Post on 03-Jun-2018
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GB_BT01_E1_1 GSM Basics
ZTE University
GSM-BSS Team
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Objective
At the end of this course, you will be able to: Understand GSM system architecture and function
State GSM common events
Describe basic calling process
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Content
GSM System Overview
GSM Common Events
Basic Calling Process
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AMPS
TACS
NMT
Others
1G
Analog
GSM
CDMAIS95
TDMAIS-136
PDC
2G
Digital
Market
Driving
3G
IMT-2000
UMTS
WCDMA
CDMA
2000
Market
Driving
TD-SCDMA
Mobile Telecommunication Technology
Evolution
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GSM History
1989GSM Standard Take effect
1
1991GSM system launched commercially
2
1994GSM enter into China
3
2000China Mobile
400 million subscribers
4
Custome
r
Demand
Competition
Technology
Development
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Development of mobile communication system
1 k
1 M
2 M
Bit/s
Messaging
SMS
Voice
Graphics
text
Medium
quality
High
quality
Mobile Office
VideoUMTSUMTS
GPRSGPRS
2002
2000
GSMGSM10 k
1999 56 k
EDGEEDGE 2001
115 k
384 k
Alwa
ys-on
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The way to 3G
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Meaning of GSM
GSM: Group Special Mobile
GSM: Global System for Mobile
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GSM specification
Field 1: General Field 2: Services
Field 3: Network Functions
Field 4: MS-BS Interfaces and Protocols Field 5: Physical Layer on Radio Path
Field 6: Speech Coding
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GSM specification
Field 7: MS Terminal Adaptor Field 8: BS-MSC Interface
Field 9: Network Inter-working
Field 10: Service Inter-working Field 11: Equipment and Model Acceptance
Specification
Field 12: Operation and Maintenance
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GSM Network development
1982: The group special mobile 1986: On-site test
1987: TDMA, RPE-LTP, GMSK
1988: MOU 1989: GSM took effect
1991: First GSM network was deployed
1992: GSM standard was frozen
1993: GSM phase 2 complete
1994: GSM phase 2+ for mobile data service
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GSM system architecture
BTS
BSC
MSC
VLR HLR AuC EIR
PSTN,ISDN...
OMCOMC
NMCX.25 links
GSM interfaces
Voicemail Server
SM-SC
MS (Mobile Station)
BSS (Base Station System)
NSS(Network Switching
Subsystem)
OMS(Operations & MaintenanceManagement)
MS
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GSM network entities
MS (Mobile Station)Mobile Equipment
Subscriber Identity Module (SIM)
BTS (Base Transceiver Station)Provide radio channels
BSC (Base Station Controller)
Radio resource management
Transcoder
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GSM network entities
HLR (Home Location Register)Database
Subscriber data
Subscriber location info.
VLR (Visitor Location Register)Database
MSRN (Mobile Station Roaming Number)
TMSI (Temporary Mobile Subscriber Identification)
Location area codeLAC
Subscriber data related to supplementary service
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GSM network entities
MSC (Mobile service Switching center)Circuit switching
AUC (Authenticate Center) :
Authenticate subscriber access
EIR (mobile station Equipment Identity Register) :
Identify terminal equipment
OMC (Operation and Maintenance Center)Provide MMI to control and monitor system
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GSM interfaces
MS BTS BSC MSC
VLR VLR
HLR
MSCEIR
Sm
Um
Abis A B
D
C
E F
G
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GSM operation band
SYSTEM P-GSM 900 E-GSM 900 GSM 1800 GSM 1900
Frequencies
- Uplink- Downlink
890 - 915 MHz935 - 960 MHz
880 - 915 MHz925 - 960 MHz
1710 - 1785 MHz1805 - 1880 MHz
1850 - 1910 MHz1930 - 1990 MHz
Wavelength ~33 cm ~33 cm ~17 cm ~16 cm
Bandwidth 25 MHz 35 MHz 75 MHz 60 MHz
Duplex Distance 45 MHz 45 MHz 95 MHz 80 MHz
Carrier Separation 200 kHz 200 kHz 200 kHz 200 kHz
Radio Channels 125 175 375 300
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Absolute radio frequency channel Number
ARFCN
GSM900 Fu (n) = 890 + 0.2n MHz
Fd (n) = Fu(n) + 45 MHz01n 124
GSM1800
Fu (n) = 1710.2 + 0.2(n-512) MHz
Fd (n) = Fu(n) + 95 MHz512 n 885
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Multiple Access Technology (MAT)
Many subscribers share commontelecommunication lines without interference to
each other.
