45651639 total-umts

1. What isa typical NodeBsensitivitylevel?
The service andloaddeterminesthe NodeBsensitivity;ingeneral,inano-loadcondition,the sensitivity
isbetween -115dBmto -125dBm. ForEricsson,the NodeBsensitivityleveliscalculatedataround:
CS12.2: -124 dBm
PS-64: -119 dBm
PS-128: -115 dBm
PS-384: -115 dBm
What isa typical UE sensitivitylevel?
The service andloaddeterminesthe UEsensitivity;ingeneral,inno-loadcondition,the sensitivityis
between -105dBmand -120dBm. For Ericsson,the UE sensitivitylevel iscalculatedataround:
CS12.2: -119 dBm
PS-64: -112 dBm
PS-128: -110 dBm
PS-384: -105 dBm

2. HSDPA: -95 dBm
What isa typical NodeBmaximumoutputpower?
The maximumNodeBoutputpowerisusually20Wor 40W, that is,43dBm or 46dBm.
What isUE maximumtransmitpowerinyourlinkbudget?
21dBm.
What isa typical antennagain?
The antennagain dependsonantennamodel;inlinkbudgetwe use around17dBi.
What isa typical maximumpathloss?
The maximumpathlossisdependentonthe service andvendorrecommendations;typicallyitisin
between135 to 140dB for urbanareas and between150to 160dB for rural areas.
What isdifference betweendBi anddBd?

3. dBi is the gainin dB fromisotropicsource;dBdis the gainfroma dipole source.
dBd + 2.15 = dBi.
What isthe difference betweendBanddBm?
dBm isa unitof powerlevel,measuredinmilli-wattsinlogarithmscale,thatis,
dBm = 10 * log(W*1000) where W isthe powerinWatts dB is not a unit,itis the difference indBm.
What is0dBm?
0dBm = 1 milli-watt.
How doesTMA work?
A TMA reducessystemnoise,improvesuplinksensitivityandleadstolongerUE batterylife.Sensitivityis
the minimuminput powerneededtogetasuitable signal-to-noise ratio(SNR) atthe outputof the
receiver. Itisdeterminedbyreceivernoise figure,thermonoise powerandrequiredSNR. Thermo
noise powerisdeterminedbybandwidthandtemperature,SNRisdeterminedby modulationtechnique,
therefore the onlyvariableisnoise figure.
The cascading noise figure canbe calculatedbyFriisequation(HeraldFriis):
NFt= NF1 + (NF2-1)/G1+ (NF3-1)/(G1*G2) + ... + (NFi-1)/(G1*G2*...*Gi)

4. As the equationshows,the firstblockimposesthe minimumandthe mostprominentnoise figure on
the system,andthe followingblocksimposeslessandlessimpacttothe systemprovidedthe gainsare
positive. Linearpassive deviceshave noise figure equaltotheirloss. A TMA typically hasa gainof 12dB.
There are typicallytopjumper,mainfeederanda bottomjumperbetweenantennaandBTS. A TMA
placednearantennawitha short jumperfromantennaprovidesthe bestnoise figure improvement –
the noise figure will be restrictedtothe topjumperloss(NF1) andTMA ((NF2-1)/G1),andthe remaining
blocks(mainfeederandbottomjumper) have little effect.
To summarize,aTMA hasa gainthat’sclose to feederloss.
What are the pros andcons (advantagesanddisadvantages) of TMA?
On the upside,aTMA reducessystemnoise,improvesuplinksensitivityandleadstolongerUE battery
life. Onthe downside,TMA imposesanadditional insertionloss(typically0.5dB) onthe downlinkand
increasessite installationandmaintenance complexity.
What istypical TMA gain?
TMA typicallyhasa12 dB gain; however,the effectivegaincomesfromnoise figure reductionandthe
gainis close or equivalenttothe feederloss.
Why TMA are installedatthe topnearthe antennaandnot the bottomnear the NodeB?
Basedon FriisEquation,havingaTMA near the BTS will have the topjumperandmainfeederlosses
(noise figures) cascadedinanda TMA will notbe able to helpsuppressthe losses.

5. What isUMTS chiprate?
3.84MHz.
What isprocessinggain?
Processinggainisthe ratioof chiprate overdata bitrate,usuallyrepresentedindecibel (dB)scale. For
example,with3.84MHzchip rate and 12.2k data rate,the processinggainis:
PG12.2k = 10 * log (3,840,000 / 12,200) = 25dB
What are the processinggainsforCSand PS services?
CS12.2: 25dB
PS-64: 18dB
PS-128: 15dB
PS-384: 10dB

6. HSDPA: 2dB
How to calculate maximumnumberof usersona cell?
To calculate the maximumnumberof users(M) ona cell,we needtoknow:
W: chip rate (forUMTS 3,840,000 chipsper second)
EbNo:Eb/Norequirement(assuming3dBfor CS-12.2k)
i: other-celltoin-cell interference ratio(assuming60%)
R: userdata rate (assuming12,200 kbpsfor CS-12.2k)
η: loadingfactor(assuming50%)
Take 12.2kbps as example:
M = W / (EnNo* (1 + i) * R) * η = 3,840,000 (3 * (1 + 0.6) * 12,200) * 0.5 = 32.8
The numberof userscouldalsobe hard-limitedbyOVSFcode space. Take CS12.2k for example:
a. A CS-12.2k bearerneeds1 SF128 code.

