The document discusses the basics of mobile communication and GSM technology. It introduces the concept of cellular networks using small cells with frequency reuse. It describes the different types of cells used and how capacity is increased through sectorization and cell splitting. The document outlines the key components of GSM architecture including the BTS, BSC, MSC, HLR, VLR, EIR and their functions. It also discusses GSM identities, frequency bands, and the evolution of mobile communication technologies.

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CM_Module_CH_01
BASICS OF MOBILE COMMUNICATION
For internal circulation of BSNL only
SRINATH VASAM
SDE (MOBILE) , RTTTC, HD
Mob: +91-9440845584 | Email: srinathvasam@bsnl.co.in
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2. Agenda
 Cellular Concept
 Fundamentals of GSM
 GSM Specifications
 GSM Architecture
 GSM elements Functions
 GSM identities
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3. What is a cell?
 Cell is the basic geographic unit of cellular system.
 Instead of using one powerful transmitter many low-powered
transmitters were placed through out a coverage area.
 The cellular concept employs variable low power levels, which allows
cells to be sized according to subscriber density and demand of a
given area.
 Cells are assigned a group of channels that is completely
different from neighbouring cells.
 The coverage area of cells is called the footprint and is limited by
a boundary so that the same group of channels can be used in
cells that are far enough apart
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4. Type of Cells
The density of population in a country is so varied that different types of cells are
used:
1. MACRO CELLS
2. MICRO CELLS
3. PICO CELLS
4. SELECTIVE CELLS
5. UMBRELLA CELLS
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5. • Group of cells in
which no frequencies
are reused is termed
as a cluster.
Clusters
Eg: A seven Cell Cluster
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6. Frequency Reuse
Cells with the same number have the same set of
frequencies
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7. Real Cell Formation
Base Station
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8. Increasing Capacity
• Cell Sectoring
– Divide cell up into angular sections, typically 3 or 6
– Increases reuse
• Cell Splitting
– Subdivide cell into smaller cells, increases the number of
channels, keep same structure
– Needs power control
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9. Sectorisation
 There are two commonly used methods of Sectorisation either using 120˚
sector or 60˚ sector, both of which reduce the number of prime interference
sources.
 The three sector case is generally used with a seven cell pattern, giving an
overall requirement for 21 channel sets as shown in Figure above.
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10. Features of Digital Cellular system
1. SMALL CELLS
2. FREQUENCY REUSE
3. SMALL, BATTERY-POWERED HANDSET
4. PERFORMANCE OF HANDOVERS
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11. Objectives of Mobile Communications
 Any time Anywhere communication
 Mobility & Roaming
 High capacity & subscriber density
 Efficient Use of Radio Spectrum
 Seamless Network Architecture
 Low Cost
 Innovative Services
 Standard Interface
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12. Evolution of mobile Technologies
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13. Generations in brief
TECHNOLOGY 1G 2G 2.5G 3G 4G
First Design 1970 1980 1985 1990 2000
Implementation 1982 1991 1999 2002 2010?
Service
Analog
Voice
Digital
Voice, SMS
Package
Data
Broadband
data up to
2 Mb/s
IP-oriented
unlimited
multimedia
data
Standards AMPS
TDMA,
CDMA,
GSM
GPRS,EDG
E
EVDO,
W-CDMA,
HSDPA
WiMAX,
HSOPA
Data Bandwidth 1.9 kbps 14.4 kbps 384 kbps 2 mbps 200 mbps
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14. Basic Mobile Telephone Service Network
There are two types of duplexing:
 Frequency Division Duplexing FDD
 Time Division Duplexing TDD
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15. Comparison
Duplexing and Multiple Access Techniques in use
No Name of System Multiple Access Duplexing
1 GSM FDMA-TDMA FDD
2 CDMA CDMA FDD
3 3G WCDMA FDD
4 4G(LTE) OFDMA TDD/FDD
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16. Frequency Bands
GSM 900 (P-GSM) : 890-915 MHz (U/L)
: 935-960 MHz (D/L)
GSM 1800 (DCS1800) : 1710-1785 MHz (U/L)
: 1805-1880 MHz (D/L)
Parameters Standard or Primary GSM 900 Band 1800 Band
Uplink Frequency 890-915 MHz 1710 - 1785 MHz
Downlink frequency 935-960 MHz 1805 – 1880 MHz
Duplex Distance 45 MHz 95 MHz
Carrier separation 200 KHz 200 KHz
Frequency Channels 124 374
Voice coder bit rate 13 Kbps 13 Kbps
Modulation GMSK GMSK
Air transmission Rate 270.8333 Kbps 270.8333 Kbps
Access Method FDMA/TDMA FDMA/TDMA
Speech Coder RPE-LTP RPE-LTP
Duplexing FDD FDD
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17. HLR AUC
VLR
EIR
Other MSC
BTS
BTS
BSC
M
S
G
B
A C
F
Abis
D
Abis
Um
Other NWs &
PSTN
GMSC
Other
MSC/ VLR
OMC
GSM- Architecture
MSC
BSS
E
NSS
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18. GSM Network Structure
Area wise identities: GCI / Cell ID, LAI, MSC/VLR ID, PLMN ID/ LRN
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19.  A GSM cell is made up of one BTS and consists of all the equipment and antennas
needed to support the traffic and signalling channels for one cell.
