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Global System for Mobilecommunications ( 1984 )

Globally accepted standard for digitalcellular communication.

Use narrowband TDMA (time divisionmultiple access) technique fortransmitting signal

GSM makes use of Frequency DivisionMultiple Access ( FDMA) and Time

Division Multiple Access ( TDMA ).It provides fundamentalrecommendation and requirement formobile set, network system. So, thereis open interface.



Lo w- cos t mobile set s and bas e stat ions (B Ss )

Hig h- qualit y s pe ec h

Imp ro ved s pec tr um effi cienc y.

In ter nat ional roaming.

Supp or t f or n ew s erv ic es .

Co mpati bility w ith Int egr at ed S erv ic es Dig ital Net wor k(IS DN) an d ot her t eleph one c ompany ser vic es .

Standar di za tion of the air an d t he net wor k in ter fac es .

Security



CDMA

GSM

TDMA

PHS(IP-Based)

64 Kbps

GPRS

115 Kbps

CDMA 1xRTT

144 Kbps

EDGE

384 Kbps

cdma20001X-EV-DV

Over 2.4 Mbps

W-CDMA(UMTS)

Up to 2 Mbps

2G2.5G

2.75G 3G

1992 - 2000+2001+

2003+

1G

1984 - 1996+

2003 - 2004+

TACS

NMT

AMPS

GSM/GPRS

(Overlay)115 Kbps

9.6 Kbps

9.6 Kbps

14.4 Kbps / 64 Kbps

9.6 Kbps

PDC

Analog Voice

Digital Voice

Packet Data

IntermediateMultimedia

Multimedia

PHS

TD-SCDMA

2 Mbps?

9.6 Kbps

iDEN

(Overlay)

iDEN

Source: U.S. Bancorp Piper Jaffray



GSM Network Structure

GSM service areaPLMN service areaMSC service areaLocation areaCell



Functions Particular to GSM

Frequ ency B and89 0-915M Hz – u pli nk93 5-960M Hz – d ownlink

Han dover

Power Con trol– 30dB d yna mic range, step s of 2dBDisc on tinuous Transm is sion (DTX )Synchron ization



Cellular concept

In terference problem

In terference and syst em ca paci ty

Fre quency r euse p att ern

Trunki ng effici ency

Ce llular envi ronme nt

Ca paci ty co nsi derations

Future t rends



Cel lu lar co mmu ni cation mea ns

co mmun icatio n b\w ce lls.Whole geo gra phi cal area is con verted

into smal l cel l and se rved by on e BT S.Cel lu lar network comp rise s nu mber

of he xag ona l cel lsClu ster : Col le ct ion of cellAdvan tage s of cel l st ru ct ures:

hig he r ca paci ty , hi ghe r numb er of usersless transm issio n po wer ne ede dmore rob ust, decen tra lize dbase statio n de al s wit h interfere nce , t ra nsmissi on areaetc. lo call y

Probl ems:fixed net work ne ede d for the base statio nshan do ver (chan gi ng from one ce ll to an othe r) ne cessa ryinte rf ere nce with other ce lls

CELLULARCOMMUNICATION



TYPES OFCELL

Macro cells(3 to 35 km):

Lar ge c ell s which se rv esrem ote a nd seg re ga ted a re as.

Microcells(0,1 to 1 km):

- Pi co c ells (0 ,0 1 t o 1km )

- Nano cell s(1m to 10 m)

{T HESE CELL AR E USED AT D ENSEPOPU LATED AR EA}



Se lectiv e c el ls : Cells

having particular coverage .Umbrella cell : Cell that islocated very high off the ground.Mainly used between mountainsand high buildings. It support allsame BTS service when they failto support mobile station. So, MSget proper signal.



Frequency Re-Use Distance

The K factor or the cluster size

Cellular coverage or Signal to interference ratio

Sectoring

I wish I could increase capacity

without adding NEW BTS!What can I do?

The need:Optimum spectrumusageMore capacity

High quality of serviceLow cost

Network capacity at required QoSwith conventional frequency plan

Subscriber growthTime

Out of Capacity!!!

