GPRS (General Packet Radio System)
General packet radio service (GPRS) is a packet-based wireless data communication service designed to replace the current circuit-switched services available on the second-generation global system for mobile communications (GSM) and time division multiple access (TDMA) IS-136 networks. GSM and TDMA networks were designed for voice communication, dividing the available bandwidth into multiple channels, each of which is constantly allocated to an individual call (circuit-switched). These channels can be used for the purpose of data transmission, but they only provide a maximum transmission speed of around 9.6Kbps (kilobits per second).
GPRS distributes packets of data from several different terminals in the system across multiple channels, making a much more efficient use of the bandwidth currently available for 'bursty' applications such as internet access. In theory, using all eight channels in a GSM network at once, a GPRS connection can achieve a data transfer rate of up to 114Kbps. These higher data rates will allow users to interact with multimedia websites and similar applications using a mobile handset or notebook computer. In theory, GPRS services should be cheaper than circuit-switched connections, with the network only being used when data is being transmitted.
GPRS communication is designed to compliment but not replace current circuit-switched networks, being used solely as an extra means of data communication. In practice, connection speeds will be significantly lower than the theoretical maximum, depending upon the amount of traffic on the network and upon the number of simultaneous channels supported by the handsets. In practice, GPRS is an evolutionary step towards enhanced data for global evolution (EDGE) and IMT-2000 systems.
As a packet-switched technology, GPRS supports the internet protocol (IP) and X.25, packet-switched standards currently used in wireline communications. As such, any service that is used on the fixed internet today will also be able to be used over GPRS. Because GPRS uses the same protocols as the internet, the networks can be seen as subsets of the internet, with the GPRS devices as hosts, potentially with their own IP addresses.
GPRS is based on a modulation technique called Gaussian minimum-shift keying (GMSK). This is where the rectangular pulses corresponding to the bitstream are filtered, using a Gaussian-shaped impulse response filter, producing lower sidelobes than would otherwise be the case. This modulation technique does not allow as high a bit rate across the air interfaces as eight-phase-shift keying (8 PSK) modulation, which is being introduced in EDGE systems.
Enabling GPRS on a GSM or TDMA network requires the addition of two core modules, the Gateway GPRS Service Node (GGSN) and the Serving GPRS Service Node (SGSN). The GGSN acts as a gateway between the GPRS network and the public data networks such as IP and X.25. They also connect to other GPRS networks to enable roaming. The SGSN provides packet routing to all of the users in its service area.
As well as the addition of these nodes, GSM and TDMA networks have to have several extra upgrades to cope with GPRS traffic. Packet control units have to be added and mobility management, air interface and security upgrades have to be performed.
Because the basic infrastructure interfaces with the existing GSM or TDMA infrastructure, the major vendors are the incumbent GSM suppliers such as Ericsson, Nokia, Motorola and Alcatel.