 A single transceiver within BTS supports eight basic radio channels of the same TDM
frame.
 A BTS is a network component that serves one cell and is controlled by a BSC. BTS
is typically able to handle three to five radio carriers.
 BTS provide radio interface directly to the mobile.
 A BTS is connected to only one BSC
 One BTS can have one or more no. of transceivers
 Performs many functions under the control of the BSC to coordinate connections with
mobiles.
The main functions of the BTS
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20. The main functions of the BSC
 Radio Resource (RR) management for the cells under its control.
 Assigns and release frequencies and timeslots for all MSs in its own area.
 Performs the inter-cell handover for MSs moving between BTS in its control.

 Reallocates frequencies to the BTSs in its area to meet locally heavy demands
during peak hours or on special events.
 Controls the power transmission of both BSSs and MSs in its area. The minimum
power level for a mobile unit is broadcast over the BCCH.
 Provides the time and frequency synchronization reference signals.
 Measures the time delay of received MS signals relative to the BTS clock. If the
received MS signal is not centred in its assigned timeslot at the BTS, The BSC can
direct the BTS to notify the MS to advance the timing such that proper
synchronization takes place.
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21. The main functions of the MSC
 Set-up of calls in GSM mobile Networks.
 The call-handling function is controlled by MSC.
 MSC coordinates the set-up of call to and from all GSM subscribers operating in its
areas.
 GMSC works GATEWAY to interconnect different PLMN s & PSTN s
 Paging & Resource allocation
 Location registration
 Encryption.
 The dynamics allocation of access resources is done in coordination with the BSS.
 Interrogation with the Databases like HLR, VLR, AUC, EIR & IN etc.
cont…..
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22.  Interworking Function (IWF): which in essence is a part of MSC, provides the
subscriber with access to data rate and protocol conversion facilities so that data
can be transmitted between GSM Data Terminal Equipment (DTE) and a land-line
DTE.
 It is the job of the IWF to provide this interfacing capability.
 Echo Canceller (EC) :EC is used on the PSTN side of the MSC for all voice
circuits. The EC is required at the MSC PSTN interface to reduce the effect of
GSM delay when the mobile is connected to the PSTN circuit.
Cont……
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23. Subscriber
Management
Center
Permanent records
- MSISDN
- IMSI
-Subscriber's service provision
Temporary records
- VLR and SGSN addresses
- Ciphering items
(Kc, Sres, Rand)
HLR
Home Location Register (HLR)
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24. Permanent records
- IMSI
- Subscriber’s service provision
Temporary records
- Ciphering items
(Kc, Sres, Rand)
- LAI - TMSI
LA1
LA4
LA2
LA3
Visitor Location Register (VLR)
VLR
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25. Ki
SRES, Kc, RAND
RAND
AUC provides
Ciphering Triplets
IMSI
HLR Request
AUC
Security
A3, A8 algorithms
Authentication Center (AUC)
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26. Equipment Identity Register (EIR)
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27. The Functions of OMC ( OMC- R & OMC-S)
 ALARM MANAGEMENT: The Operations and Maintenance Center (OMC) provides
alarm-handling functions to report and log alarms generated by the other network
entities. The maintenance personnel at the OMC can define that criticality of the
alarm. Maintenance covers both technical and administrative actions to maintain and
correct the system operation, or to restore normal operations after a breakdown, in
the shortest possible time.
 FAULT MANAGEMENT: The fault management functions of the OMC allow network
devices to be manually or automatically removed from or restored to service. The
status of network devices can be checked, and tests and diagnostics on various
devices can be invoked.
 REMOTE HANDLING: Diagnostics may be initiated remotely by the OMC. A mobile
call trace facility can also be invoked.
 PERFORMANCE MANAGEMENT: The performance management functions
included collecting traffic statistics and archiving them in disk files or displaying them
for analysis.
 CONFIGURATION MANAGEMENT: The OMC provides system change control for
the software revisions and configuration data bases in the network entities or
uploaded to the OMC. The OMC also keeps track of the different software versions
running on different subsystems of the GSM.
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28. GSM Identities
 International Mobile Subscriber Identity (IMSI): MCC+MNC+MSIN
An IMSI is assigned to each authorized GSM user. shall not exceed 15 digits.
 Temporary Mobile Subscriber Identity (TMSI): A TMSI is a MSC-VLR specific
alias that is designed to maintain user confidentiality. It is assigned by VLR only
after successful subscriber authentication.
 Mobile Station ISDN Number (MSISDN): (CC+ NSN) The MSISDN numbers is
composed of the country code (CC) followed by the National Significant Number
(NSN), which shall not exceed 15 digits.
 The Mobile Station Roaming Number (MSRN): Assigned by VLR upon demand
by the HLR on a per-call basis.(Structure as MSISDN)
The MSRN number is used by the HLR for rerouting calls to the MS.
 International Mobile Equipment Identity (IMEI): A unique identity of the equipment
used by a subscriber, it is used to ensure that only authorized users are granted
access to the system. An IMEI is never sent in cipher mode by MS.
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