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LiU-ITN-TEK-A--13/054--SE

Exploiting Tracking Area List

Concept in LTE NetworksMohsin Nawaz

2013-10-04


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LiU-ITN-TEK-A--13/054--SE

Exploiting Tracking Area List

Concept in LTE NetworksExamensarbete utfrt i Elektroteknik

vid Tekniska hgskolan vid

Linkpings universitet

Mohsin Nawaz

Examinator Di Yuan

Norrkping 2013-10-04


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Upphovsrtt

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Mohsin Nawaz


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Exploiting Tracking Area List ConceptIn Long Term Evolution Networks

Mohsin Nawaz

Wireless Networks and ElectronicsDepartment of Science and Technology(ITN)Linkping ni!ersity" Sweden


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Ab tract

Signaling o!erhead d#e to tracing and paging ser E$#ipments (Es) has always %een a

concern for the network operators& Tracking 'rea (T') is a logical gro#ping of cells in Long

Term E!ol#tion (LTE) networks& T's manage and locate Es in a LTE network& ' well known

performance consideration is that of Tracking 'rea pdate (T') o!erhead !ers#s paging

o!erhead&

LTE gi!es more flei%ility in terms of T' config#ration compared to pre!io#s generations& This

flei%ility is offered %y means of Tracking 'rea List (T'L)& T'L is epected to o!ercome certain

limitations of the con!entional T' scheme& ow to eploit this flei%ility to ha!e a T' design

that red#ces signaling o!erhead remains an open iss#e& This thesis eploits the T'L concept in

LTE networks in order to e!al#ate its performance& 'n approach to design T'L #sing E traces

is presented& The e!al#ation of its performance is done %y comparing it with the con!entional

T' and the r#le of th#m% T'L designs& The cost of collecting E traces #sing T'L is taken into

consideration when e!al#ating performance of E*trace %ased T'L design&


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Acknowled ent

+irst of all" I wo#ld like to thank 'lmighty 'llah for gi!ing me strength to accomplish this work&

I am also !ery gratef#l to my family who s#pported me d#ring this phase&

I am especially !ery pleased to show my gratit#de to my thesis s#per!isor Sara ,odarres

-a.a!i& I am !ery gratef#l for the effort she p#t thro#gho#t and witho#t her pro!ision it wo#ld

not ha!e %een accomplished&

I wo#ld also like to thank professors at ITN department at Linkping ni!ersity for the

technical s#pport they pro!ided thro#gho#t my ,asters/ degree which helped me d#ring my

thesis work&


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Techncal Defnton

The following terms are #sed thro#gho#t this thesis report&

1stGeneration (1G)

In early 0123/s S la#nched the 0 stgeneration of cell#lar network system called 'd!ance ,o%ile 4honeSystem (',4S)& It was an analog#e system %ased on fre$#ency mod#lation technology& It wasdesigned for only !oice applications&

2nGeneration (2G)

In 0110" the 5ndgeneration of cell#lar network systems %ased on circ#it switching was la#nched and

called 6lo%al System for ,o%ile 7omm#nication (6S,)& It was the first digital technology %asedsystem which also pro!ided data ser!ice along with !oice& It also laid fo#ndation to f#rther coming5&86 (64-S)" 5&986 (ED6E) and :6 networks&

!rGeneration (!G)

In 5330" the :rdgeneration of cell#lar network systems %ased on packet switching was la#nched& Thereare two standards that are termed as :6& These incl#de ni!ersal ,o%ile Telecomm#nications System(,TS) and 7D,'5333& :6 networks impro!e on packet switching %ased ser!ices& :6 networkspro!ide higher data rates compared to pre!io#s generations&

Long Term Evolution (LTE)

LTE is a candidate for ;6& LTE like :6 is %ased on /packet switching/& The difference is that LTE network

is an all I4 %ased network& LTE offers greater #p*link and down*link data rates& LTE also offers flei%ilityin network design incl#ding location management&

LTE Ile "oe

When a E is switched on %#t the network doesn/t know where eactly the E is" it is said to %e in idlemode& owe!er" the network in this case knows in which T' the E is located %#t not eactly whichcell&

LTE Active "oe

When E is connected !ia any channel like d#ring a call" the network knows in which cell the E islocated and E can send or recei!e data at any time& In this sit#ation the E is said to %e in acti!emode&

LTE #etac$ "oe

When E is powered off" it is in the detached mode& owe!er" e!en the detached mode" it is importantthat the network knows that the E is powered off&

%anover

When the recei!ed signal strength is lower than a certain le!el from the ser!ing cell with the help ofnetwork" E is shifted to another neigh%oring cell with highest signal le!el witho#t terminating the call&ando!er occ#rs when a E is shifted from one comm#nicating channel to another channel d#ring acall or data transfer thro#gh the core network& This happens to a!oid call termination when the cellgets o#t from the ser!ing range of one cell and enters the ser!ing range of another cell&


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%ar %anoverard ando!er means that %efore the connection is made with other cell" the first connection is lost&


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of F r

Figure 3.1: Symmetry limitation..............................................................................................................18

Figure 3.2: Example of TAL allocation (TA sie ! 1 cell".......................................................................1#

Figure $.1: %E trace collection................................................................................................................22

Figure $.2: Example of a ro& of %E'trace scenario matrix.....................................................................2$

Figure $.3: Start cell selection..................................................................................................................2$

Figure $.$: ext cell selection.................................................................................................................2)

Figure ).1: *ayleig+ ,istri-ution function ( ! 1"...................................................................................28

Figure ).2: /oisson ,istri-ution function ( 0 ! )"....................................................................................2#

Figure ).3: omparison of cell loa, ,istri-ution for %E'trace scenario &it+ original ,ata..................31

Figure ).$: omparison of cell +an,oer ,istri-ution for %E'trace scenario &it+ original ,ata..........32

Figure ).): Simulation setup (-loc4 ,iagram".........................................................................................3$


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nd of Tabl

Ta-le 1: Signaling oer+ea, for t+e conentional TA ,esign..................................................................35

Ta-le 2: Signaling oer+ea, for %E'trace -ase, TAL ,esign using 12)6 ()7" %E traces......................3

Ta-le 3: TA% oer+ea, of t+e %E'trace -ase, TAL ,esign.....................................................................3

Ta-le $: /aging oer+ea, for t+e %E'trace -ase, TAL ,esign................................................................38

Ta-le ): ost of ,ata collection (%E'trace scenario ".............................................................................3#

Ta-le 5: Total oer+ea, comparison for t+e t+ree TAL ,esigns...............................................................3#