7. b. Total available codesforCS-12.2k= 128 – 2 (1 SF64) – 2 (4 SF256) = 124.
c. Considersoft-handoverfactorof 1.8 and loadingfactorof 50%: 124 / 1.8 *.05 = 34 uers/cell.
What isEb/No?
By definitionEb/Noisenergybitovernoisedensity,i.e.isthe ratioof the energyperinformationbitto
the powerspectral density(of interferenceandnoise) afterdispreading.
Eb/No= ProcessingGain+ SIR
For example,if Eb/Nois5dBand processinggainis25dB thenthe SIR shouldbe -20dB or better.
What are the Eb/Notargetsin yourdesign?
The Eb/No targetsare dependentonthe service:
§ On the uplink,typicallyCSis5 to 6dB and PS is3 to 4dB – PS isabout 2dB lower.
§ On the downlink,typicallyCShas6 to 7dB and PSis 5 to 6dB – PSis about1dB lower.
Why isEb/NorequirementlowerforPSthanfor CS?

8. PS hasa bettererrorcorrectioncapabilityandcanutilize retransmission,therefore itcanaffordto a
lowerEb/No. CSis real-time andcannottolerate delaysoitneedsahigherEb/Noto maintainastronger
RF link.
What isEc/Io?
Ec/Io isthe ratio of the energyperchipinCPICH to the total receivedpowerdensity(includingCPICH
itself).
Sometimeswe sayEc/Ioandsometimeswe sayEc/No,are theydifferent?
Io = own cell interference+surroundingcell interference+noise density
No = surroundingcell interference +noise density
That is,Io isthe total receivedpowerdensityincludingCPICHof itsowncell,Noisthe total received
powerdensityexcludingCPICHof itsowncell. TechnicallyEc/Ioshouldbe the correctmeasurement
but,due to equipmentcapability,Ec/Noisactuallymeasured. InUMTS, Ec/No and Ec/Io are oftenused
interchangeably.
What isRSCP?

9. RSCPstands forReceivedSignal Code Power –the energyperchipin CPICHaveragedover512 chips.
What isSIR?
SIR isthe Signal-to-Interference Ratio –the ratioof the energyindedicatedphysicalcontrol channel bits
to the powerdensityof interference andnoise afterdispreading.
What isthe loadingfactorinyour design?
The designedloadingtypicallyis50%;however,sometimesacarriermay wantto designupto 75% load.
Give a simple definitionof pole capacity?
The uplinknoise increaseswiththe loadingexponentially. Whenthe uplinknoise approachesinfinity
thenno more userscan be addedto a cell – andthe cell loadingisclose to100% andhas reachedits
“pole capacity”.
Mathematically,tocalculate the uplinkpole capacitywe needtoknow:
W: chip rate (forUMTS 3,840,000 chipsper second)
R: userdata rate (assuming12,200 kbpsfor CS-12.2k)

10. f: other-cell toin-cell interference ratio(assuming65%)
EbNo:Eb/Norequirement(assuming5dB)
AF:Activityfactor(assuming50%)
Pole Capacity= (W/R) / ((1+f) * AF * 10^(EbNo/10)) = 120.6
To calculate the downlinkpolecapacitywe alsoneedtoknow:
α: downlinkchannelsorthogonalityfactor(assuming55%)
Pole Capacity = (W/R) / ((1- α +f) * 10^(EbNo/10)) = 64.06
What istypical pole capacityfor CS-12.2, PS-64,PS-128 andPS-384?
Withsame assumptionsasabove:
§ CS-12.2k: 120.6 (UL),64.1 (DL).
§ PS-64k: 34.8 (UL),12.8(DL).
§ PS-128k: 16.2 (UL),8.4 (DL).

11. § PS-384k: 16.2 (UL),2.8 (DL).
PS-384k has only128k on the uplink,therefore the uplinkcapacityisthe same forboth.
How manytypesof handoversare there inUMTS?
Softhandover,softerhandover,inter-frequencyhandover,inter-RAThandover,inter-RATcell change
(UE movingoutof UMTS coverage intoGSM/GPRS/EGDGE coverage).
What issoft handoverandsofterhandover?
§ Softhandover:whenaUE is connectedtocellsownedbydifferentNodeB.
§ Softerhandover:whenaUE isconnectedtocellsownedbythe same NodeB.
How doessoft/softerhandoverwork?
§ Soft/softerhandoverdownlink:UErake receiverperformsmaximumratiocombining,i.e.UE
combinesmulti-pathsignalsandforma strongersignal.
§ Softhandoveruplink:RNCperformsselectioncombining,i.e.RNCselectsthe bettersignalcoming
frommultiple NodeB.

12. § Softerhandoveruplink:NodeBperformsmaximumratiocombining,i.e.NodeB rake receiver
combinessignalsfromdifferentpathsandformsa strongersignal.
Why isthere “softhandovergain”?
Softhandovergaincomesfromthe following:
§ Macro diversitygainoverslowfading.
§ Micro diversitygainoverfastfading.
§ DownlinkloadsharingovermultipleRFlinks. Bymaintainingmultiplelinkseachlinkcouldtransmitat
a lowerpower,resultinginlowerinterference therefore again.
Brief describe the advantagesanddisadvantagesof softhandover?
Advantages:
§ Overcome fadingthroughmacrodiversity.
§ ReducedNode Bpowerwhichinturn decreasesinterference andincreasescapacity.
§ ReducedUE power(up4dB),decreasinginterference andincreasingbatterylife.

13. Disadvantages:
§ UE usingseveral radiolinksrequiresmore channelizationcodes,andmore resourcesonthe Iuband
Iur interfaces.
What are fastfadingand slowfading?
Fast fadingisalsocalledmulti-pathfading,asaresultof multi-pathpropagation. Whenmulti-path
signalsarrivingata UE, the constructive anddestructive phasescreate avariationinsignal strength.
Slowfadingisalsocalledshadowing. WhenaUE movesawayfroma cell the signal strengthdropsdown
slowly.
What are fastfadingmarginand slowfadingmargin?
To factor inthe fastfadingandslowfading,we needtohave a marginin the linkbudgetandtheyare
calledfastfadingmarginandslowfadingmargin.
In linkbudget,the fastfadingmarginisusuallysetto2-3; slow fadingmarginissetto 7-10.
What isa typical softhandovergaininyourlinkbudget?
a. CS-12.2k: 3dB (UL), 2dB (DL).

