really benefit from a chip like that," the executive
said.
The problem of the dynamic multipath for DTV receptions is not new. Field
tests results of the Advanced Television Systems Committee (ATSC)
transmission system, which were carried out in the mid-1990s, identified "the
limiting factor in terrestrial field operations is often not white noise, but rather
severe dynamic multipath on UHF and severe impulse noise on VHF."
Other chip vendors have tried to address the multipath issue, for example, by
increasing the number of filter taps in an equalizer. But until Nxtwave's chip
development, no company had ever claimed to solve the complex, dynamic
multipath issue. Nxtwave is said to have made a fundamental architectural
change to a VSB chip to address the issue.
The difference between multipath and dynamic multipath is fairly
straightforward. Discrete ghosts are often associated with multipath
conditions of large, flat surfaces, such as tall steel buildings. However,
multipath conditions can occur in areas with hills and dense foliage in fringe
areas, where a signal can travel through many paths to a DTV receiver.
When the signal is bounced back from even a slightly moving object, such as
a tree, rather than from a steady object like a building, complex ghosts could
emerge. This requires the receiver's equalizer to "work hard" to reduce the
ghosts to acceptable levels. Such complex ghosts often have a time-varying
or dynamic nature to them, and it is that dynamic behavior of the multipath
that is the most challenging for the equalizer.
Nxtwave Communications, a rapidly growing company with 35 employees,
declined to comment on its upcoming silicon announcement. The company is
said to have a number of specialists in VSB, ghost cancellation and the
transmission of DTV signals under adverse circumstances.
Engineers at DTV technology companies who have either seen or heard
about the simulation of Nxtwave's new chip hold high hopes for the
technology. "This could add a major push for DTV installation both on a PC
and on a family room TV, through an indoor antenna," one executive said.
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