by David G. Propson
Some cities have recently introduced laws to prohibit drivers from talking on mobile phones while on the road. One can picture the excuses (“That wasn’t a cell phone, officer. I just like to shave on my way to work.”) But it underscores the pervasive effects mobile phones have had on people’s lives — more than personal computers or the Internet. PCs usually stay on a desk, after all, but a lot of us take phones wherever they go.
Still, people understand much more about the inner workings of their PCs and the Internet than the phone system that patches their calls through. Though we can all tell precisely how many megahertz our PC’s processor has, few have any idea what megahertz frequency a phone transmits at. We take it on faith that it will, and swear like heathens when it doesn’t.
This column usually sets out to explain a certain technology-related acronym or obscure technical term. Mobile phone companies have created a whole slew of them, but for the most part buyers don’t pay attention to them.
Telecom companies like to argue that their TDMA-based PCS system is superior to a competitor’s non-PCS CDMA system, that any serious businessman wouldn’t be caught dead using an analog AMPS phone, and that consumers should be falling all over themselves to get a doodad with a WAP-enabled connection to the Web.
When real people buy a phone, however, they want to know two things: “Will I have coverage in my home area and the places I most often travel to?” And, “Can I get this service with the neat Nokia phone?”
What It All Means
The distinctions between different phone systems matter much more to the phone companies (and their investors) than they do to consumers. TDMA (time division multiple access) and CDMA (code division multiple access) are simply used to describe different ways companies cram as many digital signals into the air as possible.
TDMA systems never transmit more than a single conversation in any instant, but continuously cycle through all the ambient conversations in the area so that, ideally, no one misses a word. (Imagine an operator at an old-time switchboard with a single cord, plugging and unplugging the connections at incredibly high speeds.) CDMA systems, by contrast, attach a distinct code to each call and place them all into the air at once. Callers only hear the conversation that contains their code.
The two systems have real differences, but primarily affect how efficiently the phone company can run their systems and how much money they can make. The quality of callers’ conversations in terms of transmission, not content depends more on the amount of call traffic in a given area than on what switching system the service uses.
That pesky PCS, by the way, simply stands for “personal communications system,” the term the FCC gives phones that transmit over the more recently established 1900Mhz frequency, rather than 800Mhz, which was the section of the spectrum originally set aside for cell phones in 1983.
The Past, And The Future
Back then all the systems were analog and used AMPS (the advanced mobile phone service standard). You can still get an analog signal nearly anywhere in the U.S., but digital service can be more spotty. Digital systems like CDMA and TDMA offered phone companies opportunites to operate more efficiently, though, so everyone made the switch.
Digital service also allows carriers to offer services like caller ID, text messaging, and Internet access, which they are now starting to do. Last year, wireless application protocol (WAP) was widely believed to be the way callers would access the Web, but its future is no longer certain. Many developers labeled it a badly designed technology, and relatively few companies have sites designed to work with WAP. And no one has yet answered the question of who, exactly, will want to ruin their vision reading information off a mobile phone’s tiny screen.
I know: The jerk in the car ahead of me, shaving.