EDGE is a further evolution of GSM, enabling higher data rates to be achieved but using substantially the same network equipment. Effectively, it is an upgrade to GPRS. Although upgrades are required at the base station, as there are differences to the radio interface, the core network capability remains virtually unchanged, allowing migration to the new standard. EDGE stands for either Enhanced Data for Global Evolution or for Enhanced Data for GSM Evolution both are widely used and accepted.

One of the main differences between EDGE and GPRS is that EDGE uses a different form of modulation. GPRS uses the GMSK used on GSM, whereas EDGE, to achieve higher data rates, uses a higher-order modulation format in the form of 8PSK (see Chapter 3). This means that instead of the maximum payload per slot being 116 bits, as in the case of GPRS, it rises to 464 bits. The packet technology used in GPRS is carried forward to EDGE, and this means that the upgrades that are required are essentially within the BTS to enable it to transmit and receive 8PSK modulation.

EDGE offers a significant speed improvement over GPRS, but this can only be achieved under ideal conditions. The optimum radio conditions occur only when the signals in both directions are sufficiently strong, and this normally entails the mobile being reasonably close to the base station. Once a mobile starts to move, variations in signal strength are normally experienced and these degrade the quality of the link.