M T
GSM
FDMA
TDMA
CDMA
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FDMA
FDMA Identify by frequency
Time
Frequency
FDMA
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TDMA
TDMA Identify by time
Time
Frequency
TDMA
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CDMA
CDMA Identify by code
Time
Frequency
CDMA
Code
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Content
GSM System Overview GSM Common Events
Basic Calling Process
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Subscriber status
IMSI Attach
IMSI Detach
MS busy
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Location Update
Originated by MS Location info stored in
SIM
MS monitor system
infooriginatelocation update once
the new LAC is
different from that in
SIM
HLR
VLR
MSC (old)
VLR
MSC (new)
LocationUpdate
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Location Update
Type Power on
IMSI ATTACH/DETACH
Location register
MS power on/off Normal location update
MS change LA
Periodic location update
Operator decide the period(timer)
Location update when time
out
V L RM S C
LA 2LA 1
ON
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Handover
Handover: Hand-over is a process that transfers a MS thatis in setting up or busy status to a new traffic channel
Why need handover
Keep and save the call in progress
Improve network service quality
Decrease call drop rate
Decrease congestion rate
Who will be involved
MSBTSBSCMSC
MSmeasure downlink radio signal level BTSmeasure uplink radio signal level and quality and send the
results to BSC
BSCevaluate and decision of HO
MSCroutes the call to the other MSC during Inter-MSC HO
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Handover classification
Reason:
PBGT
Signal level
Signal quality
Distance
Traffic
TA:
Synchronous
Asynchronous
Position:
Intra-cell
Inter-cell
Intra-BSC
Inter-BSC
Inter-MSC
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Cell selection and Reselection
After a MS is turned on, it will attempt to
contact a common GSM PLMN, so the
MS will select an appropriate cell, and
extract from it the parameters of thecontrol channel.
MS change its service
cell in IDLE state
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Authentication and Encryption
Triplet RAND: the question asked by the network side
Ki: stored in the SIM card and AUC in a very
confidential way
SRES: signed response. It is obtained through thecalculation of subscribers unique key parameter Ki.
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Authentication process
Execute authentication when MS registersetup calllocation update and
active/deactivate supplementary service
It is optional
A3 algorithm Mobile Terminal Network
A3 algorithm
Random number generatorKi RAND
SRES'
SRES
Ki
A3 algorithm
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Encryption process
Kc: Encryption key 64-bits (A8 algorithm) A5 algorithm (exclusive or)
It is optional.
Mobile Terminal Network
A8 algorithm
Random number
generatorKiRAND
Kc
Ki
Kc
A8 algorithm
A5
Frame No.(22-bit)
Kc (64-bit)
A5
S1
(114-bit)
S2 S1 S2
MS BTS
Frame No.(22-bit)
Kc (64-bit)
(114-bit) (114-bit) (114-bit)
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Content
GSM System Overview GSM Common Events
Basic Call ing Process
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Initialization
Initialization is a random access process
Ch request (RACH)
TA, access reason
ACTSDCCH
Imm Assign SDCCHAGCH
Initial messageSDCCH
Imm Assign SDCCHAGCH
ACT ACKSDCCH
MS BTS BSC
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Location update process
(1) MS moves from one BTS to another BTS
(2) Learn to the broadcasting information
(3)(4) MS sends the LU request to MSC-A.
(5) MSC-A sends the LU message to HLR(6) HLR sends back subscriber data.
(7)(8) Subscriber data registration in the VLR.
(9) Sending LU response message
(10) Notifying the original VLR to delete subscriber data.
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Outgoing call from MS to PSTN
(1) Random access channel.
(2) Set up signaling connection between
MS and MSC.
(3) Authentication and encryption and
enter the call setup starting phase.
(4) Service channel allocation(5) Send ringing to the called subscriber,
and send back the call connection
acknowledgment signal to MS.
(6)The called subscriber offhooks to reply,
in which case a response (connection)
message is sent to MS, thus entering the
ultimate call session phase.
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Incoming call from PSTN to MS
(1) Send MSISDN number to GMSC
(2) Requests HLR for the MSC address
(3) HLR requests VLR to assign MSRN
(4) GMSC re-search for routes to set up
connection to the visited MSC by MSRN.
(5)(6) MSC obtains related subscriber data(7)(8) MSC sends paging messages
(9)(10) The MS sends back the paging
response messages, then carries out the
same steps of (1), (2), (3), (4) as shown in the
above outgoing call flow till the mobile station
rings.
(11) The mobile subscriber offhooks to answer,
thus the response (connection) message is
sent back to the fixed network
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MS to MS call
(1) MS1 dials the phone number of MS2. BSS informs MSC1 of the call.
(2) MSC1 analyzes the phone number of MS2, finds out the HLR of MS2 and sends the route
application to HLR.
(3) HLR queries the current location information of MS2 and obtains MSRN from the MSC2/VLR2.(4) MSC2/VLR2 allocates the route information, that is, MSRN and submits the MSRN to the HLR.
(5) HLR sends the MSRN to the MSC1.
(6) MSC2 sets up the call with MSC2 according to the MSRN.
(7) MSC2/VLR2 sends the paging message to MS2.
(8) MSC2/VLR2 receives the message, indicating the access of MS2 is allowed.
(9) The call between MSC2 and MSC1 is set up.
(10) MSC1 sends the successful connection signal to MS1. MS1 and MS2 can talk over the phone.
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