Radio fingerprinting is a process that identifies a cellular phone

Mobile phone

A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

 or any other radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 transmitter

Transmitter

In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...

 by the unique "fingerprint

Fingerprint

A fingerprint in its narrow sense is an impression left by the friction ridges of a human finger. In a wider use of the term, fingerprints are the traces of an impression from the friction ridges of any part of a human hand. A print from the foot can also leave an impression of friction ridges...

" that characterizes its signal transmission. An electronic

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 fingerprint makes it possible to identify a wireless

Wireless

Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...

 device by its unique radio transmission

Transmission (telecommunications)

Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...

 characteristics. Radio fingerprinting is commonly used by cellular operators to prevent cloning of cell phones. A cloned cell phone will have a same numeric equipment identity but a different radio fingerprint.

Essentially, each transmitter (cell phones are just one type of radio transmitter) has unique rise time signature when first keyed caused by the slight variations of component values during manufacture. Once the rise time signature is captured and assigned to a callsign, the use of a different transmitter using the same callsign is easily detected. Such systems are used in military signals intelligence and by radio regulatory agencies such as the U.S. Federal Communications Commission

Federal Communications Commission

The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...

(FCC) for identifying illegal transmitters. They are also used for assessing usage for billing purposes in Subscriber Mobile Radio (SMR) systems.