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Tabl of Content

+apter 1 ntro,uction............................................................................................................................16

1.1 Scope............................................................................................................................................16

1.2 9utline..........................................................................................................................................11

+apter 2 Trac4ing Area.........................................................................................................................12

2.1 Trac4ing Area...............................................................................................................................12

2.2 Location anagement..................................................................................................................12

2.3 Location Area %p,ate Sc+emes...................................................................................................12

2.$ ommon Static Location Area %p,ate Sc+emes.........................................................................13

2.$.1 Al&ays %p,ate.....................................................................................................................13

2.$.2 eer %p,ate.......................................................................................................................13

2.$.3 *eporting ells....................................................................................................................13

2.$.$ Forming LA.........................................................................................................................13

2.) ommon ;ynamic Location Area %p,ate Sc+emes....................................................................1$

2.).1 Time'-ase, %p,ate..............................................................................................................1$

2.).2 oement'-ase, %p,ate.....................................................................................................1$

2.).3 ;istance'-ase, %p,ate........................................................................................................1$

2.5 /aging Sc+emes............................................................................................................................1$

2.5.1 Simultaneous /aging...........................................................................................................1$

2.5.2 Seloc4 ;iagram of Simulation Setup............................................................................................3$

).5 umerical *esults........................................................................................................................3)

). onentional TA ..........................................................................................................................35

).8 %E'Trace -ase, TAL ,esign.........................................................................................................3


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).# ost of ;ata ollection................................................................................................................38

).16 *ule of T+um- TAL...................................................................................................................3#

).11 onclusion..................................................................................................................................$6

+apter 5 onclusion..............................................................................................................................$1


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Chapter 1 Introduction

Chapter 1 ntrod ct on

There has %een a tremendo#s growth in cell#lar comm#nications especially mo%ile %road%and

networks& Long Term E!ol#tion (LTE) is a candidate for ;6 that aims to impro!e mo%ile

comm#nications with an emphasis on mo%ile %road%and& LTE offers new feat#res that impro!e

network efficiency and performance&

,o%ility ,anagement (,,) is one of the key f#nctions in mo%ile networks& It pro!ides means

to locate ser E$#ipments (Es) and deli!er ser!ices (s#ch as calls" S,S etc&) to Es in mo%ile

networks& There are two aspects of mo%ility management" location management (also called

reacha%ility) and hando!er management (also called session contin#ity)& Location

management keeps track of Es in mo%ile networks so that when needed mo%ile phone

ser!ices can %e deli!ered to Es& ando!er management ena%les session contin#ation when

Es change cells (access points)& This thesis foc#ses on location management aspect of ,, in

LTE networks&

>ne of the key tasks of location management is to keep track of Es in the network& Tracking

'rea (T') is a logical gro#ping of cells in a network and is #sed to track and locate (page) Es&

The T' concept is similar to Location 'rea (L') concept in the circ#it*switched (7S) domain

and -o#ting 'rea (-') concept in the packet*switched (4S) domain&

1.1 Scope

This thesis aims to address T' planning and optimi.ation concepts in LTE networks& >ne of the

main considerations in T' design is to red#ce the signaling o!erhead& Signaling o!erhead

consists of #pdate o!erhead and paging o!erhead& In the standard T' #pdate (T') and

paging scheme" a E registers in a T'& The T' is recorded in ,o%ility ,anagement Entity

(,,E)& Whene!er the E mo!es to a new T'" it needs to #pdate ,,E a%o#t the new T'& The

E performs a T' to #pdate ,,E& This #pdate contri%#tes to signaling o!erhead and is

termed as T' signaling o!erhead& When the E is called" the ,,E pages all the cells

%elonging to the last registered T' for the E& This paging also contri%#tes to signaling

o!erhead and is termed as paging signaling o!erhead&

0


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1.1 Scope

T' design of a network needs to %e changed according to changing E mo%ility and

distri%#tion otherwise the T' design may ca#se more signaling o!erhead& T' design

optimi.ation often in!ol!es changing T's for cells& This change ca#ses ser!ice interr#ption

since the cells need to %e restarted for the change to take effect& To red#ce ser!ice

interr#ption the new T' design cannot differ a lot from the pre!io#s T' design&

Tracking 'rea List (T'L) is a scheme introd#ced in :644 -elease 2 ?0@& In this scheme" a cell can

%e part of m#ltiple T's& Each cell has a list of T's& The cell gi!es this list to Es& The list is kept

%y Es #ntil they enter a cell that does not %elong to any T' in the list& LTE standard allowscells to gi!e different T' lists to different Es& In ,,E" a E location is known to the

gran#larity of the T'L allocated to it&

Signaling o!erhead can %e !irt#ally eliminated if T'Ls are designed #sing E mo!ement and

call patterns (E traces)& owe!er o%taining this data is diffic#lt and costly& This thesis presents

an approach to design T'L #sing E traces& The approach is aimed to ser!e as a greenfield

design and not a re*optimi.ation&

1.2 Outline

C$apter 2 descri%es !ario#s location #pdate and paging schemes& The con!entional T'

scheme and the signaling o!erhead that is #sed thro#gho#t the thesis is also disc#ssed&

C$apter !descri%es the limitations of the con!entional T' scheme& T'L concept is introd#ced

and how it can mitigate some of the performance limitations of the con!entional T' scheme

are eplained

C$apter - descri%es how T'L can %e applied to large*scale networks and eplains the E*

trace %ased T'L design and r#le of th#m% T'L

C$apter .descri%es the design aspects of T'L schemes and present n#merical res#lts from

sim#lations

C$apter / draws concl#sion and prospects the f#t#re work

5


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Chapter 2 Tracking Area

Chapter 2 Track n Area

This chapter pro!ides an introd#ction to %asic materials and %ackgro#nd for tracking area

planning (T'4)& Signaling o!erhead form#lation for the con!entional T' scheme" which is

considered thro#gho#t the thesis" is pro!ided&

2.1 Tracking Area

T' is a gro#p of cells (similar to L') in which a E can mo!e freely witho#t performing

Tracking 'rea pdate (T') to #pdate ,o%ility ,anagement Entity (,,E) a%o#t its location

in the network&

2.2 Location Management

Location ,anagement (L,) means keeping track of idle Es within a network& Location

management ena%les network to locate Es for deli!ering calls and maintaining connections

as the Es mo!e in the network& L, consists of two stagesA finding the location of E and call

deli!ery& In the first stage" network is di!ided into L's& Es send L' when they change L's?5@& 'n L' is a gro#p of cells which are paged in case of an incoming call& 7all deli!ery to a E

is achie!ed %y finding the last registered L' and paging all the cells in that L'&

