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General Packet Radio Services (GPRS) background information

By Gillian Gamsy International
Johannesburg, 18 Mar 2002

Siemens currently has five GPRS-enabled devices in its portfolio - SX45, S45, ME45 and M50, all of which support GPRS (class B, supporting MultiSlot class 8). Siemens is excited by the potential of GPRS to effect real change in the transmission of data to mobile devices and will continue to develop products, which maximise this opportunity.

The world of mobile communications is evolving and with the explosive growth in Internet and mobile computing, the need to have access to fast and efficient mobile data is escalating.

To date, mobile phones and devices have operated across the GSM (Global System for Mobile Communication) network - the foundation on which today's thriving mobile industry has been established. However, GSM cannot sustain the speed necessary to facilitate new technological advancements and GPRS (General Packet Radio Services) which supplements the existing GSM network, goes someway to resolve this, making data transfer swifter and more efficient than ever before.

What is GPRS?

GPRS is a special system for transferring information over the GSM network. A data call is split into packets, and each packet is tagged with additional information, which tells the network where it needs to be sent and how it fits together as part of the whole original message. This reflects the IP technology used with the Internet and it allows the data to be sent without a direct circuit switched connection being made to the recipient. By using this system the packets can be routed through different parts of the network, taking advantage of spare capacity and can be re-assembled smoothly and in the correct order at the destination.

How does it work?

GSM radio channels are split into eight timeslots, each of which has the capacity to move data at 9.6Kbps. In a normal GSM data call, a user occupies one timeslot during the entire duration of the circuit switched call and makes use of the complete 9.6Kbps. Once all the GSM timeslots have been filled, any additional users are unable to enter the network. The user pays for the entire time they are connected, when they are making a data transmission, regardless of the transmitted data volume.

GPRS technology allows users to share timeslots. By sending out packets of information, individually addressed, the capacity of the network can be more efficiently used, eg pauses during the GPRS data transmission, are available for other users and will not remain unused as with normal GSM data transmissions. The GPRS system also allows costs to be more effectively managed as figures are calculated on the amount of data transmitted rather than time spent connected.

How fast is GPRS?

Speed is certainly a driving force behind the advancement of technology, as users require more wireless data more quickly. GPRS achieves faster transmission rates by using several timeslots in parallel for the data transmission. The theoretical maximum speed for GPRS is up to 171.3kbps, when all eight timeslots are used. This is about three times faster than speeds possible over today's fixed-line telecommunications, but this speed is unlikely to be reached in reality, where currently the achievable data-rate is about 40 to 50kbps.

GPRS handsets are capable of using more than one timeslot for sending and receiving data, and the most likely configuration will be three or four timeslots for receiving data and one timeslot for sending data. This will result in a realistic and possible data transfer rate of 13.4kbps for transmitting (assuming 1 Tx with Coding Scheme 2) and approx 40kbps (3Rx / CS2) or approx. 54Kbps (4Rx / CS2) for receiving data.

In reality, the speed of GPRS is dependent upon several issues: the amount of data being sent by multiple users, the configuration of handsets, the available infrastructure supporting GPRS and the overall GSM traffic in the network. All of these issues impact on the available network capacity and therefore the achievable data-rate.

Classes of GPRS

There are two different classes related to GPRS. The first represents the grade of the GPRS technology being implemented:

Class A: This terminal would support simultaneous circuit switched and packet-switched traffic, supporting simultaneous data and voice calls to be made.

Class B: This supports either circuit switched or packet switched traffic, but not at the same time and therefore either a voice or data call can be made. Incoming calls are alerted while the data transmission runs.

Class C: This terminal type is attached either as a circuit switched (GSM) or as a packet-switched (GPRS) terminal.

The second class refers to the number of timeslots the device is able to use to send and receive data.

Each GPRS device is given both a GPRS Class and a MultiSlot class. Currently, Siemens devices are GPRS Class B and support MultiSlot (MS) Class 8, which results in 4 downlinks (up to 4 Rx) and one uplink (1 Tx).

A steady evolution

It is important that the introduction of GPRS is seen as the next stage in the technological advancement of mobile communications, which began with GSM data transmission. Although GPRS does not replace WAP, it aids the evolution of wireless data through WAP, resulting in a more satisfying and enjoyable experience for the mobile phone user. It is the next step in building an efficient and exciting world of mobile data and it must be viewed positively, even if the maximum speeds are not met in the first instance. Siemens is committed to developing applications that maximise the potential of this technology, and GPRS is set to make M-banking and wireless gaming a reality for many mobile phone users. It will take time for the overall-supporting infrastructure to be developed fully throughout the industry, but it is clear that the development of GPRS will bring fresh opportunities and possibilities to the wireless world. Siemens is fully committed to supporting this process.

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Tandi Paterson
Gillian Gamsy International
(011) 728 1363
tandi@ggisa.com