14. b. PS-64k: 1dB (UL), 0dB (DL).
c. PS-128k: 1dB (UL), 0dB (DL).
d. PS-384k: 1dB (UL), 0dB (DL).
What isthe percentage intime aUE isexpectedtobe insoftor softerhandover?
TypicallyaUE shouldbe insofthandovermode at nomore than35 to 40% of the time;insofter
handovermode atabout 5% of the time.
What isa typical EiRP?
The EiRP dependsNodeBtransmitpower,cable andconnectorlossandantennagain. Witha sample
systemof 43dBm transmitpower,a3dB cable and connectorlossand a 17dBi antennagain,the EiRP =
43 – 3 + 17 = 57dBm.
How muchpowerusuallyaNodeBisallocatedtocontrol channels?
The powerallocatedtocontrol channelsmaydependonequipmentvendorrecommendation. Typically
no more than 20% of the total NodeBpowerisallocatedtocontrol channels,includingCPICH. However,
if HSDPA is deployedonthe same carrierthenthe total powerallocatedtocontrol channel maygo upto
25 to 30% because of the additional HSDPA control channelsrequired.

15. What isa typical CPICHpower?
CPICHpowertypicallytakesabout10% of the total NodeBpower. Fora 20W (43dBm) NodeB,CPICHis
around2W (33dBm).
In urbanareas where in-buildingcoverageistakencare of by in-buildinginstallations,the CPICHmay
sometimesgoaslowas 5% because:
§ The coverage area issmall since usersare close to the site,and
§ More powercan be allocatedtotrafficchannels.
How muchis yourHSDPA (max) linkpower?
HSDPA linkpoweristypically4to 5dB below the maximumNodeBmaximumoutputpower. For
example,for43dBmmaximumNodeBpowerthe HSDPA linkpoweris39dBm.
Considerdownlinkonly,whatare the majorcomponentsincalculatingmaximumpathloss,starting
fromNodeB?
§ NodeBCPICHtransmitpower.
§ Jumperandfeederconnectorloss.

16. § Antennagain.
§ Over-the-airloss.
§ Building/vehicle penetrationloss.
§ Bodyloss.
§ Etc.
What ismaximumpath-loss?
The maximumpath-lossishowmuchsignal isallowedtodropfroma transmittertoa receiverand
maintainsasgoodsignal.
Simple linkbudget:witha30dBm CPICH anda -100dBm UE sensitivity,ignoringanythinginbetween,
whatis the maximumpathloss?
30 – (–100) = 30 + 100 = 130dB.
Suppose Ihave a maximumpath-lossof 130dBm, what isthe new path-lossif a5dB bodylossisadded?

17. 125dB.
What ischannelizationcode?
Channelization codesare orthogonal codesusedtospreadthe signal andhence provideschannel
separation,thatis,channelizationcodesare usedtoseparate channelsfromacell.
How manychannelizationcodesare available?
The numberof channelizationcodesavailable isdependentonthe lengthof code. Inthe uplinkthe
lengthisdefinedasbetween4and256. In the downlinkthe lengthisdefinedasbetween4and512.
Are channelizationcodesmutuallyorthogonal? If so,whyis“OrthogonalityFactor”required inthe link
budget?
Yes,channelizationcodesare mutuallyorthogonal. Nonetheless,due tomulti-pathwithvariabletime
delay,channelsfromthe same cell are nolongerperfectlyorthogonal andmayinterferewitheach
other.
A “DownlinkOrthogonalityFactor”,typically50-60%,istherefore neededinthe linkbudgettoaccount
for the interference –andhence reducespole capacity.

18. What isscramblingcode? How manyscramblingcodesthere are?
Scramblingcodesare usedto separate cellsandUEs fromeach other,thatis, eachcell or UE should
have a unique scramblingcode. There are 512 scramblingcodesonthe downlinkandmillionsonthe
uplink.
What isscrambling“code group”?
The 512 scramblingcodesare dividedinto64code groups – eachcode group has 8 scramblingcodes.
Code groupi (i = 0 to 63) has codesfromi*8 to (i+1)*8-1,i.e.(0-7) (8-15)…(504-511).
Do youdivide scramblingcode groupsintosubgroups? Please giveanexample.
Yes,we divide the 64 code groups intosubgroups:
§ Macro layergroup:24 code groupsreservedformacro(outdoor) sites.
§ Micro layergroup:16 code groupsreservedformicro(in-building)sites.

19. § Expansiongroup:24 code groupsreservedforfuture expansionsites.
Whichservice usuallyneedshigherpower,CSorPS?
Considerdownlinkandtake CS-12.2and PS-384k for example. The processinggainis25 for CS-12.2 and
10 for PS-384. The Eb/Norequirementis7 forCS-12.2 and5 for PS-384. Therefore the power
requirementishigherforCS-12.2than PS-384.
What isEb/No requirementforHSDPA?
The Eb/No requirementforHSDPA varieswithuserbitrate (datarate),typically2for 768kbps and 5 for
2Mbps.
What is“noise rise”? What doesa highernoise rise meanintermsof networkloading?
For everynewuseraddedtothe service,additionalnoise isaddedtothe network. Thatis,eachnew
usercausesa “noise rise”. Intheory,the “noise rise”isdefinedasthe ratioof total receivedwideband
powerto the noise power. Higher“noise rise”value impliesmore usersare allowedonthe network,
and eachuser hasto transmithigherpowertoovercome the highernoise level. Thismeanssmaller
path losscan be toleratedandthe cell radiusisreduced. Tosummarize,ahighernoise rise means
highercapacityand smallerfootprint,alowernoise rise meanssmallercapacityandbiggerfootprint.
What is“pilotpollution”?

