GPRS enables us to use radio and network resources much more efficiently. The usage is optimized by acquiring the network resources only when some data is to be sent or received. Fast connectivity and high throughput are key advantages of GPRS Systems.
The miniaturization in the sizes and increase in power of the mobile devices needed more data speed and for that GPRS is being introduced to tackle the growing demand of wireless data packet service which will then result in tremendous growth of wireless internet usage. Another reason is that GPRS can easily integrate in the existing setup (GSM) with very little modifications and can be employed incrementally. GPRS is capable of dealing with the high bandwidth requirement of the heavy traffic and is better suited with the available infrastructure.
The error detection and correction along with interleaving is performed at the physical layer. Error detection and correction is being performed at many stages in the coding schemes used by GPRS. Their usage and dependence upon different factors categorize them from CS-1 to CS-4.
CS-1: The higher level of interference and low SNR is coped by the described level where maximum error detection and correction is being performed. The scheme helps avoid the data being often re-sent. Except for some cases where data delays are unacceptable they doesn’t matter for several kinds of data. The outcome of the scheme is a half code rate, i.e. input of 12 bits to the coder, gives 24 bits . The actual acquired bandwidth can be given as 9.05 kbps.
CS-2: A 2/3 encoder gives us an actual bandwidth usage of 13.4 kbps including Radio Link channel, Medium access control and header etc. The scheme is used for relatively better channels.
CS-3: The bandwidth of 15.6 kbps is achieved by the usage of a 3/4 coder.
CS-4: The situation where SNR is high and Interference is low CS-4 is applied. A bandwidth of 21.4 Kbps is achieved as correction is not applied. If all the slots are acquired will result in 21.4*8 Kbps of bandwidth.
Interleaving techniques are applied for decreasing the effects of interference and noise. Which helps in error correction and immunity to data corruption in case of loss of data.
GPRS can be regarded as an extension of the GSM Network apart from switching from Circuit to Packet switching and necessary up- gradation in the system is done which mainly includes the GGSN and SGSN. For the GSM and GPRS to work in parallel some new elements are also added to GSM architecture.
GPRS network architecture upgrades
With transition from Circuit switch to packet switching which resulted then in increased connectivity. Following new entities are added in the architecture.
SGSN: GPRS Support Node ââ‚¬” to obtain an intra-network gateway to the services .
GGSN: Gateway GPRS Support Node to act as a bridge to the outside world.
PCU: Packet Control Unit is to decide on sending data to circuit or packet switched network.
The following diagram explains the architecture and its similarity to the GSM network can easily be determined.
GPRS network architecture
serving GPRS Support Node element is responsible for a number of tasks in a GPRS network including IP elements belonging to the whole system. Beside that it also serve mobile devices as follows.
Packet routing and transfer
Logical link management
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 GPRS network architecture.
The GGSN organises the interworking between the GPRS network and external packet switched networks to which the mobiles may be connected. These may include both Internet and X.25 networks.
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 GPRS network (Packet Switched Data). The PCU itself may be a separate physical entity, or more often these days it is incorporated into the base station controller, BSC, thereby saving additional hardware costs.
GPRS network upgrading
One of the key elements for any network operator is the cost of capital expenditure (capex) to buy and establish a network. Capex costs are normally very high for a new network, and operators endeavour to avoid this and use any existing networks they may have to make the optimum use of any capital. In addition to the capex, there are the operational costs, (opex). These costs are for general maintenance and other operational costs that may be incurred. Increasing efficiency and reliability will reduce the opex costs.
Any upgrade such as that from GSM to GPRS will require new investment and operators are keen to keep this to the minimum. The upgrades for the GPRS network are not as large as starting from scratch and rolling out a new network.
The GPRS network adds to the existing GSM network. The main new entities required within the network are the SGSN and GGSN, and these are required as the starting point.
The base station subsystems require some updates. The main one is the addition of the PCU described above. Some modifications may be required to the BTS, but often only a software upgrade is required, and this may often be achieved remotely. In this way costs are kept to a minimum.
The GPRS network architecture can be viewed as an evolution of the GSM network carrying both circuit switched and packet data. The GPRS network architecture was also used as the basis for the 3G UMTS network. In this way network operators could evolve their networks through GPRS and possibly EDGE to the full 3G networks without having to replace and install more new equipment than was absolutely necessary.
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