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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.
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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
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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
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GSM Network Structure
GSM service areaPLMN service areaMSC service areaLocation areaCell
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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
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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
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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
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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}
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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.
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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
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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
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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
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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.
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b1
b2
b3
120 O CELLS 3 ANTENNASOMNI CELL 1 ANTENNA a3a1
a6a5
a4
a2
60 O CELLS 6 ANTENNAS
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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.
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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
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Mobile Station : SIM + Mobile set
Base Station Subsystem :BTS+BSC
Network Subsystem : MSC,AuC ,EIR,VLR,HLR
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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
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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
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BASE TRANSCEIVER STATION
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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
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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
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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
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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
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• 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
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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
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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.
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LOGICAL CHANNELS
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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
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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
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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
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Authentication in GSM
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Key generation and Encryption
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