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Definition: air interface

The technology used for the radio transmission between mobile devices and the base station in a cellular network (see RAN). The air interface is the wireless counterpart of the physical layer 1 in the OSI model (see OSI model).

Also called a "radio interface," the air interface defines the frequency, channel bandwidth and modulation scheme. For example, TDMA and CDMA modulation are used in GSM and CDMA cellular networks respectively, while OFDMA is used for LTE. OFDMA was also used for WiMAX. See air card, CDMA, TDMA, OFDMA, LTE and WiMAX.

The First Air Interface
In the early 1900s, this Marconi spark-gap transmitter (top) and receiver (bottom) comprised the first wireless telegraphy. Used to tap out Morse code, the spark between the two electrodes generated a mass of radio frequencies that were tuned to the desired frequency, and the current was strong enough to go a long distance. Later, oscillators generated the frequencies, and amplifiers boosted output. (Equipment courtesy of Vintage Radio and Communications Museum of Connecticut.)