Digital Advanced Mobile Phone System (D-AMPS)is a digital version of Advanced Mobile Phone Systems (AMPS), the original analog standard for cellular phones. D-AMPS uses a combination of time division multiple access (TDMA) and frequency division multiple access (FDMA). It adds TDMA to get three channels per AMPS channel, thus tripling the number of calls on a channel.
They are standardised by IS-54 and IS-136.
As in AMPS, D-AMPS also uses frequencies from 800 to 900MHz for transmission. Half of the spectrum is used for sending signals and the other half is used for receiving signals.
The frequency band is divided into 30KHz sub-bands, called channels, by FDMA.
The channels for uplink are called forward channels and the channels for downlink are called reverse channels.
TDMA is applied to each channel thus tripling the number of available channels.
Presently, all D-AMPS channels are replaced by GSM or CDMA technology.