EDGE

As its name suggests, EDGE (Enhanced Data rates for Global Evolution) is an enhancement of the GSM^TM radio access technology to provide faster bit rates for data applications, both circuit- and packet-switched. As an enhancement of the existing GSM physical layer, EDGE is realized via modifications of the existing layer 1 specifications rather than by separate, stand-alone specifications.

Other than providing improved data rates, EDGE is transparent to the service offering at the upper layers, but is an enabler for High Speed Circuit Switched Data (HSCSD) and Enhanced GPRS (EGPRS). By way of illustration, the General Packet Radio Service (GPRS) can offer a data rate of 115 kbit/s whereas EDGE can increase this to 384 kbit/s. This is comparable with the rate for early implementations of Wideband Code Division Multiple Access (W-CDMA), leading some parties to consider EDGE as a 3G technology rather than 2G (a capability of 384 kbit/s allows EDGE systems to meet the ITU's IMT-2000 requirements). However, EDGE is generally viewed as a bridge between the two generations: a sort of 2.5G.

New modulation technique

The increased data rate is accomplished by a new modulation technique (8PSK as opposed to GSM/GPRS's GMSK, yielding a three-fold increase in bit rate for an identical symbol rate) coupled with new channel coding, resulting in improved spectral efficiency. This is important, because it allows EDGE to be introduced piecemeal into existing GSM networks without disrupting the frequency reuse plan of the existing deployment.

In fact, to cater for the potentially increased sensitivity to noise in marginal coverage areas, EDGE uses a combination of 8PSK and GMSK, to give a balanced improvement in bit rate under virtually all radio conditions. The four coding schemes of GPRS are increased to nine in EDGE, and new segmentation techniques can radically improve throughput by permitting the coding scheme to be changed on the fly in case of retransmission of a segment in rapidly changing radio conditions. In addition, the packet window size increased to 1024 compared with the 64 for GPRS, resulting in more robust transmission and reception.

The implementation of EDGE is summarized in 3GPP^TM TR10.59  (later 50.058) - essentially a catalogue of Change Requests which introduced EDGE functionality into the existing specifications, for Release 98. TR 10.58 / 50.058 has not been transposed into an official ETSI publication because it does not meet the necessary criteria. It remains, however, a very useful reference document.

A variant of EDGE, called 'EDGE Compact', permits deployment in less than 1 MHz of spectrum.

EDGE is compatible with the North American cellular system, ANSI IS136.

The following is a list of recently published and frequently downloaded standards. Please use the ETSI Work Programme to find further related standards.