GPRSGeneral Packet Radio Service

Wireless roadmap

EDGE

GSM

• GSM is by far the biggest 2G system, with more than 400million subscribers (by the end of 2000) and adding 10 millionmore each month.

• As with other 2G systems, GSM handles voice efficiently, butthe support for data and Internet applications is limited.

• A data connection is established in just the same way as aregular voice call: The user dials in and a circuit-switchedconnection continues during the entire session. If the userdisconnects and wants to reconnect, the dial-in sequence hasto be repeated. This issue, coupled with the limitation thatusers are billed for the time that they are connected, createsa need for packet data for GSM.

For Data Communication:--

• 2G GSM std BW of 9.6 kbps is not sufficient

• Web browsing, file download and e-mail with attachments etc were not possible.

So data transmission capabilities of GSM were enhanced using two approaches.:

a. Connection oriented traffic channels (HSCSD)

b. Packet oriented traffic channels (GPRS)

Connection oriented traffic channels (HSCSD):Higher data rates are achieved by bundling severaltraffic channels.

• With High-Speed, Circuit -Switched Data (HSCSD), the samecircuit-switched technology is used as regular GSM, butmultiple timeslots can be used for one connection. In otherwords, one user can achieve up to 57.6Kbps of data speed.

• The first HSCSD systems appeared in 2000.

• This format enables users who are already frequentlychecking their mail and using the Internet/intranet on the goto achieve higher speeds.

Comparison of GSM & GPRS

GSM GPRS

Data Rates 9.6 Kbps 14.4 to 115.2

Kbps

Modulation

Technique

GMSK GMSK

Billing Duration of

connection

Amount of

data

transferred

Type of

Connection

Circuit – Switched

Technology

Packet -

Switched

Technology

Three key features of GPRS

• Always online. – Removes the dial-up process, making applications only one click away.

• An upgrade to existing networks (GSM and TDMA).– Operators do not have to replace their equipment; rather, GPRS is

added on top of the existing infrastructure.

• An integral part of EDGE and WCDMA. – GPRS is the packet data core network for these 3G systems.

The Need for Packet Data

• A circuit -switched connection to some site works just like aregular telephone call. You dial in to your Internet Service Provider(ISP) and have your 9.6Kbps as long as you are connected

General Packet Radio Service (GPRS) is a newbearer service for GSM that greatly improves andsimplifies wireless access to packet data networks

GPRS applies packet radio principal to transferuser data packets in an efficient way between MS &external packet data network

GPRS is a step towards 3G and is often referred toas 2.5G.

What is GPRS ?

GPRS is a step towards 3G and is often referred toas 2.5G.

Here are some key benefits of GPRS

Speed:

GPRS is packet switched.Higher connection speeds are attainable at around 14–115 kbps, avast improvement on circuit switched networks of 9.6 kbps.By combining standard GSM time slots theoretical speeds of 171.2kbps are attainable.

Always on connectivity:

GPRS is an always-on service. There is no need to dial up like you have to on a home PC forinstance. This feature is not unique to GPRS but is an importantstandard that will no doubt be a key feature for migration to 3G.It makes services instantaneously available to a device.

Reserves radio resources only when there is data to send

New and Better applications

Due to its high-speed connection and always-on connectivity GPRSenables full Internet applications and services such as videoconferencing straight to your desktop or mobile device.Users are able to explore the Internet or their own corporatenetworks more efficiently than they could when using GSM. There isoften no need to redevelop existing applications.

GSM operator Costs

GSM network providers do not have to start from scratch to deployGPRS. GPRS is an upgrade to the existing network that sits along sidethe GSM network.This makes it easier to deploy, there is little or no downtime of theexisting GSM network whilst implementation takes place, most updatesare software so they can be administered remotely and it allows GSMproviders to add value to their business at relatively small costs.

Important step on the path to 3G

Standardized by ETSI (European Telecommunications Standard Institute)

GPRS is an overlay network over the GSM

Provides Data Packet delivery service

Support for leading internet communication protocols

Billing based on volume of data transferred

Utilizes existing GSM authentication and privacy procedures

Features of GPRS:

High Data Rate

• GPRS uses radio channel i.e. 200 kHz wide

• Radio channel carries digital data stream of271 kbps

• This rate is divided into 8 time slots eachcarrying 34 kbps per time slot

• Data rate approx.~14 kbps per time slotachieved after corrections

• GPRS can combine up to 8 time slots givingdata rate of approx. ~114 kbps

1. GPRS is a 2.5G technology.2. It uses existing cellular n/w infrastructure3. S/w upgrade at base stations and the addition of a

GPRS Gateway that connects the GPRS network tothe Internet is required.

4. FDMA based multiple access techniques.5. A user is assigned to one pair of up-link and down-

link frequency channels. This is combined withtime domain i.e. packet mode communication.

6. The packets have constant length, correspondingto a GSM time slot.

1. Duplex separation: 45 MHz2. RF carrier spacing: 200 kHz3. Total number of RF Duplex channels: 1244. Number of TDMA slots on each carrier: 85. Channel allocation: 1 to 8 time slots per TDMA6. One time slot (Physical channel) : 0.577 ms7. Frame Interval: 4.615 ms

8. Asymmetric data traffic: different time slots for Uplink and downlink

9. Frequency Hopping: 217 hops/s 10. Connectivity: Packet switched data networks such as IP and

X.2511. Extra nodes:

Gateway GPRS Support Node (GGSN) andServing GPRS Support Node (SGSN)

GPRS Services

• Offers end-to-end packet switched data transfer

• Bearer Services

• PTP - Point-To-Point service

• PTM - Point-To-Multipoint service

• PTM-M Multicast service (News,whether

report)

• PTM-G Group call service (conferencing

service)