20. Simplyspeaking,whenthe numberof strongcellsexceedsthe active setsize,thereis“pilotpollution”in
the area. Typicallythe active setsize is3,so if there are more than 3 strongcellsthenthere ispilot
pollution.
Definitionof “strongcell”:pilotswithinthe handoverwindowsize fromthe strongestcell. Typical
handoverwindowsize isbetween4to 6dB. For example,if there are more than2 cells(besidesthe
strongestcell) within4dBof the strongestcell thenthere ispilotpollution.
What isa typical handoverwindowsize inyournetwork?
A handoverwindowsizeisusuallybetween4to6dB.
What is“soft handover”and“softerhandover”?
“Softhandover”iswhenUE hasconnectiontomultiple cellsondifferentNodeB.
“Softerhandover”iswhenUE has connection tomultiplecellsonsame NodeB.
In downlinkaUE can combine signalsfromdifferentcells,improvingthe signal quality. Foruplinkand
softhandover,RNCselectsthe bestsignal fromdifferentNodeB. Foruplinkandsofterhandover,a
NodeBcombinesthe signal fromdifferentsectors.

21. Duringa handover,if one cell sendsapowerdownrequestandtwocellssendapoweruprequest,shall
the UE powerup or powerdown?
Powerdown. Aslongas a goodlinkcan be maintaineditisnotnecessarytopowerup inorderto
maintainmultiple links. Maintainingunnecessarymultiplelinksincreasesnoise riseandshall be
avoided.
Suppose we are designingaCSnetworkanda PS network,isthere amajor difference inthe design
consideration?
Serverdominance isthe keydifference. InaCS networkwe shall limitthe numberof strongserversin
any givenareato nomore thanthe active setsize toavoidpilotpollution(inthe downlink). Ina PS
network,however,there isn’tsofthandoverinthe downlinksothe serverdominance isveryimportant
– meaningideallythereshouldbe onlyone dominantserverinagivenarea.
What isthe active setsize onyour network?
3.
How manyfingersdoesaUE rake receiverhave?
4.

22. What is“compressedmode”?
Before UE can performinter-frequencyorIRAThandover,itneedstohave some time tolockon to the
control channel of the otherfrequencyorsystemandlistentothe broadcast information. Certainidle
periodsare createdinradioframesfor thispurpose andiscalled“compressedmode”.
Describe the powercontrol schemesinUMTS?
§ Openloop – for UE to accessthe network,i.e.usedatcall setupor initial accesstosetUE transmit
power.
§ Closed outerloop:RNCcalculatesthe SIRtargetand sendsthe targetto NodeB(every10msframe).
§ Closedinnerloop:NodeBsendsthe TPCbitstoUE to increase or decrease the powerat1,500 timesa
second.
What isthe frequencyof powercontrol (how fast ispowercontrol)?
§ Openloop:dependsonparametersetting:
T300 – time to waitbetweenRRCretries(100msto 8000 ms,typical 1500ms)
§ Closedouterloop:100 timesa second.

23. § Closedinnerloop:1,500 timesa second.
Brieflydescribewhyopen looppowercontrol isneededandhow itworks?
§ Whena UE needstoaccess to the networkitusesRACHto beginthe process.
§ RACH isa sharedchannel onthe uplinkusedbyall UE, therefore mayencountercontention(collision)
duringmultiple useraccessattemptsandinterfere witheachother.
§ Each UE must estimate the amountof powertouse on the accessattemptsince no feedbackfromthe
NodeBexistsasitdoeson the dedicatedchannel.
§ The purpose of openlooppowercontrol isto minimize the chance of collisionandminimizethe initial
UE transmitpowertoreduce interference tootherUE.
§ Initial UE transmitpower= Primary_CPICH_Power –CPICH_RSCP+ UL_Interferrnce +
constant_Value_Cprach
§ Insteadof sendingthe whole message,a“test”(preamble) issent.
§ Wait foranswerfromNodeB.
§ If no answerfromNodeBincrease the power.
§ Try and try until succeedortimeout.

24. What ispowercontrol “headroom”?
Powercontrol “headroom”isalsocalled“powerrise”. Ina non-fadingchannel the UEneedstotransmit
a certainfixedpower. Ina fadingchennel aUE reacts to powercontrol commandsandusuallyincreases
the transmitpower. The difference betweenthe averagepowerlevelsof fadingandnon-fading
channelsiscalled“powerrise”or“headroom”.
Whenin3-way softhandover,if a UE receivespowerdownrequestfromone cell andpoweruprequest
fromthe other2 cells,shouldthe UE powerupor downand why?
Powerdown. Maintainingone goodlinkissufficienttosustainacall andhavingunnecessarystronger
linkscreatesmore interference.
Suppose twoUE are servedbythe same cell,the UE withweakerlink(poorRFcondition)usesmore
“capacity”,why doesthismean?
The UE withweakerRFlinkwill require NodeBtotransmithighertrafficpowerinordertoreachthe UE,
resultinginlesspowerforotherUE – therefore consumesmore “capacity”.
Under whatcircumstancescan a NodeBreachitscapacity? What are the capacitylimitations?
NodeBreachesitsmaximumtransmitpower,runsoutof itschannel elements,uplinknoise risereaches
itsdesigntarget,etc.
What is“cell breathing”andwhy?

