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GSM Concepts
Citation preview
For BSNL internal circulation only
WELCOME
This is a presentation for the E2-E3 Consumer
Mobility Module for the Topic: Cellular Concepts &
GSM Architecture
Eligibility: Those who have got the Upgradation from
E2 to E3.
This presentation is last updated on 27-03-2011.
You can also visit the Digital library of BSNL to see
this topic.
For BSNL internal circulation only
Learning Objective
Define cell, cluster
Characteristics of cellular system
Understand ways in better communication
Various subsystems of GSM Network
GSM Architecture
GSM network structure
Functions of mobile station
Radio subsystem
Network and switching subsystems
Operation and maintenance center
For BSNL internal circulation only
A single antenna can transmit all the
GSM carriers in a city
GSM Antenna
For BSNL internal circulation only
Capacity of the system
Extract from Traffic Table - Erlang B Model
Number
of Access
Channels
GoS
0.5%
1.0%
2 %
5 1.13 1.36 1.66
10 3.96 4.46 5.08
20 11.1 12.0 13.2
33 21.5 22.9 24.6
50 36.0 37.9 40.3
56 41.2 43.3 45.9
99 80.0 84.1 87.0
100 80.9 85.0 88.0
For BSNL internal circulation only
Capacity of the system
TRUNKING EFFICIENCY GoS 2%
Sr.No
Number of
Access
Channels
Erlang
Capacity
Number of
users
served
1 5 1.66 16
2 10 5.08 50
3 20 13.2 132
4 50 40.3 403
5 100 88.0 880
For BSNL internal circulation only
A CLUSTER OF CELLS
4
5
6
7
2
3
11 2 3 4 5 6 7
GIVEN FREQ.
RESOURCE
CELLULAR MOBILE CONCEPTS
For BSNL internal circulation only
14
2
1
3
5
6
7 2
6
3
4
5
7DR
Frequency Reuse N=7
1 2 3 4 5 6 7Frequency Reuse Pattern “N”=7
Given Freq Resource
CELLULAR MOBILE CONCEPTS
For BSNL internal circulation only
CELLULAR MOBILE CONCEPTS
WHAT IS A CELL ?
A base station (transmitter) having a number of
RF channels is called a Cell. Or it is the area as
seen by a mobile station. OR Cells are base
stations transmitting over small geographic areas.
Each cell covers a limited number of mobile
subscribers within the cell boundaries ( Coverage
area)
Typical Cell Radius Approx = 15 Km (Start up), 1
KM (Mature)
For BSNL internal circulation only
CELLULAR MOBILE CONCEPTS
WHAT IS A CLUSTER ?
A cluster is group of cells. Frequencies are nor
reused in a cluster.
The cluster is then repeated and the frequencies
are reused and system capacity is increased.
Typical cluster size is 4 or 7 cells.
For BSNL internal circulation only
Features of Digital Cellular Systems:
Small cells
Frequency reuse
Small, battery-powered handsets
Performance of handovers
Interference between cells
For BSNL internal circulation only
Cell clustering
There will be interference between the cells
using same frequency.
To reduce co-channel interference below the
acceptable level, the co-channel cells must be
set far apart.
Number of cells in a cluster is denoted by ‘K’,
also called as frequency reuse factor.
K=i²+j²+i*j where i and j are integers.
For BSNL internal circulation only
CO-CHL INTERFERENCE
R
Co Chl Interference is
a Function of “Q”
Lower Q Increased Co-Chl Interference Higher Q Reduced Co-Chl Interference
Q = D /R = 3K
For BSNL internal circulation only
Capacity/Performance Trade-offs
R
If K increases, then performance increases
If K increases, then call capacity decreases per
cell.
If K decreases, then performance decreases
If K decreases, then call capacity increases per
cell.
For BSNL internal circulation only
CELLULAR MOBILE CONCEPTS
An Example
Freq
Reuse
Pattern
Voice
Chls/Cell
Calls/Cell/hour S/I dB
4 99 2610 14
7 56 1376 18.7
12 33 739 28.3
Assume Number of Voice Channels = 395,
Average Call Duration = 2 Minutes , GoS = 2%
Using Traffic Tables we get :
For BSNL internal circulation only
CELLULAR ENVIRONMENT
COUNTER MEASURES
Power Control
Channel Coding
Interleaving
Equalization
Slow Frequency Hopping
Antenna Diversity
For BSNL internal circulation only
GSM
Various subsystems
Network Subsystem Includes the equipments and
functions related to end-to-end call.