2.3 Location Area Update Schemes

There are !ario#s L' schemes that aim at optimi.ing L' o!erhead& The schemes can %e

generally categori.ed into static and dynamic& In static L' schemes" the L's are fied and

Es perform L' when they change L's while in dynamic L' schemes" L's are %ased on

Es call and mo%ility patterns ?5@& Static L' scheme are easy to implement and are not

comp#tationally epensi!e since they do not rely on characteristics of Es& Dynamic L'

schemes are comp#tationally epensi!e and re$#ire storage of E data for comp#tation&

Dynamic L' schemes pro!ide more o!erhead red#ctions compared to static L' schemes

%#t re$#ire caref#l network design for efficient comp#tation ?;@&

:


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2.4 Common Static Location Area pdate Schemes

2.4 Common Static Location Area Update Schemes

In static L, schemes Es either perform L' when they change cell or after specific time

inter!al& Some of the common static L, schemes areA

20-01 Alwas *pate

In always #pdate scheme" each cell is a reporting cell& ' reporting cell is a cell in which a E

#pon entering sends a L' to #pdate its location in the network& L' occ#rs whene!er a E

mo!es from one cell to another cell& E sends a L' on entering a new cell& This allows the

network to know which cell a E is c#rrently located& This red#ces the paging o!erhead to

.ero %eca#se network always knows the location of each E& owe!er" L' o!erhead is

maim#m ?B@&

20-02 Never *pate

In the ne!er*#pdate scheme" L' ne!er takes place since all the cells %elong to a single L'&

This means a E mo!es %etween cells witho#t e!er performing L'& When a E is called"

network pages all the cells in the network& This res#lts in maim#m paging o!erhead&owe!er" L' is .ero ?9@&

20-0! eporting Cells

In the reporting cells scheme" there are no L's& ' E #pdates network a%o#t its location when

it enters one of the reporting cells& To locate a E" a search is cond#cted in the !icinity of the

last reporting cell !isited %y the E& The reporting cells are predefined and efficient

arrangement re$#ires E characteristics&

20-0- orming LA

This L' scheme is a com%ination of always*#pdate and ne!er*#pdate schemes& 7ells are

gro#ped into L's& Es mo!ing within a L' do not perform L's& 'n L' occ#rs whene!er a

E mo!es from one L' to another& Whene!er there is a need to locate a E" all cells in the last

known L' of the E are paged& This com%ination of always*#pdate and ne!er*#pdate schemes

pro!ide a %alance %etween L' and paging o!erheads& This L' scheme is referred to as the

standard scheme and is the ass#med scheme in this thesis&

;


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2.! Common "#namic Location Area pdate Schemes

2. Common !"namic Location Area Update Schemes

Dynamic L, offer m#ch more flei%ility The parameter of dynamic L, schemes can %e

modified to fit indi!id#al Es and scenarios& Some of the common dynamic L, schemes areA

20.01 Time34ase *pate

In time*%ased #pdate scheme" each E sends an L' after a certain period of time& This is the

simplest of the schemes since Es need to follow only their local clocks ?5@&

20.02 "ovement34ase *pate

In mo!ement*%ased #pdate scheme" a E sends an L' after it crosses %o#ndaries of a

certain n#m%er of cells (threshold)& This scheme is more comple than time*%ased %eca#se

Es need to %e aware when they cross cell %o#ndaries ?5@&

20.0! #istance34ase *pate

In distance*%ased #pdate scheme" a E sends an L' after it mo!es a certain distance since

the last L'& This scheme is the most comple since Es need to know the topology of the

network in order to calc#late distance mo!ed ?5@&

2.# $aging Schemes

4aging schemes determine how a called E will %e paged& Some of the common paging

schemes areA

20501 &imultaneous +aging

In sim#ltaneo#s paging" when a E is called all the cells in the last reported L' for the E are

sim#ltaneo#sly paged&


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2.$ %aging Schemes

of the E are paged according to their n#m%er& This pro!ides a way to red#ce paging

o!erhead since all 4's may not %e paged& owe!er" since 4's are paged se$#entially" a delay

in connection occ#rs if the E is not located in the first 4'&

2.% Tracking Area !esign Optimi&ation

nder the con!entional T' scheme" the main o%=ecti!e is to ha!e a T' design that minimi.es

total signaling o!erhead& T' of !ery small si.e will res#lt in lower paging o!erhead %#t there

will %e ecessi!e T' o!erhead& >n the other hand" T's of !ery large si.e will red#ce or

!irt#ally eliminate T' o!erhead %#t will res#lt in ecessi!e paging o!erhead&

,#ch research has %een done on this trade*off& The research done on location registration

strategies ?0B@"?09@"?02@ and paging strategies ?09@"?01@"?53@"?50@ which s#ggest special

modifications in the network and additional E information that is costly to o%tain ?:@& This is

the reason that con!entional T' concept is commonly #sed ?:@&

The con!entional T' scheme for T' and paging is followed in the thesis& This means that a

E crossing a T' %o#ndary will lead to T' and all cells in the registered T' of the called E

are paged sim#ltaneo#sly&

2.' User ()uipment States in Mo*ilit" Management

' #ser e$#ipment (E) in LTE is any de!ice s#ch as smartphone" laptop etc& that an end*#ser

#ses to comm#nicate& E is almost the same concept as ,o%ile Station (,S) or ,o%ile

Terminal (,T) #sed in pre!io#s generation of cell#lar networks& +rom a mo%ility perspecti!e" a

E can %e in three statesA LTEC'7TIE" LTECIDLE and LTECDET'7ED& In theLTEC'7TIE state" a

E is connected to the network (i&e& has an esta%lished radio connection)& In this state" thenetworks know the cell the E is in& Therefore acti!e Es do not contri%#te to T' and paging

o!erhead since network is always aware of E location in this state& In LTECIDLE state" the

network is aware a%o#t the E location to the gran#larity of a T' (a gro#p of cells) since E is

in power*conser!ation mode and does not #pdate network a%o#t its location on each cell

change& Instead it informs the network when it changes T's& In LTECDET'7ED state" the E is

in a transitory state and is in the process of searching and registering with the network&

,ost Es are in LTECIDLE mode which means that the network is aware a%o#t their location at

