Advanced Mobile Phone System (AMPS) is a first-generation (1G) analog mobile phone system standard developed by Bell Labs and introduced in America in 1983, with variants such as Total Access Communication System (TACS) available in Europe and Japanese Total Access Communication (JTAC) available in Japan.
It uses separate frequencies for every conversation, using a technique known as frequency division multiple access (FDMA). It was originally standardized as EIA/TIA/IS-3 by the American National Standards Institute (ANSI), although it was later superseded by EIA/TIA-553 and TIA interim standard IS-91.
Companies that used AMPS include Alltel, Coastel Offshore Cellular, Verizon Wireless, Moviline, Bell Mobility, Telus Mobility, and AT & T Mobility.
Though AMPS is still widely available at present, the introduction of various digital standards has become a catalyst for the decline in popularity of AMPS.
AMPS operates in the 800 MHz "Cellular" FM band. Each AMPS channel is 30 KHz wide, and is made up of two frequencies, 416 of which are in the 824-849 MHz range for transmissions from mobile stations to base stations, while the remaining 416 are in the 869-894 MHz range for transmissions from base stations to mobile stations.
Cells within a short distance of each other must use different subsets of these channels in order to avoid interference. As an effect, the number of channels available at each site is reduced considerably.
AMPS features a "back end" call setup functionality, where channels are assigned to handsets based on signal strength. This allows the reuse of the same frequency in various locations, while preventing interference. Thus, more cellular phones could be supported over a geographical area.
Due to its being an analog standard, AMPS is prone to static and noise. Conversations were also played back at call centers using a scanner, so unwanted third parties were free to eavesdrop. This disadvantage led to an epidemic known as "cloning," where an eavesdropper in possession of specialized equipment could intercept the Electronic Serial Number (ESN) of a handset and clone it to a different phone.
All calls then made by the cloned number would send billing to the owner of the original ESN. Cloning cost the mobile phone industry millions of dollars. Newer digital standards and technologies, such as Digital AMPS (D-AMPS), Global System for Mobile Communications (GSM) and Code Division Multiple Access (CDMA), featured better security and greater capacity.
Several AMPS networks were partially converted to D-AMPS, although both technologies were later superseded by CDMA2000 and GSM.