263223518 cellular communication

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Cellular Communication


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Cellular systems generations 1G rst generation' – voiceoriented systems based on

analog technology( e96: 2dvanced Mobile hone.ystems &2M.' and cordless systems

;G &second generation' voiceoriented systems basedon digital technology( more e


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7re?uency reuse is a method used by service $roviders to im$rove

the e


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Network Cells the entire network coverage area is divided into cells

based on the $rinci$le o% %re?uency reuse a cell @ basic geogra$hical unit o% a cellular network(

is the area around an antenna where a s$eci#c

%re?uency range is used( is re$resented gra$hically asa he9agonal sha$e, but in reality it is irregular insha$e

when a subscriber moves to another cell, the antennao% the new cell takes over the signal transmission

a cluster is a grou$ o% adiacent cells, usually ) cells(no %re?uency reuse is done within a cluster

the %re?uency s$ectrum is divided into subbands andeach subband is used within one cell o% the cluster

in heavy tra


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Network cells &;'


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Ty$es o% cells macrocell – their coverage is large &a$ro96 B

miles in diameter'( used in remote areas, high$ower transmitters and receivers are used

microcell – their coverage is small &hal% a milein diameter' and are used in urban Aones( low$owered transmitters and receivers are usedto avoid inter%erence with cells in another

clusters $icocell – covers areas such as building or a

tunnel


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ther cellular conce$ts handover @ moving a call %rom one Aone &%rom

the transmitterreceiver %rom one Aone' toanother Aone due to subscriber4s mobility

roaming @ allowing the subscriber tosendDreceive calls outside the service$rovider4s coverage area


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Multi$le access schemes

Frequency Division Multiple

Access

when the subscriber entersanother cell a uni?ue %re?uencyis assigned to him( used inanalog systems

Time Division Multiple

Access

each subscriber is assigned atime slot to sendDreceive a databurst( is used in digital systems

Code Division Multiple

Access

each subscriber is assigned acode which is used to multi$lythe signal sent or received bythe subscriber


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The control channel this channel is used by a cellular $hone to

indicate its $resence be%ore a %re?uencyDtimeslotDcode is allocated to him


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Cellular services voice communication

.hort Messaging .ervice &.M.'

Multimedia Messaging .ervice &MM.' Global ositioning .ystem &G.'

ireless 2$$lication rotocol &2' – to accessthe >nternet


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Cellular network com$onents


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Cellular network com$onents &;' 0T. &0ase Transceiver .tation' – main com$onent o%

a cell and it connects the subscribers to the cellularnetwork( %or transmissionDrece$tion o% in%ormation it

uses several antennas s$read across the cell 0.C &0asic .tation Controller' – it is an inter%ace

between 0T.s and it is linked to 0T.s by cable ormicrowave links( it routes calls between 0T.s( it isalso connected to the M.C

M.C &Mobile .witching Center' – the coordinator o%a cellular network, it is connected to several 0.Cs,it routes calls between 0.Cs( links the cellularnetwork with other networks like .TN through #ber

o$tics, microwave or co$$er cable


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Com$onents o% a cellular $hone

&M.- – Mobile .ubscriber -nit' radio transceiver – low $ower radio transmitter and

receiver

antenna, usually located inside the $hone

control circuitry – %ormats the data sent to and %romthe 0T.( controls signal transmission and rece$tion

manmachine inter%ace – consists %rom a key$ad anda dis$lay( is managed by the control circuitry

.ubscriber >dentity Module &.>M' – integrated circuitcard that stores the identity in%ormation o% subscriber

battery, usually 5iion, the $ower unit o% the $hone


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.etting u$ a call $rocess when $owered on, the $hone does not have a%re?uencyD time slotDode assigned to it yet( so itscans %or the control channel o% the 0T. and $icksthe strongest signal

then it sends a message &including its identi#cationnumber' to the 0T. to indicate its $resence

the 0T. sends an acknowledgement message backto the cell $hone

the $hone then registers with the 0T. and in%ormsthe 0T. o% its e9act location

a%ter the $hone is registered to the 0T., the 0T.assigns a channel to the $hone and the $hone is

ready to receive or make calls


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Making a call $rocess the subscriber dials the receiver4s number and

sends it to the 0T.

the 0T. sends to its 0.C the >8, location and

number o% the caller and also the number o% thereceiver

the 0.C %orwards this in%ormation to its M.C

the M.C routes the call to the receiver4s M.C

which is then sent to the receiver4s 0.C and thento its 0T.

the communication with the receiver4s cell $honeis established


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=eceiving a call $rocess when the receiver4 $hone is in an idle state it

listens %or the control channel o% its 0T.

