GSM Training Final

Training ProgramTraining Program

NETWORK SERVICESNETWORK SERVICES

IDEA Cellular Limited Network Services, Maharashtra 2

AN INTRODUCTION TOAN INTRODUCTION TO

GSM FundamentalsGSM Fundamentals

Global System for Mobile Global System for Mobile CommunicationCommunication


Contents

Brief History of GSM

Features of GSM

GSM Identities

GSM Network Hierarchy

Location Updating

System Architecture

- Network Architecture

Transmission Problems Traffic Cases


Cell Planning

Interference Types

Subscriber Services

Coverage of IDEA Maharashtra

GSM Tech. Specifications

Prepaid Services

Technology Comparison (GSM Vs CDMA)

GPRS(General Packet Radio Service)

EDGE(Enhanced Data rates for GSM Evolution)

Contents Contd….


•1982: CEPT(Conference of European Posts and Telecommunications) establishes a GSM group in order to develop the standards for a

pan-European cellular mobile system.

•1988: Validation of the GSM System.

•1991: Commercial launch of the GSM service.

•1992: Enlargement of the countries that signed the GSM-MoU> Coverage

of larger cities/airports.

•1993: Coverage of main roads GSM services start outside Europe.

•1995: Phase 2 of the GSM specifications Coverage of rural areas.

History of GSM


GSM Driving Forces

Need for Frequency Re-use

Need for common standards

Need for greater capacity

Demand for new services

Demand for lower cost equipment

Need for greater competition

Increased security

Advanced services


Features of GSM Spectrum efficiency

Low mobile and base stations costs

Good subjective voice quality

Compatibility with other systems such as ISDN (Integrated Services Digital Network)

Open Network Architecture

Ability to support new services classified into three groups:

-Tele-Services

-Bearer Services

-Supplementary Services


Speech Services

-Telephony(+Voice Mail)

-Emergency Calls

Short Message Service(SMS)

- SMS is similar to the paging service,but much more comprehensive,allowing bi-directional messages,store-and-forward delivery,and acknowledgement of a successful delivery.

GPRS(General Packet Radio Service)

Features of GSM Contd…

IDEA Cellular Limited

GSM IdentitiesGSM Identities In order to switch a call to mobile subscriber,the right entities need to be involved.

It is thus important to address them correctly.

Numbering plans are used to identify different networks.

- Mobile Station ISDN Number (MSISDN) : A number that uniquely identifies a mobile telephone subscription

As per CCITT recommendations,MSISDN is composed as follows

MSISDN = CC + NDC + NC + SN

CC = Country Code

NDC = National Destination Code

NC = Network Code(For Idea,it is 22/50)

SN = Subscriber Number

eg . 919822012345 = 91 + 98 + 22 + 012345


IMSI is the information which uniquely identifies a subscriber in a GSM PLMN(Public Land Mobile Network)

This number is allocated to each subscriber for a correct identification over the radio path and through the GSM PLMN network.

IMSI is used for all signaling in PLMN

IMSI is stored in the Subscriber Identity Module (SIM),HLR and serving VLR

IMSI consists of:

IMSI = MCC + MNC + MSIN

MCC = Mobile Country Code ( 3 digits)

MNC = Mobile Network Code ( 2 digits)

MSN = Mobile Subscriber Identification Number (max 10 digits)

eg : 404 + 22 + 0000123456

International Mobile Subscriber Identity (IMSI)


Mobile Station Roaming Number (MSRN)

This number is a temporary number used to route a call

HLR knows the MSC/VLR area of the subscriber

HLR requests the current MSC/VLR to allocate and return a MSRN for called subscriber.

HLR then sends the received MSRN to the GMSC,thus routing the call to the MSC/VLR where subscriber is registered.

MSRN has three parts:

MSRN = CC + NDC + SN

CC = Country Code

NDC = National Destination Code

NC = Network Operator Code

SN = Subscriber Number (Address to serving MSC )

eg. : 91 + 98 + 22 + 005XXX Where,005XXX is sent by MSC.

00 is for Pune MSC,20 is for Nagpur MSC,10 is for Goa MSC.


