SMART Communications, Inc.
SYSTRA
Introduction to GSMIntroduction to GSM
There was an increasing need for telecommunication services which prompted CEPT to specify a common mobile system for Western Europe later to be called GSM ( Global System for Mobile )
GSM later on spread throughout Eastern Europe, Africa, Asia and Australia.
GSM system primary requirements:1. There should be several network operators in each country to encourage
competition.2. The GSM system must be an open system.
3. The GSM network must be built without causing any major modifications to the existing Public Switched Telephone Networks ( PSTN ).
Advantages of GSMAdvantages of GSM
• Efficient use of radio frequencies and more tolerant to interference.• Quality of speech is better than analog systems.• Data transmission is supported.• Speech is encrypted and subscriber information security is guaranteed.• New services can be offered due to compatibility with ISDN system.• International roaming is possible.• Competition and large market results in lower prices.
Traffic Management
ObjectivesObjectives• Name the three subsystems of GSM.• Explain the mobility concept ( handover,
location update, paging ).• Describe how mobile originated and
mobile terminated calls are handled in GSM.
GSM subsystemsGSM subsystems
BSC
MSCVLR
GMSCHLR
NMS
MS
BSS
NSS
Air
A
O&M
A-bis
NSS Functions:1. Mobility Management2. Subscriber Data Handling3. Signalling ( towards other network elements )4. Call Control5. Charging6. Locating a subs for mobile terminated calls.
GSM subsystemsGSM subsystems
BSC
MSCVLR
GMSCHLR
NMS
MS
BSS
NSS
Air
A
O&M
A-bis
BSS Functions:1. Radio Path Control, BTS and TC control, Sync with MSC.2. Air and A interface signalling, Connection establishment.3. Mobility management, Speech Transcoding4. Collection of Statistical data
GSM subsystemsGSM subsystems
BSC
MSCVLR
GMSCHLR
NMS
MS
BSS
NSS
Air
A
O&M
A-bis
NMS Functions:1. Fault Management2. Configuration Management3. Performance Management
MSISDN = CC +NDC +SN
CC = Country CodeNDC = National Destination CodeSN = Subscriber #
IMSI = MCC + MNC + MSIN ( fixed 15 digits )
MCC = Mobile Country CodeMNC = Mobile Network CodeMSIN = Mobile Subscriber Identification #
LAI = MCC + MNC + LAC
MCC = Mobile Country Code (of visiting country)MNC = Mobile Network Code(of serving PLMN)LAC = Location Area Code
BTS1BSC
1
MSC
VLR1
MSCVLR2
LAI 1
MSB
First time Location Update (1)
Loc Up
HLR
IMSI RequestIMSI
HLR DBMSISDN IMSI VLR Address Sub. Data63+918+9499247 310+02+1234567890 vlr2 services
Loc Up + TMSI
Authen
BTS1BSC
1
MSC
VLR1MSC
VLR2
LAI 1
MSB
Generic Location Update
TMSI + LAIHLR
Loc Up + new TMSI
TMSI
IMSISecurity Info
Subscriber Info
UpdateDel olddata
Authentication
MS BSS MSC VLR HLR
LOCATION UPDATE REQUEST
REQUEST SUBS ID
SEND SUBS IDREQUEST SUBS INFO
SEND SUBS INFO
AUTHENTICATION
AUTHENTICATION RESPONSE
HLR UPDATE
PSTN BTS1BSC
1
MSC
VLR1
MSCVLR2
HLRHLR Enquiry
HLR DBMSISDN IMSI VLR Address Sub. Data63+918+9499247 310+02+1234567890 vlr2 services
VLR DBIMSI MSRN LAI DATA310+02+1234567890 1 services
LAI 1
MSRNPOOL
MSB
IMSI
A
B
Call Establishment (PSTNO-MT)
MSISDN
MSISDN (B)CC+ NDC + SN 63 918 9499247
IMSI = MCC+MNC+MSIN
MSRN = CC+NDC+SN
MSISDN
PSTN BTS1BSC
1
MSC
VLR1
MSCVLR2
LAI 1
MS
A
B
Call Establishment (MO-PSTNT)
MSISDN
MSISDN (A)CC+ NDC + SN 63 2 5113580HLR
VLR DBIMSI MSRN LAI Services 2 Speech
BTS1
BTS2BSC
2
BSC 1
MSC
VLR1
MSCVLR2
HLR
HLR Enquiry
LAI 1
LAI2
MSRNMS
MSB
IMSIB
C
Call Establishment (MO-MT)
MSISDN
MSISDN (C)CC+ NDC + SN 63 918 9499247
IMSI = MCC+MNC+MSIN
MSRN = CC+NDC+SN
MSISDN
HLR DBMSISDN IMSI VLR Address Sub. Data63+918+9499247 310+02+1234567890 vlr1 services
Handover (1)
MSC/VLR 1 MSC/VLR 2
BSC1 BSC2 BSC3
BTS4BTS3BTS2BTS1
PSTN
HLR
A
BMeasurement Report
Handover (2)
MSC/VLR 1 MSC/VLR 2
BSC1 BSC2 BSC3
BTS4BTS3BTS2BTS1
PSTN
HLR
B
A
I am OK
Handover (3)
MSC/VLR 1 MSC/VLR 2
BSC1 BSC2 BSC3
BTS4BTS3BTS2BTS1
PSTN
HLR
B
A
Measurement Report
Handover (4)
MSC/VLR 1 MSC/VLR 2
BSC1 BSC2 BSC3
BTS4BTS3BTS2BTS1
PSTN
HLR
B
A
I am OK
Handover (5)
MSC/VLR 1 MSC/VLR 2
BSC1 BSC2 BSC3
BTS4BTS3BTS2BTS1
PSTN
HLR
B
A
Measurement Report
Handover (6)
MSC/VLR 1 MSC/VLR 2
BSC1 BSC2 BSC3
BTS4BTS3BTS2BTS1
PSTN
HLR
B
A
I am OK
Handover (7)
