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UMTS Optimization Question & Answer

February 1, 2011

Radio Network

1. What are the optimization tools you use?

Drive test, analysis, others?

2. Are System Inormation !lo"#s $SI!% transmitte all the time?

No, system information block is multipleed with synchroni!ation channel" #ynchroni!ation

channel occupies the first time slot $%#& and #'( occupies the other ) time slots"

'. (ow oes U) "amp $syn"hronize% to a *oe!?

1" *+ uses the primary synchroni!ation channel $-#./& for slot alinment $%#

synchroni!ation&"

2" fter alinin to Node( time slot, *+ then uses secondary synchroni!ation channel $#-#./& to obtain frame synchroni!ation and scramblin code roup identification"

" *+ then uses scramblin code 'D to obtain .'./, thus campin to a Node("

+. What "oul ,e the "ause o sot hano-er ailure?

*+ issue"

Resource unavailable at taret Node("

'nade3uate #/4 threshold defined"

o +tc"

. What are the three sets in hano-er?

%he sets in handover are5

ctive set 6 the list of cells which are in soft handover with *+"

7onitored set 6 the list of cells not in active set but RN. has told *+ to monitor"o Detected set 6 list of cells detected by the *+ but not confiured in the neihbor

list"

/. What are the ma0or ieren"es ,etween SM an UMTS hano-er e"ision?

8#75
http://wirelessexam.com/category/radio-network/http://wirelessexam.com/category/radio-network/


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%ime-based mobile measures of R9ev and R:ual 6 mobile sends measurement report

every #./ period $;"

o *+ plays more part in the handover decision"

. What are the e-ents 1a3 1,3 1"3 et".?

e1a 6 a rimary .'./ enters the reportin rane, i"e" add a cell to active set"

e1b 6 a primary .'./ leaves the reportin rane, i"e" removed a cell from active set"

e1c 6 a non-active primary .'./ becomes better than an active primary .'./, i"e"replace a cell"

e1d5 chane of best cell" e1e5 a rimary .'./ becomes better than an absolute threshold"

o e1f5 a rimary .'./ becomes worse than an absolute threshold"

4. What are e-ent 2a52 an 'a5'?

+vents 2a-2d are for inter-fre3uency handover measurements and events a-d are for 'R%

handover measurements"

ea5 the *7%# cell 3uality has moved below a threshold and a 8#7 cell 3uality hadmoved above a threshold"

eb5 the 8#7 cell 3uality has moved below a threshold" ec5 the 8#7 cell 3uality has moved above a threshold"

ed5 there was a chane in the order of best 8#7 cell list"

6. What may happen when there7s a missin8 nei8h,or or an in"orre"t nei8h,or?

ccess failure and handover failure5 may attempt to access to a wron scramblin code"

Dropped call5 *+ not aware of a stron scramblin code, stron interference"

oor data throuhput"

oor voice 3uality"

+tc"

19. What "an we try to impro-e when a""ess ailure is hi8h?

hen access failure is hih we can try the followin to improve R./ performance5

'ncrease maimum *+ transmit power allowed5 7a@allowed@*9@%A@ower"

'ncrease power 3uickly5 power@4ffset@0"

'ncrease number of preambles sent in a iven preamble cycle5 preamble@Retrans@7a"


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'ncrease the number of preamble cycles5 ma@[email protected]"

'ncrease number of RR. .onnection Re3uest retries5 N00"

11. What are the "onitions you typi"ally set to tri88er I:AT hano-er?

R#. and +cB'o are used to trier 'R% handover5

R#. C -100d(m"

+cB'o C -1d(m"

12. What are the typi"al ;i you wor# on nei8h,or prioritization?

1/. What is the typi"al e-ent seuen"e o I:AT (ano-er rom ' to 2

+vent 2d 6 enterin into compressed mode 6 measurement of 28 candidates 6 +vent a 6Herification of 28 resources 6 /andover from *%RN .ommand from 8 RN. to *+

1. What are the possi,le "auses or an I:AT @ailure?

7issin 28 relations

Non availability of 28 Resources

oor 28 .overae


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7issin 8 Relations

14. What is


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2'. What is (ar (ano-er in UMTS? When will it happen?