B


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2.& ser '(uipment States in Mo)i*it# Management

the gran#larity of a T'& 7ell load and cell hando!er data is #s#ally the only realistic data

a!aila%le from a cell#lar network& owe!er" this data is for Es in LTEC'7TIE state& If it is

ass#med that Es in LTECIDLE state ha!e the same mo%ility and call pattern as the Es in

LTEC'7TIE state" a good estimation of E mo!ement and call acti!ity can %e made& This is the

ass#mption #sed in the thesis&

' E trace is de ned as the cell*to*cell mo!ement and the call arri!al pattern of a E in afi

speci c time period& E traces can %e #sed to red#ce signaling o!erhead of the network sincefi

the network can %e optimi.ed to mo!ement and call patterns of Es&

2.+ Signaling O,erhead Calculation

Let the cells in network %e denoted %y Nce**s + ? 1 @ . . . @N and the T's in the network %e

denoted %y TT A ! ? 1 @ . . . @ T . The T' each cell %elongs to can %e represented %y

t + B t1, . . . , tNC where ti is the T' of cell i& T' design t can %e represented %y an N - N

symmetric and %inary matri S(t)& Each matri elements i (t"represents whether the two cells

are in the same T' or not&

si . (t)={1 i/ ti=t .6 otherwise (2.1"Let ui%e the n#m%er of Es in cell i for a gi!en time period and h i %e the n#m%er of Es

mo!ing from cell i to cell& The !al#es of ui and h i can %e determined from cell load and

hando!er data& The amo#nt of o!erhead of one T' is denoted %y cuand o!erhead of one

paging is denoted %y cp & 7all acti!ity factor i&e& pro%a%ility that a E needs to %e paged is

denoted %y 0The total o!erhead i&e& s#m of T' and paging o!erhead is calc#lated asA

cS1( t)=iN

. N

(cu hi . (1s i . (t))+ cp

uis i .( t)) (2.2"

In (5&5)" the first term within the parenthesis is the T' o!erhead for Es mo!ing from cell ito

cellif the cells are not in the same T' and the second is the paging o!erhead for paging Es

in cell iif the two cells are in the same T' ?58@&

9


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Chapter Tracking Area List

Chapter Tracking Area List

This chapter pro!ides an introd#ction to Tracking 'rea List (T'L)" a T' scheme introd#ced in

:644 -elease 2 ?:@& This scheme allows for more flei%le T' design& It is epected that this

scheme will remo!e certain limitations of the con!entional T' scheme& 7on!entional T' which

is the most #sed T' scheme in networks today has performance limitations& This chapter

considers limitations of the con!entional T'& The idea of T'L and how it allows for a more

flei%le T' design are eplained&

3.1 Limitations o- Con,entional TA

In a con!entional T'" cells are di!ided into m#t#ally ecl#si!e sets and each set is a T'& ' E

performs a T' whene!er it changes T'& There are some limitations of con!entional T'

schemeA

!0101 +ing +ong E''ect

In con!entional T' scheme" a E performs T' whene!er it mo!es to a cell %elonging to anew T'& Whene!er a E mo!es %ack and forth %etween two cells %elonging to different T's"

there will %e ecessi!e T's& This phenomenon is referred to as the ping*pong effect&

!0102 "ass "o4ilit &ignaling Congestion

Signaling congestion may occ#r when a large of n#m%er of Es %eha!e in a similar manner"

e&g& massi!e and sim#ltaneo#s E mo!ement in train scenario& Signaling congestion is ca#sed

%y ecessi!e T's from Es in a short time inter!al&

!010! &mmetr Limitation

nder the con!entional T' scheme" if cell ' and cell < are in the same T' then neither of them

can %e in any other T'& If this limitation can %e remo!ed" signaling o!erhead may %e red#ced&

2


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.1 Limitations o/ Con3entiona* TA

Example6 7onsider the two cells ' and < in fig#re :&0& nder the con!entional T' scheme"

either the cells are in the same T' or not& +rom signaling o!erhead form#la in (5&5)" total

signaling o!erhead c0when %oth cells ' and < are in the same T' is gi!en in (:&0)

c1= cp (uA+u4) (3.1"

'nd when cell ' and < are in different T's" the signaling o!errhead c2is gi!en in (:&5)

c2=cu

(hA+hA) (3.2"

Now ass#me that if cell ' and cell < can ha!e different perspecti!es to one another e&g& cell '

considers < in a different T' %#t cell < considers cell ' in the same T' then the signaling

o!erhead c is gi!en in (:&:)

c3=cu

hA4+ cp

u4 (3.3"

+or c1>c3 and c2>c3 to %e tr#e" cp uA>cu hA4 and cu h4A>cp u4 m#st %e tr#e i&e&

when cell ' has high load and there are few Es mo!ing from ' to < and cell < has low load

and more Es mo!e from < to '& In s#ch a scenario" remo!ing symmetry limitation will lead to

a lower signaling o!erhead&

3.2 Tracking Area List

T'L concept allows for more flei%le T' design and management& In the T'L scheme #sed in

the thesis" each T' consists of one cell& This implies that the T's are non*o!erlapping& Each cell

1

5igure .16 S#mmetr# *imitation


22/46

.2 Tracking Area List

has a list of T's which is assigned to E& The E does not perform T' as long as it is in a cell

%elonging to one of the T's from the list& T' is performed when a E mo!es to a cell that is

not incl#ded in any of the T's in the c#rrent list& The E then recei!es a new T'L& The location

of E is known at the gran#larity of the T'L allocated to the E&

In fig#re :&5 a T' has only one cell& T'0 has cell 0" T'0B; has cell 0B; and so on& S#ppose cell

0 is the starting cell of E& E gets T'L of cell 0& E now mo!es from cell 0 to 0B;& Since T'

0B; is in T'L of cell 0" no T' is performed& Same holds when E mo!es to cell 0: and 030&

When E mo!es from cell 032 to cell 9" T' takes place since T'9 is not in T'L of cell 0& E

now holds T'L of cell 9& 7ell 59 and cell B3 are in T'L of cell 9 so no T' takes place& When E

enters cell 08" T' occ#rs and E gets T'L of cell 08& Thro#gho#t the mo!ement network

always knows the location of E to the gran#larity of a T'L&

T'L scheme is epected to remo!e some limitations of the con!entional T' scheme& >ne of

03

5igure .26 '7amp*e o/ TAL a**ocation 8TA size + 1 ce**9


23/46

.2 Tracking Area List

the known limitations of the con!entional T' scheme is the ping*pong effect& T'L can a!oid

ping*pong T' o!erhead %y adding two ad=acent T's in the same T'L hence eliminating T'&

