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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
IDEA Cellular Limited Network Services, Maharashtra 3
Contents
Brief History of GSM
Features of GSM
GSM Identities
GSM Network Hierarchy
Location Updating
System Architecture
- Network Architecture
Transmission Problems Traffic Cases
IDEA Cellular Limited Network Services, Maharashtra 4
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….
IDEA Cellular Limited Network Services, Maharashtra 5
•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
IDEA Cellular Limited Network Services, Maharashtra 6
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
IDEA Cellular Limited Network Services, Maharashtra 7
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
IDEA Cellular Limited Network Services, Maharashtra 8
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
IDEA Cellular Limited Network Services, Maharashtra 10
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)
IDEA Cellular Limited Network Services, Maharashtra 11
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.
IDEA Cellular Limited Network Services, Maharashtra 12
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.
IDEA Cellular Limited Network Services, Maharashtra 13
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.
IDEA Cellular Limited Network Services, Maharashtra 14
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.
IDEA Cellular Limited Network Services, Maharashtra 15
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.
IDEA Cellular Limited Network Services, Maharashtra 16
Cell
Location Area
MSC/VLR Area
MSC
VLR
PLMN Service Area
HLR
MSCMSC
VLR
GSM AREA
GSM Network Hierarchy
IDEA Cellular Limited Network Services, Maharashtra 17
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
IDEA Cellular Limited Network Services, Maharashtra 18
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.
IDEA Cellular Limited Network Services, Maharashtra 19
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 :
IDEA Cellular Limited Network Services, Maharashtra 20
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
IDEA Cellular Limited Network Services, Maharashtra 21
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
IDEA Cellular Limited Network Services, Maharashtra 22
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
IDEA Cellular Limited Network Services, Maharashtra 23
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.
IDEA Cellular Limited Network Services, Maharashtra 24
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
IDEA Cellular Limited Network Services, Maharashtra 25
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.
LA2
Cell
Cell Cell
IDEA Cellular Limited Network Services, Maharashtra 26
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.
LA2
Cell
Cell Cell
IDEA Cellular Limited Network Services, Maharashtra 27
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.
LA2
Cell
Cell Cell
• Location Update Not Required
IDEA Cellular Limited Network Services, Maharashtra 28
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.
LA2
Cell
Cell Cell
IDEA Cellular Limited Network Services, Maharashtra 29
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.
LA2
Cell
Cell Cell
•Location Update Required because subscriber moved to new location area.
IDEA Cellular Limited Network Services, Maharashtra 30
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
IDEA Cellular Limited Network Services, Maharashtra 31
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.
IDEA Cellular Limited Network Services, Maharashtra 32
Network Architecture
OMC
HLR
AUC
EIR
MSC
VLR
BSC
BTS
MS
Switching System(SS)
Base Station System(BSS)
IDEA Cellular Limited Network Services, Maharashtra 33
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
IDEA Cellular Limited Network Services, Maharashtra 34
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).
IDEA Cellular Limited Network Services, Maharashtra 35
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).
IDEA Cellular Limited Network Services, Maharashtra 36
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)
IDEA Cellular Limited Network Services, Maharashtra 37
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
IDEA Cellular Limited Network Services, Maharashtra 38
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
IDEA Cellular Limited Network Services, Maharashtra 39
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
IDEA Cellular Limited Network Services, Maharashtra 40
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
IDEA Cellular Limited Network Services, Maharashtra 41
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
IDEA Cellular Limited Network Services, Maharashtra 42
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
IDEA Cellular Limited Network Services, Maharashtra 43
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
IDEA Cellular Limited Network Services, Maharashtra 44
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
IDEA Cellular Limited Network Services, Maharashtra 45
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
IDEA Cellular Limited Network Services, Maharashtra 46
Path Loss
As the MS moves away from the Base Station the signal strength reduces
IDEA Cellular Limited Network Services, Maharashtra 47
Path Loss
As the MS moves away from the Base Station the signal strength reduces
IDEA Cellular Limited Network Services, Maharashtra 48
Path Loss
As the MS moves away from the Base Station the signal strength reduces
IDEA Cellular Limited Network Services, Maharashtra 49
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
As the MS moves away from the Base Station the signal strength reduces
IDEA Cellular Limited Network Services, Maharashtra 50
Shadowing
More often we observe hills ,trees and buildings between MS and the BTS
IDEA Cellular Limited Network Services, Maharashtra 51
Shadowing
More often we observe hills ,trees and buildings between MS and the BTS
IDEA Cellular Limited Network Services, Maharashtra 52
Shadowing
More often we observe hills ,trees and buildings between MS and the BTS
IDEA Cellular Limited Network Services, Maharashtra 53
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
More often we observe hills ,trees and buildings between MS and the BTS
IDEA Cellular Limited Network Services, Maharashtra 54
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.
IDEA Cellular Limited Network Services, Maharashtra 55
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
IDEA Cellular Limited Network Services, Maharashtra 56
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.
IDEA Cellular Limited Network Services, Maharashtra 57
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
IDEA Cellular Limited Network Services, Maharashtra 58
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
IDEA Cellular Limited Network Services, Maharashtra 59
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
IDEA Cellular Limited Network Services, Maharashtra 60
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
IDEA Cellular Limited Network Services, Maharashtra 61
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”.
IDEA Cellular Limited Network Services, Maharashtra 62
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
IDEA Cellular Limited Network Services, Maharashtra 63
The Hexagon Cell Shape
Real world planning must consider the fact that radio propagation is very much dependent on Terrain and other factors.
IDEA Cellular Limited Network Services, Maharashtra 64
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
IDEA Cellular Limited Network Services, Maharashtra 65
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.
IDEA Cellular Limited Network Services, Maharashtra 66
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.
IDEA Cellular Limited Network Services, Maharashtra 67
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.
IDEA Cellular Limited Network Services, Maharashtra 68
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
IDEA Cellular Limited Network Services, Maharashtra 69
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.
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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.
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Coverage of IDEA Maharashtra
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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
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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
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- 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…
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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)
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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.
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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.
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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.
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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.
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