Gsm Overviews

8/4/2019 Gsm Overviews

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BSNL OBJECTIVESOBJECTIVES

Describe the Cellular Concept

Explain the GSM Access Network

Explain the GSM Core Network

Explain the GPRS Core Network

->GSM (Global System for Mobile

Communications).

->It is a standard set developed by the European

Telecommunications Standards Institute (ETSI) to

describe technologies for second generation (or

"2G") digital cellular networks.

->Developed as a replacement for first generation

analog cellular networks, the GSM standard

originally described a digital, circuit switched

network optimized for full duplex voice telephony.

->The standard was expanded over time to include

first circuit switched data transport, then packet

data trans ort via GPRS.

->The GSM standard is succeeded by the

third generation (or "3G") UMTS standard

developed by the 3GPP.

->GSM networks will evolve further as they

begin to incorporate fourth generation (or

") LTE Advanced standards.

-> "GSM" is a trademark owned by the GSM

Association.

BSNL Technical details

GSM cell site antennas in the Deutsches

Museum, Munich, Germany

=>>GSM is a cellular network, which means thatmobile phones connect to it by searching for cells in

the immediate vicinity.

=>> There are five different cell sizes in a GSM

network²macro, micro, pico, femto and umbrellaCells.

=>> The coverage area of each cell varies according

to the implementation environment.

=>> Macro cells can be regarded as cells where the

base station antenna is installed on a mast or a

building above average roof top level. they are

typically used in urban areas

=>> Picocells are small cells whose coverage

diameter is a few dozen metres; they are

mainly used indoors.

=>> Femtocells are cells designed for use in

residential or small business environments

and connect to the service providers network

via a broadband internet connection. =>>Umbrella cells are used to cover shadowed

regions of smaller cells and fill in gaps in

coverage between those cells.

BSNL Communication - Mobile

TelephoneExchange

SubscriberLine(2W)

Inter-Exchange

Junction

Mobile SwitchingCentre (MSC)

BSC BTSMS

CELLULAR MOBILE CONCEPTS

WHAT IS A CELL ?

� A base station (transmitter) having a number of

RF channels is called a cell.

� Each cell covers a a limited number of mobile

subscribers within the cell boundaries

( Coverage area) .

� Typical Cell Radius Aprrox = 30 Km(Start up), 1 KM (Mature) .

Top of a cellular radio towerA cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell

Top of acellular radio tower

=>>A cellular network is a radio network

distributed over land areas called cells,each served by at least one fixed-location

transceiver known as a cell site or base

station.

=>>When joined together these cells provide

radio coverage over a wide geographic area.

=>> This enables a large number of portable

transceivers (e.g., mobile phones, pagers, etc.) tocommunicate with each other and with fixed

transceivers and telephones anywhere in the

network, via base stations, even if some of thetransceivers are moving through more than one

cell during transmission.

VoiceChannels

Or control

channels

Lines to

A RADIO CELL

BSNL Fundamental problems

� Radio range, or coverage

� No. of channels, or voice circuits

� Full, seamless service coverage

� Large no. of subscribers in the range

of millions

BSNL GSM Specifications

Carrier Separation - 200 kHz

No. of RF Carriers - 124

Access Method - TDMA/FDMA

Modulation Method - GMSK

Transmission Rate - 270.833 Kbps

Speech Coding - Full rate 13 Kbps

Half rate 6.5 Kbps

Duplex Distance - 45 MHz

GSM FDMA

(Frequency Division Multiple Access

25 MHz 25 MHz

Mobile to Base

890.2 890.4 890.6(MHz)

Base to Mobile

935.2 935.4 935.6

200 kHz45MHz

Channel layout and frequency bands of operation

890 935 960915

200 kHz

BSNL FDMA

� Frequency Division Multiple Access or

FDMA is a channel access method used

in multiple-access protocols as a

channelization protocol.

� FDMA gives users an individual

allocation of one or several frequencybands, or channels. It is particularly

commonplace in satellite

communication.