International Mobile Station Equipment Identity (IMEI)

IMEI is used for equipment identity

IMEI consists of :

IMEI = TAC + FAC + SNR + sp

TAC = Type Approval Code ( 6 digit )

FAC = Final Assembly Code (2 digit ) identifies manufacturer

SNR = Serial Number ( 6 digit )

sp = spare for future use ( 1 digit )

eg. : 352518 + 00 + 581976 + 3

Where, 35 is for Nokia Handsets.

IMEI length is 15 digits.


Location Area Identity (LAI)

Used for Location Updating of Mobile Subscribers

LAI consists of :

LAI = MCC + MNC + LAC

MCC = Mobile Country Code (same numbering plan as in IMSI)

MNC = Mobile Network Code ,identifies the GSM PLMN in that country (as in IMSI )

LAC = Location Area Code ,identifies Location Area within GSM PLMN.Length is 16 bits thus 65536 location areas can be defined in one GSM PLMN.

eg. 404 +22 + 10000 where 10000 is the LAC for Pune.


Cell Global Identity (CGI)

Used to identify a cell within the GSM network

Only a CI parameter is added to LAI

CI = cell Identity,identifies a cell within a location area,max 16 digits

eg. 404 + 22 + 10000 + 726

Where,

404 + 22 + 10000 is the LAI for Pune and 726 is the CI of one of the cells of Pune.CI is different for all the three sectors of the cell.


Base Station Identity Code (BSIC) :

Allows mobile station to distinguish between different neighboring base stations.

BSIC consists of :

BSIC = NCC + BCC

NCC = Network Colour Code ( 3 bits ).Used to identify operators on each side of the border

BCC = Base Station Colour Code (3 bits ),identifies Base Station to help distinguish between BTS using the same BCCH frequencies

eg. 71

Where 7 is the NCC for IDEA Operator.

and 1 is the BCC.BCC can range from 0 to 7.


Cell

Location Area

MSC/VLR Area

MSC

VLR

PLMN Service Area

HLR

MSCMSC

VLR

GSM AREA

GSM Network Hierarchy


Cell

Area covered by the BTS which transmits and receives signals on Radio Channels

Cell provides the complete coverage for the designed area

Each cell is allocated a number of Radio Channels.The MS and BTS communicate over these radio channels.

Cell is identified by a number called CGI –Cell Global Identification

Cell


Types of Cells

Different density of population gives the need for different types of cells: Macro Cells Micro Cells Selective Cells Umbrella Cells

- Macro Cell : Large cells for remotely and scarcely populated area.

- Micro Cell : Cells used in densely populated areas Area is divided into smaller cells hence number of channels are increased. Capacity is also increased Power level is decreased,thus reducing interference.


Used to define a cell with full coverage. Cells with particular coverage and shape such as a tunnel are called selective cells.

Umbrella Cell : An umbrella cell covers several small micro cells Power level of Umbrella Cell is kept high compared to micro cells forming the umbrella cell. Umbrella cell thus handles high speed mobiles reducing internal handovers Mobile thus stays longer within the same Umbrella Cell

Selective Cell :


A group of Cells form a Location Area Location Area is identified by Location Area Identity (LAI) Within the location area

A Paging Message is broadcast to inform the MS of an incoming call. VLR need not be updated when subscriber moves between different Location Areas. Each BTS in a Location Areas is controlled by a BSC . Each Location Area can be served by one or more BSC One Location Area can be served by one MSC only.

Location Area

Cell

Cell Cell

LA


MSC/VLR Area

Cell

Location Area

MSC/VLR Area

MSC

VLR

Contains one or more Location Areas Calls to subscribers within that service area will be routed to the MSC serving the service area

LA1

LA2

Service Area

Cell

Cell Cell

Cell

Cell Cell

MSC and VLR are combined to form one unit Area served by this MSC/VLR is called as MSC/VLR Area


PLMN Area

One or More MSC/VLR areas are combined to form a PLMN Area

HLR HLR 1

PLMN Area is the area covered by one network operator

Each PLMN area has atleast one HLR which contains the data for subscribers within its PLMN area

More than one HLR can be used depending on the number of subscribers

Cell

MSC/VLR Area 1

MSC 1

VLRLocation Area Location Area

MSC/VLR Area 2

MSC 2

VLR

Cell


GSM Area

Cell

GSM AREA

PLMN AREA

MSC/VLR AREA

Geographical Area within which GSM Service is available Consists of all PLMN areas within GSM Subscriber in a GSM area can continuously use the network.


