Subject: [NEXTEL-1] UWB: Could it uniPHY?

From: [email-masked]
Date: Sun, 15 Feb 2004 04:04:45 -0500

UWB: Could it uniPHY?
Patrick Mannion
Feb 09, 2004 (10:00 AM)

URL: http://www.commsdesign.com/showArticle.jhtml?articleID=17602473

MANHASSET, N.Y. — A radio maker says it has found a way for ultrawideband
systems based on differing technologies to get along.

PulseLink Inc. is preparing to detail for members of the IEEE 802.15.3a task
group a Common Signaling Protocol that allows
coexistence of multiple UWB physical layers that would otherwise obliterate one
another.

The company is hoping to orchestrate an orderly introduction of UWB while
sidestepping the rift between competing UWB standards
proposals now deadlocked before that task group.

The protocol will be unveiled before task group members on Feb. 23 in an ad hoc
meeting at PulseLink's facility in Carlsbad, Calif.
The meeting will take place without a formal nod from IEEE, said task group
chairman Bob Heile. Heile described the philosophy
behind the Common Signaling Protocol (CSP) as essentially sound. "Whenever you
have unlicensed bands, you run the risk of
interference, so some level of coordination between devices is a good idea. It's
good etiquette," he said.

To make that happen, PulseLink is proposing a separate low-data-rate physical
(PHY) layer, on the order of 1 to 2 Mbits, that would
function as a signaling channel between two co-located UWB devices. Using
time-division multiple access (TDMA), "this channel would arbitrate between them
[as to] who's going to take what frames and when," said CTO John Santhoff, who
co-founded PulseLink in 2000.

Santhoff said the company has "an implementation that we have been working on
in-house. What we are offering the IEEE is an
open framework on which they can build and customize the concept to fit their
specific needs and requirements." PulseLink, he said,
will offer its core patents "under RAND [reasonable and nondiscriminatory]
licensing."

Some industry watchers last week hailed the proposal as smoothing the way for
the use of disparate physical layers, thereby
allowing UWB innovation to continue unabated. On the downside, others questioned
the value of coexistence without interoperability,
as well as the wisdom of encouraging the development of multiple PHYs. That
could ultimately create a burden for the OEMs that
must support them and confusion among end users, critics said.

PulseLink professes no bias toward either of the UWB technologies now on the
table before IEEE: the proposal of the Multiband-OFDM

Alliance (MBOA) or the Motorola-led DS-CDMA approach. The 802.15.3a group's
effort to define a physical layer for high-speed
personal-area networking at up to 480 Mbits/second over 1 meter has ground to a
halt, with both sides refusing to compromise on
what are vastly different technologies. The rift has raised the possibility that
the two camps will define de facto standards and let the
market decide.

According to Santhoff at PulseLink, the only way to resolve the issue is with
some kind of intelligence that would keep two different
devices from radiating into the same time slot. That is the thinking behind the
Common Signaling Protocol.

"This didn't come up until the [UWB] schism got as bad as it did," said Bruce
Watkins, PulseLink's president and chief executive
officer. "We couldn't care less [which proposal wins], except it's going to be
bad for all of us if people start buying UWB devices that
don't work."

PulseLink makes UWB radios for wireless LANs and appears to be close to
deployment. Its potential market could get hammered if
different vendors bring out multiple UWB radios that can't talk to one another
to coordinate transmissions.

CEO Watkins hopes to forestall a scenario whereby devices introduced in five to
10 years would interfere with technology that comes
out today. He reported that Motorola Inc. "likes the [CSP] concept a lot-they
appreciate that there's going to be other PHYs" besides
the direct-sequence CDMA one that the company and its UWB-silicon subsidiary,
the former Xtreme Spectrum, espouses.
Along with requiring minimum overhead and power, the CSP's low-data-rate channel
also has the attraction of longer range, based
on the physics of rate vs. distance. "It actually extends beyond the normal
range of the communications devices themselves, so it
can be a very reliable protocol," said Santhoff. The channel could also be used
for geopositioning applications, he added, where
accuracy improves with the number of devices taking part in the coordination.

At a fundamental level, "the proposal takes advantage of the fact that nobody is
ever radiating [energy] more than 10 percent of the
time, even at the highest rate," Santhoff said. CSP "can use that empty time to
interleave [the disparate radios' signals] so there
won't be delays or latencies." Interleaving is performed by the TDMA-based
media-access controller (MAC).

Given the wariness of both Motorola and the MBOA in modifying their designs,
PulseLink takes pains to emphasize CSP's two possible implementation paths-one
in firmware, the other requiring only minor hardware modifications at the
receiver.

Options for generating the low-rate signals between the two completely different
modulation schemes are numerous, said Santhoff.
Indeed, "It can be as simple as on/off keying." The orthogonal
frequency-division multiplexing radio used in the MBOA proposal
would "turn all its carriers on and off together," while the DS-CDMA radio in
the Motorola scheme "would just detect whether it [the
other radio] is there or not," he said-or vice versa.

To detect signals on the receivers of both types of radios, the protocol relies
on similarities in their signal chains, right up to the
output of their respective analog-to-digital converters. There, the MAC will
detect and decode the difference in pulse widths among
OFDM, DS-CDMA and CSP signals as they emerge.

"The [DS-]CDMA solution is looking to sample something on the order of 1
nanosecond, we're talking [for CSP] something about 100
ns, while the OFDM signal is 333 ns," said Santhoff. "This detection and
decoding can be easily performed by the MAC and
implemented with a firmware upgrade." PulseLink is aware that some
implementations will require more than a simple firmware
upgrade, however, which is the reasoning behind the second path. "In a
worst-case scenario," said Santhoff, "we propose putting an
inexpensive modulation detector at the output of the last LNA [low-noise
amplifier] that would be able to recover the modulation for
the low-rate channel." He estimates this would take only 0.1 to 0.2 mm2 of die
space.

However, both schemes are only outlines, Santhoff said, and "the final
implementation is up to the standards body." The company
promises to make its intellectual property available on a fair and reasonable
basis if CSP becomes part of the UWB standard."We will
contribute [IP] on the same basis as everyone else," Santhoff said.

Although Motorola looks favorably on PulseLink's idea, some of the MBOA member
companies were less than enthusiastic last week.
"It is unlikely to succeed," said Stephen Wood, UWB market strategist for Intel
Corp.'s Communications Technology Lab (Hillsboro,
Ore.). Mark Fidler, senior engineer-scientist at the Imaging and Printing
Systems Division of Hewlett-Packard Co., thinks the proposal
"has merit, as it allows forward migration and will allow other technologies to
evolve. But it has flaws," he said.
Coexistence, unlike interoperability, "only allows devices to operate side by
side," Fidler said. "But the end user would much rather
have a bunch of devices that would communicate with each other, and this doesn't
provide that." In addition, he said, the scheme will
promote differentiation without bringing much extra value to the end user.

"Most of the large nonsemiconductor companies want a single PHY," he said. "They
don't want multiple product definitions that aren't
based on the merit of the product but on which radio it has. . . . What I don't
want to do is come out of the chute with 10 different
PHY layers."

Fidler said he aligned with the MBOA camp within the 802.15.3a group "for
performance reasons only." HP doesn't have "a vested
interest in the silicon side."

For Fidler, the essentials for UWB are interoperability, ease of implementation
and broad company support.

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