/ard /andover in *7%# is a break before make type /andover

't can happen in the inter RN. boundaries where there is no 'ur link"

2+. What is the typi"al all Setup Time or a ' U) to ' U) all? What are the possi,le:@ relate "auses or a elaye ST in this type o "all?

to ) seconds

7ultiple RR. ttempts $*+ is on poor coverae 6 need more than ccess ttempt&

Delayed ae Responses

/ih 9oad on ain andBor ccess .hannel

ain B ccess arameters

2. What is Sot (ano-er O-erhea? What is the typi"al -alue in UMTS networ#?

#oft /andover 4verhead is calculated in two ways" 1& verae ctive #et #i!e 6 %otal%raffic B rimary %raffic" 2& #econdary B %otal %raffic

%ypical Halues are like 1"L $v ctive #et #i!e& or E $#econdary B %otal &

2/. What will happen to the Sot (ano-er O-erhea when you apply O*S on the

networ#? An Why?

ith 4.N#, the interference $load& increases" %his leads to reduction in +cB'o of a ilot,which reduces the pilot spillovers" Reduction in ilot #pillover will reduce the #oft

/andover 4verhead"

2. What are the possi,le "auses or an A""ess @ailure in UMTS?

7issin Neihbors

oor .overae

ilot ollution B #pillover

oor .ell Reselection

.ore Network 'ssues

Non 6 availability of resources" dmission .ontrol denies

/ardware 'ssues

'mproper R./ arameters +ternal 'nterference

24. $@O: ):ISSO* )B% What is :TW


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#ystem Ref oint for +BBB Node( is at the output of %7 $(etween %7 and ntenna&

'9. What are the typi"al -alues or Dreportin8ran8e1a7 an Dreportin8ran8e1,7?

d( and d( respectively"

'1. What will ,e the impa"t when you "han8e Dreportin8ran8e1a7 rom ' to + ! an

Dtimetotri88er1a7 199 to '29 ms3 without "han8in8 any other parameters?

Reduction in number of +vent1a

Delayed +vent1a trier

Reduction in verae ctive #et #i!e

Delay in +vent1a could increase D9 interference, which could lead to a drop call or

increase in verae ower er *ser $reduction in cell capacity&

'2. What is Amission ontrol?

dmission .ontrol is an alorithm which controls the Resource llocation for a new call

and additional resource allocation for an eistin call" 'ncase, if a cell is heavily a loadedand enouh resources in terms of power, codes or .+s are not available, admission

control denies permission for the additional resource re3uirement"

''. What is on8estion ontrol?

.onestion .ontrol monitors the dynamic utili!ation of specific cell resources andinsures that overload conditions do not occur" 'f overload conditions do occur,

.onestion .ontrol will immediately restrict dmission .ontrol from rantin additional

resources" 'n addition, .onestion .ontrol will attempt to resolve the conestion byeither down switchin, or terminatin eistin users" 4nce the conestion is corrected,

the conestion resolution actions will cease, and dmission .ontrol will be enabled"

:elate Arti"les

UMTS


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#tandard deviation error5 the smaller the better, usually L to )d("

7ean error5 the smaller the better, usually 2 to"

Root mean s3uare error5 the smaller the better, usually

.orrelation coefficient5 the larer the better, usually L0E to )0E"

2. What is the minimum num,er o ,ins reuire or a "ertain propa8ation moel?

%he more bins the more likely to come up with a ood model" *sually a minimum of 2,000

bines is considered acceptable, but sometimes as low as 00 bins may be accepted"

'. (ow many s"ram,lin8 "oes are there?

%here are 12 scramblin codes in the downlink and 1,LLL,21 codes in the uplink"

+. (ow many s"ram,lin8 "oe 8roups are there or ownlin#?

%here are ; code roups, each roup has < scramblin codes"

. an we assi8n same s"ram,lin8 "oes to sister se"tors $se"tors on same site%?

No, because scramblin code on the downlink is used for cell identity" s a re3uirement,

scramblin codes have to maintain a safe separation to avoid interference"

/. Are s"ram,lin8 "oes ortho8onal?

No, scramblin codes are not orthoonal since they are not synchroni!ed at each receiver" %hey

are pseudo random se3uences of codes"

. an we assi8n s"ram,lin8 "oes 13 2 an ' to sister se"tors?

