GPRS General Packet Radio Service Tutorial

- GPRS technology, General Packet Radio Service, provides the basic GSM upgrade technology used to provide packet data at up to 172 kbps.

GSM was the most successful second generation cellular technology, but the need for higher data rates spawned new developments to enable data to be transferred at much higher rates.

The first system to make an impact on the market was GPRS. The letters GPRS stand for General Packet Radio System, GPRS technology enabled much higher data rates to be conveyed over a cellular network when compared to GSM that was voice centric.

GPRS technology became the first stepping-stone on the path between the second-generation GSM cellular technology and the 3G W-CDMA / UMTS system. With GPRS technology offering data services with data rates up to a maximum of 172 kbps, facilities such as web browsing and other services requiring data transfer became possible. Although some data could be transferred using GSM, the rate was too slow for real data applications.

What is GPRS? - benefits

GPRS technology brings a number of benefits for users and network operators alike over the basic GSM system. It was widely deployed to provide a realistic data capability via cellular telecommunications technology.

base station of the type that can used GPRS
GPRS technology offered some significant benefits when it was launched:

  • Speed:   One of the headline benefits of GPRS technology is that it offers a much higher data rate than was possible with GSM. Rates up to 172 kbps are possible, although the maximum data rates realistically achievable under most conditions will be in the range 15 - 40 kbps.
  • Packet switched operation:   Unlike GSM which was used circuit switched techniques, GPRS technology uses packet switching in line with the Internet. This makes far more efficient use of the available capacity, and it allows greater commonality with Internet techniques.
  • Always on connectivity:   A further advantage of GPRS is that it offers an "Always On" capability. When using circuit switched techniques, charges are based on the time a circuit is used, i.e. how long the call is. For packet switched technology charges are for the amount of data carried as this is what uses the services provider's capacity. Accordingly, always on connectivity is possible.
  • More applications:   The packet switched technology including the always on connectivity combined with the higher data rates opens up many more possibilities for new applications. One of the chief growth areas that arose from GPRS was the Blackberry form of mobile or PDA. This provided for remote email applications along with web browsing, etc.
  • CAPEX and OPEX:   The Capital expenditure (CAPEX) and operational expenditure (OPEX) are two major concerns for operators. As GPRS was an upgrade to existing GSM networks (often implemented as a software upgrade achieved remotely), the capital expenditure for introducing GPRS technology was not as high as deploying a complete new network. Additionally OPEX was not greatly affected as the basic base-station infrastructure remained basically the same. It was mainly new core network elements that were required.

The GSM and GPRS elements of the system operate separately. The GSM technology still carries the voice calls, while GPRS technology is used for the data. As a result voice and data can be sent and received simultaneously. Some people refer to the system as GSM GPRS.

Note on GSM:

GSM or Global System for Mobile Telecommunications was initially a European mobile telecommunications system. It was the most successful 2G system, and was adopted globally. Allowing roaming, text messages and many other features above the basic voice, it was highly successful in meeting the needs of the users.

Click for a GSM tutorial

In order to further develop the capability of GPRS, further advances were made and another system known as EDGE or Enhanced GPRS, EGPRS was developed.

Note on EDGE:

GSM EDGE, Enhanced Data rates for GSM Evolution, was the evolution of GSM, & GPRS which used 8PSK modulation to achieve data transfer rates up to 384 kbps..

Click for a EDGE tutorial

What is GPRS? - packet switching

The key element of GPRS technology is that it uses packet switched data rather than circuit switched data, and this technique makes much more efficient use of the available capacity. This is because most data transfer occurs in what is often termed a "bursty" fashion. The transfer occurs in short peaks, followed by breaks when there is little or no activity.

Using a traditional approach a circuit is switched permanently to a particular user. This is known as a circuit switched mode. In view of the "bursty" nature of data transfer it means that there are periods when it will not be carrying data.

To improve the situation the overall capacity can be shared between several users. To achieve this, the data is split into packets and tags inserted into the packet to provide the destination address. Packets from several sources can then be transmitted over the link. As it is unlikely that the data burst for different users will occur all at the same time, by sharing the overall resource in this fashion, the channel, or combined channels can be used far more efficiently. This approach is known as packet switching, and it is at the core of many cellular data systems, and in this case GPRS.

Packet Switching vs Circuit Switching
Circuit Switched Mode Packet Switched Mode
IMSI attach GPRS attach
Call setup TBF establishment
PDP context activation
Call state (bi-directional) Block transfer (uni-directional)
Exclusive use of channel Channel shared between users
Calls cleared on completion Always on

GPRS network

GPRS and GSM are able to operate alongside one another on the same network, and using the same base stations. However upgrades are needed. The network upgrades reflect many of those needed for 3G, and in this way the investment in converting a network for GPRS prepares the core infrastructure for later evolution to a 3G W-CDMA / UMTS.

The upgraded network, as described in later pages of this tutorial, has both the elements used for GSM as well as new entities that are used for the GPRS packet data service.

The upgrades that were required for GPRS also formed the basis of the network required for the 3G deployments (UMTS Rel 99). In this way the investment required for GPRS would not be a one off investment used only on GPRS, it also formed the basis of the network for further developments. In this way GPRS became a stepping stone used for the migration from 2G to 3G.

Read more about GPRS network.

GPRS mobiles

Not only does the network need to be upgraded for GPRS, but new GPRS mobiles were also required. It is not possible to upgrade an existing GSM mobile for use as a GPRS mobile, although GSM mobiles can be used for GSM speech on a network that also carries GPRS. To utilise GPRS new modes are required to enable it to transmit the data in the required format.

With the incorporation of packet data into the network, this allowed far greater levels of functionality to be accessed by mobiles. As a result a new breed of mobiles started to appear. These PDAs were able to provide email and Internet browsing, and they were widely used especially by businesses as they allowed their key people to remain in touch with the office at all times.

What is GPRS? key parameters

The key parameters for the GPRS, General Packet Radio System, are tabulated below:

What is GPRS? - the key parameters
Parameter Specification
Channel Bandwidth 200 kHz
Modulation type GMSK
Data handling Packet data
Max data rate 172 kbps

GPRS technology offered a significant improvement in the data transfer capacity over existing cellular systems. It enabled many of the first email and web browsing phones such as PDAs, Blackberrys, etc to be launched. Accordingly GPRS technology heralded the beginning of a new era in cellular communications where the mobile phone capabilities allowed significantly more than voice calls and simple texts. GPRS enabled real data applications to be used and the new phones to become mobile computers on the move allowing businessmen to be always in touch with the office and domestic users to be able to use many more data applications.

By Ian Poole

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