BSNL FDMA

=>> FDMA, like other Multiple

Access systems, coordinates

access between multiple users.

Alternatives include TDMA,

CDMA, or SDMA.

GSM TDMA

(Time Division Multiple Access)

45 MHz

Frequency

F2¶F1¶

(Cell transmit)

F2F1(Cell Rx)

Amplitude

Typical TDMA/ FDMA frame structure

BSNL TDMA

� Time division multiple access (TDMA) is a

channel access method for shared medium

networks.

� It allows several users to share the same

frequency channel by dividing the signal into

different time slots.

� The users transmit in rapid succession, one

after the other, each using its own time slot.

BSNL TDMA

� This allows multiple stations to share the same

transmission medium (e.g. radio frequency

channel) while using only a part of its channel

capacity.

� TDMA is used in the digital 2G Cellular

system much as Global System for Mobile

Communication (GSM).

BSNL FDMA/TDMA Scheme

890.0890.2

890.4890.6

890.8891.0

891.2 915.8

BURSTF

LOGICAL CHANNELS� USER INFORMATION( TRAFFIC)

� SIGNALLING INFORMATION (CONTROL)

GSM RF CHANNELS

Network Architecture

MSC VLR

PSTNISDN

Networks

Air interface

MSC VLR

BSCBSC

1 BSC=1024 TRU

A Interface

A-bis interface

NETWORK ARCHITECTURE

� Network architecture is the design of a

communications network.

� It is a framework for the specificationof a network's physical components

and their functional organization and

configuration, its operationalprinciples and procedures, as well as

data formats used in its operation.

BSNL NETWORK ARCHITECTURE

� In telecommunication, the specification

of a network architecture may also

include a detailed description of

products and services delivered via a

communications network, as well as

detailed rate and billing structures

under which services are compensated

GSM Network Structure

� GSM Service Area: Total area served by thecombination of all member countries where a mobile canbe served.

� PLMN Service Area: It is one N/W area.

� MSC Service Area: There can many MSC/VLR in onePLMN area.It is one Mobile Exch. Area.

� GMSC: All I/C calls for PLMN N/W will be routedthrough GMSC. In a GSM/PLMN N/W all mobileterminated calls will be routed to a Gateway MSC. Callconnections between PLMNs , or to fixed N/Ws must berouted to a GMSC.The GMSC contains the Inter workingfunctions to make these connections.

� Location Area

� Cells

LOCATION AREA : There are several LA in a MSC/VLR

combination. A LA is a part of the MSC/VLR service area in

which a MS may move freely without updating location

information to the MSC/VLR exchange that control the LA.

Within a LA a paging message is broadcast in order to find

the called mobile subs. LA can be identified by system using

the LAI.

CELL : A cell is an identity served by one BTS. The MS

distinguishes between cells using the BASE STATIONIDENTIFICATION CODE(BSIC) that the cell site broadcast

over the air.

GSM Network Structure

MSC/VLR

LA 1 LA 2

MSC Service Area

MSC/VLR

LA 1 LA 2

C = Cell

Functions of Mobile Station

� Voice and data transmission

� Frequency and time synchronization

� Monitoring of power and signal quality of

the surrounding cells

� Provision of location updates even during

inactive state

� Equalization of multi path distortions

Mobile Station

� Portable, vehicle mounted, hand held

� MS identified by unique IMEI(International

Mobile Equipment Identity).

� Shall display at least last ten received,dialled and missed calls.

� Minimum talk time of 1hr 30 min. and

standby time of 80 hrs.

� 160 characters long SMS.

Mobile Identification Numbers

MSISDN

IMSI� International mobile subscriber¶s

Identity

� The IMSI is an unique identity which isused internationally and used within thenetwork to identify the mobile subscribers.

� The IMSI is stored on the subscriber identity module (SIM), the HLR, VLR andAC database.