Mes"

4. In IS56 we ha-e a


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%he coverae thresholds are based on *+ sensitivity, fadin and penetration loss" ssumin *+

sensitivity of -110d(m, fade marin of d(5

4utdoor5 -110d(m sensitivity d( fade marin O -10d(m"

'n-vehicle5 -110d(m d(


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1. What are the typi"al reasons o ailure in Monte arlo simulation?

Downlink +bBNo failure $.apacity&"

Downlink +bBNo failure $Rane&"

*plink +bBNo failure"

9ow pilot #'R" Noise rise limit reached"

+tc"

14. What oes Ftrai" spreaG mean?

=%raffic spread> means spreadin traffic $number of terminals& in a cell coverae area"

16. >o you use li-e trai" or e-en5loa trai" in your esi8n?

$Depends&"

:elate Arti"les

UMTS UT:A* Question & Answer

February 1, 2011

Radio Network

1. What are the intera"es ,etween ea"h UT:A* "omponent?

*u5 *+ to Node(

'ub5 Node( to RN.

'ur5 RN. to RN.

'u5 RN. to 7#.

2. !riely es"ri,e the U) to UT:A* proto"ol sta"# $air intera"e layers%.

%he radio interface is divided into layers5

1"


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7.5 responsible for multiplein data from multiple applications onto physical

channels in preparation for over-the-air transmition"

R9.5 sements the data streams into frames that are small enouh to be transmitted overthe radio link"

" Upper layer$9&5 vertically partitioned into 2 planes5 control plane for sinalin and userplan for bearer traffic"

::$Radio Resource .ontrol& is the control plan protocol5 controls the radio resourcesfor the access network"

'n implementation5

1" *+ has all layers"

2" Node( has hysical 9ayer"

" RN. had 7. layer and RR. layer"

'. !riely es"ri,e UMTS air intera"e "hannel types an their un"tions.

%here are types of channels across air interface 6 physical channel, transport channel andloical channel5

1" hysical .hannel5 carries data between physical layers of *+ and Node("

2" %ransport .hannel5 carries data between physical layer and 7. layer"

" 9oical .hannel5 carries data between 7. layer and RR. layer"

+. i-e some eHamples o


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o Dedicated channel5 DD./, D../"

. What are the :: operation moes?

'dle mode and connected mode"

/. What are the :: states?

%here are ; RR. #tates5 .ell@D./, .ell@F./, *R@./ and .ell@./"

*R O *%RN Reistration rea"

. What are transparent moe3 a"#nowle8e moe an una"#nowle8e moe?

%ransparent mode corresponds to the lowest service of the R9. layer, no

controls and no detection of missin data"

*nacknowleded mode offers the possibility of sement and concatenate of data but noerror correction or retransmission therefore no uarantee of delivery"

cknowleded mode offers, in addition to *7 mode functions, acknowledement oftransmission, flow control, error correction and retransmission"

4. Whi"h layer$s% perorm "ipherin8 un"tion?

RR. 6 for acknowleded mode $7& and unacknowleded mode $*7&"

7. 6 for transparent mode $%7&"

6. What is OS@?

4rthoonal Hariable #preadin Factor"

19. (ow many OS@ "oe spa"es are a-aila,le?

%otal 4H#F codes O 2"

Reserved5 1 #F; for #-.../, 1 #F2 for .'./, -.../, './ and './ each"

o %otal available code space O 2 6 ; $1 #F;& 6 ; $; #F2& O 2;


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No, because =1111P> $2 times& is used by .'./"

1'. What are the sym,ol rates $,its per sym,ol% or !


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Radio Network

1. What is a typi"al *oe! sensiti-ity le-el?

%he service and load determines the Node( sensitivityT in eneral, in a no-load condition, the

sensitivity is between -11d(m to -12d(m" For +ricsson, the Node( sensitivity level iscalculated at around5

.#12"25 -12; d(m

#-;5 -11) d(m

#-12


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%he maimum path loss is dependent on the service and vendor recommendationsT typically it is

in between 1 to 1;0d( for urban areas and between 10 to 10d( for rural areas"

. What is ieren"e ,etween !i an !?

d(i is the ain in d( from isotropic sourceT d(d is the ain from a dipole source"

d(d 2"1 O d(i"

4. What is the ieren"e ,etween ! an !m?

d(m is a unit of power level, measured in milli-watts in loarithm scale, that is,

d(m O 10 Q lo$Q1000& where is the power in atts

d( is not a unit, it is the difference in d(m"

6. What is 9!m?

0d(m O 1 milli-watt"

19. (ow oes TMA wor#?