MSC/VLR 1 MSC/VLR 2
BSC1 BSC2 BSC3
BTS4BTS3BTS2BTS1
PSTN
HLR
B
A
Review QuestionsReview Questions
1. Which is the following does not contain subscriber data?
a) HLRb) VLRc) MSCd) SIM
2. The format of IMSI is:
a) CC + NDC + SNb) MCC + MNC + MSINc) MCC + MNC + LACd) Operator specific 32 bit number
3. The three subsystem of GSM are:
a) NMS, PSTN, MSb) NMS, BSS, MSc) NSS, BSS, MSd) NSS, BSS, NMS
4. Which of the following will result in a HLR Enquiry?
a) PSTN originated – PSTN terminated callb) Mobile originated – PSTN terminated callc) PSTN originated – Mobile terminated calld) None of the above
5. A Location area
1. Is a geographical area under one BSC.2. Is equal to one MSC area.3. Is equal to one cell.4. Is identified by a unique Location Area Identity.
6. Which of the following combination best describes the BSS.
1. BSC, TC, BTS2. MS, BSC, BTS3. TC, Submultiplexer, BTS4. BSC, BTS, MS
7. The BSS
1. Is responsible for radio network control.2. Is located between Air and A interfaces.3. Gets synchronization from MSC4. All of the above.
8. Name two reasons for performing a handover.
9. Name 4 different handover cases.
Transmission
ObjectivesObjectives• Differentiate between physical and logical
channels.• List and describe the twelve different
types of logical channels and their functions.
• Describe how air interface properties affect the transmission of speech between MS and network and explain GSM solutions to these problems.
• Describe the main function of transcoders.• List 3 BSC/BTS connections.
ACCESS METHODSFDMA CDMA TDMAFrequency Division Code Division Time Division
f1
f2
f3
TDMA is usedin GSM system
FRAME STRUCTURE1 TDMA Frame = 8 TDMA Time Slots
0 1 2 3 4 5 6 7
4.615 ms
Tail Data F Training DataF TailOr Speech
Flag
3 000
57 1 26 1 57 3
Burst 148 bits
156.25 bits 0.577 ms
Basic TDMA frame, timeslot and burst structure
F D T T T T T TS D T T T T T TB D T T T T T TB D T T T T T TB D T T T T T TB D T T T T T TC D T T T T T TC D T T T T T TC D T T T T T TC D T T T T T TF D T T T T T TS D T T T T T TC D A T A T A TC D T T T T T TC D T T T T T TC D T T T T T T
TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS74.615 ms
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1 Frame (Downlink - BTS transmit) 1 carrier = 200 kHz
F = FCCHS = SCHB = BCCHC = PCH or AGCHD = SDCCHA = SACCHT = TCH
R D T T T T T TR D T T T T T TR D T T T T T TR D T T T T T TR D T T T T T T R D T T T T T TR D T T T T T TR D T T T T T TR D T T T T T TR D T T T T T TR D T T T T T TR D T T T T T TR D A I A I A IR D T T T T T TR D T T T T T TR D T T T T T T
TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS74.615 ms
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1 Frame(Uplink - Mobile transmit) 1 carrier = 200 kHz
R = RACHA = SACCHT = TCH
LOGICAL CHANNELSOn every physical channel, a number oflogical channels are mapped. Each logical channel is used for a specific purpose.
11 Logical Channels in the GSM system:2 are used for Traffic9 are used for Control Signaling
LOGICAL CHANNELSTRAFFIC CHANNELS (TCH)
Full Rate ChannelHalf Rate Channel
CONTROL CHANNELS (with horrible abbreviations!)Broadcast Channels (BCH)
Frequency Correction Channel (FCCH)Synchronization Channel (SCH)Broadcast Control Channel (BCCH)
Common Control Channels (CCCH)Paging Channel (PCH)Random Access Channel (RACH)Access Grant Channel (AGCH)
Dedicated Control Channels (DCCH)Stand alone Dedicated Control Channel (SDCCH)Slow Associated Control Channel (SACCH)Fast Associated Control Channel (FACCH)
Hey! Don’t shoutat me, lower your
power...
