GPRS Architecture

Packet-switched technique vs. circuit-switched

In circuit-switching, resources (e.g. a channel) are allocated to user for duration of connection
Inefficient use of resources
User pays for the whole connection
High QoS: channel maintains real-time connection
In packet-switching, resources are allocated to user only for the time it takes to send each packet
A channel can serve many users
User pays by the packet
Ideal for bursty data connections

Packet-switched

1.High bit rates
2.Shared bandwidth
3.Variable access times
4.Friendly bill (based on volume)
5.Robust application support
6.Frequent transmission of small volumes


Circuit-switched
1.Low bit rates
2.Reserved bandwidth
3.Fixed access time
4.Unfriendly bill (based on duration)
5.Limited application support
6.Large volumes


GPRS network architecture is built on top of the existing GSM network infrastructure.
To support packet switched functionality, GPRS introduces several new nodes in addition to the network nodes in the GSM.
There exist a Gateway GPRS Support Node (GGSN) and a Serving Support Node (SGSN). There is a backbone network that connects the SGSN and GGSN node together. Some of the existing GSM nodes should be upgraded with GPRS functionality.

PACKET AND CIRCUIT-SWITCHED DATA TRANSFER

In any kind of network the information can travel using either packet-switched (PS) or circuit-switched (CS) mode.
In general, circuit-switched mode is better for a connection set up for the purpose of a constant information flow.
A dedicated resource for this purpose is allocated throughout the connection.
Packet-switched mode is better for “bursty” connections in which short amounts of data are exchanged between the users over long time periods or for infrequent transmissions of big data volumes.
In this case no physical resources are dedicated for the purpose of the connection.
In principle, every burst of data will be routed separately within the network.
it takes to send each packet
A channel can serve many users
User pays by the pacIn circuit-switching, resources (e.g. a channel) are allocated to user for duration of connection
Inefficient use of resources
User pays for the whole connection
High QoS: channel maintains real-time connection
In packet-switching, resources are allocated to user only for the time ket
Ideal for bursty data connections

General Packet Radio Service (GPRS)

Introduction
Part I
GPRS Architecture
Part II
Bearer Services and Supplementary Services
Mobility Management
GPRS Limitations

introduction

Around 1994, the GSM phase 2 standards were enhanced to include a number of new and improved services.
These enhancements became known as GSM Phase 2 Plus.
One of the new features proposed in 1994 was a new service, true packet radio service known as GPRS
The purpose of GPRS (General Packet Radio Service) is to provide an efficient system aimed at data transfer for mobile users.
GPRS allows a user with suitable mobile station to occupy multiple time slots on a TRX, there by making it possible to occupy of all 8 timeslots if they are available.
The GSM system will be largely reused, though new hardware needs to be integrated in the existing network.
GPRS (General Packet Radio Service)
Reuse the existing GSM infrastructure (not standalone)
Introduce packet-switched routing functionality
Better data transfer rates due to multi-slot operation
Low cost and connectivity-oriented
Migration Path to 3G Networks

BTS–Base Transceiver Station

BTS provides physical connection of an MS to the network in the form of Air Interface.
On the other side BTS connected to BSC thru Abis-interface.
Cabinet size is reduced substantially from 1991 to current.
Functionality and basic structure largely unchanged.
A BTS cabinet can have up to 16 TRX (GSM recommendation)

TRX – Most important module of BTS from signal processing point of view

Consists of a low frequency part for signal processing and a high frequency part for modulation/demodulation.

Both parts are connected by a separate or integrated Frequency hopping unit.
All other parts of BTS are associated with TRX and perform auxiliary or admin tasks.

Base Station System (BSS)

The Base Station System (BSS) is responsible for all the radio related functions in the system, such as:
Radio communication with the mobile units
Handover of calls in progress between cells
Management of all radio network resources and cell configuration data.


A BSS consists of the following elements:

• One or more BTSs (base transceiver station)

• One BSC (base station controller)

• One TRAU (transcoding rate and adaptation unit).

Capacity and Frequency Re-use

It is the number of frequencies in a cell that determines the cell’s capacity.
However, a cellular network can overcome this constraint and maximize the number of subscribers that it can service by using frequency re-use.
Each company with a license to operate a mobile network is allocated a limited number of frequencies.
Depending on the traffic load and the availability of frequencies, a cell may have one or more frequencies allocated to it.
It is important when allocating frequencies that interference is avoided.
Frequency re-use means that two radio channels within the same network can use exactly the same pair of frequencies, provided that there is a sufficient geographical distance.
The tighter frequency re-use plan, the greater the capacity potential of the networkInterference can be caused by a variety of factors.
A common factor is the use of similar frequencies close to each other. The higher interference, the lower call quality.
To provide coverage to all the subscribers, frequencies must be reused many times at different geographical locations in order to provide a network with sufficient capacity.
The same frequencies can not be re-used in neighboring cells as they would interfere with each other so special patterns of frequency usage are determined during the planning of the network.

These frequency re-use patterns ensure that any frequencies being re-used are located at a sufficient distance apart to ensure that there is little interference between them.
The term “frequency re-use distance” is used to describe the distance between two identical frequencies in a re-use pattern.
The lower frequency re-use distance, the more capacity will be available in the network.