'nother limitation of the con!entional T' scheme is the mass mo%ility scenario e&g& Es in a

train crossing o!er to a new T'& T'L has the a%ility to assign E specific T'Ls& ence the cells

along the train track can assign different T'Ls to Es& The E in the train will ha!e different

T'Ls and hence will not perform T' at the same time mitigating mass T's&

00


24/46

Chapter 4 Imp*ementing TAL Scheme in Ce**u*ar Networks

Chapter ! ple ent n TA "che e n Cell lar #etwork

's disc#ssed T'L is epected to remo!e some limitations of the con!entional T' scheme& The

main challenge is how to apply T'L in large*scale networks& Tailoring T'L according to E

mo!ement and all pattern is the key to ha!ing an optimal T'L config#ration that will red#ce

signaling o!erhead& '!aila%ility of indi!id#al E mo!ement and call patterns wo#ld facilitate

generating an optim#m T'L that co#ld essentially eliminate signaling o!erheadA Each E

wo#ld get a specific T'L containing all cells it is epected to tra!erse thro#gh #ntil it is paged&Indi!id#al E mo!ement and call patterns is costly to o%tain& 'lso the !alidity of the

information is limited %eca#se E traces is the history of Es mo!ement and the f#t#re

mo!ement and call patterns for Es might change&

4.1 U(trace *ased TAL

6etting traces for idle Es was a costly and infeasi%le eercise in pre!io#s cell#lar

technologies& LTE howe!er offers some possi%ilities for collecting a small part of E traces&

>ne possi%ility is the #se of applications s#pporting 64S to collect E mo!ement and call

data& 'nother possi%ility is to ha!e a T'L config#ration that will facilitate collecting E trace

data&

T'L scheme in LTE offers the flei%ility of gi!ing E specific T'L and this can %e #sed to collect

a percentage of E traces& If the network gi!es a list to a E that only contains the #pdating

cell" then it is possi%le to trace that specific E in the network& 7onsider the scenario in +ig#re

;&0&


25/46

4.1 ':trace )ased TAL

The amo#nt of T' performed %y the traced Es is the cost of collecting part of the E traces&

There is no paging o!erhead associated with traced Es since their location is always known&

4.2 U(trace scenario

The E mo!ement directly affects the signaling o!erhead ?05@& In other words" signalingo!erhead is dependent on the E traces& In order to compare the T'L scheme and the

con!entional T' scheme" %oth m#st %e applied to the same E*trace scenario& ' E*trace

scenario is a set of E mo!ement and call pattern o!er a gi!en time that matches a gi!en set

of cell load and hando!er data& There can %e n#mero#s E*trace scenarios for one set of cell

load and hando!er data& E*trace scenario is generated #sing a mo%ility model& E*trace

scenario is dependent on the mo%ility model" the amo#nt and speed of each E/s mo!ement&

'ss#me that cell hando!er" cell load and call intensity factor 0data are a!aila%le for a network&

0:

5igure 4.16 ' trace co**ection


26/46

4.2 ':trace scenario

The generation of E*trace scenario start with determining the starting cell for each E& 7ells

with high load are more pro%a%le to %e the starting cells for Es& The pro%a%ility that a cell iis

the starting cell is calc#lated as in (;&0)&

%start( i)=ui

k=1

N

uk (;&0)

where"%start pro%a%ility that cell iis the starting cell

ui cell load of cell iN total n#m%er of cells

The net cell for a E is dependent on the last !isited cell of a E& The E will mo!e to

neigh%ors of last cell with high n#m%er of hando!ers& The pro%a%ility that cell is the net cell

for the E" gi!en that the last cell was i" is calc#lated as in (;&5)&

%ne7t(i , .)= hi .

k=1

N

hik (;&5)

where"%ne7t8(i , ) pro%a%ility that the net cell is when the c#rrent cell is i

hi cell hando!ers from cell ito cell

N total n#m%er of cells

the E*trace scenario is defined as a matri& The n#m%er of rows is e$#al to the n#m%er of

Es & The E*trace scenario matri is for a gi!en time d#ration T& Time d#ration T is di!ided

into e$#al time inter!als t& The ser!ing cell of E u in the time inter!al t is represented %yelement at (u,t"of the scenario matri& The d#ration of each inter!al is Dt. The dimension of

the scenario matri is T

t. The first col#mn of the matri is calc#lated #sing (;&0) and the

remaining col#mns are calc#lated #sing (;&5)&


27/46


+ig#re ;&5 ill#strates how a row of a E*trace scenario matri looks like& The time inter!alTis

di!ided into 03 inter!als 8t1,...,t1;99 with Dt d#ration each& The E remain in cell i for one Dt"

then mo!es to celland stays there for :Dt & +inally the E mo!es to cell kand stay there for

the rest of the time&

The E*trace scenario matrices are pop#lated #sing %startand%ne7tas in (;&0) and (;&5)& Start cell

for each E is selected #sing%startwhile the s#%se$#ent cell are selected #sing%ne7t& +ig#re ;&:

and +ig#re ;&; eplains start cell and net cell for each E& ' random n#m%er is generated

%etween B6@1C& +rom the +ig#re ;&:"%startfor cellis closest to the generated random n#m%er&Th#s" cellis selected as the starting cell& >nce the starting cell is selected" the net cell is

determined #sing %ne7t& ' random n#m%er is generated %etween B6@1C& The neigh%or cell of

ha!ing%ne7tclosest to the generated random n#m%er is selected& +rom +ig#re ;&; cell )has

pro%a%ility closest to the random n#m%er& Th#s" cell )is selected as the net cell&

08

5igure 4.26 '7amp*e o/ a row o/ ':trace scenario matri7

5igure 4.6 Start ce** se*ection


28/46


4.3 Aggregated !ata -rom U(trace Scenario

E*trace scenario matri is generated #sing start cell and net cell pro%a%ilities which are

%ased on cell load and cell hando!er data respecti!ely& The cell load and hando!er from the

E*trace scenario needs to %e aggregated to match the original data&

The aggregated cell load uiof a cell iis the ratio of total time spent %y Es in cell ito the time

d#ration of the E*trace scenario matri& Similarly the aggregated cell hando!ers from cell ito

k is the n#m%er of times Es mo!e from cell i to cell kin the E*trace scenario matri& In

+ig#re ;&5 if it is s#pposed that Dt 0 and T 03 then the aggregated cell load data is ui

