important wcdma technical question answer

8/12/2019 Important WCDMA Technical Question Answer

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Important WCDMA technical Q/A.

What is a typical NodeB sensitivity level?

The service and load determines the NodeB sensitivity; in general, in a no-load condition,the sensitivity is between -115dBm to -125dBm. For Ericsson, the NodeB sensitivitylevel is calc lated at aro nd!

"#12.2! -12$ dBm%#-&$! -11' dBm%#-12(! -115 dBm%#-)($! -115 dBm

What is a typical UE sensitivity level?

The service and load determines the *E sensitivity; in general, in no-load condition, thesensitivity is between -1+5dBm and -12+dBm. For Ericsson, the *E sensitivity level iscalc lated at aro nd!

"#12.2! -11' dBm%#-&$! -112 dBm%#-12(! -11+ dBm%#-)($! -1+5 dBm

# % ! -'5 dBm

What is a typical NodeB ma im!m o!tp!t po"er?

The ma/im m NodeB o t0 t 0ower is s ally 2+ or $+ , that is, $)dBm or $&dBm.

What is UE ma im!m transmit po"er in yo!r lin# $!d%et?

21dBm.

What is a typical antenna %ain?

The antenna gain de0ends on antenna model; in lin b dget we se aro nd 13dBi.

What is a typical ma im!m path loss?

The ma/im m 0ath loss is de0endent on the service and vendor recommendations;ty0ically it is in between 1)5 to 1$+dB 4or rban areas and between 15+ to 1&+dB 4orr ral areas.

What is di&&erence $et"een dBi and dBd?

dBi is the gain in dB 4rom isotro0ic so rce; dBd is the gain 4rom a di0ole so rce.


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dBd 2.15 6 dBi.

What is the di&&erence $et"een dB and dBm?

dBm is a nit o4 0ower level, meas red in milli-watts in logarithm scale, that is,

dBm 6 1+ 7 log8 71+++9 where is the 0ower in atts dB is not a nit, it is thedi44erence in dBm.

What is 'dBm?

+dBm 6 1 milli-watt.

(o" does )MA "or#?

T: red ces system noise, im0roves 0lin sensitivity and leads to longer *E batteryli4e. #ensitivity is the minim m in0 t 0ower needed to get a s itable signal-to-noise ratio8#N 9 at the o t0 t o4 the receiver. ?1 8NF)-19>8?17?29 ... 8NFi-19>8?17?27...7?i9

s the e= ation shows, the 4irst bloc im0oses the minim m and the most 0rominentnoise 4ig re on the system, and the 4ollowing bloc s im0oses less and less im0act to thesystem 0rovided the gains are 0ositive. @inear 0assive devices have noise 4ig re e= al totheir loss. T: ty0ically has a gain o4 12dB.

There are ty0ically to0 A m0er, main 4eeder and a bottom A m0er between antenna andBT#. T: 0laced near antenna with a short A m0er 4rom antenna 0rovides the bestnoise 4ig re im0rovement the noise 4ig re will be restricted to the to0 A m0er loss8NF19 and T: 88NF2-19>?19, and the remaining bloc s 8main 4eeder and bottom

A m0er9 have little e44ect.

To s mmariCe, a T: has a gain thatDs close to 4eeder loss.

What are the pros and cons *advanta%es and disadvanta%es+ o& )MA?

n the 0side, a T: red ces system noise, im0roves 0lin sensitivity and leads tolonger *E battery li4e. n the downside, T: im0oses an additional insertion loss8ty0ically +.5dB9 on the downlin and increases site installation and maintenancecom0le/ity.


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What is typical )MA %ain?

T: ty0ically has a 12 dB gain; however, the e44ective gain comes 4rom noise 4ig rered ction and the gain is close or e= ivalent to the 4eeder loss.

Why )MA are installed at the top near the antenna and not the $ottom near theNodeB?

Based on Friis E= ation, having a T: near the BT# will have the to0 A m0er and main4eeder losses 8noise 4ig res9 cascaded in and a T: will not be able to hel0 s 00ress thelosses.

