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Basic Telecom concepts Various Wireless Technologies Cellular concepts & Principal of cellular Comm. GSM Network Architecture GSM channel Architecture Call Flows in GSM GSM Planning steps (Nominal Plan & RF surveys) Alternative means of wireless communication Walkie - Talkie Pagers Trunked private radios Mobile Phone - the magic technology that enables everyone to communicate anywhere with anybody. Till 1982 Cellular Systems were exclusively Analog Radio Technology. Advanced Mobile Phone Service (AMPS) U.S. standard on the 800 MHz Band Total Access Communication System (TACS) U.K. standard on 900 MHz band Nordic Mobile Telephone System (NMT) Scandinavian standard on the 450 & 900 MHz band
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Tempus Telcosys (P) Limited
Telecom Tutorials
Wednesday, April 12, 2023www.tempustelcosys.com
GSM Fundamentals & RF Survey
What you will learn here?
Basic Telecom conceptsVarious Wireless TechnologiesCellular concepts & Principal of cellular Comm.GSM Network ArchitectureGSM channel ArchitectureCall Flows in GSMGSM Planning steps (Nominal Plan & RF surveys)
Wednesday, April 12, 2023www.tempustelcosys.com
BASIC Telephony
Wednesday, April 12, 2023www.tempustelcosys.com
• Signaling• Traffic
• Off Hook
• Dial Tone
• Dialing Digits
• RBT
• Conversation
SWITCH / EXCHANGE
• Ring
• Off Hook & Conversation
Wireless Communication
Alternative means of wireless communicationWalkie - TalkiePagersTrunked private radios
Mobile Phone - the magic technology that enables everyone to communicate anywhere with anybody.
Wednesday, April 12, 2023www.tempustelcosys.com
Wireless Telephony
Wednesday, April 12, 2023www.tempustelcosys.com
BTS BTS
MSC
Different Standards WorldwideTill 1982 Cellular Systems were exclusively Analog Radio Technology.
Advanced Mobile Phone Service (AMPS)
U.S. standard on the 800 MHz Band
Total Access Communication System (TACS)
U.K. standard on 900 MHz band
Nordic Mobile Telephone System (NMT)
Scandinavian standard on the 450 & 900 MHz band
Wednesday, April 12, 2023www.tempustelcosys.com
Different Standards WorldwideGSM - 900
The term GSM-900 is used for any GSM system which operates in any 900 MHz band.
P-GSM - 900
P-GSM-900 band is the primary band for GSM-900 Frequency band for primary GSM-900 (P-GSM-900) : 2 x 25 MHz
890 – 915 MHz for MS to BTS (uplink)
935 – 960 MHz for BTS to MS (downlink)
E-GSM - 900
In some countries, GSM-900 is allowed to operate in part or in all of the following extension band. E-GSM-900 (Extended GSM-900) band includes the primary band (P-GSM-900) and the extension band :
880 – 890 MHz for MS to BTS (uplink)
925 – 935 MHz for BTS to MS (downlink)R-GSM-900
R-GSM-900 (Railway GSM-900) band includes the primary band (P-GSM-900) and the following extension band:
876 – 890 MHz for MS to BTS (uplink)921 – 935 MHz for BTS to MS (downlink)
GSM-1800
Frequency band: 2 x 75 MHz
1710 – 1785 MHz for MS to BTs (uplink)1805 – 1880 MHz for BTS to MS (downlink)
Wednesday, April 12, 2023www.tempustelcosys.com
Industry Vs Technology Spread
Telecom Service Providers/OperatorsGSM
CDMABasic-WLL
Internet ServicesLong Distance
VendorTelecom Consultancy
Wednesday, April 12, 2023www.tempustelcosys.com
Analog Mobile Telephony
End of 1980’s Analog Systems unable to meet continuing
demands
Severely confined spectrum allocations
Interference in multipath fading environment
Incompatibility among various analog systems
Inability to substantially reduce the cost of mobile
terminals and infrastructure required
Wednesday, April 12, 2023www.tempustelcosys.com
Digital Mobile Telephony
Spectrum space - most limited and precious
resource
Solution - further multiplex traffic (time domain)
Can be realized with Digital Techniques only
Wednesday, April 12, 2023www.tempustelcosys.com
GSM History and Organization
1979 Europe wide frequency band reserved for Cellular
1982 “Groupe Speciale Mobile” created within CEPT1986 GSM had full time in Paris1988 ETSI takes over GSM Committee 1990 The phase 1 GSM Recommendations
frozen1991 GSM Committee renamed “Special Mobile Group” and GSM renamed as “Global
System for Mobile Communication”1992 GSM launched for commercial
operations
Wednesday, April 12, 2023www.tempustelcosys.com
Cellular Communication
A cellular system links Mobile subscribers to Public
Telephone System or to another Mobile
subscribers.