25. The cell coverage shrinksasthe loadingincreases,thisiscalledcellbreathing.
In the uplink,asmore and more UE are servedbya cell,eachUE needstotransmithigherpowerto
compensate forthe uplinknoise rise. Asaconsequence,the UEwithweakerlink(UEat greater
distance) maynothave enoughpowertoreach the NodeB – therefore acoverage shrinkage.
In the downlink,the NodeBalsoneedstotransmithigherpowerasmore UE are beingserved. Asa
consequence UEwithweakerlink(greaterdistance)maynotbe reachable bythe NodeB.
Is UMTS an uplink-limitedordownlink-limitedsystem?
A UMTS systemcouldbe eitheruplink-limitedordownlink-limiteddependingonthe loading. Inalightly
loadedsystem,the UEtransmitpowersetsa coverage limitationtherefore itisuplink-limited. Ina
heavilyloadedsystem, the NodeBtransmitpowerlimitsthe numberof UEs itcan serve therefore itis
downlink-limited.
What isthe impactof higherdata rate oncoverage?
Higherdata rate has lowerprocessinggainandtherefore aNodeBneedstotransmitmore powerto
meetthe requiredEb/No;thismeansthe coverage issmallerforhigherdatarate.
What isOCNS?

26. OCNSstandsfor Orthogonal Channel Noise Simulator. Itisa simulatednetworkloadusuallyby
increasingthe noise rise figure inthe NodeB.
What are the interfacesbetweeneachUTRAN component?
Uu: UE to NodeB
Iub:NodeBto RNC
Iur: RNCto RNC
Iu: RNCto MSC
Brieflydescribethe UEto UTRAN protocol stack (airinterface layers).
The radio interface isdividedinto3layers:
1. Physical layer(Layer1,L1): usedtotransmitdata overthe air, responsible forchannel coding,
interleaving,repetition,modulation,powercontrol,macro-diversitycombining.
2. Linklayer(L2): issplitinto2 sub-layers–MediumAccessControl (MAC) andRadio LinkControl
(RLC).
· MAC: responsible formultiplexingdatafrommultiple applicationsontophysicalchannelsin
preparationforover-the-airtransmition.

27. · RLC: segmentsthe datastreamsintoframesthatare small enoughtobe transmittedoverthe radio
link.
3. Upper layer(L3):verticallypartitionedinto2planes:control plane forsignalinganduserplanfor
bearertraffic.
· RRC (RadioResource Control) isthe control planprotocol:controlsthe radioresourcesforthe access
network.
In implementation:
1. UE has all 3 layers.
2. NodeBhasPhysical Layer.
3. RNC hadMAC layerandRRC layer.
BrieflydescribeUMTS airinterface channel typesandtheirfunctions.
There are 3 typesof channelsacrossairinterface – physical channel,transportchannelandlogical
channel:
§ Physical Channel:carriesdatabetweenphysical layersof UE and NodeB.
§ TransportChannel:carriesdata betweenphysical layerandMAClayer.

28. § Logical Channel:carriesdatabetweenMAClayerandRRC layer.
Give some examplesof Physical,TransportandLogical channels.
1. Logical Channel:
· Control channel:BCCH,PCCH,CCCH,DCCH.
· Trafficchannel:DTCH,CTCH.
2. Transport Channel:
· Commoncontrol channel:BCH,FACH,PCH,RACH, CPCH.
· Dedicatedchannel:DCH,DSCH.
2. Physical Channel:
· Commoncontrol channel:P-CCPCH,S-CCPCH,P-SCH,S-SCH,CPICH,AICH,PICH,PDSCH,PRACH,
PCPCH,CD/CA-ICH.
· Dedicatedchannel:DPDCH,DPCCH.
What are the RRC operationmodes?

29. Idle mode andconnectedmode.
What are the RRC states?
There are 4 RRC States:Cell_DCH,Cell_FACH,URA_PCHandCell_PCH.
URA = UTRAN RegistrationArea.
What are transparentmode,acknowledgedmode andunacknowledgedmode?
§ Transparentmode correspondstothe lowestserviceof the RLC layer,nocontrolsandno detectionof
missingdata.

30. § Unacknowledgedmode offersthe possibilityof segmentandconcatenate of databutno error
correctionor retransmissiontherefore noguarantee of delivery.
§ Acknowledgedmodeoffers,inadditiontoUM mode functions,acknowledgementof transmission,
flowcontrol,errorcorrectionandretransmission.
Whichlayer(s) performcipheringfunction?
RRC – foracknowledgedmode (AM) andunacknowledgedmode (UM).
MAC – fortransparentmode (TM).
What isOVSF?
Orthogonal Variable SpreadingFactor.
How manyOVSFcode spacesare available?
§ Total OVSFcodes= 256.
§ Reserved:1SF64 forS-CCPCH,1 SF256 forCPICH,P-CCPCH,PICHand AICHeach.
§ Total available code space = 256 – 4 (1 SF64) – 4 (4 SF256) = 248.

31. Can code space limitthe cell capacity?
Yes,cell capacitycan be hard-limitedbycode space. Take CS-12.2k forexample:
§ A CS-12.2k bearerneeds1 SF128 code.
§ Total available codesforCS-12.2k= 128 – 2 (1 SF64) – 2 (4 SF256) = 124.
§ Considersoft-handoverfactorof 1.8: 124 / 1.8 = 68 uers/cell.
Can a userhave OVSFcode as “1111”?
No,because “1111…” (256 times) isusedbyCPICH.
What are the symbol rates(bitspersymbol) forBPSK,QPSK,8PSKand16QAM?
§ BPSK:1.
§ QPSK:2.
§ 8PSK: 3.

