Analog vs. Digital
Most twentieth-century radio systems were designed to transmit sound, which is an analog signal: it varies continuously and is usually represented as a wave. Because electromagnetic radiation is also a wave, this made transmitters and receivers relatively simple. Whether in broadcasting or cellular telephony, a radio terminal is a device for converting sound waves to radio waves and back again. Television uses the same principle, including light as well as sound.
Wireless networks are increasingly being used for computer data, which is inherently digital. Instead of a continuous waveform, it consists of a series of pulses. Many sound and video applications are also beginning to use digital signals, though new digital services ...
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