It removes the fixed wiring used in a traditional
telephone installation.
Mobile subscriber is able to move around, perhaps
can travel
in a vehicle or on foot & still make & receive call.
Wednesday, April 12, 2023www.tempustelcosys.com
Road Map of Mobile Communication
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WHAT IS CELLULAR TELEPHONY ?
CONSIDERATIONS -
FREQUENCY
SUBSCRIBER DENSITY
COVERAGE
Wednesday, April 12, 2023www.tempustelcosys.com
Base Station
Base Station
Base Station
Base Station
Base Station
Base Station
The Cell
Cellular Radio involves dividing
a large service area into
regions called “cells.”
Each cell has the equipment to
switch, transmit and receive
calls.
Cells - Reduce the need of High
powered transmission
Cells - Conventionally regarded
as being hexagonal, but in
reality they are irregularly
shaped.
Cell shape is determined by the
nature of the surrounding
area e.g. Hills , tall building
etc.
Wednesday, April 12, 2023www.tempustelcosys.com
Cell Size
Wednesday, April 12, 2023www.tempustelcosys.com
Large Cells
35 Km
Remote Areas
High Transmission Power
Few subscribers
Small Cells
Near about 1 KM Urban Areas Low Transmission
Power Many Subscribers
Coverage & Capacity
CoveragePercentage of the
geographical area covered by cellular service where mobile telephony is available
Capacity - Number of calls that can
be handled in a certain area within a certain period of time.
Capacity can also refer to the probability that users will be denied access to a system due to the simple unavailability of radio channels. Wednesday, April 12, 2023www.tempustelcosys.com
GSM - IN CELLULAR TELEPHONY
Each Cell in the Cellular Network consists of one or more RF carriers.An RF carrier is a pair of radio frequencies
One used in upward direction by MS - UplinkOther used in downward direction by BTS - DownlinkThe transmit and receive frequencies are separated
by a gap of 45 MHz in GSM of 75 MHz in DCS.There are 124 carries in GSM Band. With each carrier carrying 7 timeslots, only 124 x 7 = 868 calls can be made! Frequency Reuse is the solution
Wednesday, April 12, 2023www.tempustelcosys.com
Frequency & ARFCN
Wednesday, April 12, 2023www.tempustelcosys.com
ul=
890
to
915
MH
z
dl=
935
to
960
MH
z
Ful(n) = 890.0 + (0.2) *n MHz
Fdl(n) = Ful + 45 MHz
where n =ARFCN ; 1 n 124
GSM Bandwidth & Main Parameters900 MHz & 1800 MHz
Wednesday, April 12, 2023www.tempustelcosys.com
1710 1785 1805 1880
duplex distance: 95 MHz
890 915 935 960
duplex distance: 45 MHz
Multiple Access Methods
Wednesday, April 12, 2023www.tempustelcosys.com
Multiple Access Methods
Wednesday, April 12, 2023www.tempustelcosys.com
FrequencyTime
Power
TDMA
Frequency
Time
Power
FDMA
FrequencyTime
Power
CDMA
CODE
FDMA: AMPS & NAMPS• Each user occupies a private Frequency,
protected from interference through physical separation from other users on the same frequency
• TDMA: IS-136, GSM• Each user occupies a specific frequency
but only during an assigned time slot. The frequency is used by other users during other time slots.
