Question
What is the difference between analog and digital cell phones?

Answer
The three most popular cellular services in the U.S. are normal analog cell phones (AMPS), Digital cell phones, and PCS. Analog cellular service is the subject of the HSW article on cell phones and you can learn all about it there.

The are two popular digital systems. One is generically known as "digital service", and the other is clearly branded as "PCS". "Digital service" uses newer, digital phones, but they communicate with normal AMPS towers. A call is set up using the normal AMPS protocol, and then the conversation is transmitted digitally. (You can read the HSW article on CDs for more information on changing analog signals to digital signals). Digital phones chop a single AMPS voice channel into three digital channels using a technique called Time Division Multiple Access (TDMA). All that means is that three phones can share the same channel, and they each uderstand that they will only use the channel part of the time. So one phone uses the channel for a subset of a second, then the second phone uses it, then the third, and the cycle repeats. Digital cell phones, as you can see, are a hybrid between the existing analog system and digital technology.

PCS phones are complete digital and they use a whole separate set of towers at a whole separate set of frequencies between 1.85 and 2.15 GHz. Because of the higher frequencies, there must be more towers closer together. Because it is completely digital, encyption and error correcting codes can make the call much clearer and nearly impossible to intercept. PCS normally bundles in other services like paging, caller ID and even email.

How Stuff Works Power Panel

Table of Contents A complete list of all HSW articles About Marshall Brain Information about the creator of HSW Search Search for any word or concept in HSW Citing HSW Information about citing HSW in articles and papers Question of the Day Ask questions or browse hundreds in the archive Books A variety of books for people interested in how stuff works HSW Newsletter Sign up to receive the monthly HSW newsletter Contacting HSW Contact HSW directly with email What's New Review newsletters to chart HSW's development Awards Check out HSW's awards and reviews! Disclaimer The disclaimer required by the lawyer Author Information Learn how you can write for HSW HSW Fan Buttons Link to HSW with these snazzy fan buttons! Suggestions Leave a suggestion in the suggestion box

How Stuff Works (http://www.howstuffworks.com) is a production of BYG Publishing, Inc. http://www.bygpub.com - questions@bygpub.com P.O. Box 40492 - Raleigh, NC 27629

© 1998 BYG Publishing, Inc. All rights reserved.