i% there is an incoming call the 0.C and 0T. sends

a message to the cells in the area where thereceiver4s $hone is located

the $hone monitors its message and com$aresthe number %rom the message with its own

i% the numbers matches the cell $hone sends anacknowledgement to the 0T.

a%ter authentication, the communication isestablished between the caller and the receiver


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Global .ystem %or Mobile

Communication &G.M'


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G.M characteristics $revious standard in cellular communication

were restrictive

G.M – global digital standard %or cellular $honesthat oered roaming %acility

#rst named Grou$e .$ecial Mobile and used inEuro$e( then usage e9tended to othercontinents

G.M o$erate in %re?uency bands: !++MFA, 1++MFA, 1!++ MFA

G.M $rovides voice and data services


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.ubscriber >dentity Module &.>M'

card .>M – a memory card &integrated circuit' holding

identity in%ormation, $hone book etc6

G.M system su$$ort .>M cards

other systems, like C8M2 do not su$$ort .>Mcards, but have something similar called =e-sable >denti#cation Module &=->M'


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>nternational Mobile .ubscriber

>dentity &>M.>' key >M.> – a 1digit uni?ue number $rovided by the

service $rovider and incor$orated in the .>Mcard which identi#es the subscriber

>M.> enables a service $rovider to link a $honenumber with a subscriber

#rst " digits o% the >M.> are the country code


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Tem$orary Mobile .ubscriber

>dentity &TM.>' key TM.> – is a tem$orary number, shorter than the

>M.>, assigned by the service $rovider to the$hone on a tem$orary basis

TM.> key identi#es the $hone and its owner inthe cell it is located( when the $hone moves toa dierent cell it gets a new TM.> key

as TM.> keys are shorter than >M.> keys they aremore e key are used %or securing G.M networks


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G.M architecture


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0ase .tation .ubsystem &0..'


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F5=, J5= and E>= registers Fome 5ocation =egister &F5=' is a database

maintained by the service $rovider containing$ermanent data about each subscriber &i6e6 location,activity status, account status, call %orwarding$re%erence, caller identi#cation $re%erence'

Jisitor 5ocation =egister &J5=' – database that storestem$orary data about a subscriber( it is ke$t in theM.C o% the o% the area the subscriber is located in(

when the subscriber moves to a new area the newM.C re?uests this J5= %rom the F5= o% the old M.C

E?ui$ment >dentity =egister &E>=' – database locatednear the M.C and containing in%ormation identi%yingcell $hones


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2uthentication Center &2uC' 1st level security mechanism %or a G.M cellularnetwork

is a database that stores the list o% authoriAed

subscribers o% a G.M network it is linked to the M.C and checks the identity o%

each user trying to connect

also $rovides encry$tion $arameters to secure a

call made in the network


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G.M Mobile .witching Center

&M.C' is a switching center o% the G.M network(coordinates 0.Cs linked to it


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G.M Channels


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G.M 2ccess .cheme and

Channel .tructure G.M uses 78M2 and T8M2 to transmit voice and data

the u$link channel between the cell $hone and the0T. uses 78M2 and a s$eci#c %re?uency band

the downlink channel between the 0T. and the cell$hone uses a dierent %re?uency band and the T8M2techni?ue

there is su


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G.M u$linkDdownlink %re?uency

bands used

GSMFrequency

band

Uplink/BTSTransmit

Donlink/BTS!eceive

!++ MFA !"!B+ MFA !+!1 MFA

1++ MFA 1+1+ MFA 1)1+1) MFA

1!++ MFA 1!"+1!!+ MFA 1+1!1+ MFA


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G.M u$linkDdownlink %re?uency

bands u$link and downlink take $lace in dierent time

slots using T8M2

u$link and downlink channels have a bandwidtho% ; MFA

these channels are %urther s$lit u$ in a 1;*carrier %re?uencies &1 control channels and therest as tra


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G.M Control Channel is used to communicate management data

&setting u$ calls, location' between 0T. and thecell $hone within a G.M cell

only data is e9changed through the controlchannel &no voice' a s$eci#c %re?uency %rom the %re?uency band

allocated to a cell and a s$eci#c time slot areallocated %or the control channel &beacon

%re?uency'( a single control channel %or a cell G.M control channels can have the %ollowing

ty$es: broadcast channel common control channel dedicated control channel


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0roadcast Channel ty$e o% control channel used %or the initialsynchroniAation between the cell $hone and the0T.

is com$osed %rom: 7re?uency Correction Channel &7CCF' – is com$osed %rom

a se?uence o% 1* Aeros transmitted by the 0T. .ynchroniAation Channel &.CF' – %ollows the 7CCF and

contains 0T. identi#cation and location in%ormation

0roadcast Control Channel &0CCF' – contains the%re?uency allocation in%ormation used by cell $hones toadLust their %re?uency to that o% the network( iscontinuously broadcasted by the 0T.


