EDGE (ENHANCED DATA GSM ENVIRONMENT)
HIGH-SPEED MOBILE DATA STANDARD
Enhanced data for global evolution (EDGE) is a high-speed mobile data standard,
intended to enable second-generation global system for mobile communication
(GSM) and time division multiple access (TDMA) networks to transmit data at up to
384 kilobits per second (Kbps). As it was initially developed just for GSM systems, it
has also been called GSM384. Ericsson intended the technology for those network
operators who failed to win spectrum auctions for third-generation networks to allow
high-speed data transmission.
EDGE provides speed enhancements by changing the type of modulation used and
making a better use of the carrier currently used, for example the 200kHz carrier in
GSM systems. EDGE also provides an evolutionary path to third-generation
IMT-2000-compliant systems, such as universal mobile telephone systems (UMTS),
by implementing some of the changes expected in the later implementation in
EDGE builds upon enhancements provided by general packet radio service
(GPRS) and high-speed circuit switched data (HSCSD) technologies that are
currently being tested and deployed. It enables a greater data-transmission speed
to be achieved in good conditions, especially near the base stations, by
implementing an eight-phase-shift keying (8 PSK) modulation instead of Gaussian
minimum-shift keying (GMSK).
For EDGE to be effective it should be installed along with the packet-switching
upgrades used for GPRS. This entails the addition of two types of nodes to the
network: the gateway GPRS service node (GGSN) and the serving GPRS service
node (SGSN). The GGSN connects to packet-switched networks such as internet
protocol (IP) and X.25, along with other GPRS networks, while the SGSN provides
the packet-switched link to mobile stations.
The additional implementation of EDGE systems requires just one EDGE
transceiver unit to be added to each cell, with the base stations receiving remote
software upgrades. EDGE can co-exist with the existing GSM traffic, switching to
EDGE mode automatically.
GPRS is based on a modulation technique called Gaussian minimum-shift keying
(GMSK). This modulation technique does not allow as high a bit rate across the air
interfaces as 8 PSK modulation if introduced into EDGE systems. 8 PSK modulation
automatically adapts to local radio conditions, offering the fastest transfer rates
near to the base stations, in good conditions. It offers up to 48Kbps per channel,
compared to 14Kbps per channel with GPRS and 9.6Kbps per channel for GSM. By
also allowing the simultaneous use of multiple channels, the technology allows
rates of up to 384Kbps, using all eight GSM channels.
Because the basic infrastructure interfaces with the existing GPRS, GSM or TDMA
infrastructure, the major vendors are the incumbent GPRS and GSM suppliers such
as Ericsson, Nokia, Motorola and Alcatel.
By providing an upgrade route for GSM/GPRS and TDMA networks, EDGE forms
part of the evolution to IMT-2000 systems. Since GPRS is already being deployed,
and IMT-2000 is not expected until 2002, there is a definite window of opportunity
for EDGE systems to fill in as a stop-gap measure.