Cellular 4kbps vocoders

Double Or Nothing
Margo McCall July 15, 2002 Wireless Week

CDMA and non-CDMA carriers alike seek major capacity gains. But the way
in which they will boost their networks varies. New vocoders could
improve the odds.

While CDMA carriers such as Verizon Wireless and Sprint PCS expect to
double their network capacity through 1XRTT upgrades, non-CDMA carriers
in the United States don't plan to linger behind. They hope to rack up
similar gains through new vocoder technology that carriers around the
world eventually may deploy.

Nextel Communications Inc. was ready to embrace 1XRTT as a means of
migrating to 3G. But then Motorola Inc. came along with a 4 KB vocoder
that produced the same results as 1X-at a fraction of the cost.
Upgrading its iDEN network will cost Nextel far less than pursuing an
entirely different technology. And so far, the half-rate vocoder-which
Motorola claims will beef up capacity about 80 percent-apparently is
working well.

Tests are ahead of schedule and early indications show voice quality is
preserved, the biggest challenge in reducing bits. "It tested as good or
better than existing technology," says Nextel spokeswoman Audrey
Schaeffer.

AT&T Wireless and Cingular Wireless are both using adaptive multirate,
or AMR, vocoder technology to tease capacity gains out of their networks
as they complete their GSM overlays. "This is a smart vocoder," says
Dave Williams, Cingular's vice president of strategic planning. "It
switches coding schemes. It uses the coding scheme that's more efficient
and uses less bits as you move toward the edge of the cell with more
interference."

Early tests are promising, in terms of both voice quality and capacity.
"The results are very, very favorable," he says.

Members of the wireless networking community have tried for years to
successfully lower the vocoder bit rate without seriously affecting
voice quality. Vocoders contained in handsets are responsible for
converting analog voice signals coming in through the handset microphone
to digital signals and back again, so the voice signal can be understood
on the other end. The digital signal is compressed from 64 KB to about
12 KB by running it through speech algorithms.

Until recently, forcing bit rates below that rate caused deterioration
of voice quality, says Jim Gunn, an associate with the Dallas research
firm Forward Concepts. Gunn says AMR should greatly help AT&T Wireless
and Cingular, both of which elected to take a GSM/GPRS/EDGE migration
route. "There's no question that the GSM community has been handicapped
in terms of capacity," says Gunn, whose study on network capacity is
targeted for release in the third quarter. "This should enable them to
double the capacity on their networks."

European GSM carriers reportedly are taking a wait-and-see approach.
Williams says Cingular is slated to be the first carrier in the world to
roll out AMR vocoders. Ericsson, Nokia and Siemens-the vendors hired to
carry out Cingular's billion network upgrade-are supplying the AMR
vocoders.

If the technology works as well as promised, European carriers could
well change their 3G migration paths from UMTS to EDGE, which most
previously abandoned. "Everybody is waiting on this," Gunn says. "The
decision by AT&T Wireless and Cingular is going to be the big catalyst."

Just as with 1XRTT, compatible handsets are necessary to realize the
capacity gains. AT&T Wireless spokesman Ritch Blasi says phones with AMR
capability should be available by the end of the year. Cingular's first
850/1900 MHz GSM handset and some of its GAIT handsets, which are
designed to roam between TDMA and GSM networks, will be equipped with
AMR chips.

Schaeffer says Nextel isn't worried about getting handsets to its
customers, since millions of new phones are put into service each year,
both through new customers and existing customers opting for upgrades.
"It will be transparent to the customer. Nobody needs to do anything.
For every two phones sold, it will be like adding one," she says.

Eventually, every handset manufactured will be equipped with AMR chips.
But handsets could initially be a hang-up, says Gartner analyst Bryan
Prohm, because delays have become an almost expected part of rolling out
significant volumes of wireless phones when technology advances.
"They're really hanging their hats on the new vocoders to improve
technology. It will give them room to maneuver. The question becomes,
'How quickly can you percolate this through the customer base?'"

Peter Friedland, an analyst with W.R. Hambrecht & Co., agrees. "AMR will
give them more bang for the buck. But realistically, it's going to take
a long time to get all of those customers using GSM."

Cingular, the nation's second-largest carrier, has more than 22 million
customers. While nearly one-third already use the GSM network, the
remainder are using TDMA. AT&T Wireless' 18 million customers all use
TDMA. Blasi says the speed of the transition isn't critical because AT&T
Wireless has adequate spectrum. Williams says realizing full capacity
gains from AMR vocoders will take up to two years.

Besides awaiting handsets with new vocoders, the carriers must install
new software and circuit boards in each base station. But the real
success of AMR vocoders comes down to voice quality. "The real proof of
the pudding is when they put it out in the field and subscribers respond
to it," says Gunn.