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Common Control Channels ty$e o% control chan6 used %or call initiation is com$osed o%:

aging Channel &CF' – the 0T. uses this channel toin%orm the cell $hone about an incoming call( the cell

$hone $eriodically monitors this channel =andom 2ccess Channel &=2CF' – is an u$link channel

used by the cell $hone to initiate a call( the cell $honeuses this channel only when re?uired( i% ; $hones try toaccess the =2CF at the same time, they cause

inter%erence and will wait a random time be%ore they tryagain( once a cell $hone correctly accesses the =2CF, 0T.send an acknowledgement

2ccess Grant Channel &2GCF' – channel used to set u$ acall( once the cell $hone has used CF or =2CF to receive

or initiate a call, it uses 2GCF to communicate to the 0T.


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8edicated Control Channels control channel sed to manage calls is com$rised %rom:

.tandalone 8edicated Control Channel &.8CCF' – used

along with .2CCF to send and receive messages( relayssignalling in%ormation .low 2ssociated Control Channel &.2CCF' – on the

downlink 0T. broadcasts messages o% the beacon%re?uency o% neighboring cells to the cell $hones( on the

u$link 0T. receives acknowledgement messages %romthe cell $hone

7ast 2ssociated Control Channel &72CCF' – used totransmit unscheduled urgent messages( 72CCF is %asterthan .2CCF as it can carry + messages $er second,while .2CCF an caryy only *6


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Tra


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G.M Call rocessing


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>nitialiAing a call &;'


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Making a call16 when thee $hone needs to make a call it sends an accessre?uest &containing $hone identi#cation, number' using=2CF to the 0T.( i% another cell $hone tries to send anaccess re?uest at the same time the messages might get

corru$ted, in this case both cell $hones wait a random timeinterval be%ore trying to send again

;6 then the 0T. authenticates the cell $hone and sends anacknowledgement to the cell $hone

"6 the 0T. assigns a s$eci#c voice channel and time slot to

the cell $hone and transmits the cell $hone re?uest to theM.C via 0.C

*6 the M.C ?ueries F5= and J5= and based on the in%ormationobtained it routes the call to the receiver4s 0.C and 0T.

6 the cell $hone uses the voice channel and time slot

assigned to it by the 0T. to communicate with the receiver


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Making a call &;'


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=eceiving a call16 when a re?uest to deliver a call is made in the network, theM.C or the receiver4s home area ?ueries the F5=( i% the cell$hone is located in its home area the call is trans%erred to thereceiver( i% the cell $hone is located outside its home area, theF5= maintains a record o% the J5= attached to the cell $hone

;6 based on this record, the M.C notes the location o% the J5=and indicated the corres$onding 0.C about the incoming call

"6 the 0.C routes the call to the $articular 0T. which uses the$aging channel to alert the $hone

*6 the receiver cell $hone monitors the $aging channel

$eriodically and once it receives the call alert %rom the 0T. itres$onds to the 0T.

6 the 0T. communicates a channel and a time slot %or the cell$hone to communicate

B6 now the call is established


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=eceiving a call &;'


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G.M .ecurity ersonal >denti#cation Number

&>N'

-ser 2uthentication TM.>based .ecurity


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ersonal >denti#cation Number

&>N' the >N is stored on the .>M card o% the cell$hone

when the cell $hone is turned on, the .>M checks

the >N( in case o% " consecutive %aulty >N in$utsa -K &ersonal -nblocking Key' is asked %or

in case o% 1+ %aulty -K in$uts, the .>M is lockedand the subscriber must ask a new .>M

this security measure is within the cell $hone andthe service $rovider is not involved


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-ser 2uthentication a mechanism %or encry$ting messages in a G.M

network the network sends random data to the cell $hone

&=2N8' each cell $hone is allocated a secret key &K>' using =2N8 and K> and the 2" encry$tion

algorithm the cell $hone generates a signed result&.=E.' which is then sent to the network

a similar $rocess takes $lace in the network whichgenerates a signed result s$eci#c to the cell$hone

the network com$ares its .=E. with the .=E.generated by the $hone and in case o% a matchthe cell $hone is connected to the network


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TM.>Key 0ased .ecurity is most used in a G.M cellular network a TM.> key $rovides a tem$orary identi#cation to

a cell $hone and is $rovided by the network u$on

authentication a TM.> key kee$s changing according to the

location o% the cell $hone this way $reventingunauthoriAed access to a channel and $reventingintruder %rom tracing location

the ma$$ing between >M.> and TM.> keys ishandled by the J5=

>.M> are used only when the .>M is used %or the#rst time


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.-0M>TTE8 0:M22NK .F2=M2

263223518 cellular communication

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