GPRS (General Packet Radio Service) is an integrated version of the Global System for Mobile (GSM) network switching subsystem. GPRS is primarily a mobile data service which allows 2G and 3G networks to impart IP packets to other foreign networks like internet. Second generation cellular technology which transmitted about 56-114 kbps data, is combined with GPRS to produce a much higher rate (nearly 172 kbps) of data transfer. So GPRS is sometimes termed as 2.5G.
Packet Data- GPRS
GPRS technology is based on the packet data transfer to various destinations. Traditionally data was transferred by circuit switched data where a circuit is transferred permanently to a particular external network. So the data was not supplied to all the allotted destinations at the same time. In order to change the situation and make the data available at all destinations at the same time, GPRS technology has been constructed. In this advance cellular technology, the overall data is divided into small packets which are then transferred to their respective proposed destinations. This innovative technology is called packet transfer or packet switching of data.
GPRS Network and its Upgradation
GPRS network is not an all new technology. It is rather an upgraded technology. GPRS is upgraded with some new elements which boost up its performance. For GPRS to function efficiently the following entities are combined with it.
SGSN or the Serving GPRS Support Node element. Its main task is to transmit IP data within the GPRS network. Its other functions include encrypting destination to the packet data and thereby transferring them, managing movement and linking of data, verifying the authentication of data packets, and also charging the data.
GGSN or the Gateway GPRS Support Node. This entity is specially designed to serve within the GPRS network. The primary function of this node is to receive pre-addresses data and forward them to their right destination. But before sending the data, GGSN clarifies whether the external network is active or not.
PCU or the Packet Control Unit. Its function is to identify the data type, i.e., whether the data is circuit switched data or a packet switch data and then transfer them to GSM and GPRS networks respectively.
But upgrading the GPRS network is rather cost effective. One needs to purchase these new elements and then install them in the network for upgradation which increases the expenditure for setting up the system.
GMSK Modulation
GMSK or the Gaussian Minimum Shift Keying kind of phase modulation which is used for better transmission in wireless network service providers. Previously GMSK modulation was used in GSM network as it used to save power consumption and increases battery life. GMSK modulation also provided high spectral efficiency and less interference with the unwanted bandwidth. GPRS is also build on the same platform which is shared by GSM and hence GPRS uses the same phase modulation as GSM, i.e. GMSK modulation.
Mobiles with GPRS and their Classes
We confront various mobiles and smart phones which are incorporated with GPRS network services. The remarkable benefit about GPRS in our mobiles is that GPRS supports data as well as voice transmission to external network. But the level of data services provided in mobiles can be different. These mobile data service quality and application is classified in following classes.
Class A which provides connectivity to both GPRS as well as GSM networks at the same time.
Class B category provides connectivity to GPRS and GSM networks but not at the same time.
Class C category also provides connectivity to GPRS and GSM networks but the user is supposed to manually switch the required network.
There are other classes of mobile data services which have GPRS connectivity. The entire range is given below with their rate of transmission.
Software Layers
Software plays a major role in mobile technology. But these softwares are classified into different layers for different kind of mobiles to keep pace with the latest data oriented networks.
First Layer- It is the Physical Link Layer which creates a physical connection between the mobile and the working platform.
Second Layer- It is the Radio Link and Medium access Layer which creates a radio as well as logical connection between the mobile and the working station.
Third Layer- Finally the logical Link Layer which transmits the sourced data to the respective mobile.
GPRS Encoding Technique
In order to detect and correct error in the data, GPRS encoding technique has been developed. There are various levels of error detection which is summarized below.
CS-1: This level of encoding technique is the most efficient one as it detects and corrects error in the data maintaining maximum accuracy. In this level, the ultimate result after detection and correction is termed as half code rate as for every 12 bits that enter this level, the output is 24 bits.
CS-2: This coding technique is for superior quality channels as it encodes at a rate of 2/3.
CS-3: This mostly performs at ¾ encoding rate.
CS-4: This kind of encoding is used for high signal quality and low intercession level of data transmission.
GPRS Channel Distribution
There are various channels allocated for GPRS to function efficiently. These are mainly physical as well as logical channels which are responsible to carry data and provide signal to the external network. There are two kinds of channels, viz, Physical channel or the Packet data Channel and the Logical Channel or the Packet Timing Advance Control Channel.
Physical Channel or the Packet data Channel in GPRS acts similarly like the GSM base station. It has the same power profile and same time management as the GSM structure.
Logical Channel or the Packet Timing Advance Control Channels are groups of channels which are either broadcasting channels or common control channels.
Packet Broadcast Central Channel: This kind of broadcasting channels, broadcasts information and informs incoming calls in the mobiles.
Packet Paging Channel: This is a common downlink control channel which alerts the mobile to get ready to receive the incoming calls.
Packet Access Grant Channel: This common downlink channel is assigned to inform the mobile about designated traffic channel after the mobile receives information about the incoming calls.
Packet Notification Channel: This common downlink channel is assigned for point-to-point multicasting.
Packet Random Access Channel: This is an uplink channel which is assigned to initiate the data in the uplink.
GPRS Operating Technique
The GPRS operating technique has been summarized in the below diagram
Advantages of a GPRS Cellular Technology
Due to high rate of data transfer, the speed offered by GPRS is very high.
Packet Switch Data technology enables much higher efficiency of data transmission to the internet.
The advancement and efficiency of Packet Switch Data initiates to develop new variety of mobile applications.
Also the Packet Switch data technology remains in ‘always on’ mode. This technology makes GPRS much more advance from GSM circuit switch technology.
GPRS is just an upgraded version of GSM and so the expense for setting up the GPRS network in work stations is much less than installing an overall new network.
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