The standardisation work of GSM-based systems has its roots in the 1980s, when a standardisation body 'Groupe Special Mobile' (GSM) 1 was created within the Conference Europeenne des Postes et Telecommunications (CEPT), whose task was to develop a unique digital radio communication system for Europe, at 900 MHz.Since the early days of GSM development, the system has experienced extensive modifications in several steps to fulfil the increasing demand from the operators and cellular users. The main part of the basic GSM system development during the last decade until spring 2000 has been conducted in European Telecommunications Standards Institute (ETSI) Special Mobile Group (SMG) and its technical sub-committees, as well as in T1P1, which had the responsibility of the PCS1900 MHz specifications in the United States.Currently, the further evolution of the GSM-based systems is handled under the 3rd Generation Partnership Project (3GPP), which is a joint effort of several standardisation organisations around the world to define a global third-generation UMTS (universal mobile communication system) cellular system. The main components of this system are the UMTS terrestrial radio access network (UTRAN) based on wideband code division multiple access (WCDMA) radio technology and GSM/EDGE radio access network (GERAN) based on global system for mobile communications (GSM)/enhanced data rates for global evolution (EDGE) radio technology.In the following sections, an introduction of the evolution steps of the GSM specifications is presented.

One step in the evolution of the real-time GSM services is the Enhanced Circuit Switched Data (ECSD) which is being developed in ETSI as GSM Phase 2+ work item (EDGE Phase 1) parallel to Enhanced General Packet Radio Service (EGPRS). ECSD radio interface deploys 8-PSK modulation in addition to GMSK and thus enables higher data throughput per time slot. This paper gives an overview of the ECSD concept and examples of applications that it supports. The focus is in the link level and the radio network level performance of different ECSD data rates in various test environments. It is shown that by utilising the proper link adaptation mechanism, even demanding transparent high data rate services, like video, can be supported with a good coverage.

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