BROADCAST CHANNELSall downlink!
FCCH
SCH TDMA#…BSIC...
BCCH
Hey. I’m aGSM xmitter!
GSM?
GSM!!!
LA…neigbors…cell info…max power...
Ok…ok
COMMON CONTROL CHANNELS
PCH downlink only
Hello! You have a call.
RACH uplink only
Hello! I have to setup a call.
I need SDCCH.
AGCH downlink only
Ok. Use SDCCH.
DEDICATED CONTROL CHANNELSuplink and downlink
SDCCH
SACCHtiming advanceMS power
FACCH
handover
On SDCCH:-call set up signaling-location updating-periodic registration-IMSI attach/detach-SMS-facsimileetc…..
On SACCH-mobile transmits signalstrength on ncell quality
Don’t shout at me/I can’t hear you.
FADINGSsignal level (dB)
log (distance)
global mean value
log normal fadinglocal mean valueslow fadingshadowinglong-term fading
rayleigh fadingfast fadingshort-term fading
so many namesto make life
worst!
FAST FADINGsignal level (dB)
log (distance)
• present due to the fact that the mobile antenna is lowerthan the surrounding structures such as trees and buildings. ( Multipath propagation )• peak-to-peak distance is ~ lambda/2 (in GSM ~ 17 cm)• affects the signal quality and can lead to signal level belowthe receiver sensitivity.
SOLUTIONS:• use more power at the transmitter (providing a fading margin).• use space diversity.
SLOW FADINGsignal level (dB)
log (distance)
• if we smooth out the fast fading, the signal variationreceived is called the “local mean” or the slow fading.• caused by obstructions near the mobile such asbuildings, bridges and trees and this may cause a rapid change of the local mean (in the range of 5 to 50 meters).( Shadowing )• because slow fading reduces the average strengthreceived, the total coverage from the transmitter is reduced.
SOLUTION:• fading margin must be used.
Concept of Multiplexing
Network Planning
ObjectivesObjectives• List the main steps of the radio network
planning process.• Define the main radio network
parameters.• Explain how frequencies are reused.
THE CELL PLANNING PROCESS
Traffic and Coverage Analysis
Nominal Cell Plan
Surveys
System Design
Implementation
System Tuning
TRAFFIC DATA
Based on ERICSSON
Initial PlanningSystem Growth
THE CELL PLANNING PROCESS
Traffic and Coverage Analysis
Nominal Cell Plan
Surveys
System Design
Implementation
System Tuning
TRAFFIC DATA
Based on ERICSSON
Initial PlanningSystem Growth
geographical area.expected need ofcapacity.
cell pattern on a map.coverage & interferenceprediction.
visit sites whereradio equipmentwill be placed.perform radiomeasurements.dimensioning of the
rbs equipment, BSC & MSC.CDD is filled out.
system installation,commissioningand testing are performed.
continually evaluated todetermine how well it meetsthe demand.
CHANNEL PLANNING
CELL PLANNINGThe simplest solution to acell planning problem is tohave one cell and use allavailable carriers in that cell.
1 cell24 carriers
f1 - f24
CELL PLANNINGA cellular system is basedupon re-use of the same setof carriers, which is obtainedby dividing the area needingcoverage into smaller areas (cells) which together formclusters.
f1 f1
f1f1
24
24
24
24
RE-USE PATTERNSRe-using the carrier frequencies according to well-provenre-use patterns , neither co-channel interference nor adjacent channel interference should become a problem,if the cells have homogenous propagation properties forthe radio waves.
The re-use patterns recommendedfor GSM are:
• 4/12 pattern• 3/9 pattern
4/12 means that there are 4 three sector sites supporting 12 cells
4/12 RE-USE PATTERN
D3
D2
D1
A1
A2
A3
C1
C2
C3
B1
B2
B3
D3
D2
D1
A1
A2
A3
C1
C2
C3
B1
B2
B3
D3
D2
D1
A1
A2
A3
C1
C1
C3
B1
B2
B3
D3
D2
D1
D3
D2
D1
B1
B2
B3
B1
B2
B3
C2
3/9 RE-USE PATTERN
C1
C2
C3
A1
A2
A3
B1
B2
B3
C1
C2
C3
A1
A2
A3
B1
B2
B3
C1
C2
C3
A1
A2
A3
B1
B2
B3
C1
C2
C3
A1
A2
A3
B1
B2
B3
C1
C2
C3
A1
A2
A3
B1
B2
B3
Thank you very much . . .
from Smart Communicationsfrom Smart Communications