LA1Cell

Cell Cell

Location Updating In order to route an incoming call it is necessary that the network should

know the location of the subscriber As the subscriber roams through the network,the MS informs the network of the current location .This process is called as Location Updating.

• Location Update Done.

LA2

Cell

Cell Cell


LA1Cell

Cell Cell



LA2

Cell

Cell Cell


LA1Cell

Cell Cell



LA2

Cell

Cell Cell


LA1Cell

Cell Cell



LA2

Cell

Cell Cell

• Location Update Not Required


LA1Cell

Cell Cell



LA2

Cell

Cell Cell


LA1Cell

Cell Cell



LA2

Cell

Cell Cell

•Location Update Required because subscriber moved to new location area.


Attached / Detached

- MS is busy,eg. Call in progress

- MS is idle

MS is DETACHED when

MS can be ATTACHED when

- MS is turned ON

- MS is turned OFF


System Architecture

A GSM system is basically designed as a combination of three major subsystems:

– the Network Switching Sub System (NSS) or (SSS)

– Base Station Subsystem (BSS)

– the Operation Support Subsystem (OSS). The Mobile Station (MS) is usually considered to be part of the BSS.


Network Architecture

OMC

HLR

AUC

EIR

MSC

VLR

BSC

BTS

MS

Switching System(SS)

Base Station System(BSS)


It Consists of two main elements: The mobile equipment or terminal The Subscriber Identity Module (SIM)

Mobile Equipment/Terminal:

There are different types of terminals distinguished principally be their power and application:

- Fixed Terminals: The ones installed in cars.Max. allowed output power is 20W.

- GSM Portable Terminals: The ones installed in vehicles.Max. allowed output power is 8W.

- Handheld Terminals: Which have experienced biggest success because of their decreasing weight and volume.They emit up to 2W power.With evolution of technologies the max. allowed power has decreased to 0.8W.

Mobile Station


SIM (Subscriber Identity Module)

Smart card which identifies the terminal.

Protected by a four-digit Personal Identification Number (PIN). In order to identify the subscriber to the system, the SIM card contains some parameters of the user such as its International Mobile Subscriber Identity (IMSI).


Base Station System(BSS) BTS

BSC

MS

Base Station Subsystem (BSS)

BSC

BTS

Incharge of Transmission and Reception.

Divided into two parts:

- Base Transreceiver Station (BTS) or Base Station (BS).

Connects MS and SS (Switching Subsystem)

- Base Station Controller (BSC).


Corresponds to the transceivers and antennas used in each cell of the network.

Size of the cell depends on BTS’s transmitting power

BSC

BTSBTS

BSC

Base Station Trans Receiver (BTS):

BSC controls one or more number of BTS’s.

Controls handovers,frequency hopping,exchange functions and radio frequency power levels of BTS’s.

Base Station Controller (BSC):

Base Station Subsystem (BSS)


Switching Subsystem (SS) The switching subsystem includes the equipment and functions related to

end-to-end calls, management of subscribers, mobility,and interface with the fixed PSTN.

The network and the switching subsystem together include the main switching functions of GSM as well as the databases needed for subscriber data and mobility management.

Switching Subsystem consists of:

- Mobile Switch Center (MSC)

MSC

HLR

AUC

EIRVLR- Visitor Location Register (VLR)

- Home Location Register (HLR)

- Authentication Center (AUC)

- Equipment Identity Register (EIR) MSC

VLR HLR EIR

AUC


Decides whether to grant access to an MS to make a call Charging Management. Tone and Announcements.

Gateway Mobile Services Switching Center (GMSC): Interface between mobile cellular network and the PSTN. In charge of routing calls from the fixed network towards a GSM user.

Performs switching functions of the network.

Provides connection to other networks.

Call Control and Mobility Management.

Management of MSC-Subscriber Signaling.

Interface to HLR,VLR,EIR.

