Advanced Mobile Phone System (AMPS) is the U.S. cellular radiotelephone system in the 850 MHzfrequency range. AMPS operates in the 824 MHz to 849 MHz frequency range in the uplink; the downlink is 869 MHz to 894 MHz.
The initial channel count of AMPS was 666 channels with a channel width of 30 kHz. Later, the number of channels was increased to 832 after widening the uplink and downlink ranges. Transmission uses frequency division multiplexing( FDM); signaling is in pulse code modulation with Manchester coding at 10 kbit/s. AMPS uses a modem-controlled digital interface to control the analog voice channels. AMPS also exists with digital voice transmission under the designation D-AMPS and in a narrowband version as N-AMPS.
AMPS was developed in the 1970s and has been predominantly implemented as an island network since about 1984. Today, it is the most widely used mobile communications standard, used in around 90 countries worldwide.