Wireless Communications

All communications using radio waves and other electromagnetic waves not guided by fibers, wires, or waveguides (including visible and invisible light) are wireless. However, the term has come to refer primarily to the exchange of digital information by means of radio, especially by mobile telephones (cellular phones) and by wireless broadband computer networks.

The standard type of mobile wireless telephone is known today as a cellular or cell phone because the physical landscape is partitioned into “cells” or send-receive areas served by different antenna towers. If a cell phone is within range of a given mobile phone tower, it can send and receive calls through that antenna: if it moves from the range of one tower into the range of a nearby tower, the call is transferred automatically from one tower to the next (handed over). If a cell phone moves out of range of any mobile phone tower, it cannot send or receive calls.

As of 2005, more than 2 billion people were using cell phones globally. In some developing countries where telephone service had historically been patchy or nonexistent, it was proving cheaper to jump straight to cell phones than to deploy traditional copper land telephone lines.

Cell phones use digital signaling to encode voice data. In the United States, cell phones use frequencies between 824 MHz (million of Hertz or cycles per second) and 894 MHz. Each phone sends and receives simultaneously on slightly different frequencies so that full-duplex (two-way) conversation is possible.

Another type of wireless communication that is reshaping modern society is the wireless networking of computers. Several technologies have been used to connect computers wirelessly to networks. For example, geostationary satellites—satellites orbiting at an altitude of 22,300 miles (35,786 km), so that from a point on the surface of the turning earth they appear to hang motionless in the sky—exchange signals in the .5–1.5 GHz (gigahertz) band with small dish antennas on the ground, allowing people in remote locations to connect at high data rates with the World Wide Web. However, the majority of people with high-speed access to the Internet are connected through wired technologies such as DSL (digital subscriber loop).

Over short distances computers can access the Internet through Wi-Fi, a wireless local area network technology. To use Wi-Fi, a computer must be within transmit-receive range of an access point, which is a device that is connected to the Internet through a

broadband connection of its own and that can handle simultaneous two-way communications with some number of distributed devices (“clients”). Wi-Fi uses frequencies near 2.4 GHz. The frequency bands used for Wi-Fi have not required a license in the U.S. since 1985, which was crucial to the development of the Wi-Fi technology. The industry standard describing Wi-Fi, which makes it possible for various manufacturers to make Wi-Fi devices that are guaranteed to work together, was first agreed upon by industry experts in 1997.

Wi-Fi and related technologies allow people to move about while remaining connected to the Internet. To connect, a user need only move into the range of an access point and turn their computer on (assuming it is equipped with an appropriate transceiver, as most laptops are today). At least 100 million people were using Wi-Fi as of 2006. A competing, longer-range, higher-speed technology called WiMAX was under development but had not yet been widely deployed.

Larry Gilman