Radio Subsystem Includes the equipments and
functions related to the management of the
connections on the radio path.
Operations and Maintenance subsystem Includes
the operation and maintenance of GSM equipment
for the radio and network interface.
For BSNL internal circulation only
Network Architecture
B
T
S
MSC VLR
HLR
PSTN
ISDN
Data
Networks
(
Air interface
OSS
B
T
S
B
T
SMSC VLR
BSCBSC
1 MSC=16 BSC
1 BSC=1024 TRU
A Interface
A-bis interface
BSC:BASE STATION CONTROLLER, BTS: BASE TRANSRECEIVER STATION, OSS: OPERATION AND SUPPORT
SUBSYSTEM.ss
For BSNL internal circulation only
GSM ARCHITECTURE
MSC
BSC
GMSC
AUC
BTS
BSC
BTS
BTS
BTS
BTS
HLR
PSTN
VLR
Voice/Data-Circuit
EIR
Netowrk
Management
For BSNL internal circulation only
GSM ARCHITECTURE
ME
SIM
BTS
BTS
BSC
BSC
MSC
HLR
EIR
VLR
AuC
Mobile Station Base Station Subsystem Network Subsystem
PSTN ISDN
PSPDN CSPDN
Um Abis
A
OMC
For BSNL internal circulation only
GSM Network Structure
GSM Service Area: Total area served by the combination of
all member countries where a mobile can be served.
PLMN Service Area: It is one N/W area.
MSC Service Area: There can many MSC/VLR in one PLMN
area . It is one Mobile Exch. Area.
GMSC: All I/C calls for PLMN N/W will be routed through
GMSC. Call connections between PLMNs , or to fixed N/Ws
must be routed to a GMSC. The GMSC contains the Inter
working functions to make these connections.
For BSNL internal circulation only
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.
LOCATION AREA
For BSNL internal circulation only
CELL
A cell is an identity served by one BTS.
It is area of Transmission/Reception between
MS and BTS.
The MS distinguishes between cells using the
BASE STATION IDENTIFICATION CODE(BSIC)
that the cell site broadcast over the air.
For BSNL internal circulation only
GSM PLMN Service Area
V
MSC
MSC
MSC
MSC
VLR
VLR
VLRI
II
IV
III
I
VLR
For BSNL internal circulation only
GSM Cells
MSC
VLR
LA1
LA2
LA3
LA6LA4
LA5
C
1
C
2
C3
C6C
5
C4
C=CELL
For BSNL internal circulation only
GSM
Relation between areas in GSM
Location AreaCell
Location AreaMSC Service AreaPLMN Service Area
GSM Service Area
For BSNL internal circulation only
GSM
LA Coding
MCC
LAI
LACMN
C3 digit 3 digit 2 Octets
MCC:Mobile Country Code,
MNC: Mobile N/W Code,
LAC: Location Area Code
For BSNL internal circulation only
FUNCTIONS OF MOBILE STATION
Voice and data transmission
Frequency and time synchronization.
Monitoring of power and signal quality of the Serving
& surrounding cells.
Provision of location updates even during inactive
state.
Equalization of multi path distortions.
For BSNL internal circulation only
Mobile Equipment
Portable, vehicle mounted, hand held
Mobile equipment is identified by unique IMEI(International Mobile equipment Identity)
Shall display at least last ten received, dialled and missed calls
Should Have Minimum talk time of 1hr 30 min. and standby time of 80 hrs
160 characters long SMS
For BSNL internal circulation only
SIM Card
Subscribers Identity module
Has Unique Subscriber’s ID:IMSI and ISDN
PIN( Personal Identification Number)
Key Ki ( Authentication key) , Kc (Cipheringkey) and A3, A5 and A8 algorithms
SIM has CPU, ROM, RAM and EPROM
For BSNL internal circulation only
MSISDN
Mobile Subscriber’s ISDN Number
The MSISDN is registered in the telephone directory and used by the calling party for dialing.
IT Is consists of
MCC-Mobile country Code
NDS-Network Destination Code--Give Routing Information to reach HLR
N(S)N--National Significant Number
CC NDC SN
1 to 3 digits Variable Variable
N(S)N
For BSNL internal circulation only
IMSI
International mobile subscriber’s Identity
The IMSI is an unique identity assigned to each authorized GSM User.