3&5" u 3&: and uk 3&8& The hando!er data is h i 0 and h k 0&

4.4 /ule o- Thum* TAL

-#le of th#m% T'L design is proposed in ?:@& It offers a way of designing T'L witho#t the need

of E traces& -#le of th#m% is #sed for performance e!al#ation of E*trace %ased T'L design&

To eplain r#le of th#m% T'L design" consider a network with only two cells iand& The T'L of

cell ican either %e FiG or ?i, & nder the ass#mption that T's can only ha!e one cell& +or the

first case where TAL(i" ! ?i@all E performing hando!er from to iwill perform an #pdate&

The res#lting #pdate o!erhead will %e cuh i & There will %e no paging o!erhead since there is

only one T' in T'L& +or the second case where TAL(i" ! ?i, " there will %e no #pdate o!erhead

for Es mo!ing from cellto ias %oth cells are in the T'L of Es" howe!er there will %e paging

o!erhead since the network needs to search for called E in cells iand& The res#lting paging

o!erhead is gi!en as 0cpui& To minimi.e o!erhead res#lting from cell i" a T'L design is chosen

that gi!es a lower o!erhead& In other words" if cu

h i H 0cp

uithen TAL(i" ! ?i ,and TAL(i" ! ?i

0B

5igure 4.46 Ne7t ce** se*ection


29/46

4.4 cp

u i6 otherwise

($.3"

+or a large*scale network" r#le of th#m% T'L design pro!ides a local minim#m and not the

glo%al minim#m since each cell is optimi.ing T'L with respect to its own perspecti!e #sing its

data witho#t taking into acco#nt the effect of other cells on their modified T'L&

09


30/46

Chapter ! "esign and Simu*ation


31/46

!.1 Introduction

hi n#m%er of cell hando!er from cell

ito

uk cell load of cell kN total no& of cells

The a!erage n#m%er of mo!es 8>mo3es) from the original data is 0 mo!e per E& This is #sed as

the mean of the -ayleigh f#nction& +ig#re 8&0 shows the -ayleigh distri%#tion f#nction #sed to

generate E tracesA

7all d#ration for Es is determined #sing 4oisson distri%#tion with? 8 (a!erage calld#ration)& The distri%#tion is shown in +ig#re 8&5&

01

5igure !.16 + 19

0 1 0 2 0 3 0 4 0 5 0 6 00

0 . 1

0 . 2

0 . 3

0 . 4

0 . 5

0 . 6

0 . 7

0 . 8

X : 1

Y : 0 . 7 1 5 4

N u m b e r o f m o v e s

P

ro

b

a

b

ility

moves


32/46

!.1 Introduction

'lgorithm I eplains the algorithm #sed for generating a E*trace scenario matri& ' random&

M is the E*trace scenario matri&>mo3esis the a!erage n#m%er of mo!es calc#lated as in (8&0)&

Algorit$m I 7 Generating *E Traces

fori = 1:N calculate Pstart(i) using (4.1)

end

fori = 1:N

forj = 1:N calculate Pnext(i) using (4.2)

end

end

forx = 1:USERS

generate random numer et!een " and 1# dra! cell $rom Pstartusing random numer# add dra!n cell to ue%trace scenario matrix & x1#

end

trace'lengt = "#

forx = 1:USERS dra! num'mo*es using Ra+leig'random(,mo*es)#

whilenum'mo*es - "

forj = 2:trace'lengt

re*ious cell = &x(j%1)# ifando*er $rom re*ious cell to cells - "

dra! cell $rom Pnext(i/j) using random numer# add dra!n cell to ue%trace scenario matrix &x i#

num'mo*es = num'mo*es 0 1# else

53

5igure !.26 %oisson distri)ution /unction 8 ? + !9


33/46

!.1 Introduction

&xj = &x(j%1)#

end

end

end

end

50


34/46

!.2 Mo)i*it# Mode* @eri/ication

.2 Mo*ilit" Model eri-ication

The aggregated cell load and hando!er data from E*trace scenario matrices can %e #sed to

!erify against original data& 'ggregated cell load of cell iis defined as the n#m%er of times

cell iappears in E*trace scenario matri di!ided %y the total n#m%er of time inter!als T

t .

+ig#re 8&; compares aggregated cell load gi!en %y (8&5) from one of the E*trace scenario to

original cell load data& +ig#re 8&; compares aggregated cell hando!er from E*trace scenario I

to original cell hando!er data&

u i =ni t

T ().2"

where"

ni n#m%er of times cell iappears in E traces

Dt time d#ration of inter!als

T total time d#ration for E*traces

55

5igure !.6 Comparison o/ ce** *oad distri)ution /or ':trace scenario I with origina* data


35/46

!.2 Mo)i*it# Mode* @eri/ication

The res#lts show that altho#gh there are some !isi%le differences" aggregated data to some

etent resem%les the original data&

.3 Con,entional Tracking Area !esign

+or con!entional T' design" aggregated cell load and hando!er from the fi!e E*trace

scenario matrices is #sed& The data is #sed as inp#t to 74LEJ ?00@ to generate optim#m

con!entional T' designs for each scenario& The model #sed %y 74LEJ is defined in ?02@&

.4 U(Trace *ased TAL !esign

To generate E*trace %ased T'L design" the optim#m con!entional T' design is #sed as the

initial T'L& Since the optim#m con!entional T' design gi!es the lowest possi%le signalingo!erhead for con!entional case" it is a good starting point& To eplain how initial T'L is formed

from con!entional T' design consider a TA1s#ch that TA1 ! ?a,)where aand )are cells&

The T'L of cell a and ) %ecomes ?a,)& The T'L is optimi.ed %y addingKremo!ing cells

repeatedly and calc#lating signaling o!erhead after each change& If the change in T'L res#lts

in a lower o!erhead than con!entional case (which ser!es as the starting reference)" the

change is kept otherwise it is discarded& The new lower o!erhead is set as the new reference&

The process is repeated for T'L of each cell and a final T'L for each cell is o%tained&

5:

5igure !.46 Comparison o/ ce** hando3er distri)ution /or ':trace scenario I with origina* data


