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Let's get personal about new digital mobile services.

If you've ever used mobile telephone service, you know how convenient the service can be. And if you're a student of the industry, as many of us are, you also know that cellular mobile service "ain't what it used to be."

Back in the early to mid-80s, cellular phones were rather heavy affairs permanently mounted inside a car. Electronics were (and still are) generally installed in the trunk. The phone was fixed in the vehicle. Your "mobility" was limited to wherever the car happened to be.

Today that's all changed. Now you can carry your phone with you in a briefcase. The batteries give you several hours on standby, and four to six hours actual talk time.

However, a revolution in mobile communications is just around the corner. It's digital cellular service, and it has a few new terms you should know. When we say, "Let's get personal," we are describing the next generation of digital mobile communications services.

Look for an entirely new generation of products and services to be sold under the umbrella called "personal communications services" or PCS. When advanced cellular service elements are organized together, we have a "personal communications network," or PCN.

This month's column is the first of a two-parter discussing PCS and PCN technologies. Part 1 will briefly discuss the technical aspects of digital cellular. Part 2 will discuss the planning and management implications of PCS/PCN technology.

Cellular service first appeared commercially in 1983. It is formally called advanced mobile phone service, or AMPS. Cellular service has been wildly successful. Annual subscriber growth, according to the Cellular Telecommunications Industry Association (CTIA), averaged between 51% and 75% over the past five years.

Over the years, the cost for AMPS has dropped steadily. In 1985, a car phone could easily cost $1,200 to $2,000. Today prices range from $200 to $300 in major market areas. Portable units were $3,500; now they are $500.

Now a whole new generation of hand-held units is appearing. Motorola recently unveiled a unit that weighs only 7.7 ounces, yet provides over two hours of talk time (with its battery pack). Pretty soon you'll carry a phone in your pocket.

Developments like this, and many others, sold lots of cellular phones.

But analog service is rapidly reaching capacity. Relief is needed, and soon.

Coming to the rescue is digital cellular service. Several technological improvements have been necessary to speed the development of digital cellular service: digital switching, efficient speech encoding, microcell technology and enhanced access modes.

Microcell technology is similar to conventional cellular technology, except that cells are much smaller in size. In cities, cells can be as small as a city block or even a floor of an office building. Adding thousands of subscribers to a microcell area requires a very efficient system for processing calls within the microcell and for following subscriber movements (or roams) to another microcell.

To better handle large numbers of mobile users over available radio frequencies, digital techniques are required.

Several access modes are competing for industry standard: the front runner is TDMA (time division multiple access), which digitizes voice signals (similar to PCM and ADPCM) and interleaves multiple conversations over individual frequencies. TDMA boosts channel capacity by a factor of three.

Another interesting techniques is CDMA (code division multiple access). It uses spread spectrum techniques to provide more channel efficiency than TDMA (about double the capacity).

One of the major concerns right now is the availability of frequency spectrum to support PCN services. Among many different ranges being evaluated, the private microwave range, approximately 1850-1990 MHz, appears the odds-on favorite. But until the FCC formally rules, the industry must wait.

In the meantime, digital cellular will be introduced into existing cellular frequencies.

Microcell technologies will still be tested and perfected, but will only see limited use until the FCC rules on the spectrum issue.

Currently, in the Washington, D.C., and Baltimore areas, a company called American Personal Communications (APC) is running a PCN trial. Several hundred people are participating. The service is one-way outgoing, using a technique called "telepoint" which was pioneered in the U.K.

Service rates are very low: $15 per month, including the pocket-sized phone, and 13 cents per minute for local calls.

APC's trial differs from others in that subscribers are paying for the service. As the trial progresses in 1992, APC plans to add handsets with integrated pagers.

Editor's Note: This month marks Paul Kirvan's 60th appearance in Communications News . . . five years of exploring the human side of telecomm management.
COPYRIGHT 1992 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Communications Management
Author:Kirvan, Paul
Publication:Communications News
Article Type:Column
Date:Jan 1, 1992
Words:757
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