Mobile Services Switching Center (MSC):

HLR

AUC

VLR EIR

MSCMSC


Home Location Register (HLR)

Database that stores information of Subscribers within its MSC/VLR area

Subscriber Number

Details of supplementary services ,whether subscriber can make international calls etc

Subscriber Authentication Parameters ,which is obtained from AUC

HLR

AUC

MSC

VLR EIRHLR


HLR

AUC

MSC

VLR EIR

The VLR constitutes the database that supports the MSC in the storage and retrieval of the data of subscribers present in its area.

The VLR supports a mobile paging and tracking subsystem in the local area where the mobile is presently roaming.

A VLR may be in charge of one or several Location Areas.

Visitor Location Register (VLR)

VLR


HLR

AUC

MSC

VLR EIR

Authentication information and ciphering keys are stored in a database within the AUC, which protects the user information against unwanted disclosure and access.

The HLR is responsible for the "authentication" of the subscriber each time he makes or receives a call.AUC only generates the authentication parameters.

The AUC, which actually performs this function, is a separate GSM entity that will often be physically included with the HLR.

Authentication Centre (AUC)

AUC


HLR

AUC

MSC

VLR EIR

EIR is a database that stores the IMEI numbers for all registered MS.

There are three classes of MS that are stored in the database, and each group has different characteristics.

– White List: contains those IMEIs that are known to have been assigned to valid MS’s.

– Black List: contains IMEIs of mobiles that have been reported stolen.

– Gray List: contains IMEIs of mobiles that have problems (for example, faulty software, wrong make of the equipment). This list contains all MSs with faults not important enough for barring.

Equipment Identity Register (EIR)

EIR


The main purpose of the OMC is to perform all operations and maintenance functions on elements of the GSM PLMN system.

The OMC uses a separate Telecommunications Management Network (TMN) to communicate with the various components of the GSM system. In general, it is done through leased lines on the PSTN or other fixed networks.

In our Network,OMC is not separate.It is a part of the BSC only.

Operation and Maintenance Centre (OMC)

OMCOMC


Location Updating in new MSC/VLR Area

MSC 2

VLR-2 HLR

• MS is registered in new MSC/VLR

• VLR sends message to network’s HLR

• HLR thus gets the new location

• VLR can now get subscriber parameters from HLR

HLR then :— updates the location of subscriber

— sends subscriber information to VLR— instructs VLR of old MSC to erase subscriber data

MSC 1

VLR-1

LA1Cell

Cell Cell

LA2Cell

Cell Cell


Transmission Problems In radio communication the transmission quality varies from one

place to another.

Two major factors affecting quality of transmission are:

1. Distance between transmitter and receiver

2. Reflections or obstructions due to man made or natural structures

- General Transmission problems affecting Transmission Quality:

Path Loss

Shadowing

Multi path Fading


Path Loss

As the MS moves away from the Base Station the signal strength reduces


Path Loss



Path Loss



Path Loss

This decrease in strength is called PATH LOSS.

Power Loss α d2f2 where,d is the distance from the BTS

f is the frequency

Thus power decreases with distance and frequency

But in the cellular system,due to the presence of Base Station this problem does not occur as a new transmission path is established before the previous is broken



Shadowing

More often we observe hills ,trees and buildings between MS and the BTS


Shadowing



Shadowing



This environmental attenuation of radio signal is called SHADOWING.

Thus signal strength increases or decreases depending on the presence of obstacles between the Tx and Rx antenna

Thus a mobile subscriber experiences both PATH LOSS and SHADOWING

Shadowing



Signal transmitted by a BTS may be interfered by:

Trees

Buildings

Hills

Other Vehicles

Multi Path Fading

This produces more than one path between the BTS and MS.

Thus some signals may be cancelled which reduces the signal strength.


Traffic Cases

Call from PSTN Subscriber to a Mobile Subscriber

Call from a Mobile Subscriber to a PSTN Subscriber

Call from a Mobile Subscriber to a Mobile Subscriber

Call from PSTN to Mobile when a Mobile Subscriber is in Roaming

Call from Mobile to Mobile when a Mobile Subscriber is in Roaming


PSTN EXCH

PSTN EXCH

GMSC

HLR VLR

MSC

MS

BTS

BSC

1. MSISDN

2. MSISDN

3. MSISDN

4. IMSI

5. MSRN6. MSRN

First,the PSTN subscriber dials the GSM subscriber’s number(MSISDN).The PSTN routes the call to the nearest Gateway MSC(GMSC)The GMSC interrogates the HLR where the subscriber is registered to find where the subscriber is currently located i.e. the MSC service area. GMSC requests a Mobile Station Random Number(MSRN).The MSRN is a temporary number used by the GMSC to route the call to the correct MSC in the service area currently being visited by the MS.The HLR interrogates the VLR for routing information.

