GSM EDGE basics
- Use of 8PSK modulation: In order to achieve the higher data rates within GSM EDGE, the modulation format can be changed from GMSK to 8PSK. This provides a significant advantage in being able to convey 3 bits per symbol, thereby increasing the maximum data rate. This upgrade requires a change to the base station. Sometimes hardware upgrades may be required, although it is often simply a software change.
- Base station: Apart from the upgrade to incorporate the 8PSK modulation capability, other small changes are required to the base station. These are normally relatively small and can often be accomplished by software upgrades.
- Upgrade to network architecture: GSM EDGE provides the capability for IP based data transfer. As a result, additional network elements are required. These are the same as those needed for GPRS and later for UMTS. In this way the introduction of EDGE technology is part of the overall migration path from GSM to UMTS.
The two main additional nodes required for the network are the Gateway GPRS Service Node (GGSN) and the Serving GPRS Service Node (SGSN). The GGSN connects to packet-switched networks such as the Internet and other GPRS networks. The SGSN provides the packet-switched link to mobile stations.
- Mobile stations: It is necessary to have a GSM EDGE handset that is EDGE compatible. As it is not possible to upgrade handsets, this means that the user needs to buy a new GSM EDGE handset.
GSM EDGE evolution specification overview
|Multiple Access Technology||FDMA / TDMA|
|Channel Spacing||200 kHz|
|Slots per channel||8|
|Frame duration||4.615 ms|
|Latency||Below 100 ms|
|Overall symbol rate||270 k symbols / s|
|Overall modulation bit rate||810 kbps|
|Radio data rate per time slot||69.2 kbps|
|Max user data rate per time slot||59.2 kbps (MCS-9)|
|Max user data rate when using 8 time slots||473.6 kbps **|
** A maximum user data rate of 384 kbps is often seen quoted as the data rate for GSM EDGE. This data rate corresponds to the International Telecommunications Union (ITU) definition of the data rate limit required for a service to fulfill the International Mobile Telecommunications-2000 (IMT-2000) standard(i.e. 3G) in a pedestrian environment.