SYSTRA

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.


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


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


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


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

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