What is UM), chip rate?

).($: C.

What is processin% %ain?

%rocessing gain is the ratio o4 chi0 rate over data bit rate, s ally re0resented in decibel8dB9 scale. For e/am0le, with ).($: C chi0 rate and 12.2 data rate, the 0rocessing gainis!

%? 12.2 6 1+ 7 log 8),($+,+++ > 12,2++9 6 25dB

What are the processin% %ains &or C, and -, services?

"#12.2! 25dB%#-&$! 1(dB%#-12(! 15dB%#-)($! 1+dB

# % ! 2dB

(o" to calc!late ma im!m n!m$er o& !sers on a cell?

To calc late the ma/im m n mber o4 sers 8 M 9 on a cell, we need to now!

W ! chi0 rate 84or *:T# ),($+,+++ chi0s 0er second9 EbNo ! Eb>No re= irement 8ass ming )dB 4or "#-12.2 9i! other-cell to in-cell inter4erence ratio 8ass ming &+ 9

R! ser data rate 8ass ming 12,2++ b0s 4or "#-12.2 9G! loading 4actor 8ass ming 5+ 9

Ta e 12.2 b0s as e/am0le!: 6 > 8EnNo 7 81 i9 7 9 7 G 6 ),($+,+++ 8) 7 81 +.&9 7 12,2++9 7 +.5 6 )2.(

The n mber o4 sers co ld also be hard-limited by H#F code s0ace. Ta e "#12.2 4ore/am0le!

a. "#-12.2 bearer needs 1 #F12( code. b. Total available codes 4or "#-12.2 6 12( 2 81 #F&$9 2 8$ #F25&9 6 12$.


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c. "onsider so4t-handover 4actor o4 1.( and loading 4actor o4 5+ ! 12$ > 1.( 7.+56 )$ sers>cell.

What is E$/No?

By de4inition Eb>No is energy bit over noise density, i.e. is the ratio o4 the energy 0erin4ormation bit to the 0ower s0ectral density 8o4 inter4erence and noise9 a4ter dis0reading.

Eb>No 6 %rocessing ?ain #No is 5dB and 0rocessing gain is 25dB then the #< sho ld be -2+dBor better.

What are the E$/No tar%ets in yo!r desi%n?

The Eb>No targets are de0endent on the service!

I n the 0lin , ty0ically "# is 5 to &dB and %# is ) to $dB %# is abo t 2dB lower.I n the downlin , ty0ically "# has & to 3dB and %# is 5 to &dB %# is abo t 1dB

lower.

Why is E$/No re !irement lo"er &or -, than &or C,?

%# has a better error correction ca0ability and can tiliCe retransmission, there4ore it cana44ord to a lower Eb>No. "# is real-time and cannot tolerate delay so it needs a higherEb>No to maintain a stronger F lin .

What is Ec/Io?

Ec>


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What is ,I0?

#< is the #ignal-to- 9 > 881 f 9 7 F 7 1+L8EbNo>1+99 6 12+.&

To calc late the downlin 0ole ca0acity we also need to now!! downlin channels orthogonality 4actor 8ass ming 55 9

%ole "a0acity 6 8 > 9 > 881- f 9 7 1+L8EbNo>1+99 6 &$.+&

What is typical pole capacity &or C,234.4 -,256 -,2347 and -,2876?

ith same ass m0tions as above!I "#-12.2 ! 12+.& 8*@9, &$.1 8 @9.I %#-&$ ! )$.( 8*@9, 12.(8 @9.I %#-12( ! 1&.2 8*@9, (.$ 8 @9.I %#-)($ ! 1&.2 8*@9, 2.( 8 @9.

%#-)($ has only 12( on the 0lin , there4ore the 0lin ca0acity is the same 4or both.

(o" many types o& handovers are there in UM),?

#o4t handover, so4ter handover, inter-4re= ency handover, inter- T handover, inter- T

cell change 8*E moving o t o4 *:T# coverage into ?#:>?% #>E? ?E coverage9.What is so&t handover and so&ter handover?