32. § 16QAM: 4.
BrieflydescribeUMTS frame structure.
§ UMTS frame duration= 10ms.
§ Each frame is dividedinto15timeslots.
§ Each timeslotisdividedinto2560 chips.
§ Therefore 2560 chips/TS* 15 TS/frame * (1000ms/10ms) frame/sec=3,840,000 chip/sec.
What iscell selectioncriterion?
Cell selectionisbasedon:
a. Qmean:the average SIR of the targetcell.
b. Qmin:minimumrequiredSIR.
c. Pcompensation:acorrectionvalue fordifference UEclasses.
S = Qmean- Qmin- Pcompensation

33. d. If S>0 thenthe cell isa validcandidate.
e. A UE will campon the cell withthe highestS.
BrieflydescribeCapacityManagementanditsfunctions:
CapacityManagementisresponsible forthe control of the loadinthe cell. Itconsistsof 3 main
functions:
DedicatedMonitoredResource Handling:tracksutilizationof critical resourcesof the system.
AdmissionControl:accepts/refusesadmissionrequestsbasedonthe currentloadonthe dedicated
monitoredresourcesandthe characteristicsof the request
CongestionControl:detects/resolvesoverloadsituations
What are the major4 KPIsin propagationmodel tuningandtypical acceptable values?
The 4 KPIsare standarddeviationerror,rootmeansquare error,meanerror andcorrelationcoefficient.
The typical acceptable valuesare:
§ Standarddeviationerror: the smallerthe better,usually7 to 9dB.
§ Mean error:the smallerthe better,usually2to3.

34. § Root meansquare error:the smallerthe better,usually
§ Correlationcoefficient:the largerthe better,usually70% to90%.
What isthe minimumnumberof binsrequiredforacertainpropagationmodel?
The more binsthe more likelytocome upwitha good model. Usuallyaminimumof 2,000 binesis
consideredacceptable,butsometimesaslow as 500 binsmay be accepted.
How manyscramblingcodesare there?
There are 512 scrambling codesinthe downlinkand16,777,216 codesin the uplink.
How manyscramblingcode groupsare there fordownlink?
There are 64 code groups,each grouphas 8 scramblingcodes.
Can we assignsame scramblingcodestosistersectors(sectorsonsame site)?
No,because scramblingcode onthe downlinkisusedforcell identity. Asa requirement,scrambling
codeshave to maintainasafe separationtoavoidinterference.

35. Are scramblingcodesorthogonal?
No,scramblingcodesare not orthogonal since theyare notsynchronizedateachreceiver. Theyare
pseudorandomsequencesof codes.
Can we assignscramblingcodes1,2 and 3 to sistersectors?
Yes.
In IS-95 we have a PN reuse factor(PN stepsize) andtherefore cannotuse all 512 PN codes,whyisn’tit
necessaryforUMTS scramblingcodes?
Because IS-95 isa synchronizednetwork,differentPN codeshave the same code sequencewithatime
shift,thereforewe needtomaintainacertainPN stepsize toavoidmulti-pathproblem. Forexample,if
twosectors inthe neighborhoodhave asmall PN separationthensignal arrivingfromcell A mayruninto
the time domainof cell B, causinginterference.
UMTS, on the otherhand,isnot a synchronizednetworkandall scramblingcodesare mutually
orthogonal sono needtomaintaina stepsize.
What are coverage thresholdsinyourUMTS designandwhy?

36. The coverage thresholdsare basedonUE sensitivity,fadingandpenetrationloss. AssumingUE
sensitivityof -110dBm,fade marginof 5dB:
§ Outdoor:-110dBm sensitivity+5dB fade margin= -105dBm.
§ In-vehicle:-110dBm+ 5dB + 8dB in-vehiclepenetrationloss=-97dBm.
§ In-building:-110dBm+ 5dB + 15dB in-buildingpenetrationloss=-90dBm.
What isthe Ec/Iotarget inyour design?
The Ec/Io target typicallyisbetween -12to-14dB. However,if anetworkisdesignedfordatathenthe
Ec/Io targetcouldgo higherto around -10dB because serverdominance ismore critical fora data
network – since there isn’tsoftware inthe downlink.
What is“Monte Carlo simulation”?
Since UMTS coverage isdependentonthe loading,staticcoverage andqualityanalysis(RSCPandEc/Io)
representsthe networkperformance inno-loadcondition. Monte Carlosimulationisthereforeusedto
illustrate networkperformance undersimulatedloadingconsition.
What isthe keydifference betweenastaticanalysisanda Monte Carlo simulation?

37. Staticanalysiscan onlyshowRSCPand Ec/Ioin no-loadcondition. Monte Carlosimulationnotonlycan
showRSCPand Ec/Io insimulatedloadingconditionbutalsocan show manymore others:meanserved,
cell loading,uplinkanddownlinkcapacitylimitsreached,etc.
What shouldbe runfirst(whatinformationshouldbe readyandloaded) before runningaMonte Carlo
simulation?
Before runningMonte Carlosimulation,the followingshouldbe completedorinplace.
§ Run prediction.
§ Spreadthe traffic.
§ Define terminaltypes.
How manysnap shotsand iterationdoyouusuallyhave whenrunningMonte Carlosimulation?
(Dependonsoftware tool recommendations).
What are the designKPI’s?
(RSCP,Ec/Io,meanserved,softhandoverratio…)
What plotsdo youusuallycheckafter runningMonte Carlofor trouble spots?

38. (RSCP,Ec/Io,service probability,reasonsforfailure…)
What are the typical reasonsof failure inMonte Carlosimulation?
§ DownlinkEb/Nofailure (Capacity).
§ DownlinkEb/Nofailure (Range).
§ UplinkEb/Nofailure.
§ Low pilotSIR.
§ Noise rise limitreached.
§ Etc.
What does“trafficspread”mean?
“Trafficspread”meansspreadingtraffic(numberof terminals) inacell coverage area.
Do youuse live trafficoreven-loadtrafficinyourdesign?