In the HLR,the MSISDN is translated into an International Mobile Subscriber Identity (IMSI) and sent to the VLR.

The VLR selects a roaming number(MSRN) and links it to the IMSI for the duration of the call.VLR sends the MSRN to the HLR

The GMSC uses this number to route the call to the MSC.

The MSC checks the VLR for Location Area of the Subscriber.

Call from PSTN to a Mobile Subscriber

HLR forwards the MSRN to the GMSC.The call can then be switched via the BSS to the Mobile Subscriber.


VLR

Call Acknowledgement

PSTN

B-Number

Call from a Mobile Subscriber to a PSTN Subscriber

A call request message is sent by the MS to the MSC/VLR.This message is processed by the MSC/VLR by:• Marking the MS “busy”• Completing the Authentication Procedure• Preparing for Ciphering• Checking the mobile subscriber’s categories

If the MS is being granted access to the network,then a call request acknowledgement is sent from the MSC/VLR to the MS.

The MS in turns sends the B-number and this is switched the MSC/VLR to the PSTN.When the call has been set up by the PSTN,the MSC/VLR will allocate a TCH to the MS and the call will be connected.

MSC

Call Request

BTS

Call Request


VLR-1

Call Acknowledgement

MSC

VLR-2

Page Message

MSISDN

GMSC

MSISDN

HLR

MSISDN, MSRN Request

IMSI

MSRN Request

MSRN

MSRN

MSC

Call Request

BTS

BSC BSC

BTS

Call from a Mobile Subscriber to a Mobile Subscriber

Subscriber A sends the B-number(MSISDN) to the MSC/VLR-1.

The MSC/VLR-1 analyses the B-number(MSISDN) and routes the call to the GMSC.The GMSC sends an MSRN request to the HLR.The HLR converts the MSISDN to IMSI and sends the MSRN request to the VLR-2.The VLR-2 sends a MSRN to the HLR and the HLR sends it to the GMSC.The B-subscriber’s MSC/VLR routes the call to the BSC which then sends the page message to the B-subscriber.

When the B-subscriber responds to the page message,a traffic channel is allocated from both A and B-subscriber BSC’s and the call is connected.

Subscriber A Subscriber B

Subscriber A sends a call request to the MSC/VLR-1.This message is processed by the MSC/VLR-1 by marking the MS “busy”,completing the Authentication procedure,preparing for Ciphering and checking the Mobile Subscriber’s categories.

If the MS is being granted access to the network,then a call request acknowledgement is sent from the MSC/VLR-1 to the MS.The GMSC now uses MSRN to route the call to the B-Subscriber’s MSC/VLR-2


Call from PSTN to Mobile in Roaming

HLR-Pune

MSC/VLR-Mumbai

GMSC

Call Request

BSC

BTS

Roaming Subscriber

PSTN EXCH

PSTN EXCH

PUNE MUMBAI

MSRN

PSTN Subscriber

Paging


Call from Mobile to Mobile in Roaming

HLR-Pune

MSC/VLR-Mumbai

BSC

BTS

Roaming Subscriber

PUNE MUMBAI

MSRN

Calling Subscriber

Paging

MSC

Call Request

BTS

BSC


Cell Planning Initial information required for cell planning is:

The likely geographical distribution of Mobile Units.

The traffic behavior of subscribers.

The required quality of service.

The required geographical coverage.

All Cell Planning begins by making a “Nominal Cell Plan”.

This is a proposed layout of cells which meet the given:

Quality

Coverage

Capacity

requirements.

The traffic calculations are done with a unit called “Erlangs”.


Cell: The area that is covered from a BTS.

Omni Cell: A Cell with an omni-directional BTS antenna system.

Sector Cell: A Cell with a (uni-) directional BTS antenna system.

Site: The geographical location where the RBS equipment is stored,and the BTS antennas are mounted.

3-Sector-Site: A site with equipment for three sector cells.