%7 reduces system noise, improves uplink sensitivity and leads to loner *+ battery life"

#ensitivity is the minimum input power needed to et a suitable sinal-to-noise ratio $#NR& at

the output of the receiver" 't is determined by receiver noise fiure, thermo noise power and

re3uired #NR" %hermo noise power is determined by bandwidth and temperature, #NR isdetermined by modulation techni3ue, therefore the only variable is noise fiure"

%he cascadin noise fiure can be calculated by Friis e3uation $/erald Friis&5

NFtO NF1 $NF2-1&B81 $NF-1&B$81Q82& P $NFi-1&B$81Q82QPQ8i&

s the e3uation shows, the first block imposes the minimum and the most prominent noise fiure

on the system, and the followin blocks imposes less and less impact to the system provided theains are positive" 9inear passive devices have noise fiure e3ual to their loss" %7 typically

has a ain of 12d("

%here are typically top Uumper, main feeder and a bottom Uumper between antenna and (%#"

%7 placed near antenna with a short Uumper from antenna provides the best noise fiureimprovement 6 the noise fiure will be restricted to the top Uumper loss $NF1& and %7 $$NF2-

1&B81&, and the remainin blocks $main feeder and bottom Uumper& have little effect"

%o summari!e, a %7 has a ain thatJs close to feeder loss"


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11. What are the pros an "ons $a-anta8es an isa-anta8es% o TMA?

4n the upside, a %7 reduces system noise, improves uplink sensitivity and leads to loner *+

battery life" 4n the downside, %7 imposes an additional insertion loss $typically 0"d(& on thedownlink and increases site installation and maintenance compleity"

12. What is typi"al TMA 8ain?

%7 typically has a 12 d( ainT however, the effective ain comes from noise fiure reduction

and the ain is close or e3uivalent to the feeder loss"

1'. Why TMA are installe at the top near the antenna an not the ,ottom near the

*oe!?

(ased on Friis +3uation, havin a %7 near the (%# will have the top Uumper and main feeder

losses $noise fiures& cascaded in and a %7 will not be able to help suppress the losses"

1+. What is UMTS "hip rate?

"


16/28

EbNo5 +bBNo re3uirement $assumin d( for .#-12"2k&

i5 other-cell to in-cell interference ratio $assumin 0E&

R5 user data rate $assumin 12,200 kbps for .#-12"2k&

V5 loadin factor $assumin 0E&

%ake 12"2kbps as eample5

7 O B $+nNo Q $1 i& Q R& Q V O ,


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+cB'o is the ratio of the enery per chip in .'./ to the total received power density $includin

.'./ itself&"

22. Sometimes we say )"EIo an sometimes we say )"E*o3 are they ierent?

'o O own cell interference surroundin cell interference noise density

No O surroundin cell interference noise density

%hat is, 'o is the total received power density includin .'./ of its own cell, No is the total

received power density ecludin .'./ of its own cell" %echnically +cB'o should be the

correct measurement but, due to e3uipment capability, +cBNo is actually measured" 'n *7%#,+cBNo and +cB'o are often used interchaneably"

2'. What is :S


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'2. !rie es"ri,e the a-anta8es an isa-anta8es o sot hano-er?

dvantaes5

4vercome fadin throuh macro diversity"

Reduced Node ( power which in turn decreases interference and increases capacity"o Reduced *+ power $up ;d(&, decreasin interference and increasin battery life"

Disadvantaes5

*+ usin several radio links re3uires more channeli!ation codes, and more resources on

the 'ub and 'ur interfaces"

''. What are ast ain8 an slow ain8?

Fast fadin is also called multi-path fadin, as a result of multi-path propaation" hen multi-

path sinals arrivin at a *+, the constructive and destructive phases create a variation in sinalstrenth"

#low fadin is also called shadowin" hen a *+ moves away from a cell the sinal strenthdrops down slowly"

'+. What are ast ain8 mar8in an slow ain8 mar8in?

%o factor in the fast fadin and slow fadin, we need to have a marin in the link budet and

they are called fast fadin marin and slow fadin marin"

'n link budet, the fast fadin marin is usually set to 2-T slow fadin marin is set to L-10"

'. What is a typi"al sot hano-er 8ain in your lin# ,u8et?