LIMITED FREQUNCY BAND FOR COMMUNICATION LEADS TO LESSCAPACITY AND POOR QUALITY DUE TO INTERFARANCE

SOLUTION ACHIEVED BY



The K factor and Frequency Re-UseDistance

i

j

1

2

34

5

6

7

Frequency re-use distance is based on the cluster size K

The cluster size is specified in terms of the offset of the center of acluster from the center of the adjacent cluster

K = i2 + ij + j 2

K = 2 2 + 2*1 + 1 2

K = 4 + 2 + 1

K = 7

D = √ 3K * R

D = 4.58R

12

35

6

7

D

R



Uplink and downlink

Up Link (Trans) : When signaltravel from MS to BTS.

Down Link (Receive) :When signal travel from BTS to MS .

For frequency band (900MHz)UPLINK – 890-915MHz DOWNLINK –935-960MHz

Duplex pacing – 45MHz



Co channel interference

Interference between same frequency transmitted by twodifferent BTS.

Occurs when the same carrier frequency reaches the singlereceiver.

Plan the cell structure in such a way that two or more BTShaving same frequency doesn’t interfere with each other.Hence there is no co-channel interference.



b1

b2

b3

120 O CELLS 3 ANTENNASOMNI CELL 1 ANTENNA a3a1

a6a5

a4

a2

60 O CELLS 6 ANTENNAS



Principal Of Sectorization

Omni Directional Cells

120 degree Sectors

60 Degree sectorsEach Sector in a Site has its own allocation of Radio Carriers.

AdvantageBy frequent reuse of frequency more capacitycan be achieved.



Typical 2G Architecture

BTS

BSCMSC/VLR

HLRBSC

GMSC

CO

BSC

BSCMSC/VLR

CO

PSTN

PLMN

CO

Tandem Tandem

SMS-SC

PSDN

BT S — Base T ransc ei ver St atio nBSC — Base Sta tion Con trol ler

MSC — Mo bi le Swi tc hi ng Cen terVL R — Vi sitor Locat ion Reg isterHL R — Home Locatio n Reg ister



Mobile Station : SIM + Mobile set

Base Station Subsystem :BTS+BSC

Network Subsystem : MSC,AuC ,EIR,VLR,HLR



Permanent SIM Card DataIM card t ype

C card ident ifi cat ion - serial number of cardIM serv ice t able - lis t of servic es s ubsc ribed to

MSI

INUK - pers onal unbloc king key

ut henticati on k ey Ki and A3, A5, and A8 al gorithm s

Dynamic SIM Card Data•Lo cation In for mat ion

– TMS I, L AI, LA u pdat e t imer , u pdat e s tatu s• Ciphe ri ng k ey Kc an d s eq uenc e numb er• BCC H in for matio n

– Lis t of c ar rier f re quen ci es f or c ell selec tio n du ring ha ndov er and c allsetup•Lis t o f bl oc ked P LMNs•HPLMN sear ch

– per iod of time in w hic h MS s ear che rs for home netw or k bef or e itchec ks fo r othe r net wor ks



MS Services• Full rate voice service - 13kb/s• Enhanced full rate voice service - 12.5kb/s• Half rate speech service - 6.5kb/s• Transparent data rate service – 14.4kb/s, 9.6kb/s, 4.8kb/s, 2.4kb/s• Short Message Service (SMS) – Maximum of 160 characters



BASE TRANSCEIVER STATION



Functions of BTS

• Enc oding , en cry ption , mu ltiplex in g, modulat ion, and radio signal tr ans mis sio n• Dec od ing, dec rypti on, demult iplex ing and demodul ation of r ec eiv ed r adiosigna ls

• Eac h B TS s erv es a single ce ll• Suppor t fo r full- and half- rat e s pe ec h c odec• Cont rol of f re quenc y hopp ing• Rand om ac cess det ec tion• Timing adv anc e• Uplink ra dio c hannel meas ure ments

