What is GPRS
GPRS stands for ‘General Packet Radio Service’. It is a packed based data communication service that was developed solely for its integration in to GSM cellular networks in order to provide the subscribers of the network with non real time internet usage in applications such as e-mail retrieval and faxes. It also supports asymmetric web browsing i.e. browsing where there is minimal upload by the user.
How does a GPRS system works? In a GSM network, the whole frequency band is divided in to 25 kHz frequency channels that are used as control channels or voice channels. Each of these voice channels is further divided in to eight time slots using TDMA. These slots are assigned to users dynamically via the control channels for uplink and downlink of voice. Now the GPRS service, borrows some of these slots for the purpose of data communication. A GPRS enable mobile is always kept tuned to these data channels by the use of control channels.
On these borrowed TDMA channels, data is transmitted in the form of packets. Each packet has its destination and source IP address and it is by the use of this addressing that a mobile unit is able to acknowledge the packets meant for it while it discards the rest of the packets. The task of error detection and correction in these packets is left on the mobile applications accessing these packets.
GPRS system uses the same modulation scheme of Gaussian Minimum Shift Keying as in case of GSM. The maximum data rate that a single GPRS data channel can support is 21.4 kbps. Although the users can be provided with higher data rates by allowing combined access to multiple channels. With increase in the number of subscribers accessing the GPRS channels at the same time, the data rates for each user decreases.
For upgrading GSM networks in order to integrate GPRS, routers and internet gateways are installed at the base station antennas of the network along with changes made in the software of the Base Station Controller regarding the channel allocation in the system. No changes are required to be made in the Mobile Switching Centre Architecture or in the RF equipment of the Base Stations.
Though the GPRS system was initially designed for upgrading data communication services in GSM Networks, it was also quickly adapted by IS-136 TDMA system in USA. Thus the GPRS system is said to belong to 2.5G Cellular TDMA Networks by providing a near term solution for data communication to 2G TDMA Networks.