Making Waves.

look inside the world of cell phones and pagers and catch a glimpse of the wireless future

In an average day, my pager goes off about 20 times, and I might use my cell phone four times," says 18-year-old Mara Gorrell of Springfield, Virginia. "Without them, my friends would never be able to reach me and my parents couldn't find me in an emergency."

Join the club, Mara. More than 68 million Americans now use cell phones, and at least as many carry pagers. "Most of my friends have had pagers for a few years," Mara says, casually. "Cell phones are less common because they're too expensive."

Mara's wireless gizmos depend on one essential: invisible waves of energy called electromagnetic waves. Both tools receive these waves, and cell phones also shoot them out so you can place a call any moment of the day.

How do invisible waves transmit messages across the country? How are scientists scrambling to make wireless communication better and cheaper?

air waves

Hold your hand in the air for three seconds. Look out: Thousands of electromagnetic waves just bounced off or cruised right through your palm.

The atmosphere is crammed with electromagnetic waves flashing at the speed of light, or 300,000 km/sec (186,000 mi/sec). What are these waves? Light is one type of electro-magnetic wave. Radios and non-cable TVs use another type: radio waves (see "Sharing the Frequencies, " p 20).

Electromagnetic waves vary in frequency, or the amount of energy they contain. Together, all waves--from low-frequency radio waves to high-energy X rays--make up what scientists call the electromagnetic spectrum.

a slice of the spectrum

Every time you turn your radio dial to hit a different station, your radio picks up a new frequency of waves. Using different frequencies keeps signals from different stations from getting scrambled--and stops your cell-phone conversation from being broadcast to the world. How?

Waves of different frequencies share "air space" without getting mixed up. That's because governments assign each type of wireless device--radio, pager, cell phone--one precise slice of the electromagnetic spectrum to use.

For example, cell phones can use frequencies between 800 and 900 megahertz (a unit of frequency measurement). Every cell phone in a cell, or area of wireless service, uses a slightly different frequency between 800 and 900 megahertz. So how does Mara's cell phone "choose" a frequency?

As soon as Mara switches on her phone, powerful computers inside a building called a switching office assign her phone an unused frequency. A microphone inside Mara's phone turns her voice into waves of that frequency --just as the microphone in an ordinary phone turns your voice into electrical signals. Say Mara is calling her friend Jeremy's cell phone in Los Angeles. A network of antennae send Mara's signal (series of waves shaped to carry her voice) across the country to Jeremy's cell--possibly relaying the signal through a satellite on the way. Computers in Jeremy's local switching station note an incoming call, and assign Jeremy's phone a frequency for that call. Then a receiver in Jeremy's phone turns Mara's signal back into a familiar voice.

future waves

In the past 15 years, scientists and companies have built more than 100,000 cell towers (antennas placed on buildings or towers) and programmed more than 500,000 computers to guide signals from one end of the country to another. "There's no stopping the growth rate of the wireless industry," says wireless expert and futurist Joseph Pelton at George Washington University in Washington, D.C. The problem? If each device needs a different frequency, there may not be enough frequencies to go around.

Scientists and companies are busily solving the problem two ways. First, they're working on digital, or coded, systems that turn data--like a voice--into a unique code made of a series of zeros and ones. Digital systems allow wave frequencies to carry a greater amount of data.

Second, companies are dividing cities into smaller cells. Why? The same frequency can be used in different cells without the waves interfering. Smaller cells allow one frequency to be reused more often, so more people can go wireless. "Today, we have maybe 50 cells covering a city," says Pelton. "In the future we may break up a city into 5,000 cells."

Our teen expert sees a rosy--and cheaper--wireless future: "I'm pretty sure that every single teenager will have a cell phone and beeper five to 15 years from now," Mara predicts. "The fad won't end. It's becoming a necessity."

Pelton agrees--almost. "I think 10 to 15 years from now people will have a phone with a built-in pager, and it will also send and receive faxes and e-mail. The wireless units may even become small enough to wear like pins, or on our belts."

pager debate

In 20 states, laws have banned the use of pagers and cell phones in schools. In other states, individual schools have crafted their own policies. Should students have the right to bring cell phones and pagers to school?

no

"I don't think you should be allowed to bring a beeper or cell phone to school. It interrupts classes."

Christopher Hardin, 16 Lake County, FL

yes

"Some kids have busy lives and use beepers to keep in touch. But if a beeper disrupts the classroom, it should be taken away."

Chanel Jennings, 17 Queens, NY

maybe

"It depends. A lot of students have pagers just to show off. But it's good to have in case your parents need to reach you in an emergency."

Tahira Ikharo, 13 Oakland, CA

sharing the frequencies

What part of the electromagnetic spectrum do your favorite wireless gadgets use? To find out, just find the gadget on the chart below. Then trace a line to the frequency scale on the left. (MHz means megahertz, or 1 million hertz, and GHz means gigahertz, or 1 billion hertz.) The years along the bottom show when the wireless gadget was invented. What's in the wireless future? The question mark says it all.

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