• CDMA• Each user occupies a signal on a
particular frequency simultaneously with many other users, but is uniquely distinguishable by correlation with a special code used only by this user
Frequency Reuse Pattern
Three types of frequency reuse patterns
7 Cell reuse pattern
4 cell reuse pattern
3 cell reuse pattern
Wednesday, April 12, 2023www.tempustelcosys.com
Wednesday, April 12, 2023www.tempustelcosys.com
c2
c1
c3
a1
a3
b1
b2
b3
Cell Re-use
Wednesday, April 12, 2023www.tempustelcosys.com
2
45
6
7D
Principal Of Sectorization
Omni Directional Cells
120 degree Sectors
60 Degree sectors
Each Sector in a Site has its own allocation of Radio Carriers
Advantage
By frequent reuse of frequency more capacity can be achieved
Wednesday, April 12, 2023www.tempustelcosys.com
Wednesday, April 12, 2023www.tempustelcosys.com
OMNI CELL
1 ANTENNA
b1
b2
b3
120O CELLS
3 ANTENNAS
60O CELLS
6 ANTENNAS
a1 a3
a4a6
a5
a2
Handovers
Wednesday, April 12, 2023www.tempustelcosys.com
Hard HandoffAnalog, TDMA and GSM
Soft HandoffCDMA
Break before Make Make before Break
Features of GSM
Compatibility
Noise Robust
Increased Capacity & Flexibility
Use of Standard Open Interfaces
Improved Security & Confidentiality
Cleaner Handovers
Subscriber Identification
ISDN Compatibility
Enhanced Range of ServicesWednesday, April 12, 2023www.tempustelcosys.com
Mobile Station Identities
Wednesday, April 12, 2023www.tempustelcosys.com
GSM NETWORK ELEMENTS
Wednesday, April 12, 2023www.tempustelcosys.com
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BSC
VLR
HLR EI
R
OMC
SMSC
BC
AUC
VMSC
MSC
Abi
s
A
MS
BTS
BTS
BTS
BTS BTS
BTS
BTS
BTS
BSC
BSC
PSTN
VLR
TRAU HLREIR
OMC
SMSC
BC
AUC
VMSC
MSC
Abi
s
A
OML
GSM Network ComponentsMobile Station consists of two parts-
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
ME
Hardware e.g. Telephone, Fax Machine, Computer.
SIM
Smart Card which plugs into the ME.
Wednesday, April 12, 2023www.tempustelcosys.com
Mobile Equipment
Class Power O/p 1 20 W
2 8 W
3 5 W
4 2 W
5 0.8 W
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Typical Settings
SIM(IMSI)
IMSI(International Mobile Subscriber Identity)Transmitted over Air Interface on initialization
Permanently stored on SIM card
15 digit Decimal
Wednesday, April 12, 2023www.tempustelcosys.com
SIM
MSISDN
10 digit number to which a subscriber is being called.
PIN (Personal Identification Number)
Four digit PIN
An internal security to Protect the SIM from illegal use.
Card blocks itself after three wrong entries
Wednesday, April 12, 2023www.tempustelcosys.com
SIM (TMSI)
Temporary Mobile Subscriber Identity
Periodically changed by the System Management on instances like location update etc.
Reason for use of TMSI
To prevent a possible intruder from identifying GSM users, TMSI is used
Management
Assignment, Administration & Updating is performed by VLR.
Wednesday, April 12, 2023www.tempustelcosys.com
Base Station System (BSS)BSS (Base Station System)
BSC (Base Site Controller)
BTS (Base Transceiver Station)
XCDR (Transcoder)
Wednesday, April 12, 2023www.tempustelcosys.com
Network Switching System (NSS)
XCDR
BSC
BTS
TranscoderConverts 64 Kbps PCM circuits from MSC to 16 Kbps BSS circuits.
Each 30 channel 2 Mbps PCM link can carry 120 GSM - specified voice channels.
G e n e r a l l y ,Tr a n s c o d e r i s c o l l o c a t e d w i t h M S Cs o a s t o r e d u c e t h e n u m b e r o f2 M b p s A - l i n k st o e ffi c i e n t l y u s e t h e B W .
Wednesday, April 12, 2023www.tempustelcosys.com
Base Station System (BSS)BSC
Conveys information to/from BTS
Connects terrestrial circuits & Air Interface Channels
Controls handovers between BTSs under itself
BTSContains RF Hardware
Limited control functionality
1 - 6 carriers in a BTS Cabinet
7 - 48 simultaneous calls per BTS
Wednesday, April 12, 2023www.tempustelcosys.com
BSS ConfigurationCollocated BTS
Remote BTS
Star Configuration
Daisy Chain BTS Loop Configuration
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BSC
BTS
BTS
BTS
All B
TS
on
1 E1
BSC
BTS
BTS
BTS
BTS
Network Switching System(NSS)NSS (Network Switching System)
MSC (Mobile Switching Centre)
HLR (Home Location Register)
VLR (Visitor Location Register)
EIR (Equipment Identity Register)
AUC (Authentication Centre)
IWF (Interworking Function)
EC (Echo Canceller)
Wednesday, April 12, 2023www.tempustelcosys.com
GSM Network ComponentMSC
Call Switching
Operation & Management Support
Internetwork Interworking
Collects call billing data
Gateway MSC
MSC which provides interface between PSTN & BSS’s in the GSM Network.