39. (Depends).
What are the optimizationtoolsyouuse?
Drive test,analysis,others?
Are SystemInformationBlocks(SIB) transmittedall the time?
No,systeminformationblockismultiplexedwithsynchronizationchannel. Synchronizationchannel
occupiesthe firsttime slot(TS) andSIB occupiesthe other9 time slots.
How doesUE camp (synchronize) toaNodeB?
1. UE usesthe primarysynchronizationchannel (P-SCH) forslotalignment(TSsynchronization).
2. AfteraligningtoNodeBtime slot,UEthenusessecondarysynchronizationchannel (S-SCH) to
obtainframe synchronizationandscramblingcode groupidentification.
3. UE thenusesscramblingcode IDto obtain CPICH,thuscampingto a NodeB.

40. What couldbe the cause of soft handoverfailure?
§ UE issue.
§ Resource unavailable attargetNodeB.
§ Inadequate SHOthresholddefined.
§ Etc.
What are the three setsinhandover?
The 3 setsin handoverare:
§ Active set– the listof cellswhichare insofthandoverwithUE.
§ Monitoredset– the listof cellsnotinactive setbut RNChas toldUE to monitor.
§ Detectedset– listof cellsdetectedbythe UE but notconfiguredinthe neighborlist.
What are the majordifferencesbetweenGSMandUMTS handoverdecision?

41. GSM:
§ Time-basedmobilemeasuresof RxLevandRxQual – mobile sendsmeasurementreporteverySACH
period(480ms).
§ BSC instructsmobile tohandoverbasedonthese reports.
UMTS:
§ Event-triggeredreporting–UE sendsa measurementreportonlyoncertainevent“triggers”.
§ UE playsmore part inthe handoverdecision.
What are the events1a,1b, 1c, etc.?
§ e1a – a PrimaryCPICHentersthe reportingrange,i.e.add a cell toactive set.
§ e1b – a primaryCPICHleavesthe reportingrange,i.e.removedacell fromactive set.
§ e1c – a non-active primaryCPICHbecomesbetterthananactive primaryCPICH,i.e.replace acell.

42. § e1d: change of bestcell.
§ e1e:a PrimaryCPICHbecomesbetterthananabsolute threshold.
§ e1f:a PrimaryCPICHbecomesworse thananabsolute threshold.
What are event2a-2dand 3a-3d?
Events2a-2d are for inter-frequencyhandovermeasurementsandevents3a-3dare forIRAT handover
measurements.
§ e3a: the UMTS cell qualityhasmovedbelow athresholdandaGSM cell qualityhadmovedabove a
threshold.
§ e3b: the GSM cell qualityhasmovedbelowathreshold.
§ e3c: the GSM cell qualityhasmovedabove athreshold.
§ e3d: there wasa change in the orderof bestGSM cell list.
What may happenwhenthere’samissingneighbororan incorrectneighbor?

43. § Accessfailure andhandoverfailure:mayattempttoaccessto a wrongscramblingcode.
§ Droppedcall:UE notaware of a strongscramblingcode,stronginterference.
§ Poordata throughput.
§ Poorvoice quality.
§ Etc.
What can we try to improve whenaccessfailure ishigh?
Whenaccess failure ishighwe cantry the followingtoimprove RACH performance:
§ Increase maximumUEtransmitpowerallowed:Max_allowed_UL_TX_Power.
§ Increase powerquickly:power_Offset_P0.
§ Increase numberof preamblessentinagivenpreamblecycle:preamble_Retrans_Max.
§ Increase the numberof preamble cycles:max_Preamble_Cycle.

44. § Increase numberof RRC ConnectionRequestretries:N300.
What are the conditionsyoutypicallysettotriggerIRAThandover?
RSCPand Ec/Io are usedtotriggerIRAT handover:
§ RSCP≤ -100dBm.
§ Ec/Io ≤ -16dBm.
What are the typical KPIsyouuse to measure a networkandwhatcriteria?
§ Accessfailure rate (≤2%).
§ Call setuptime (CS:over95% of the time < 6-secondfor mobile-to-PSTN,9-secondformobile-mobile.
PS: over95% of the time < 5-second).
§ Droppedcall rate (≤ 2%).
§ BLER: over 95% of the blocks≤ 2%.
§ Average DL/UL throughputforPSD:210kbps for loaded,240kbpsfor unloaded.
What isthe typical UE transmitpower?

45. Varies- mostof the time below0dBm.
Have your usedEricssonTEMS? If so:
§ Do youknowhow to create commandsequence?
§ What are the call sequencesyoutypicallyhave? CSlongcall,CSshort call,PSDcall,etc.
§ What are the typical commandsyouhave forCS and PS call?
§ Do youregularlystopandrestart a new logfile? Whyand whentostop and start a new file?
§ How doyou stopa logfile? Stopcommandsequence first,waitandmake sure all equipmentare in
idle mode before stoplogging.
Didyou workon neighborprioritization?
Please explain.
What isthe typical eventsequence of IRATHandoverfrom3G to 2G

46. § Event2d – enteringintocompressedmode –measurementof 2G candidates – Event3a – Verification
of 2G resources –Handoverfrom UTRAN Commandfrom3G RNC to UE
What are the possible causesforanIRATFailure?
§ Missing2G relations
§ Nonavailabilityof 2G Resources
§ Poor2G Coverage
§ Missing3G Relations
What isPagingSuccessRatio?What is the typical PSRthat you have seenina UMTS network?