Uplink: When signal travels from MS(Mobile Station) to BTS(Base Transreceiver Station),it is called uplink.

Downlink: When signal travels from BTS(Base Transreceiver Station to MS(Mobile Station),it is called downlink.

Repeater: It is a bi-directional RF(Radio Frequency) amplifier system that picks up the signals from an existing base station(donor),amplifies it and redirects it to the subscribers.It extends coverage to another area.

Booster: It is an amplifier which is used to amplify the signal level at any place and throw the signal in the same area.It is generally used for indoor coverage.

Important Definitions


The Hexagon Cell Shape

Real world planning must consider the fact that radio propagation is very much dependent on Terrain and other factors.


Handover

Handover is a process in which an MS in active connection state is moved to another radio channel

Handover can occur : Within the same BSC area : BSC has to make connection to

the new BTS

Different BSC area but same MSC/VLR area : BSC has to make connection with new BSC and from this BSC to new BTS .The new BTS then connects to the MS

Different MSC/VLR area : Both MSC/VLRs are now involved.

- MSC/VLR1 sends a Handover Request to MSC/VLR2.

- New BSC sets up connection to new BTS.

- When connection is ready,new BSC informs old BSC and in turn the MS to execute Handover


Interference Types Co-Channel interference(C/I): It is the ratio of the level of the received desired

signal level to the level of the received undesired signal level.

It is caused by frequency reuse in the cellular network.

If a system can tolerate a lot of co-channel interference,cells using the same channels can be located closer to each other.

The greater tolerance a system can offer w.r.t co-channel interference,the greater the capacity it can offer.


Adjacent Channel Interference(C/A):

It occurs,for eg.,when a BTS transmitting on a frequency ‘f’,picks up a signal from a mobile station or BTS in another cell transmitting on a neighboring frequency.

A neighboring frequency is a frequency which is 200Khz higher or lower than ‘f’.

“f+200kHz” ADJACENT

Received Signal

StrengthChannel “f”

Adjacent Channel

“f+200kHz”

Because these frequencies are adjacent,(only separated by 200 kHz),some of the power in the adjacent frequency will ‘break through’ the receiver filter for frequency ‘f’ and cause interference.


Subscriber Services

Telecommunication services are divided into:

~ Tele-services : Provides subscriber with all necessary terminal equipment to communicate with other subscriber.

~ Supplementary Services : Accomplished by complementing various GSM Services

- Tele-services :

Speech : Most fundamental service offered in order to make and receive calls to fixed and mobile subscribers all over the world.

Facsimile group : This service facilitates a GSM connected fax to communicate with any analogue fax in the fixed network.

Short Message services (SMS) : A message consisting of around 160 messages to be sent to subscriber.It can be sent even if mobile is switched off.


SMS Cell Broadcast : A short message can be broadcasted to all mobile within a certain geographical area.

DTMF : Dual Tone Multi Frequency is a tone signaling scheme often used for various control purposes via the telephone network.

Voice Mail : Service is an answering machine which records the voice of calling subscriber and can be listened to whenever required using a personal code.

- Supplementary Services :

Call Forwarding : Service gives subscriber facility to forward incoming calls to another number under different conditions:

- Call forward on MS not reachable

- Call forwarding when MS is busy

- Call forwarding on no reply

- Call forward unconditional


Barring of outgoing calls : The subscriber can activate or deactivate service from the mobile station.Conditions of Call Barring are:

- Barring of all outgoing calls

- Barring all outgoing international calls

- Barring of all outgoing international calls except those directed to home PLMN

Barring of Incoming Calls : Bars subscribers incoming calls.Conditions for this barring are:

- Barring of all incoming calls

- Barring of incoming calls when roaming outside home PLMN

Advice of charge : Provides subscriber with information required to calculate an estimate of charge for a call.

Call Waiting : Subscriber is notified of an incoming call when one call is in progress.

Call Hold : Allows subscriber to switch between calls ,keeping the other on hold.


Multi-party service : Enables a mobile subscriber to establish a multi-party conservation.

Calling line Identification Presentation Services : This service provides both restriction and presentation of calling line identity.Presentation allows calling number to be displayed whereas restriction prevents the display of calling number.

Connected line Identification Restriction : This services allows/disallows the called party’s number to be displayed.

