Wireless communication. How wireless communication works

Wireless communication involves sending and receiving information through the air or through space via electromagnetic waves, most often as radio waves. Wireless devices send and receive signals over distances ranging from a few feet or meters to thousands of miles or kilometers. Many people use such small wireless communication devices as cordless telephones, walkie-talkies, pagers, and cellular telephones.

The military often uses larger wireless units that can be carried or mounted in vehicles. All communications to aircraft and sea vessels are wireless. Artificial satellites relay telephone calls in the form of microwave transmissions. The remote-control devices that control home electronic equipment use infrared light waves.

How wireless communication works. Essentially any information that people use can be transmitted wirelessly, including sound, text, still images, and video. A basic wireless communication system consists of three elements: (1) a transmitter, (2) a receiver, and (3) a wireless channel. The transmitter and receiver are electronic devices, and the wireless channel is the set of paths over which the signals travel to reach the receiver.

Unlike wire-based systems, wireless systems can function when the transmitter or receiver, or both, are moving. As the paths of the signals change, however, the signals can fade or become distorted. Thus, communication is generally less reliable over a wireless system than over a wire-based system.

The signals propagate(travel) via a carrier wave. This wave begins as a continuous wave pattern, but it is modulated (altered) in one or more of three ways to include a representation of the information. In amplitude modulation (AM), changes in the strength of the carrier wave represent the information. Frequency modulation [FM) varies the number of cycles per second of the carrier wave.

Phase modulation (PM) alters the phase of the carrier wave by shifting a wave to its negative value, resulting in the periodic occurrence of two wave crests or troughs in a row rather than alternating crests and troughs. Information in digital (numeric) form may be sent via any of the three modulation methods.

History. Wireless communications began in the late 1880's when the German physicist Heinrich Hertz showed that electromagnetic waves existed and could be transmitted and received through the air. He thus proved theories proposed in the 1860's by the Scottish scientist James Clerk Maxwell. In 1 891 , Nikola Tesla, an American inventor from Austria-Hungary, invented the Tesla coil, a device that is still used in wireless communication.

The Italian American inventor Guglielmo Marconi made one of the earliest long-distance wireless transmissions in 1895. Since the early 1980's, the number of wireless systems that use digital technology has greatly increased.