- GSM EDGE cellular technology is an upgrade to the existing GSM / GPRS networks, and can often be implemented as a software upgrade to existing GSM / GPRS networks.
- GSM EDGE evolution can provide data rates of up to 384 kbps, and this means that it offers a significantly higher data rate than GPRS.
There are a number of key elements in the upgrade from GSM or GPRS to EDGE. The GSM EDGE technology requires a number of new elements to be added to the system:
- 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 main new network architecture entities that are needed for the EDGE upgrade are:
- SGSN: GPRS Support Node - this forms a gateway to the services within the network.
- GGSN: Gateway GPRS Support Node which forms the gateway to the outside world.
- PCU: Packet Control Unit which differentiates whether data is to be routed to the packet switched or circuit switched networks.
The SGSN or Serving GPRS Support Node element of the GPRS network provides a number of takes focussed on the IP elements of the overall system. It provides a variety of services to the mobiles:
- Packet routing and transfer
- Mobility management
- Logical link management
- Charging data
There is a location register within the SGSN and this stores location information (e.g., current cell, current VLR). It also stores the user profiles (e.g., IMSI, packet addresses used) for all the GPRS users registered with the particular SGSN.
The GGSN, Gateway GPRS Support Node is one of the most important entities within the GSM EDGE network architecture. The GGSN can be considered to be a combination of a gateway, router and firewall as it hides the internal network to the outside. In operation, when the GGSN receives data addressed to a specific user, it checks if the user is active, then forwarding the data. In the opposite direction, packet data from the mobile is routed to the right destination network by the GGSN.
The PCU or Packet Control Unit is a hardware router that is added to the BSC. It differentiates data destined for the standard GSM network (circuit switched data) and data destined for the EDGE network (Packet Switched Data).