A new approach to delivering wireless signals, known as
"spatial processing," is gaining credibility as a means of vastly increasing the
data or voice capacity of a given spectrum block.
Lucent Technologies, following a Bell Laboratories
demonstration of a tenfold capacity increase over a standard wireless link, has
inaugurated a high-priority product-development effort, officials said.
"While there is still a great deal of applied research
required before we apply this discovery, we are very excited about its potential
implications for our future wireless systems," said Jim Brewington, president of
Lucent's wireless-networks group.
Lucent is not alone in applying new algorithms in wireless
transmission to achieve transmission of multiple-user signals simultaneously over the same
frequency.
The leader in the field -- ArrayCom Inc., based in San
Jose, Calif. -- has been supplying spatial-processing solutions through its
"IntelliWave" wireless-local-loop system for two years. ArrayCom has contracts
for commercial deployments in Japan, the Philippines and China, as well as a manufacturing
and distribution agreement with a major telecommunications-equipment supplier in Latin
America.
The commercial applications so far use the air interface
developed for the "Personal Handyphone System" that is used in Japan, which
provides a fixed service with support for "neighborhood roaming," as well.
The latest deployments -- over the facilities of wireless
carrier Guangzhou Telecom in China and those of SMART Communications in the Philippines --
are using an enhanced-PHS air interface, said Christine Oliver, spokeswoman for ArrayCom.
But ArrayCom has not succeeded in winning support on the
WLL front among domestic carriers, although many players in personal-communications
services and cellular have made known their intentions to add WLL services to their
packages.
"We're still talking with a number of companies,
but there's nothing to report," Oliver said.
Another player now entering the spatial-processing field is
Ericsson Inc., which is supplying a dual-user per-channel system for a test over the GSM
(Global System for Mobile Communications) wireless network of Mannesman Mobilfunk in
Germany. Ericsson is expected to deliver a commercial product within the next year or so.
ArrayCom chairman and co-founder Martin Cooper welcomed the
developments at Lucent and Ericsson as a sign that the concepts underlying spatial
processing are finally taking hold among major players.
"These endorsements send a clear message to the
wireless industry that integrating adaptive smart-antenna systems into system development
is now a competitive imperative," Cooper said.
"The benefit of this spatial processing to an operator
is generally up to a tenfold increase or more in the capacity of typical base
stations," he added.
Dubbed "BLAST," the Lucent approach involves new
algorithms written by senior engineers at Bell Labs. The company said it promises to
provide gains of as much as 20 times existing wireless-carrying capacity, company
spokesman Dick Muldoon said. But he declined to say how long it will take the company to
develop the technology into a commercial product.
Such algorithms are used to separate signals coming into a
base station from multiple transmission points over the same frequency, using the varied
physical scattering properties of the multiple paths to sort them out.
In the case of the BLAST system, a single user's
signals are subdivided into multiple substreams and sent out over the same frequency band
via multiple-antenna transmitters.
At the receiving end, multiple antennas pick up the
substreams, which are superimposed together on each antenna.
High-speed signal processors look at all of the signals
from all of the antennas simultaneously, first extracting the strongest substream, then
proceeding with the remaining weaker signals until the full information stream is
recovered and recomposed, all in an instant of time. This results in a transmission of 20
to 40 bits per hertz -- far exceeding traditional capacity, officials said.
One of the challenges that Lucent must deal with is finding
a way to tightly integrate the antenna processing, Muldoon said.
"It takes time to find better ways to do
multiple-antenna processing," he added.
Such antenna processing -- using phased-array technology --
is key to the system that ArrayCom has developed, Oliver noted. The latest version of the
system, now undergoing tests, is capable of supporting three simultaneous users over the
same frequency in the same time slot, she said.
ArrayCom is working on a variety of WLL systems for the
domestic market, including CDMA (code-division multiple access) at 1.9 megahertz and
analog cellular.
"We're a good year away from a CDMA
version," she added.
Success will open the capacity of existing wireless
providers to the point where supplying broadband-data services -- now a key goal of the
International Telecommunications Union's third-generation initiative -- will be
doable without painful sacrifices in mobile-service bandwidth.
"The breakthrough results prove the feasibility of a
technology that leapfrogs what we assumed about the limitations of radio
communications," Brewington said.