36/46

!.4 ':Trace )ased TAL "esign

Algorit$m II 7 TAL esign 4ase on *E3traces

sa*e x ue'traces as art'ue'traces#calculate total o*eread con*'3 $or con*entional 5 design#

sa*e con*'3 as re$erence o*eread re$'3sa*e con*entional 5 design con*'5 as otimum 56 ot'56#

fori = 1:N

forj = 1:N

ifj is not in 56 o$ i add j to 56 o$ i#

sa*e modi$ied 56 as ne!'56#calculate o*eread ne!'3 using ne!'56 $rom art'ue'traces#

ifne!'3 7 re$'3sa*e ne!'3 as re$'3#

sa*e ne!'56 as ot'56#

else

remo*e j $rom 56 o$ i#

end

else

remo*e j $rom 56 o$ i#

sa*e modi$ied 56 as ne!'56#calculate o*eread ne!'3 using ne!'56 $rom art'ue'traces#

ifne!'3 7 re$'3sa*e ne!'3 as re$'3#

sa*e ne!'56 as ot'56#else

add j to 56 o$ i#

end

end end

end

The optimi.ation of E*trace %ased T'L design in!ol!es applying changed T'Ls to the E*

trace scenarios and determine total o!erhead& The T'L is optimi.ed #sing mo%ility and call

pattern for different percentage (7) of total E traces (sample E traces)& The reason forconsidering part of the E traces (sample E traces) is that data needed to generate E traces

has an associated cost as eplained in Section ;&0& Therefore m#ltiple T'L config#rations

optimi.ed #sing different n#m%er of sample Es are generated to see how T'L performance

!aries for different n#m%er of sample Es&

5;


37/46

!.! *ock "iagram o/ Simu*ation Setup

. lock !iagram o- Simulation Setup

The %lock diagram of the sim#lation set#p is shown %elowA

+ollowing is a description of the different %locks in the %lock diagramA

0& The original data is from real*life network of Lis%on consisting of cell load and cell

hando!er

58

5igure !.!6 Simu*ation setup 8)*ock diagram9


38/46

!.! *ock "iagram o/ Simu*ation Setup

5& 'lgorithm I is #sed to generate a E traces scenario from the original data

:& 'ggregated cell load and cell hando!er are calc#lated from E*trace scenario matri

;& sing aggregated data and E*trace scenario the con!entional T' design is optimi.ed

#sing 74LEJ ?00@

8& The con!entional T' design is applied to the E traces and the signaling o!erhead is

calc#lated

B& Different n#m%er of E traces (sample E traces) are selected

9& E*trace %ased T'L design is generated for different n#m%er of sample E traces

2& Signaling o!erhead is calc#lated %y applying E*trace %ased T'L designs to E traces

1& 7ost of data collection is calc#lated for different n#m%er of sample E traces

03& sing E*trace scenario" signaling o!erhead is calc#lated for E*trace %ased T'Ls

00& -#le of Th#m% T'L design is generated as descri%ed in Section ;&;

.# umerical /esults

E*trace %ased T'L design algorithm and the r#le of th#m% T'L algorithm are implemented in

,'TL'< -5331% ?0:@& The performance of E*trace %ased T'L design is compared with %oth

the con!entional T' and the r#le of th#m% T'L designs& The performance e!al#ation is done

%y applying the T'L designs to 8 different E*trace scenarios& The signaling o!erhead is

calc#lated %y #sing E traces for the 8 scenarios& Each time a E makes a hando!er to a cell

that is not in its T'L" cuis added to the o!erall o!erhead& When a E is paged" a cost e$#al to

(L t a *:1)cp " whereL t a *is the length of E T'L" is added to the o!erall signaling o!erhead& '

called E does not contri%#te to T' d#ring the call d#ration&

5B


39/46

!.B Con3entiona* TA

.% Con,entional TA

The performance e!al#ation of con!entional T' design is done %y applying the design to E*

trace scenarios& Ta%le 0 gi!es the signaling o!erhead for the 8 E*trace scenarios& The res#lts

show that the o!erall signaling o!erheads for the 8 E*trace scenarios are !ery close& The

reason is that the E*trace scenarios are all %ased on the same original data (cell load and

hando!er data)&

%E Trace Scenario TA% /aging Total

1 ##6.6 23).2 122).2

2 #52.6 23#.5 1261.5

88).6 25$.5 11$#.5

4 #36.6 2)3.$ 1183.$

! 8#2.6 2$.6 1155.6

Ta)*e 16 Signa*ing o3erhead /or the con3entiona* TA design

59


40/46

!.& ':Trace )ased TAL design

.' U(Trace *ased TAL design

E*trace %ased T'L config#rations for different E*trace scenarios are generated& T'L

config#rations are generated for different n#m%er of E traces& The different n#m%er of E

traces #sed were 083" :33" 983" 0333" 0583" 0983" 5333 and 5833& 'll the res#lts are not

presented& Ta%le : presents the res#lts are for a case with 0583 E traces and compares them

to the corresponding con!entional T' config#ration&

%E'Trace ScenarioCon3entiona* TA TAL

TA% /aging TA% /aging

I )6 #@) 1 16@5

II 3$ )@# 1 5@6

III 3# 12@1 2 13@1

I@ 3$ 11@) 2 13@1

@ $8 )@) $ 5@$

Ta)*e 26 Signa*ing o3erhead /or ':trace )ased TAL design using 12!; 8!9 ' traces

+rom Ta%le 8 it is seen that E*trace %ased T'L design offers considera%le red#ction in T'

o!erhead compared to the con!entional T' config#ration for the collected E traces& There is

howe!er a slight increase in paging o!erhead& To e!al#ate performance for large*scale

networks" E*trace %ased T'L config#rations for different percentage of E traces are applied

to all E traces for the 8 E*trace scenarios& Ta%le : presents T' o!erhead res#lts and

compares them to the con!entional T' config#ration&

%E Trace Scenario

um-er of sample %E traces

onentional TA;esign1)6 366 )6 1666 12)6 1)6 2666 2)66

I 826 53 )1 )3# )6$ $)1 $16 358 ##6@6

II 8$) 13 58$ 536 )$# )61 $$) #52@6

III #5 5 )## )8$ )$6 $# $8# 3## 88)@6

I@ 88$ 8)$ 2$ 55$ )8) )63 $85 $$ #36@6

@ 862 2 5$2 )#5 ))3 $#5 $) $1# 8#2@6

Ta)*e 6 TA o3erhead o/ the ':trace )ased TAL design

52


41/46

!.& ':Trace )ased TAL design

+rom Ta%le : it is seen that T' cost is red#ced as the n#m%er of sample E traces increase

i&e& when data from more E traces is #sed in impro!ing the E*trace %ased T'L design& This is

!alid for all the 8 E*trace scenarios& E!en #sing data from 083 E traces" the E*trace %ased

T'L design yield a lower T' o!erhead compared to con!entional T' design for all scenarios&

