The GPRS (General Packet Radio Service) standard is an evolution of the GSM standard, and for that reason is sometimes called GSM++ (or GMS 2+). As it is a second-generation telephony standard that allows a transition to third generation (3G), the GPRS standard is generally classified as 2.5G.
GPRS extends the architecture of the GSM standard to allow packet data transfers with theoretical data rates on the order of 171.2 Kbit/s (up to 114 Kbit/s, in practice). Thanks to its packet transfer mode, data transmissions only use the network when necessary. The GPRS standard therefore allows the user to be billed by volume of data rather than by the duration of the connection, which means, in particular, that the user can remain connected at no extra cost.
For voice transport, the GPRS standard uses the GSM network architecture, and offers access to data networks (in particular the Internet) using the IP protocol or the X.25 protocol.
GPRS supports new features not available with the GSM standard, which can be generally categorised into the following service classes:
Point to point services (PTP): the ability to connect in client-server mode to a machine on an IP network,
Point to multipoint services (PTMP): the ability to send a packet to a group of recipients (Multicast).
Short message services (SMS),
Architecture of the GPRS network
Integration of GPRS into a GSM architecture requires the addition of new network nodes called GSN (GPRS support nodes) located on a backbone network:
the SGSN (Serving GPRS Support Node) router manages the addresses of the terminals in the cell and provides the packet transfer interface with the GGSN gateway.
the GGSN (Gateway GPRS Support Node) gateway interfaces with other data networks (the Internet). In particular, the GGSN is responsible for providing an IP address to the mobile terminals throughout the duration of their connection.
Quality of service
GPRS integrates the concept of Quality of Service (written QoS), in other words, the ability to adapt the service to the needs of an application. The service quality criteria are the following:
- reliability. GPRS defines 3 reliability classes
The GPRS standard defines 4 encoding schemes, called CS-1, CS-2, CS-3 and CS-4. Each scheme defines the level of protection of the packets against interference so as to be able to degrade the signal according to the distance of the mobile terminals from the base stations. The higher the protection, the lower the throughput: Encoding scheme Throughput Protection
CS-1 9.05 Kbit/s Normal (signalling)
CS-2 13.4 Kbit/s Slightly lower
CS-3 15.6 Kbit/s Reduced
CS-4 21.4 Kbit/s No error correction
The EDGE (Enhanced Data Rates for GSM Evolution.) standard is an evolution of the GSM standard that modifies the type of modulation. Like the GPRS standard, the EDGE standard is intended to be a transition to third generation mobile telephony (3G). The term 2.75G is also used to describe the EDGE standard.
EDGE uses a different modulation than the modulation used by GSM (EDGE uses 8-PSK modulation), which means that base stations and mobile terminals need to be modified to support it.
EDGE increases the data rate by a factor of 3 but with a smaller coverage area. In theory, EDGE supports throughput of up to 384 Kbit/s for fixed stations (pedestrians and slow vehicles) and up to 144 Kbit/s for mobile stations (fast vehicles).
High Speed Downlink Packet Access (HSDPA) is a packet-based data service in W-CDMA downlink with data transmission up to 8-10 Mbps (and 20 Mbps for MIMO systems) over a 5MHz bandwidth in WCDMA downlink. HSDPA implementations includes Adaptive Modulation and Coding (AMC), Multiple-Input Multiple-Output (MIMO), Hybrid Automatic Request (HARQ), fast cell search, and advanced receiver design.
In 3rd generation partnership project (3GPP) standards, Release 4 specifications provide efficient IP support enabling provision of services through an all-IP core network and Release 5 specifications focus on HSDPA to provide data rates up to approximately 10 Mbps to support packet-based multimedia services. MIMO systems are the work item in Release 6 specifications, which will support even higher data transmission rates up to 20 Mbps. HSDPA is evolved from and backward compatible with Release 99 WCDMA systems.
Currently (2002) 3GPP is undertaking a feasibility study on high-speed downlink packet access.