Chapter 01.Overview of Gsm

8/9/2019 Chapter 01.Overview of Gsm

1/31

E1E1--E2 CME2 CM

For internal circulation of BSNLonly

OverviewOverview ofof GSMGSM

22/3/2011


2/31

AGENDA

Cellular Concept

Reuse of FrequencyTypes of cells

GSM Architecture

GSM NW elements

GSM Areas



3/31

Cellular Systems

A cell corresponds to the covering area of one

transmitter or a small collection of transmitters.

The size of a cell is determined by the transmitter's

power.

transmitters in order to enable the efficient reuse of the

frequencies.



4/31

Reuse of Frequency

Frequencies used in a cell will be reused several cells

away.

The distance between the cells using the same

frequency must be sufficient to avoid interference.

capacity in number of users.



5/31

Cluster

Group of cells.

The number of cells in a cluster must be determined so

that the cluster can be repeated continuously within the

covering area of an operator.

, , .



6/31

A cluster is a group of cells

No channels are reused within a cluster

Clusters

A seven Cell Cluster



7/31

Deciding the cluster size

The smaller the number of cells per cluster is, the bigger

the number of channels per cell will be. The capacity of

each cell will be therefore increased

However a balance must be found in order to avoid the

clusters when small size clusters are opted.



8/31

Types of Cells

Macro cells :-large cells for remote and sparsely

populated areas

Micro cells:- for densely populated areas

Selective cells:-cells with a particular shape and

covera e for e . Cells located at the entrances of

tunnels where coverage of 360 degrees is not

needed

Umbrella cells:-covers several micro cells; reduce the

number of handovers



9/31

Different Types of Cells

MACRO-CELL:antenna radiating above roofs

---> Wide Coverage ( 35 km)

EXTENDED-CELL:

macro cell with system coverage

extension ( 120 km) for coasts...

MICRO-CELL:

Antenna below the roofs

---> small coverage


10/31

Architecture of GSM NW



11/31

Mobile Station

Mobile Station = Terminal + SIM

Terminal can be fixed (20W), portable (8W), Handheld (

2W, 0.8W)

The only element that personalizes a terminal is the SIM

-

Identification Number (PIN)



12/31

Functions of SIM

Authentication of the validity of the MS when

accessing the networkUser authentication

Storage of subscriber-related information, which can

be: data fixed during administrative phase (e.g.,subscriber identification), and temporary network

data (e.g., cell location identity).



13/31

Base station Subsystem-BTS

BTS (Base Transceiver Station) is usually placed in thecenter of a cell

Corresponds to the transceivers and antennas used in

each cellHas between 1 and 16 transceivers depending on the

density of users in the cell.



14/31

Base station Subsystem-BSC

BSC (Base Station Controller) controls a group of BTS

and manages their radio resources

Is in charge of handovers, frequency hopping, exchange

functions and control of the radio frequency power levels

.



15/31

Network and Switching Subsystem

The Mobile services Switching Center (MSC)

The Gateway Mobile services Switching Center

(GMSC)Home Location Register (HLR)

Visitor Location Register (VLR)

The Authentication Center (AuC)The Equipment Identity Register (EIR)



16/31

Functions of MSC

Call handling (w.r.t.mobile nature e.g., paging)

Management of logical radio-link channel during calls

Management of MSC-BSS signalling protocol

Handling location registration and ensuring interworking

between Mobile Station and VLR

- -

Acting as a gateway MSC to interrogate the HLR

Exchange of signalling with other system entities

Standard functions of a local exchange switch in the fixed

network (example: charging)



17/31

HLR contains

Identity of mobile subscriber

ISDN directory number of mobile station

Subscription information on teleservices and bearer

services

Supplementary services

Location information for call routing



18/31

VLR contains

Identity of mobile subscriber

Any temporary mobile subscriber identity

ISDN directory number of mobile

A directory number to route calls to a roaming station

Copy of (part of) the subscriber data from the HLR



19/31

EIR Lists

White or Valid list - List of valid MS equipment identities

Grey or Monitored list - List of suspected mobiles under

observation

Black or prohibited list - List of mobiles for which service

.



20/31

Authentication Centre (AuC)

Contains subscriber authentication data called

Authentication Keys (Ki)

Generates security related parameters needed toauthorize service using Ki

Generates unique data pattern called a Cipher Key

(Kc) needed for encrypting user speech and data



21/31

Other NW elements

The Operations and Maintenance Center (OMC)-R is

the centralized maintenance and diagnostic heart of the

BSS. It allows the network provider to operate, administer,

and monitor the functioning of the BSS.

Billing Centre: periodically polls the disk records of each

.

Service Center: The Service Center interfaces with the

MSCs to provide special services, such as the SMS

Note:The Billing Center and Service Center are not a

basic part of the GSM system.



22/31

GSM AREAS



23/31

Frequency Bands

The band 890-915 MHz has been allocated for the uplink

direction (transmitting from the mobile station to the

base station).

The band 935-960 MHz has been allocated for the

the mobile station).



24/31

Discontinuous Transmission

Works on VAD (Voice Activity Detection)

DTX helps to reduce interference between different cells

and to increase the capacity of the system.

It also extends the life of a mobile's battery.

connection is dead.



25/31

From receiverEarpiece

Comfortnoise

speech

decoder

Digital toAnalogConverter

Discontinuous Transmission

Features

To transmitterMicrophone speech

encoder

Voice Activity

Detection

Analog toDigitalConverter



26/31

Timing Advance

The aim of the TA is that the signals coming from

different mobiles arrive to the base station at the right

time.The base station measures the timing delay of the

mobile stations.

If the bursts corresponding to a mobile station arrivetoo late and overlap with other bursts, the base

station tells, this mobile, to advance the transmission

of its bursts.



27/31

Power Control

Power levels are adjusted so that the power is nearly the

same for each burst.

A base station also controls its power level.

The mobile station measures the strength and the

.

If the mobile station does not receive correctly the signal,

the base station changes its power level.



28/31

Power Control

BTS commands MS at different

distances to use different power levels

so that the power arriving at the BTSs Rx is

approximately the same for each TS



29/31

Discontinuous Reception

It is a method used to conserve the mobile station's

power.

The paging channel is divided into sub channels

corresponding to single mobile stations.

' '

in the sleep mode during the other sub channels of the

paging channel.



30/31

Equalization

An equalizer estimates the channel impulse response

of the GSM system and then constructs an inversefilter.

The receiver knows which training sequence it must

wait for. The equalizer will then, comparing the

received training sequence with the training

sequence it was expecting, compute the coefficients

of the channel impulse response.



31/31


Date post:	01-Jun-2018
Category:	Documents
Upload:	dheermit8082
View:	223 times
Download:	0 times

Chapter 01.Overview of Gsm

Documents