Wednesday, April 12, 2023www.tempustelcosys.com
Home Location Register (HLR)
Reference database for the Subscriber profiles-
Subscriber ID (IMSI & MSISDN)
Current VLR Address
Supplementary Services subscribed
Supplementary Service Information
Subscriber Status (Registered/deregistered)
Authentication Key and AUC functionality
TMSI
MSRN
Wednesday, April 12, 2023www.tempustelcosys.com
Visitor Location Register (VLR)
Temporary Data, which exists as long as the subscriber is active in a particular Coverage area.
Contains the following-Mobile Status (Busy/ Free/ No Answer/etc.)
Location Area Identity (LAI)
TMSI
MSRN (Mobile Station Roaming Number)
Wednesday, April 12, 2023www.tempustelcosys.com
Location Update
Wednesday, April 12, 2023www.tempustelcosys.com
GSM Interfaces
Um MS - BTS
Abis BTS - BSC
A BSC - MSC
B MSC - VLR
C MSC - HLR
D VLR - HLR
E MSC - MSC
F MSC - EIR
G VLR - VLR
H HLR - AUCWednesday, April 12, 2023www.tempustelcosys.com
Basic Processes
AUTHENTICATION
CIPHERING
REGISTRATION
CALL ESTABLISHMENT
HANDOVER / HANDOFF
ROAMING
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Transmission Media
Access Network
Microwave 15 /23 GHz
Backbone Network
Microwave 7 GHz
Optical Fibers
Leased Line( From Dot or any other service provider on any media)
Wednesday, April 12, 2023www.tempustelcosys.com
Channels On Air InterfacePhysical Channel Logical Channel
Physical Channel
Physical channel is the medium over which the information is carried.
Logical Channel
Logical channels consists of the information carried over the Physical Channel.
Wednesday, April 12, 2023www.tempustelcosys.com
LOGICAL CHANNELS
Wednesday, April 12, 2023www.tempustelcosys.com
0 1 2 3 4 5 6 7
3
57 encrypted
57 encrypted
26 training
1S
1S
3T
8.25GP
3T
577S
TDMA Frame
GSM Channels
Wednesday, April 12, 2023www.tempustelcosys.com
Control Channel
Wednesday, April 12, 2023www.tempustelcosys.com
DCCH(Dedicated Channels)Downlink & Uplink
CCCH(Common Control Chan)Downlink & Uplink
Synch.Channels
RACHRandom Access Channel
CBCHCell Broadcast Channel
SDCCHStandalone dedicated control channel
ACCHAssociated Control Channels
SACCHSlow associated Control Channel
FACCHFast Associated Control Channel
PCH/AGCHPaging/Access grant
FCCHFrequency Correction channel
Control Channels
BCH ( Broadcast channels )Downlink only
BCCHBroadcast control channel
SCHSynchronization channel
Broadcast Channels (BCH)BCH channels are all downlink and are allocated to timeslot zero.
Channels are:
• FCCH: Frequency control channel sends the mobile a burst of all ‘0’
bits which allows it to fine tune to the downlink frequency
• SCH: Synchronization channel sends the absolute value of the frame number (FN), which is the internal clock of the BTS, together with the Base Station Identity Code (BSIC)
• BCCH: Broadcast Control Channel sends radio resource
management and control messages, Location Area Code and so on.
Some messages go to all mobiles, others just to those that are in the
idle state
Wednesday, April 12, 2023www.tempustelcosys.com
Common Control Channels (CCCH)
•CCCH contains all point to multi-point downlink channels (BTS to
several MSs) and the uplink Random Access Channel:
• CBCH: Cell Broadcast Channel is an optional channel for general
information such as road traffic reports sent in the form of SMS
• PCH: Paging Channel sends paging signal to inform mobile of a call
• RACH: Random Access Channel is sent by the MS to request a
channel from the BTS or accept a handover to another BTS.
