There are three leading digital cellular standards, GSM, CDMA and D-AMPS.

• GSM uses TDMA, which allows eight simultaneous communications on a single radio multiplexer. By end-1997 there will be 215 operators in over 100 countries. GSM data services were first introduced in 1994 and use PC Cards with a mobile phone and a mobile PC or a handheld to provide switched fax and data services operating at 9.6Kbit/s.
  
  Developments are in progress which will enable data transmission speeds of up to 38.4Kbit/s. Some operators in Europe are expected to introduce the service in early 1998, but only the newer data cards, introduced in 1996, are able to operate at this higher speed. This High Speed Circuit Switched Data (HSCSD) is a new service expected to be available in 1998 where a single user is allocated not one time slot, as in the standard circuit switched option, but several. Using up to eight time slots would give a transmission rate of 76.8Kbit/s. General Packet Radio Services (GPRS) technology should be available in 1999 where subscribers are provided with a packet connection over the GSM network. It will interwork with circuit switched and provide 14Kbit/s over a single time slot and 115Kbit/s over eight time slots.

• CDMA will be the main rival technology for GSM for the world cellular markets of the late 1990s. In CDMA networks each user occupies the full bandwidth at the base station and interference suppression techniques are used. Each handset communicating with a base station is allocated a unique code which gives total security of communication. The system is the US standard IS-95, and it will offer data, fax and short message services during 1998. There are plans to roll out high speed circuit switched and packet data services by 1999.
  
  
• D-AMPS, or IS-136 TDMA, is the digital variant of the AMPS analogue technology used on all the US 800Mhz cellular networks. A 1.9Ghz option has been implemented for some of the PCS networks and it is expected that data services will be introduced in 1998.