D-AMPS is now called Time Division Multiple Access/IS-136.
D-AMPS (Digital-Advanced Mobile Phone Service), sometimes spelled DAMPS, is a digital version of AMPS (Advanced Mobile Phone Service), the original analog standard for cellular telephone phone service in the United States. Both D-AMPS and AMPS are now used in many countries. D-AMPS adds time division multiple access (TDMA) to AMPS to get three channels for each AMPS channel, tripling the number of calls that can be handled on a channel. D-AMPS is Interim Standard-136 from the Electronics Industries Assocation/Telecommunication Industries Assocation (EIA/TIA).
Like AMPS, D-AMPS uses frequency ranges within the 800 and 900 Megahertz (MHz) electromagnetic radiation spectrum. Each service provider can use half of the 824-849 MHz range for receiving signals from cellular phones and half the 869-894 MHz range for transmitting to cellular phones. The bands are divided into 30 kHz sub-bands, called channels. The receiving channels are called reverse channels and the sending channels are called forward channels. The division of the spectrum into sub-band channels is achieved by using frequency division multiple access (FDMA). The time division multiple access processing (TDMA) is added to each sub-band channel created with FDMA to triple the number of channels available.
Although AMPS and D-AMPS originated for the North American cellular telephone market, they are now used worldwide with over 74 million subscribers, according to Ericsson, one of the major cellular phone manufacturers. D-AMPS is one of three digital wireless technologies that use TDMA. The other two are GSM and PDC. Each of these technologies interprets TDMA differently so they are not compatible. An advantage of D-AMPS is that it is easier to upgrade to from an existing analog AMPS network. An alternative to D-AMPS and the other two TDMA technologies is direct sequence code division multiple access (CDMA).