47. § PSR – PagingResponsestothe PagingAttempts
§ About90%
What are the possible causesforalowerPSR?
§ Non-continuousRFCoverage –UE goinginand out of coverage area frequently
§ VeryHigh‘PeriodicLocationUpdate Timer’ –KeepingUEsin VLRlongtime afterit movedoutof
coverage
§ LowerPagingChannel Power

48. § AccessChannel ParameterIssues
§ Delayed LocationUpdate whencrossingthe LA / CN Boundaries
What are the possible causesforaDrop Call on a UMTS network?
§ PoorCoverage (DL / UL)
§ PilotPollution/PilotSpillover
§ MissingNeighbor
§ SC Collisions
§ DelayedHandovers

49. § Noresource availability(Congestion)forHandin
§ Loss of Synchronization
§ Fast Fading
§ DelayedIRATTriggers
§ Hardware Issues
§ External Interference
A UE isservedby2 or 3 SCin AS.It isidentifyingaSCfrom 3rd tier,Strongerand meetsthe criteriafor
Event1a or Event1c.But SHO didnot happenbecause of missingneighborrelations?How doyou
optimize thisissue?
§ Studythe Pilotspilloverfromthe 3rdTier SCand control its coverage

50. § Evenaftercontrollingthe coverage,if the spilloveristhere,Addthe neighbor.
A UE isservedby2 SC inAS,a SC is cominginto MonitoredSetand Event1ais triggered. ButUE is not
receivingActiveSetUpdate fromNodeBandthe call drops.What couldbe possible causesforthisdrop?
§ DelayedHandover
§ Loss of Synchronization
§ Fast Fading
§ PilotPollution/Spilloverissues

51. What isHard HandoverinUMTS? Whenwill ithappen?
§ Hard HandoverinUMTS isa breakbefore make type Handover
§ It can happeninthe interRNCboundarieswhere thereisnoIurlink.
What isthe typical Call SetupTime fora 3G UE to 3G UE Call?What are the possible RFrelatedcauses
for a delayedCSTinthistype of call?

52. § 6 to 9 seconds
§ Multiple RRCAttempts(UEis onpoor coverage – needmore thanAccessAttempt)
§ DelayedPage Responses
§ High Load onPagingand/orAccessChannel
§ Paging/ AccessParameters
What isSoft HandoverOverhead?Whatisthe typical value inUMTS network?

53. § SoftHandoverOverheadiscalculatedintwoways.1) Average Active SetSize –Total Traffic / Primary
Traffic.2) Secondary/ Total Traffic
§ Typical Valuesare like 1.7(AvgActive SetSize) or35% (Secondary/Total )
What will happentothe SoftHandoverOverheadwhenyouapplyOCNSonthe network?AndWhy?
§ WithOCNS,the interference(load)increases.ThisleadstoreductioninEc/Ioof a Pilot,whichreduces
the pilotspillovers.ReductioninPilotSpilloverwill reduce the SoftHandoverOverhead.

54. What are the possible causesforanAccessFailure inUMTS?
§ MissingNeighbors
§ Poor Coverage
§ PilotPollution/Spillover
§ Poor Cell Reselection
§ Core NetworkIssues

55. § Non – availabilityof resources.AdmissionControl denies
§ Hardware Issues
§ ImproperRACH Parameters
§ External Interference
(FORERICSSON EXPERIENCED) Whatis RTWP? What isthe significance of it?

56. § ReceivedTotal Wide-bandPower
§ It givesthe Total UplinkPower(Interference) level receivedatNodeB
(FORERICSSON EXPERIENCED) Whatis the SystemReference Pointatwhichall the PowerLevelsare
measuredinEricssonNodeB?

57. § SystemRef PointforE///NodeBisat the outputof TMA (BetweenTMA and Antenna)
What are the typical valuesfor‘reportingrange1a’and‘reportingrange1b’?

58. § 3 dB and5 dB respectively.
What will be the impactwhenyouchange ‘reportingrange1a’from3 to 4 dB and ‘timetotrigger1a’100
to 320 ms,withoutchanginganyotherparameters?

59. § Reductioninnumberof Event1a
§ DelayedEvent1atrigger
§ ReductioninAverage Active SetSize
§ Delayin Event1acouldincrease DL interference,whichcouldleadtoadrop call or increase in
Average PowerPerUser(reductionincell capacity)

60. What isAdmissionControl?
§ AdmissionControl isanalgorithmwhichcontrolsthe Resource Allocationforanew call and
additional resource allocationforanexistingcall.Incase,if acell isheavilyaloadedandenough
resourcesintermsof power,codesor CEs are notavailable,admissioncontrol deniespermissionforthe
additional resource requirement.
What isCongestionControl?

61. § Congestion Control monitorsthe dynamicutilizationof specificcell resourcesandinsuresthat
overloadconditionsdonotoccur. If overloadconditionsdooccur,CongestionControl will immediately
restrictAdmissionControl fromgrantingadditionalresources. In addition,CongestionControl will
attemptto resolve the congestionbyeitherdownswitching,orterminatingexistingusers. Once the
congestioniscorrected,the congestionresolutionactionswillcease,andAdmissionControlwillbe
enabled.

62. What isthe maximumnumberof ChannelizationCodesthatcanbe allocatedforHS,as per 3GPP
standard?

63. § 15 codesof SF16.
What is‘Code Multiplexing’inHSDPA?

64. Sharingthe HS Channelization Codesamongmore thanone HSuserswithinthe 2ms TTI period.
(FORERICSSON EXPERIENCED) InEricssonSystem, how isthe PowerallocatedforHSDPA>
Powerunutilizedby 99 PS,CS and CommanChannels,isusedforHS(PHS = Pmax - hsPowerMargin -
Pnon-HS)

65. What are Eventsthatcan triggerthe HSDPA Cell Change?
§ Event1d HS – Change of BestCell inthe Active Set

66. § Event1b or Event1c – Removal of the BestCell fromthe Active Set
How istypicallythe Call SetupTime of aCSV call calculatedinUMTS usingL3 messages?
CST iscalculatedas the time difference between‘Alerting’andthe firstRRCConnectionRequest(Call
Initiation) messages.