Leaders vie for position in mobile computing.

The race is on to provide the wireless communications links needed by the growing ranks of mobile computer users.

Notebook computers, the primary mobile platform, accounted for 13% of personal computer sales in 1992. That figure is expected to increase to 25% within the next couple of years, with notebooks outselling desktop machines by the late 1990s. In addition, pen-based computers and personal digital assistants such as Apple's Newton will push demand for wireless communications.

Communications giants AT&T, MCI, GTE and the regional Bell operating companies are positioning themselves for the upcoming fray, along with such powerhouses as Motorola and TRW. And the Federal Communications Commission appears ready to open the field to new entries by reallocating parts of the frequency spectrum for wireless networks to support personal communications services (PCS).

The PCS networks will coexist with the cellular and packet-radio networks now in place. However, they will operate from a great many more locations. Unlike a cellular unit, which can have a range of about 20 miles, the PCS device will be limited to perhaps a few thousand feet. But it will send signals to many more transmitter stations that will be much smaller, cheaper and easier to install than cellular stations. Because the user is never far from a transmitter, PCS units will work within buildings and tunnels.

Under a new policy, the FCC will auction the PCS frequencies rather than using a lottery, awarding licenses to the highest bidder and turning the money over to the U.S. Treasury. It hopes to begin assigning licenses by early next year.

Meanwhile, AT&T is shoring up its position, buying a minority stake in McCaw Cellular Communications, Inc., the largest provider of conventional cellular service in the U.S. It has also agreed to license patents from Spectrum Information Technologies, Inc. for transmitting data over cellular networks. One patent covers a software design that easily separates data from voice transmissions over a cellular network, obviating the need for cellular phone companies to build separate digital data networks.

AT&T's licensing agreement also covers its affiliates, including McCaw, which is working on a project to send data in packets during idle times on cellular voice channels. The so-called Cellular Digital Packet Data, or CDPD project, is a joint technology development effort by IBM and a consortium of national cellular companies, including McCaw, Ameritech Mobile Communications, Inc., Bell Atlantic Mobile Systems and GTE Mobile.

MCI is involved with a different type of consortium, one that hopes to win a license to build a national personal communications network. In its consortium, MCI would be a national manager in charge of network services, technical standards and national marketing. Other members would build and operate personal communications services systems and provide equipment and software.

Low-orbit satellite

Other proposals for international wireless networks use low-orbiting satellites as communications relays for the mobile computers. Because the satellites circle the earth at distances of a few hundred to several thousand miles, they appear to move across the sky. The only way to provide continuous service is to launch them in a series so that one will always appear overhead just as another is disappearing over the horizon.

Compared with geostationary satellites in orbits 22,300 miles above the Equator, which seem to hover over one spot on earth, the low-orbiting models need less power, are easier to launch and can pick up signals from weak transmitters. They also avoid the delays with geostationary satellites caused by the signal's 45,000-mile round trip.

TRW of Cleveland, Ohio, has advanced a $1.3 billion, 12-satellite plan called Odyssey, while New York-based Loral Corp. has proposed an $830 million, 48-satellite plan in a joint venture with Qualcomm, Inc. of San Diego. The satellites link the mobile devices to regional ground stations, which switch and route the traffic over long-distance phone lines.

An ambitious $3.4 billion plan by Motorola, known as the Iridium project, uses 77 more sophisticated satellites to pick up traffic from mobile users anywhere on earth, relaying it from satellite to satellite and bypassing long-distance companies.

For mobile users who can't wait, Motorola and its partner, IBM, have opened their Ardis packet-radio national data network to public use. Plus, in October, RAM Mobile Data, Inc. and its financial backer, Bell South, will launch the Mobitex packet-data radio network.

The Ardis network was developed from an IBM-operated private network and serves more than 8,000 cities in the 50 states, Puerto Rico and the Virgin Islands. Monthly service charges run from $100 to $150. Mobitex will be available in more than 6,000 U.S. cities for a monthly charge of $50 to $80. Both services also charge a nominal fee for each packet sent.