Launching personal communications services with a multitude of standards may be the way for industry to sort out the benefits of each technology, but it could set consumers up for chaos and confusion, said longtime wireless architect Jesse Russell.
The AT&T Bell Laboratories engineer is concerned about the lack of interoperability that will result when PCS networks based on different technologies are switched on in the next few years.
“The use of different technologies gets unwieldy above two or three. We need to ensure that these different standards in the same frequency don’t grow without bounds, creating problems,” said Russell, who also is chairman of the mobile and PCS division of the Telecommunications Industry Association.
When cellular service began 12 years ago, the Federal Communications Commission mandated the use of analog American Mobile Phone System technology. It wasn’t a difficult choice because few other technologies were available.
Today there are seven technologies vying for a spot in the wireless market, each providing certain advantages to operators.
In the face of such choice, the industry isn’t able to select one technology at this time, said Jim Caile, vice president of marketing for Motorola Inc.’s Cellular Subscriber Group. “Absent a directive from the FCC, industry isn’t prepared to make that kind of distillation now. If we would have had to, we would not have come out with anything in a timely fashion,” Caile said.
So both cellular and PCS operators are making technology choices based on what they hope to accomplish with their system.
“But as we move into digital, there is no compatibility base, as with analog,” Russell said. Cellular operators say they will continue to have analog technology in their networks, but most also are switching large parts of their systems to digital to expand system capacity.
Some cellular operators are deploying Time Division Multiple Access, in which users are assigned a specific time position. Others have chosen Code Division Multiple Access, in which users are allocated a unique code sequence. Consequently, the two networks can’t interoperate without specialized switching equipment.
Because both TDMA and CDMA are North American standards, there is a way to overlay the technologies if an operator wanted to migrate from one to the other, said Doreen Salzano, district manager of terminal relationships and interoperability management at AT&T Network Systems Group.
The matter becomes technologically tricky when PCS operators choose the Global System for Mobile communications technology, a European, TDMA-based system also called DCS-1900.
Because GSM is not a North American standard, it is more difficult to set up a migration from GSM to another technology, although it can be done, Salzano said. Omnipoint Corp. of Colorado Springs, Colo. has created a spread spectrum composite CDMA/TDMA technology that the firm says can be used to upgrade GSM.
Other technologies vying to appear in the market include a broadband CDMA system promoted by InterDigital Communications Corp. and OKI telecom. Manufacturer L.M. Ericsson is offering equipment for Digital European Cordless Telecommunications technology, an in-building communications system based on TDMA. Several manufacturers are backing PACS technology, a hybrid of the Wide Area Communications System and Japanese Personal Handyphone System.
And in the middle of it all will be the consumer who just wants to buy a phone and receive service, Russell said.
“Customers used to benefit from a common device (analog). We don’t want to confuse the consumer who gets a phone that won’t work in certain networks, especially if you believe that customers roam,” Russell said.
Salzano said TDMA and CDMA networks could be interconnected with switches to operate as a single network. “But that doesn’t always make sense because then you’d have to have a handset for both. Everything doesn’t have to interoperate to be a success if it’s offering a niche service,” Salzano said.
Numerous cellular operators intend to use dual-mode combination handsets, which embrace a specific digital technology and analog, such as a TDMA-analog or CDMA-analog phone.
Cellular operators with PCS properties, such as AT&T Wireless Services, are planning to use a dual-frequency handset, one that can operate at both 800 MHz cellular spectrum and 1.8 GHz PCS frequency.
“Dual band is viable because the (digital) logic stays the same, only you add a frequency band,” said Bob Stozek, director of product management at Motorola’s Cellular Infrastructure Group.
Salzano and Stozek said dual-mode and dual-frequency handsets are possible, but they don’t expect a dual-technology handset to be developed at this time.
“It would be a very large unit, expensive and there would be a small niche market,” Stozek said. Salzano said dual-mode and dual-frequency phones provide enough complexity for the present, and she expects to see operators developing technology migration strategies for the future. “That’s why equipment must allow for flexibility,” she said.
Russell said standards selection is a very complex process that requires the participation of manufacturers and operators.
“The FCC gave TIA stewardship for the volunteer standards process. But with so much competition, it’s difficult to get them to come together,” Russell said.
So far, two of the three largest operators with nationwide PCS licenses have selected CDMA technology for their networks, PCS PrimeCo L.P. and Sprint Telecommunications Venture. The third large operator, AT&T Wireless Services will use TDMA technology.
Pacific Telesis Mobile Services has announced it will build a GSM network in its Los Angeles and San Francisco markets. Other large PCS operators have yet to announce their selection.
Eric Schimmel, TIA’s vice president of mobile communications/network, said introducing multiple technologies affects the cost of handsets. “If manufacturers would all build the same thing, prices would be lower,” he said.