I #o4t handover! when a *E is connected to cells owned by di44erent NodeB.I #o4ter handover! when a *E is connected to cells owned by the same NodeB.

(o" does so&t/so&ter handover "or#?


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I #o4t>so4ter handover downlin ! *E ra e receiver 0er4orms ma/im m ratiocombining, i.e. *E combines m lti-0ath signals and 4orm a stronger signal.

I #o4t handover 0lin ! N" 0er4orms selection combining, i.e. N" selects the better signal coming 4rom m lti0le NodeB.

I #o4ter handover 0lin ! NodeB 0er4orms ma/im m ratio combining, i.e. NodeB

ra e receiver combines signals 4rom di44erent 0aths and 4orms a stronger signal.Why is there 9so&t handover %ain:?

#o4t handover gain comes 4rom the 4ollowing!

I :acro diversity gain over slow 4ading.I :icro diversity gain over 4ast 4ading.I ownlin load sharing over m lti0le F lin s. By maintaining m lti0le lin s each

lin co ld transmit at a lower 0ower, res lting in lower inter4erence there4ore again.

Brie& descri$e the advanta%es and disadvanta%es o& so&t handover?dvantages!

I vercome 4ading thro gh macro diversity.I ed ced Node B 0ower which in t rn decreases inter4erence and increases ca0acity.I ed ced *E 0ower 8 0 $dB9, decreasing inter4erence and increasing battery li4e.

isadvantages!I *E sing several radio lin s re= ires more channeliCation codes, and more reso rces

on the < b and < r inter4aces.

What are &ast &adin% and slo" &adin%?

Fast 4ading is also called m lti-0ath 4ading, as a res lt o4 m lti-0ath 0ro0agation. henm lti-0ath signals arriving at a *E, the constr ctive and destr ctive 0hases create avariation in signal strength.

#low 4ading is also called shadowing. hen a *E moves away 4rom a cell the signalstrength dro0s down slowly.

What are &ast &adin% mar%in and slo" &adin% mar%in?

To 4actor in the 4ast 4ading and slow 4ading, we need to have a margin in the lin b dget

and they are called 4ast 4ading margin and slow 4ading margin.


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b. %#-&$ ! 1dB 8*@9, +dB 8 @9.

c. %#-12( ! 1dB 8*@9, +dB 8 @9.

d. %#-)($ ! 1dB 8*@9, +dB 8 @9.

What is the percenta%e in time a UE is e pected to $e in so&t or so&ter handover?

Ty0ically a *E sho ld be in so4t handover mode at no more than )5 to $+ o4 the time;in so4ter handover mode at abo t 5 o4 the time.

What is a typical Ei0-?

The Ei % de0ends NodeB transmit 0ower, cable and connector loss and antenna gain.ith a sam0le system o4 $)dBm transmit 0ower, a )dB cable and connector loss and a

13dBi antenna gain, the Ei % 6 $) ) 13 6 53dBm.

(o" m!ch po"er !s!ally a NodeB is allocated to control channels?

The 0ower allocated to control channels may de0end on e= i0ment vendorrecommendation. Ty0ically no more than 2+ o4 the total NodeB 0ower is allocated tocontrol channels, incl ding "%


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I B ilding > vehicle 0enetration loss.I Body loss.I Etc.

What is ma im!m path2loss?

The ma/im m 0ath-loss is how m ch signal is allowed to dro0 4rom a transmitter to areceiver and maintains as good signal.

,imple lin# $!d%et< "ith a 8'dBm C-IC( and a 23''dBm UE sensitivity i%norin%anythin% in $et"een "hat is the ma im!m path loss?

)+ 8 1++9 6 )+ 1++ 6 1)+dB.

,!ppose I have a ma im!m path2loss o& 38'dBm "hat is the ne" path2loss i& a =dB$ody loss is added?

125dB.

What is channeli>ation code?

"hanneliCation codes are orthogonal codes sed to s0read the signal and hence 0rovideschannel se0aration, that is, channeliCation codes are sed to se0arate channels 4rom a cell.