FUNCTION OF BTS -I

� Encodes, encrypts, multiplexes, modulates and

feeds the RF signals to the antenna

� Transcoding and rate adaption Functionality

� Time and frequency synchronisation signals

transmission.

FUNCTIONS OF BSC-I

� It is connected to BTS and offloads MSC

� Radio resource management

� Inter-cell handover

� Reallocation of frequencies

� Power control

MSC-BSC Configurations

BTSBTS

Configuration -6 Multi - cell site =multi--BTS site

Many single

cell sites

Single - cell site

Configuration -1

Multi - cell site (sector Cells

Configuration -5

MCC: Mobile Switching Centre

BSS: Base Station System

BSC: Base Station Controller

BTS: Base Transceiver Station

BTS BTS

GSMMSC ( MOBILE SWITCHING CENTRE)

Manages communication between GSM & other

network

Call setup functions, basic switching are done

MSC takes into account the RR allocation in

addition to normal exchange functions

MSC does gateway function while its customersroams to other network by using HLR /VLR

MSC Functions - I

Paging, specifically call handling

Location updationHandover management

Billing for all subscribers based in its area

Reallocation of frequencies to BTSs in its area

to meet heavy demands

General Packet Radio System

BackboneNetwork

Corporate

Network

Corporate

Network

EDGETRUMS

BTS BSC MSC/VLR

SMS-G /IW MSC

AUCHLRMS

SGSN GGSN

Network Evolution

GPRS Architecture

SGSN HLR

ISDN / PSTN / PLMN

Network

IP-Backbone

Network

ExternalIP Network

External

X.25 Network

MSC/VLR

A GSM Interface

Abis GSM Interface (Proprietary of M/s Ericsson)

AUC Authentication Center

BSC Base Station Center

BSS Base Station System

BTS Base Transceiver Station

EIR Equipment Identity Register GGSN Gateway GPRS Support Node

GMSC Gateway Mobile services Switching Center

Gx GPRS Interfaces

HLR Home Location Register

MS Mobile Station

MSC Mobile services Switch ing Center

MT Mobile Terminal

SGSN Serving GPRS Support Node

TE Terminal Equipment

Um Air Interface

VLR Visitor Location Register

GPRS Network ElementsGSM Network Elements Traffic & Signaling Signaling

BSNL GPRS COMPONENTS

� To ensure the interworking of the PLMN, PDN

and the wireless networks, two new major

components are required.

� These components are called GPRS Support

Nodes.

� There are two types of GPRS Support Nodes

1. Serving GPRS Support Node (SGSN)2. Gateway GPRS Support Node (GGSN)

BSNL Serving GPRS Support Node (SGSN)

An SGSN delivers packets to mobile stations

within its service area. SGSNs send queries to

Home Location Registers (HLRs) to obtain profiledata of GPRS subscribers.

SGSNs detect new GPRS mobile stations in a

given service area; and, finally, SGSNs process

registration of new mobile subscribers and keep arecord of their location inside a given service area.

BSNL Gateway GPRS Support Node (GGSN)

GGSNs are used as interfaces to external PDNs.

GGSNs maintain routing information that is

necessary to tunnel the Protocol Data Units(PDUs) to the SGSNs that service particular

mobile stations.

Other functions include network and subscriber

screening and address mapping. One or moreGGSNs may support multiple SGSNs.

BSNL GPRS Network Enhancements

In addition to the new GPRS components,existing GSM and TDMA network elements mustalso be enhanced in order to support GPRS.

The following two pieces of equipment must beenhanced:

Base Station System (BSS): must be enhanced torecognize and send user data to the SGSN that isserving the area.

Home Location Register (HLR): must be enhanced toregister GPRS user profiles and respond to queriesoriginating from SGSNs regarding these profiles.

BSNL Advantages of GPRS

� Increased revenues by moving in to the mobile

data market

� Gain new subscribers requiring the data services

without investing in to PCs to gain internet access

� Retain current subscribers by offering new

services

� Reduce costs due to efficient use of network resources

Thanks

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