.#-12"2k5 d( $*9&, 2d( $D9&"

#-;k5 1d( $*9&, 0d( $D9&"

#-12


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'4. (ow mu"h power usually a *oe! is allo"ate to "ontrol "hannels?

%he power allocated to control channels may depend on e3uipment vendor recommendation"

%ypically no more than 20E of the total Node( power is allocated to control channels, includin.'./" /owever, if /#D is deployed on the same carrier then the total power allocated to

control channel may o up to 2 to 0E because of the additional /#D control channelsre3uired"

'6. What is a typi"al


21/28

++. Suppose I ha-e a maHimum path5loss o 1'9!m3 what is the new path5loss i a !

,oy loss is ae?

12d("

+. What is "hannelization "oe?

.hanneli!ation codes are orthoonal codes used to spread the sinal and hence provides channel

separation, that is, channeli!ation codes are used to separate channels from a cell"

+/. (ow many "hannelization "oes are a-aila,le?

%he number of channeli!ation codes available is dependent on the lenth of code" 'n the uplink

the lenth is defined as between ; and 2" 'n the downlink the lenth is defined as between ;and 12"

+. Are "hannelization "oes mutually ortho8onal? I so3 why is FOrtho8onality @a"torGreuire in the lin# ,u8et?

Mes, channeli!ation codes are mutually orthoonal" Nonetheless, due to multi-path with variabletime delay, channels from the same cell are no loner perfectly orthoonal and may interfere

with each other"

=Downlink 4rthoonality Factor>, typically 0-0E, is therefore needed in the link budet to

account for the interference 6 and hence reduces pole capacity"

+4. What is s"ram,lin8 "oe? (ow many s"ram,lin8 "oes there are?

#cramblin codes are used to separate cells and *+s from each other, that is, each cell or *+

should have a uni3ue scramblin code" %here are 12 scramblin codes on the downlink and

millions on the uplink"

+6. What is s"ram,lin8 F"oe 8roupG?

%he 12 scramblin codes are divided into ; code roups 6 each code roup has < scramblincodes"

.ode roup i$iO 0 to & has codes from iQ< to $i1&Q


22/28

1. Whi"h ser-i"e usually nees hi8her power3 S or " 'n theory, the =noise rise> is defined as the ratio of total received

wideband power to the noise power" /iher =noise rise> value implies more users are allowed

on the network, and each user has to transmit hiher power to overcome the hiher noise level"%his means smaller path loss can be tolerated and the cell radius is reduced" %o summari!e, a

hiher noise rise means hiher capacity and smaller footprint, a lower noise rise means smaller

capacity and bier footprint"

+. What is Fpilot pollutionG?

#imply speakin, when the number of stron cells eceeds the active set si!e, there is =pilotpollution> in the area" %ypically the active set si!e is , so if there are more than stron cells

then there is pilot pollution"

Definition of =stron cell>5 pilots within the handover window si!e from the stronest cell"%ypical handover window si!e is between ; to d(" For eample, if there are more than 2 cells

$besides the stronest cell& within ;d( of the stronest cell then there is pilot pollution"

. What is a typi"al hano-er winow size in your networ#?

handover window si!e is usually between ; to d("

/. What is Fsot hano-erG an Fsoter hano-erG?

=#oft handover> is when *+ has connection to multiple cells on different Node("

=#ofter handover> is when *+ has connection to multiple cells on same Node("

'n downlink a *+ can combine sinals from different cells, improvin the sinal 3uality" For

uplink and soft handover, RN. selects the best sinal from different Node(" For uplink and

softer handover, a Node( combines the sinal from different sectors"


23/28

. >urin8 a hano-er3 i one "ell sens a power own reuest an two "ells sen a power

up reuest3 shall the U) power up or power own?

ower down" s lon as a ood link can be maintained it is not necessary to power up in orderto maintain multiple links" 7aintainin unnecessary multiple links increases noise rise and shall

be avoided"

4. Suppose we are esi8nin8 a S networ# an a es"ri,e the power "ontrol s"hemes in UMTS?

4pen loop 6 for *+ to access the network, i"e" used at call setup or initial access to set

*+ transmit power"

.losed outer loop5 RN. calculates the #'R taret and sends the taret to Node( $every10ms frame&"

.losed inner loop5 Node( sends the %. bits to *+ to increase or decrease the power at

1,00 times a second"

/'. What is the reuen"y o power "ontrol $how ast is power "ontrol%?

