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CDPD: It Died So Faster Cell Service Could Live

cdpdNearly 100 years after Guglielmo Marconi successfully transmitted and received electronic signals via his wireless telegraphic invention, a budding wireless network is poised to become the mobile data transmission route of the future.

The Cellular Digital Packet Data (CDPD) network is designed to let cellular subscribers send digital data from mobile PCs over existing cellular networks. Mixing a myriad of technologies, including the ability to send packets of data over cellular airwaves instead of traditional analog transmission, CDPD could provide PC users with quick and reliable data transmission, analysts said.

“CDPD is going to happen and it will be a tremendous challenge for RAM [Mobile Data Inc.] and Ardis,” said Paul Callahan, senior industry analyst for Forrester Research Inc., a market-research firm in Cambridge, Mass. “When it’s available, CDPD will basically be as cheap as [RAM Mobile’s] Mobitex or Ardis’ on-line service charge, and the modems could be a lot smaller if not the same size” as traditional modems, he added.

CDPD will initially target industrial users with applications ranging from telemetry and point-of-sale to transportation. Its broader success, however, will depend on several factors: how quickly it can be rolled out, price, reliability of the network and the breadth of products designed for it, observers said.

Drumming up support

The technology has the backing of nine cellular carriers, which make up the bulk of U.S. cellular service providers, while PC makers such as IBM and Apple Computer Inc. are promising a host of CDPD applications for early next year.

The cellular carriers face the challenge of upgrading their national networks to handle data as well as voice — and handling it more efficiently than many voice calls are handled today. Many users of cellular services complain about lost signals when traveling away from cell sites and the annoyance of dealing with different phone systems.

“The problems with voice are the same problems with data — you check in and go through the whole thing and it seems to be an inconvenience,” said Richard Barg, an attorney in Atlanta, who uses cellular phones. “[With cellular] data, if it’s using a nationwide network using the same standard, you have something analogous to interstate commerce: no restrictions and barriers.”

Cellular carriers plan to add to their networks equipment such as mobile data gateways, enabling data packets to be routed to their proper destination. Base station receivers also will be required at each cell site for mobile radios sending and receiving data, said Rob Mechaley, vice president of technology development for McCaw Cellular Communications Inc. in Kirkland, Wash.

A key aspect of CDPD lies in a technique called “channel hopping,” which parcels out data over existing analog voice channels that are not being used for regular voice calls. Channel hopping differs from another cellular technique called cellular spectrum, which is used by Cellular Data Inc. (CDI) and dedicates the radio spectrum to broadcast signals to bay stations.

As a result, CDPD data calls will be subject to less interruption, and data-transmission speeds will reach 19.2K bps on a 30KHz channel; competing networks such as CDI include capacities of up to 4,800 bps. Ardis earlier this year opened up its protocols to support transmission speeds as high as 19.2K bps.

Modem makers incorporating the CDPD specification will likely have to add new circuitry to their standard Hayes AT Command Set modems, while software developers will simply need to add new APIs to their messaging applications, said Craig McCaw, chairman and CEO of McCaw.

“The fundamental driver of CDPD is incredibly simple,” he said. “All the facilities and power are in place, and the spectrum has been allocated.”

As a result, costs should remain comparable to existing products; for example, standard CDPD-compatible PCMCIA Type II modems are expected to be priced around $360 to $380, he said.

Other costs, however, may be more prohibitive. Early users could face steep subscription charges — as much as $50 to $75 per month — as well as connect-time charges for each data transmission, analysts said.

The monthly charge for using RAM Mobile’s Mobitex packet-radio network is $25, plus 5 cents for each 100-byte file or 12.5 cents for a 512-byte file.

“I would not pay $100 per month for transmitting data,” said Barg, the Atlanta attorney. “The current cost of carrying a laptop around is $100 per month.”

While Ardis and CDI plan to link their networks to CDPD, RAM Mobile plans to compete head to head with the technology, said Don Grust, product manager for RAM Mobile in New York.

“Whereas CDPD is not even in release 1.0, we are on release 13 and 14 and have plans for 15 and 16 next year,” said Grust.

Mobitex, which is expected to cover 90 percent of the U.S. population by mid-1993, will provide a more reliable method of sending E-mail over the airwaves for several years to come, he added.

At least one large corporate PC site, however, is looking forward to CDPD. “To me it’s a very exciting technology,” said Sheldon Laube, national director of information and technology at Price Waterhouse, a New York-based accounting firm. “If you need to let staff in the field contact home, they can do so without finding a phone.

“No technology is perfect,” he added, “but we want to make [CDPD] work, and the carriers want to make it work.”

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