The paging cost for E*trace %ased T'L design and con!entional T' design for 8 different E

trace scenarios is calc#lated and presented in Ta%le ;&

%E Trace Scenarioum-er of sample %E traces onentional TA

;esign1)6 366 )6 1666 12)6 1)6 2666 2)66

I 238@2 23@# 2$)@ 2$$@) 2$5@3 2$1 23#@3 2$2@1 22)@

II 2$3@# 2$) 2$$@3 2$@5 2)1@8 2)6@# 2))@2 2)2@8 233@

III 258@3 26@ 22 26@ 23@5 2 21@ 283@2 2)2@)

I@ 2)3@$ 2))@# 251@3 25$@2 25$@1 25)@# 258@2 2)3@1 2$1@#

@ 25@$ 283@3 28) 2#6 2#)@$ 363 2#8@) 366@2 258@)

Ta)*e 46 %aging o3erhead /or the ':trace )ased TAL design

The res#lts show that paging o!erhead increases slightly for E*trace %ased T'L design& Thecost of T' is 03 times more than paging& E*trace %ased T'L config#rations are optimi.ed

for T' more than paging& There is a trade*off %etween #pdate and paging o!erheads i&e& if

one increases the other decreases and !ice !ersa& E*trace %ased T'L design red#ces T'

o!erhead considera%ly while there is a small increase in paging o!erhead& owe!er" the total

o!erhead is still considera%ly lower than con!entional T' design&

.+ Cost o- !ata Collection

's descri%ed in Section ;&0" E traces are collected #sing special T'L config#ration& This T'L

config#ration is #sed for certain Es (sample Es) for a certain amo#nt of time& The Es

perform #pdate whene!er they change a cell& This ena%les to track E mo!ement for the time

period& The location of sample Es is known to the gran#larity of cell& ence there is no

paging o!erhead and the cost of data collection is the T' o!erhead generated %y sample

Es& This cost m#st also %e considered when e!al#ating E*trace %ased T'L design since E

traces are prere$#isite for designing it& Ta%le 8 present the o!erall o!erhead and the

associated model cost #sing E*trace scenario I&

51


42/46

!. Cost o/ "ata Co**ection

um-er of Sample %Es onentional TA

;esign Total 9er+ea,

ost of ;ata

ollection

1!;

121)@

16)8@2 $

;; 1666@# #6

B!; 815@ 218

1;;; 83@) 2#1

12!; )6@3 358

1B!; 5#2 )1

2;;; 5$#@3 )#)

2!;; 516@1 3

Ta)*e !6 Cost o/ data co**ection 8':trace scenario I9

+rom Ta%le 8 it is seen that generating E*trace %ased T'L #sing more sample E traces offers

more red#ction in o!erall o!erhead& owe!er" the cost of data increases as n#m%er of sample

Es ad!ersely impacting the performance of E*trace %ased T'L design compared to

con!entional T' design& ence" it is not ad!antageo#s to collect E traces #sing T'L&

.1 /ule o- Thum* TAL

-#le of th#m% T'L design as eplained in Section ;&; is also #sed to generated T'L for the 8

E*trace scenarios& Ta%le B presents the res#lts& The res#lts are compared to %oth

con!entional T' and E*trace %ased T'L designs&

Sc+eme Scenario Scenario Scenario Scenario = Scenario =


43/46

!.11 Conc*usion

.11 Conclusion

This chapter compares the performance of E*trace %ased T'L design to con!entional T'

scheme& The n#merical res#lts show that T'L schemes ha!e the potential to considera%ly

red#ce signaling o!erhead compared to the con!entional T' scheme& E!en #sing as small as

083 E traces to generate a T'L config#ration and applying to a large*scale network yields a

lower signaling o!erhead compared to the con!entional T' scheme& sing more E traces to

design T'L f#rther red#ces signaling o!erhead& The draw%ack howe!er is the cost associated

with collecting E traces& The high cost makes T'L an infeasi%le approach for collecting E

traces and red#ces its performance& The compared r#le of th#m% approach for designing T'L

performed %etter&


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Chapter $ Conc*usion

Chapter & Concl on

The aim of the thesis work has %een to eploit T'L concept in LTE networks& The T'L concept

is a relati!ely new concept and this thesis work was aimed to eplore how T'L concept can

red#ce total o!erhead of a network& 'n approach for designing T'L #sing traces was pro!ided

and e!al#ated against con!entional T' scheme and T'L design %y r#le of th#m% approach&

The res#lts show that T'L pro!ides %etter performance (lower signaling o!erhead) compared

to the con!entional T' design for the #sed network scenario& The draw%ack howe!er is thecost for collecting E traces& -#le of th#m% is a fast and simple approach for designing T'Ls

for large*scale networks&

The need to red#ce o!erhead is a key factor in today/s mo%ile networks d#e to increasing

n#m%er of #sers& This is a hot research topic for researches& The introd#ction of LTE has made

this research more interesting d#e to the flei%ility it offers in designing a network compared

to pre!io#s generations& The concept of T'L is an interesting research area s#%=ect %#t !ery

limited research on the topic is a!aila%le as the concept is $#ite new& T'Ls ha!e the potentialto red#ce o!erhead and also allow for easy re*config#ration of the network&

+#t#re work can %e directed towards generating a %etter algorithm to design T'L

config#rations& +#rther red#ctions can %e made in o!erhead %y pro!iding E specific T'Ls i&e&

assigning each E entering a partic#lar cell a T'L that is designed considering E mo!ement

and call history&

:5


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%eferen

?0@ :644& TS 5:&;30 M !2&B&3" 6eneral 4acket -adio Ser!ices (64-S) enhancements for E!ol!edni!ersal Terrestrial -adio 'ccess Network (E*T-'N) access" :6 -elease 2" 5331&httpAKKwww&:gpp&orgKftpKspecsKarchi!eK5:seriesK5:&;30K

?5@


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?0B@ Naor" V& Le!y" & " P,inimi.ing the wireless cost of tracking mo%ile #sersA an adapti!e thresholdscheme"P IN+>7>, /12& Se!enteenth 'nn#al Roint 7onference of the IEEE 7omp#ter and

7omm#nications Societies& 4roceedings& IEEE" !ol&5" pp&953M959 !ol&5" 51 ,arM5 'pr 0112&

?09@ 'kyildi. I& +&" o R& S& ,& Lin & ct 0119&

?50@ Wang W& 'kyildi. I& +& St%er 6& L& 7h#ng ptimi.ation and 4erformanceE!al#ationU Licentiate Thesis No& 0;9:" Linkping ni!ersity" 5300&

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