4pen loop5 depends on parameter settin5

%00 6 time to wait between RR. retries $100ms to


24/28

.losed outer loop5 100 times a second"

.losed inner loop5 1,00 times a second"

/+. !riely es"ri,e why open loop power "ontrol is neee an how it wor#s?

hen a *+ needs to access to the network it uses R./ to bein the process" R./ is a shared channel on the uplink used by all *+, therefore may encounter

contention $collision& durin multiple user access attempts and interfere with each other"

+ach *+ must estimate the amount of power to use on the access attempt since nofeedback from the Node( eists as it does on the dedicated channel"

%he purpose of open loop power control is to minimi!e the chance of collision and

minimi!e the initial *+ transmit power to reduce interference to other *+"

'nitial *+ transmit power O rimary@.'./@ower 6 .'./@R#. *9@'nterferrnce constant@[email protected]

'nstead of sendin the whole messae, a =test> $preamble& is sent" ait for answer from Node("

'f no answer from Node( increase the power"

%ry and try until succeed or timeout"

/. What is power "ontrol FhearoomG?

ower control =headroom> is also called =power rise>" 'n a non-fadin channel the *+ needs to

transmit a certain fied power" 'n a fadin chennel a *+ reacts to power control commands andusually increases the transmit power" %he difference between the averae power levels of fadin

and non-fadin channels is called =power rise> or =headroom>"

//. When in '5way sot hano-er3 i a U) re"ei-es power own reuest rom one "ell an

power up reuest rom the other 2 "ells3 shoul the U) power up or own an why?

ower down" 7aintainin one ood link is sufficient to sustain a call and havin unnecessarystroner links creates more interference"

/. Suppose two U) are ser-e ,y the same "ell3 the U) with wea#er lin# $poor :@

"onition% uses more F"apa"ityG3 why oes this mean?

%he *+ with weaker RF link will re3uire Node( to transmit hiher traffic power in order to

reach the *+, resultin in less power for other *+ 6 therefore consumes more =capacity>"

/4. Uner what "ir"umstan"es "an a *oe! rea"h its "apa"ity? What are the "apa"ity

limitations?

Node( reaches its maimum transmit power, runs out of its channel elements, uplink noise risereaches its desin taret, etc"


25/28

/6. What is F"ell ,reathin8G an why?

%he cell coverae shrinks as the loadin increases, this is called cell breathin"

'n the uplink, as more and more *+ are served by a cell, each *+ needs to transmit hiher power

to compensate for the uplink noise rise" s a conse3uence, the *+ with weaker link $*+ atreater distance& may not have enouh power to reach the Node( 6 therefore a coverae

shrinkae"

'n the downlink, the Node( also needs to transmit hiher power as more *+ are bein served"

s a conse3uence *+ with weaker link $reater distance& may not be reachable by the Node("

9. Is UMTS an uplin#5limite or ownlin#5limite system?

*7%# system could be either uplink-limited or downlink-limited dependin on the loadin"

'n a lihtly loaded system, the *+ transmit power sets a coverae limitation therefore it is

uplink-limited" 'n a heavily loaded system, the Node( transmit power limits the number of *+sit can serve therefore it is downlink-limited"

1. What is the impa"t o hi8her ata rate on "o-era8e?

/iher data rate has lower processin ain and therefore a Node( needs to transmit more power

to meet the re3uired +bBNoT this means the coverae is smaller for hiher data rate"

2. What is O*S?

4.N# stands for 4rthoonal .hannel Noise #imulator" 't is a simulated network load usually by

increasin the noise rise fiure in the Node("

492.11 *etwor# Ar"hite"ture

7arch ;, 2011


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+" 2 7/!

F" 0 7/!

Answer: C

QU)STIO* 2

hat are three operational channel widths specified by the


27/28

Answer: D

QU)STIO*

hat carrier sense mechanisms are deployed by the '+++


28/28

(" 2";010 6 2";L0 8/!

." 2";000 6 2";L2 8/!

D" 2";000 6 2";

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UMTS Question