Functions of the BSC

• RR manag ement for BTS s unde r cont ro l• Int erc ell ha ndov er•Alloc ates a c ha nnel for t he dur ation of a call• Reallo cation of fr eq uenc ies among B TSs• Power m anage ment• Time and fr equ enc y s ync s igna l for BTS s• Time delay meas ur emen ts of re ceiv ed signal fr om MS• Per for ms t runk ing to r educ e line c apac ity bet wee nBSS an d MS C• Pro vides in ter fac e t o O MC



Functions of MSC

• Paging• Call management• Dynamic resource allocation• Location registration• IWF with different networks• Handover management• Billing• Encryption

• Gateway to SMS centre•Switching call, controlling call, and logging calls



Data Stored in VLR

• IMSI• MSISDN• MSRN• TMSI• LA where MS is located• Supplementary serviceparameters• Authentication key, query and

response from AuC• ID of current MSC

Data Stored in HLR

• Permanent– IMSI– MSISDN– MS category - payphone or not– Roaming restrictions– Supplementary servicesparameters– Closed User Group (CUG)

membership– Authentication key Ki Data• Temporary– LMSI (Local MS ID)– RAND/SRES and Kc– MSRN

– VLR address– MSC address– Roaming restrictions– SMS messages waiting



Authentication Center (AUC) - Protects against intruders in air interface-

Maintains authentication keys and algorithms andprovides security triplets ( RAND,SRES,Kc)- Generally associated with HLR

Equipment Identity Register (EIR)- Database that is used to track handsets using

the IMEI (International Mobile Equipment Identity)- Made up of three sub-classes: The White List, The

Black List and the Gray List- Only one EIR per PLMN



• Three areas of responsibility – Subscription management – Network operation and maintenance – Mobile equipment management• Network elements of OSS

– Operations and Maintenance Centre (OMC) – Authentication Centre (AuC) – Equipment Identity Register (EIR)

Operation subsystem Function

OM C F un ct io ns

• Alarm Handling• Fault Management• Performance Management• Configuration Management• Software Version Management• Network Statistics Data Collection

• Network Status Control



Network Management Centre• Single NMC per network• Traffic management for whole network• High-level alarm handling• Manages unstaffed OMC• Provide network planners with network interface and data collectiontool



Channels On Air Interface

Physical Channel

Logical Channel

Physical Channel

Physical channel is the medium overwhich the information is carried.

Logical Channel

Logical channels consists of theinformation carried over the PhysicalChannel.



LOGICAL CHANNELS



de

LOGICAL CHANNELS

TRAFFIC SIGNALLIN

G

FULL RATEBm 22.8 Kb/S

HALF RATELm 11.4 Kb/S

BROADCAST COMMON CONTROL

FCCH SCH BCCH

PCHRACH

AGCH

SDCCH SACCH

DEDICATED

FACCH

DOWN LINK ONLY

UPLINK ONLY

CH -- FREQUENCY CORRECTION CHANNELH -- SYNCHRONISATION CHANNELCH -- BROADCAST CONTROL CHANNELH -- PAGING CHANNELCH -- RANDOM ACCESS CHANNELCH -- ACCESS GRANTED CHANNELCCH -- STAND ALONE DEDICATED CONTROL CHANNELCCH -- SLOW ASSOCIATED CONTROL CHANNEL

CCH -- FAST ASSOCIATED CONTROL CHANNEL



Location update from the mobile

RACH send channel request

AGCH receive SDCCH

SDCCH authenticate

SDCCH switch to cipher mode

SDCCH request for location updating

SDCCH authenticate response

SDCCH cipher mode acknowledge

SDCCH allocate TMSI

SDCCH acknowledge new TMSI

SDCCH switch idle update mode



Call establishment from a mobile

RACH send channel request

AGCH receive SDCCH

SDCCH do the authentication and TMSI allocation

SDCCH require traffic channel assignment

SDCCH send call establishment request

SDCCH send the setup message and desired number

FACCH switch to traffic channel and send ack (steal bits)

FACCH receive alert signal ringing sound

FACCH acknowledge connect message and use TCH

TCH conversation continues

FACCH receive connect message



Authentication in GSM



Key generation and Encryption

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