Growing up CDMA, IS-95 pioneers clear early deployment hurdles

The Second Annual CDMA World Congress in Singapore provided a rare opportunity to hear technological war stories from carriers pioneering IS-95 code division multiple access technology. And while system buildout hasn't exactly been a bed of roses, most operators are jubilant about their experiences.

Wireless carriers heralded what for many was their first year of success with IS-95 CDMA, despite rumors that some companies needed more cell sites than expected. At issue were link budget calculations, which subtract expected power losses from a transmitter's output in order to estimate link margins. Link margins represent transmission strength in the face of multipath fading and weather influences, and are used to determine whether additional sites are needed to guarantee coverage in a particular area.

Canada's BC Tel Mobility has been pleased with the performance of CDMA, according to Ferdi Schell, vice president of engineering. The carrier introduced Canada's first 800 MHz CDMA networks two months ago in British Columbia.

The rule of thumb is that CDMA offers a 3-to-1 capacity gain over AMPS, thus requiring only one CDMA base station to every three for an AMPS system. BC Tel overbuilt, installing one CDMA base station for every single AMPS site that it operated. The deployment was intentional rather than a response to any perceived CDMA coverage problems, Schell said.

"We wanted customers to go to areas where they had not had analog coverage and find that they could get digital service," he said.

But other carriers have struggled with their CDMA deployments. For example, in dense suburban areas in the eastern and northern parts of Singapore, tall buildings degrade RF propagation, said Finbarr O'Kane, manager of CDMA switch planning for Singapore carrier MobileOne. In addition, MobileOne had used existing GSM traffic as a guide for the CDMA network, but there were many deviations from predicted use. Consequently, the carrier had to relocate numerous CDMA sites to enhance coverage.

Such a problem can be found in any wireless network, not just those based on CDMA, noted Chris Osborn, marketing manager for the personal communications division of Motorola's Cellular Infrastructure Group. MobileOne's deployment was also hamstrung by Singapore's siting rules that require antennas to be placed on off-street buildings so equipment is more concealed, he said.

If some CDMA carriers have been disappointed in the number of sites required, they may have started out believing some CDMA supporters' more ostentatious claims such as a 40-times capacity improvement over AMPS, Osborn noted. Qualcomm now maintains that CDMA can provide 10 to 20 times the capacity of AMPS, although most manufacturers prefer the more conservative prediction of three times the capacity of AMPS.

Another difficulty concerned dropped calls during CDMA hard handoffs. CDMA is known for its soft handoff capability, whereby a mobile phone stays in touch with multiple base stations and uses the strongest signal. But hard handoffs also are required between or sometimes within networks. MobileOne is testing Qualcomm's Pilot Beacon to alleviate hard handoff problems, O'Kane said.

Despite the hurdles, the IS-95 CDMA backers present a unified force. Operators worldwide are expected to begin using the cdmaOne brand name in their marketing efforts, indicating a change from marketing simply features and benefits to providing a technological identity for consumers to seek.

"We will aggressively embrace the cdmaOne brand and use it in our advertising," noted Clyde Smith, vice president of technology at Alltel Communications. "We don't want to focus on the technology, but we believe CDMA is a clear choice, and we will market that."

AT&T RIDES THE INTERNET AT&T Wireless Services has begun offering Internet messaging services to its Digital PCS, PocketNet and paging customers. Internet e-mail messages can be sent to customers' devices using existing e-mail applications or from the AT&T Web Message Center.

SPRINT SPECTRUM SPREADS American Personal Communications has struck roaming agreements with Pacific Bell Mobile Services and BellSouth Mobility DCS. Sprint Spectrum GSM customers in the Washington/Baltimore region can now roam in parts of California, Nevada, Tennessee and North and South Carolina.