The IMSI is stored on the subscriber identity module (SIM), the HLR, VLR and AUC database.
For BSNL internal circulation only
IMSI
3 digits
MCC MNC MSIN
3 digits Not more than 9 digits
IMSI : Not more than 15 digits
MCC--Mobile Country Code, (ITU)
MNC—Mobile Network National Code, assigned by
Administration(DOT).
Mobile station Identification Number. It identifies the subs.
In a PLMN. First 3 digit identifies the Logical HLR-id of
Mobile subs.(Operator)
For BSNL internal circulation only
TMSI
Temporary Mobile subscriber’s Identity
It is MSC/VLR specific alias designed to maintain user confidentiality.
The VLR assigns a TMSI to each mobile subscribers entering the VLR area.
Assigned only after successful authentication.
TMSI changes on location update
For BSNL internal circulation only
MSRN
Mobile Station Roaming Number
MSRN--is a temporary identity which is assigned during the establishment of a I/C call to a roaming subs.
The MSRN is used in the HLR to set up a connection to the visited MSC/VLR.
It is assigned on demand by HLR on per call basis.
CC NDC SN
CC--Country Code, NDC--National Destination Code, SN-- Subs.
No.
For BSNL internal circulation only
RADIO /BASE STATION
SUB SYSTEM (RSS) /BSS
n BTS n BTS
BSC
BSC
BSC
MSC/VLR
RSS
For BSNL internal circulation only
Base Station System
It is set of BTS equipments and BSC as seen by MSC through A interface.
BSS may be composed of one or more cells(BTS).
The interface between BTS and BSC is A-bisinterface.
BSS is composed by BTS and BSC.
BTS serves one cell and controlled by BSC.
BTS handles 1 to 12 carriers and serves 8 to 90 subscribers simultaneously.
For BSNL internal circulation only
FUNCTION OF BTS -I
Transmit and receive signals from MS over air interface
Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna
Transcoding and rate adaption Functionality
Time and frequency synchronization signals transmission.
Transcoding to bring 13 Kbps speech to data rate of 16 Kbps and combining four of these signals to 64 Kbps. As these channels are to be mapped on PCM voice channels on A-bis interface.
For BSNL internal circulation only
FUNCTION OF BTS -II
Timing Advance is determined by BSC and BTS signals MS for proper Timing Advance.
Frequency hopping
Random access detection and sending it to BSC for channel assignment.
Uplink radio channel measurements corresponding to Downlink measurement made by MS.
For BSNL internal circulation only
TRANSCODER
This device takes 13 kbps speech adds additional synchronisation data to bring upto level of 16 kbps.
Four channels are combined in transcoder to provide 64 kbps channel within bss.
O/p data rate of transcoder is 64 kbps.
30 such 64 kbps channels are multiplexed on to 2.048 MBPS on A-bis CHANNEL. This carries 120 speech and control signals.
For BSNL internal circulation only
FUNCTIONS OF BSC-I
It is connected to BTS at one side and MSC on other side.
Radio resource management for cells under its control.
Asigns frequencies and timeslots to MS in its area.
Inter-cell handover (INTRA BSS)
Reallocation of frequencies to the BTSs in its area.
Power control of BTS and MS
For BSNL internal circulation only
FUNCTIONS OF BSC-II
Time delay measurement of the received signals from MS with respect to BTS clock.
Performs traffic concentration to reduce the number of lines from BSC to MSC.
Provides the time and frequency synchronization signal broadcasted by BTS.
For BSNL internal circulation only
Network and Switching Subsystem
(NSS)
MSC
(PSTN)
VLR
HLR AUC
EIR
D
C
SS7 Signaling
Traffic Path
F
(BSS)
A
E
Other
MSC
For BSNL internal circulation only
GSM
MSC ( MOBILE SWITCHING CENTRE)
Manages communication between GSMusers & users of other network
Call setup functions, basic switching are doneby MSC.
MSC takes into account the impact of RRsallocation and mobile nature of User inaddition to normal exchange functions.
MSC performs Switching function for allmobiles located in MSC service area.
For BSNL internal circulation only
MSC Functions - I
Paging, specifically call handling
Location updation
Handover management
Billing for all subscribers based in its area.