Closed user group : Enables subscribers connected to the PLMN/ISDN and possibly other networks to form groups to and from which access is restricted.Members of group can communicate with each other but not generally with users outside the group.


Coverage of IDEA Maharashtra


Frequency Band :Up link 890 MHz -915 MHzDown link 935 MHz -960 MHzDuplex distance 45 MHzCarrier distance 200 KHzModulation GMSKAccess method TDMA & FDMA

GSM Tech. Specifications


Prepaid is a service where in subscriber has to pay in advance

Features of Prepaid service :

- Rechargeable options

- Customized messages

- Multiple languages and automatic language selection

- Fixed number auto-dialing

- Automatic expiration date

- Warning messages

- User friendly management of activation,deactivation and recharges

- Short message services (SMS)

Prepaid Services


- Call forwarding

- Call cost and after call balance (depending on the operator)

- Other promotional features benefits

- Almost all services that are available for postpaid subscribers can be availed by a prepaid subscriber

Prepaid Services Contd…


Prepaid Subscribers are charged online for their services using the IN (Intelligent Network )

IN contains database of balance of each prepaid subscriber in terms of Rupees

IN also contains Voucher Database and Tariff Tables

Before a prepaid subscriber originates a call or sends an SMS, MSC interrogates with IN. IN checks subscriber balance, reserves the amount applicable to that call from subscribers balance and then lets the call complete.

Once subscribers balance reaches zero or his validity period expires,he can buy a new voucher and update.

Prepaid Services/IN(Intelligent Network)


Air Interface Techniques Different techniques are adopted to use the same frequency

band by different users without causing interference.

Some of the Air Interface Access techniques are:

TDMA FDMA CDMA

- FDMA (Frequency Division Multiple Access ) : Available spectrum is divided into a number of radio channels of specified bandwidth.

- CDMA (Code Division Multiple Access ) : All users share the same radio frequency at the same time and are channelised by using unique assigned code.

- TDMA (Time Division Multiple Access ) : Channel is divided into a number of Time Slots.


GSM Vs CDMA

Radio Channel is divided into sequential time slots

Frequency is channelized by using unique access code

Used in most developed nations and has more than 500 million subscribers all over the world

Used mostly in South Korea,North America,Australia,Taiwan and parts of China.Has 80 million subscribers

GSM Mobiles have a SIM card which has many functions and is convenient . ( eg You can change handset w/o change of number or settings)

CDMA Mobiles do not have SIM cards hence one has to stick to the same handset wherever he goes

Range from tower is approx 35 kms Range from tower is approx 110 kms

Power output from GSM phone is 2 W Power output from CDMA phone is 200 mW

Talk-time is high due to pulse nature Talk-time is low as it transmits all time

As the number of users over network increases voice quality remains good

As the number of users increases over the network,voice quality deteriorates.

Data transmission speed is only 56 kbps.But can be improved with GPRS and EDGE

Data transmission is high from 153 Kbps to 614 Kbps.


GPRS (General Packet Radio Service )

Non-voice value added service

GPRS offers faster data transmission via a GSM network within a range of 9.6 Kbps to 115 Kbps

Users can make a telephone call and receive data at the same time i.e. one can make calls and receive E-Mail messages at the same time

- Features of GPRS :

- Speed :Provides a max speed of 21 Kbps per time slot (Depending on quality of network & number of simultaneous users)

- Instant Connectivity: GPRS facilitates instant connections whereby information can be sent or received immediately as the need arises, subject to radio coverage. No dial-up modem connection is necessary.

- New and Better Applications : All applications available over internet will be enabled in GPRS such as FTP,chat E-mail etc.


EDGE (Enhanced Data Rates for GSM Evolution)

An add-on to GPRS and cannot work alone

It allows consumers to connect to the Internet and send and receive data, including digital images, web pages and photographs, three times faster than an ordinary GSM/GPRS network .

EDGE enables GSM operators to offer higher-speed mobile-data access, serve more mobile-data customers, and free up GSM network capacity to accommodate additional voice traffic, as compared to GPRS.

Provides higher throughput and capacity by adding new modulation and coding to GPRS and by making radio link adjustments to protocols.

IDEA CELLUAR LTD is the First Operator to provide EDGE services in INDIA.


Documents

GSM Training Final