A channel request is sent in response to a PCH message.
• AGCH: Access Grant Channel allocates a dedicated channel
(SDCCH) to the mobile
• NCH: Notification Channel informs MS about incoming group or
broadcast callsWednesday, April 12, 2023www.tempustelcosys.com
Dedicated Control Channels (DCCH)
SDCCH( Standalone Dedicated Control Channel )
Uplink and Downlink
Used for call setup, location update and SMS.
SACCH( Slow Associated Control Channel )
Used on Uplink and Downlink only in dedicated mode.
Uplink SACCH messages - Measurement reports.
Downlink SACCH messages - control info.
FACCH( Fast Associated Control Channel )
Uplink and Downlink.
Associated with TCH only.
Wednesday, April 12, 2023www.tempustelcosys.com
BURST
The Time Slots are arranged in a sequence , conventionally numbered 0 to 7.
Each repetition of this sequence is called a TDMA Frame.
The information content carried in one time slot is called a “burst”.
Wednesday, April 12, 2023www.tempustelcosys.com
GSM Burst & TDMA Frame
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0 1 2 3 4 5 6 7 2 4 5 6 730 1
FRAME 1 FRAME 2
Training SequenceInformation Information
GUARD PERIOD
GUARD PERIOD
TAIL BITS TAIL BITS
Wednesday, April 12, 2023www.tempustelcosys.com
0 7
TDMA frame = 4.615 ms
= BURST PERIOD
0
Mobile To Land Sequence
Wednesday, April 12, 2023www.tempustelcosys.com
1
3
CHANNEL REQUEST
DCCH ASSIGN
SIGNALLING LINKESTABLISHED
REQUEST FOR SERVICE
SET CIPHER MODE
SET-UP
EQUIPMENT ID REQUEST
AUTHENTICATION
MS BSS MSC VLR HLR PSTNEIR
RACH
AGCH
SDCCH
SDCCH
Call Info7
4
6
5
2CR
CC
Call Contt.
Wednesday, April 12, 2023www.tempustelcosys.com
8COMPLELTE CALL
CALL PROCEEDING
9 ASSIGNMENT COMMAND
INITIAL & FINALADDRESS (IFAM)
ASSIGNMENT COMPLETE (ACM)10
ANSWER(ANS)
11
CONNECT ACKNOWLEDGE
SDCCH
SDCCH
ASSIGNMENT COMPLELTE
MS HEARS RINGTONEFROM LAND PHONE
ALTERING
RING TONESTOPS
CONNECT
(channel)
(TCH)
FACCH
FACCH
FACCH
TCH
(circuit)
FAACH
BILLING STARTS
Hello!
MS BSS MSC
VLR HLR PSTN EIR
GSM Planning StepsVarious steps are listed below
CW surveyModel TuningNominal PlanningRF site SurveysRealized PlanningFrequency Planning
ImplementationOptimization
Drive TestingPerformance Analysis
Wednesday, April 12, 2023www.tempustelcosys.com
Nominal PlanningIt consists of planning a set of sites on planning tool so as to predict
the coverage of the target areaTool needs to be made intelligent so as to predict the coverage as
close as possible to actual coverageCoverage plots are based on customer intension of providing indoor
and outdoor coverage
Wednesday, April 12, 2023www.tempustelcosys.com
Nominal PlanningIt consists of planning a set of sites on planning tool so as to predict
the coverage of the target areaTool needs to be made intelligent so as to predict the coverage as
close as possible to actual coverageCoverage plots are based on customer intension of providing indoor
and outdoor coverage
Wednesday, April 12, 2023www.tempustelcosys.com
Clutter Types
Clutter typesDense Urban
UrbanSub Urban
RuralWater
VegetationIndustrial
Forest
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RF surveysEach nominal has a search ring defined by the RF PlannerCandidates needs to be identified as close as possible to
the nominal within the search ringHeight, orientations & antenna placement at site are the key RF parameter which are based upon the coverage
requirement in the areaMajor obstructions and clutter type in various directions
to be observed on RF survey
Wednesday, April 12, 2023www.tempustelcosys.com
RF surveysEquipment required for RF Survey
GPSDigital Camera
BinocularsMagnetic Compass
Measuring Tape
There might be 3 or more candidates surveys for one site
Each candidate would have an RF survey form and panoramic associated with it
Wednesday, April 12, 2023www.tempustelcosys.com