4. BSNL
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)
6. 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
7. BSNL
FERQUENCY SCARCITY PROBLEM
Tel
Ex.
WIRED NETWORK
100,000 50 Khz = 5 Ghz (NOT POSSIBLE)
Hence Individual RF Loop is not extended
But a Common group of channels is shared
CELLULAR MOBILE CONCEPTS
BW for Telephony speech:
3KHz increases to 25 KHz with FM for Radio Trans.
14. BSNL
14
GSM Network Structure
• GSM Service Area: Total area served by the
combination of all member countries where a mobile can
be served.
• 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. In a GSM/PLMN N/W all mobile
terminated calls will be routed to a Gateway MSC. 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.
• Location Area
• Cells
15. BSNL
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 STATION
IDENTIFICATION CODE(BSIC) that the cell site broadcast
over the air.
GSM Network Structure
18. BSNL
MSC/VLR
LA 1 LA 2
LA 6
LA 3
LA 4
LA 5
C1
C5
C4
C7
C2
C3
C6
GSM
Cells
C = Cell
19. BSNL
19
GSM
Relation between areas in GSM
Location AreaCell
Area served by a BTS
Location Area
MSC Service Area
PLMN Service Area
GSM Service Area
20. BSNL
20
GSM
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
21. BSNL
21
GSM
Mobile Station
• Portable, vehicle mounted, hand held
• MS identified by unique IMEI(International Mobile Equipment
Identity)
• Shell 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
23. BSNL
23
GSM IMSI
• International mobile subscriber’s
Identity
• The IMSI is an unique identity which is
used internationally and used within the
network to identify the mobile subscribers.
• The IMSI is stored on the subscriber
identity module (SIM), the HLR, VLR and
AC database.
25. BSNL
25
GSM
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.
• 11 power classes from .01 watts to 320 watts
26. BSNL
26
GSM
FUNCTION OF BTS -II
• Frequency hopping
• Random access detection
• Uplink radio channel measurements
• BTS mainly consists of a set of transceivers
(TRX).
27. BSNL
27
GSM
FUNCTIONS OF BSC-I
• It is connected to BTS and offloads MSC
• Radio resource management
• Inter-cell handover
• Reallocation of frequencies
• Power control
28. BSNL
28
GSM
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.
29. BSNL
30
GSM
MSC-BSS Configurations
BTS
BTS
BTS
A-bis
BSC
BSS
Configuration -6
Multi - cell site =
multi--BTS site
Many single
cell sites
BSS
MSC
BTS
A
A
A
Single - cell site
Configuration -1
Multi - cell site (sector Cells
Configuration -5
MSC: Mobile Switching Centre
BSS: Base Station System
BSC: Base Station Controller
BTS: Base Transceiver Station
A-bis
BTS BTS
BTS
30. BSNL
31
GSM
MSC ( 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 customers
roams to other network by using HLR /VLR
31. BSNL
32
GSM
MSC Functions - I
Paging, specifically call handling
Location updation
Handover management
Billing for all subscribers based in its area
Reallocation of frequencies to BTSs in its area
to meet heavy demands
32. BSNL
33
GSM
MSC Functions - II
Echo canceller operation control
Signaling interface to databases like HLR,
VLR.
Gateway to SMS between SMS centers and
subscribers
33. BSNL
34
GSM
VISITOR LOCATION REGISTER (VLR)-I
It controls those 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 its area.
IMSI detach and attach operation
34. BSNL
35
GSM
Home Location Register(HLR)-I
• Reference store for subscriber’s parameters,
numbers, authentication & Encryption values.
• 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.
35. BSNL
36
GSM
Home Location Register(HLR)-II
Data stored is changed only by man-machine.
Category of MS ( whether pay phone or not )
Roaming restriction ( allowed or not ).
Supplementary services like call forwarding
Permanent data in HLR
36. BSNL
37
Temporary data in HLR
The data changes from call to call & is
dynamic
VLR address, MSC address.
Messages waiting data used for SMS
GSM
Home Location Register(HLR)-II