Handles different identities and numbers relatedto MS.
Identities are used in interface part of MS andMSC and Numbers in fixed part of network.
Transfer encryption parameters from VLR to BSSand MS for carrying out ciphering.
For BSNL internal circulation only
GSM MSC Functions - II
Echo canceller operation control
Signaling interface to databases like HLR,VLR.
Gateway to SMS between SMS centers andsubscribers
Handle interworking function while working asGMSC
For BSNL internal circulation only
VISITOR LOCATION REGISTER
(VLR)-I
It is collocated with MSC.
It constitute database that support the MSC instorage and retrieval of subscribers data
It controls mobiles roaming in its area.
VLR reduces the number of queries to HLR
One VLR may be incharge of one or more LA.
VLR is updated by HLR on entry of MS itsarea.
VLR assigns TMSI which keeps on changing.
For BSNL internal circulation only
Data Stored in VLR
The data is present in VLR as long as MS isregistered in area associated with it. Socalled as Dynamic or temporary database.
VLR Stores following data
IMSI & TMSI
MSISDN
MSRN.
Location Area
Supplementary service parameters
MS category
Authentication Key
For BSNL internal circulation only
Home Location Register(HLR)-I
It constitute database that permanently store datarelated to given set of subscribers.
It is a reference database for subscribers parameter.
It stores various identification numbers and address,authentication parameters, services subscribed andspecial routing information.
Current subscriber status and associated VLR.
Both VLR and HLR can be implemented in the
same equipment in an MSC.
One PLMN may contain one or several HLR.
It stores SMS gateway identification till SMS isdelivered to MS.
For BSNL internal circulation only
Home Location Register(HLR)-II
Permanent data in HLR
IMSI, MS-ISDN number.
Category of MS ( whether pay phone or not )
Roaming restriction ( allowed or not ).
Supplementary services like call forwarding
For BSNL internal circulation only
GSM
Home Location Register(HLR)-III
Temporary data in HLR
The data changes from call to call & isdynamic
MSRN
RAND /SRES and Kc
VLR address, MSC address.
Messages waiting data used for SMS
For BSNL internal circulation only
GSM
AUTHENTICATION CENTRE (AUC )-I
AUC is a separate entity but physicallyincluded in HLR
Protect communication through air interfaceagainst intruders .
Authentication (Ki) and ciphering (Kc) keysare stored in this data base.
Keys change randomly with each call
Keys are never transmitted to MS on air butOnly calculated response are sent.
For BSNL internal circulation only
AUTHENTICATION & ENCRIPTION
• AUC
Database
Generation
of Random
Number
RANDRAND
IMSI1
IMSI3
IMSI2
ki1
ki2
ki3
RANDSRESKc
Algorithm for
Ciphering
A8
Algorithm for
Authenticatio
n
A3
Kc
64 bits
SRES
32 bits
HLR
For BSNL internal circulation only
GSMEQUIPMENT IDENTITY REGISTER ( EIR )
This data base stores IMEI for all registeredmobile equipments .
IMEI is unique identity of Mobile Equipment.
Only one EIR per PLMN.
Three classes of Mobile Equipments stored inEIR are
White list : IMEI, assigned to valid ME.
Black list : IMEI reported stolen
Gray list: IMEI having problems like faultysoftware, wrong make of equipment etc.
For BSNL internal circulation only
It provide the Interfacing Capability to DataN/Ws.
IWF. A part of MSC, provides the subscriber withaccess to data rate and protocol conversionfacilities so that data can be transmittedbetween GSM Data Terminal Equipment ( DTE )and a land line DTE.
INTERWORKING FUNCTION
For BSNL internal circulation only
ECHO CANCELER(EC)
It is used on PSTN side of MSC for all voicecalls.
It is required to reduce the effect of GSM delay(Echo) when mobile is connected to PSTN circuit.
It cancels delay of the order of 70 ms.
For BSNL internal circulation only
The centralized operation of the variousunits in the system and functions needed tomaintain the subsystems.
Dynamic monitoring and controlling of thenetwork
Operations and Maintenance Centre(OMC)
For BSNL internal circulation only
Functions
-O&M data function
-Configuration management
-Fault report and alarm handling
-Performance supervision/management
-Storage of system software and data
Functions Of OMC