AMPS

AMPS stands for Advanced Mobile Phone System, the first cellular mobile telephone standard deployed commercially in the United States. Launched by Bell Labs in 1973 and approved by the FCC in 1982, AMPS was a 900 MHz analog system that replaced earlier car phone networks by dividing coverage areas into cells, each served by a low-power transmitter. This cellular architecture allowed frequency reuse at safe distances and dramatically increased capacity compared to earlier mobile telephone service.

The system used frequency modulation (FM) on the voice channel and operated with 30 kHz channel spacing. Each call occupied one dedicated channel for the duration of the connection. AMPS networks required a network of base stations connected by landline, microwave, or fiber links to mobile telephone switching offices (MTSOs). A mobile unit transmitted on one frequency and received on another, with the base station handling the switchover automatically as the caller moved between cells.

Implementation and international reach

AMPS deployment began in Chicago in 1983 and expanded across North America through the 1980s and 1990s. The standard was adopted internationally under different names: in Japan it became JAMPS, and Europe developed its own analog standard, C-450, before moving to digital GSM. Peak AMPS network capacity ran roughly 1,600 simultaneous calls per cell, constrained by the 25 MHz allocation. Handoff between cells was handled at 0.9 second intervals in most implementations, sometimes audible as a brief click.

The network required subscriber authentication through MIN (mobile identification number) and ESN (equipment serial number) pairs. Handset power output ranged from 0.6 watts for portable units to 3 watts for mobile car phones. AMPS networks remained in operation for nearly thirty years; the FCC required carriers to maintain AMPS service until February 2022, though most had migrated customers to digital networks (CDMA, GSM, LTE) well before the formal sunset date.

AMPS is historically significant as the foundation of modern cellular architecture, even though no working knowledge of its technical operation is needed in contemporary telecom work. Engineers and technicians encounter AMPS primarily in legacy system decommissioning, spectrum reassignment, and historical documentation of network evolution.