Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, June 10, 1990 TAG: 9006070016
SECTION: BUSINESS PAGE: A-13 EDITION: METRO
SOURCE: Keith Bradsher the New York Times
DATELINE: LENGTH: Long
Yet some of the biggest names in telecommunications worldwide are pushing hard to develop wireless telephone systems.
This new type of cellular network is sometimes billed in the industry as the "poor man's cellular" because it may prove far less expensive than existing systems and may possibly be competitive with traditional wired networks.
Many more people in an area could use the system at once than can use cellular simultaneously.
The new system could also use pocket-size phones, or even phones the size of a belt buckle, that would be far lighter and more convenient than existing cellular phones.
Millicom Inc., a small New York communications company, is the first out of the gate in the United States.
Last month it won experimental licenses from the Federal Communications Commission to build pilot systems in Houston and Orlando, Fla., that would use the tiny phones beginning in 1992.
In Britain, the government awarded commercial licenses last December to three consortiums that plan to spend $1.7 billion apiece for the construction of so-called personal communications networks on a nationwide scale, with service beginning in London in late 1992.
These personal networks would use phones so light that they could be carried anywhere. The systems would use many more transmitters than conventional cellular systems, would operate at lower power and, most likely, at a frequency that is twice as high.
Experts say these features should make it possible to create systems with millions of subscribers.
With construction costs spread over a broader base, personal networks could become cheaper than cellular service and may become competitive with wired service.
The higher frequency and low power mean that signals do not go around corners well and are easily blocked by walls and floors of buildings.
But engineers say these properties actually represent advantages because they enable the same frequency to be used for calls on different floors of a single skyscraper without the signals becoming scrambled.
However, high-frequency transmissions also bounce off walls and windows easily, which may cause interference.
The handsets for personal networks are little more than short-range, sophisticated walkie-talkies.
For a call to a party in an office building or in another part of the city, a handset sends a signal to a transmitter, which relays the signal to another transmitter either over local telephone lines or by a direct microwave beam.
The second transmitter then broadcasts the signal to the handset of the desired party.
Experts say the handsets will be smaller and lighter than portable cellular telephones because they will need to send a signal only several hundred feet, instead of several miles, and so will function on batteries that are smaller and hold less power.
The higher frequency will make it possible to conceal the antenna inside the phone.
Personal networks are intended initially for use by office workers and pedestrians in dense urban areas. Tests have shown that the systems have trouble in fast-moving cars.
Cellular companies, along with consultants, Wall Street analysts and money managers associated with the industry, are skeptical about the need for high-frequency personal networks.
Cellular service providers could easily get into the personal network business by setting aside some of their channels for low-power transmitters and handsets if they see sufficient demand, said Haynes Griffin, the chairman of the Cellular Telecommunications Association.
Cellular companies, he added, have the advantage of having already built a national network of transmitters.
Telecommunications equipment producers sense a large potential market and are more enthusiastic than the cellular companies about high-frequency personal networks.
LM Ericsson of Sweden is testing personal networks at cellular frequencies but plans to manufacture systems for the higher frequency.
Cellular frequencies for personal networks are "not where we see the future," said Peter Bergenhag, a spokesman for the company.
While Millicom plans citywide personal networks, Ericsson envisions systems based in a single office building that could be gradually expanded to cover office workers who visit neighborhood restaurants and stores.
Current providers of cellular service have a large band of a lower part of the radio-wave spectrum allocated for their exclusive use.
Every city or region can accommodate two cellular companies, each of which receives half the band and breaks it into 832 channels.
Those channels are used by each transmitter, which may cover an area of one or two city blocks or many square miles.
Each channel can now accommodate one conversation, although the introduction of digital technology will triple the capacity in the next several years.
The number of users in the vicinity of a single transmitter is limited to 832 at any one time.
Companies working on personal networks in the United States face an obstacle that British concerns do not: the needed high frequencies are already in use.
Oil companies and utilities use some of them for data transmissions from wells and pipelines, while corporations use some to beam data back and forth between office buildings.
The government, which has many frequencies, uses some for space communications.
Millicom has proposed a solution to this problem.
In its tests in Orlando and Houston, the company hopes to perfect a system in which transmitters rapidly change frequencies to take advantage of whichever one is least used at any moment.
And instead of dividing up calls by frequency, as is done in existing cellular systems, the company plans to have each transmitter code and electronically combine calls to transmit all of them in a given area at the same time on the same frequency.
Each handset would decipher only the call that bore its code, and both transmitter and handset would simultaneously change frequencies as many as 30 times during a call to minimize interference.
If successful, the system could accommodate many calls without interfering with existing users of high frequencies.
Military services in Europe and the United States already use such "spread spectrum" radio systems as an anti-jamming measure.
Millicom has not built a working handset, saying that it first wanted to see whether it would get a license.
The handset could be built now with recently developed technology, said Jesse Russell, the director of the cellular transmissions laboratory at Bell Laboratories, the research arm of AT&T.
The inclusion of the spread spectrum technique helped Millicom win its FCC licenses.
"It's exactly that concept that the commission rather liked," said Thomas Stanley, the FCC's chief engineer.
The alternative would have been to take frequency from existing users.
Pacific Telesis, one of the seven regional Bell operating companies, is exploring ways to use coded transmissions at current cellular frequencies.
But higher-frequency transmissions are more suited to the technique because they can carry much more information, and thus many more calls, at the same time.
Another technical challenge to the deployment of personal networks lies in ensuring that conversations are not disrupted when a phone user passes out of range of one transmitter and into the range of the next.
This problem bedeviled the early development of cellular telephones, and is more serious for personal networks because each transmitter covers an area that may be several hundred feet across instead of several miles across.
A phone user in a fast-moving car could be changing transmitters several times a minute.
Experimental personal network technology cannot accommodate vehicles moving through small transmitter "cells" at more than 20 to 30 miles per hour, Russell said.
But speeds of 50 to 60 miles an hour should become possible within several years, he added.
Bell Laboratories is working on ways to install small computers in each transmitter to coordinate the handoff of calls.
Current cellular systems rely on a single computer system controlling many transmitters, and the time it takes to send messages between the computer and the transmitter slows handoffs, Russell said.
by CNB