(o" many channeli>ation codes are availa$le?

The n mber o4 channeliCation codes available is de0endent on the length o4 code.


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The 512 scrambling codes are divided into &$ code gro 0s each code gro 0 has (scrambling codes.

"ode gro 0 i 8i 6 + to &)9 has codes 4rom i7( to 8 i 197(-1, i.e. 8+-39 8(-159O85+$-5119.

Do yo! divide scram$lin% code %ro!ps into s!$%ro!ps? -lease %ive an e ample.

es, we divide the &$ code gro 0s into s bgro 0s!

I :acro layer gro 0! 2$ code gro 0s reserved 4or macro 8o tdoor9 sites.I :icro layer gro 0! 1& code gro 0s reserved 4or micro 8in-b ilding9 sites.I E/0ansion gro 0! 2$ code gro 0s reserved 4or 4 t re e/0ansion sites.

Which service !s!ally needs hi%her po"er C, or -,?

"onsider downlin and ta e "#-12.2 and %#-)($ 4or e/am0le. The 0rocessing gain is25 4or "#-12.2 and 1+ 4or %#-)($. The Eb>No re= irement is 3 4or "#-12.2 and 5 4or %#-)($. There4ore the 0ower re= irement is higher 4or "#-12.2 than %#-)($.

What is E$/No re !irement &or (,D-A?

The Eb>No re= irement 4or # % varies with ser bit rate 8data rate9, ty0ically 2 4or3&( b0s and 5 4or 2:b0s.

What is 9noise rise:? What does a hi%her noise rise mean in terms o& net"or#loadin%?

For every new ser added to the service, additional noise is added to the networ . Thatis, each new ser ca ses a Jnoise riseK. e in yo!r net"or#?

handover window siCe is s ally between $ to &dB.


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What is 9so&t handover: and 9so&ter handover:?

J#o4t handoverK is when *E has connection to m lti0le cells on di44erent NodeB.

J#o4ter handoverK is when *E has connection to m lti0le cells on same NodeB.


11/27

What is the &re !ency o& po"er control *ho" &ast is po"er control+?

I 0en loo0! de0ends on 0arameter setting!T)++ time to wait between " retries 81++ms to (+++ ms, ty0ical 15++ms9

I "losed o ter loo0! 1++ times a second.I "losed inner loo0! 1,5++ times a second.

Brie&ly descri$e "hy open loop po"er control is needed and ho" it "or#s?

I hen a *E needs to access to the networ it ses " to begin the 0rocess.I " is a shared channel on the 0lin sed by all *E, there4ore may enco nter

contention 8collision9 d ring m lti0le ser access attem0ts and inter4ere with eachother.

I Each *E m st estimate the amo nt o4 0ower to se on the access attem0t since no4eedbac 4rom the NodeB e/ists as it does on the dedicated channel.

I The 0 r0ose o4 o0en loo0 0ower control is to minimiCe the chance o4 collision andminimiCe the initial *E transmit 0ower to red ce inter4erence to other *E.

I


12/27

NodeB reaches its ma/im m transmit 0ower, r ns o t o4 its channel elements, 0linnoise rise reaches its design target, etc.

What is 9cell $reathin%: and "hy?

The cell coverage shrin s as the loading increases, this is called cell breathing.


13/27

2. in# layer 8@29! is s0lit into 2 s b-layers :edi m ccess "ontrol 8: "9and adio @in "ontrol 8 @"9.Q : "! res0onsible 4or m lti0le/ing data 4rom m lti0le a00lications onto

0hysical channels in 0re0aration 4or over-the-air transmit ion.

Q @"! segments the data streams into 4rames that are small eno gh to betransmitted over the radio lin .

). Upper layer 8@)9! vertically 0artitioned into 2 0lanes! control 0lane 4orsignaling and ser 0lan 4or bearer tra44ic.Q 00C 8 adio eso rce "ontrol9 is the control 0lan 0rotocol! controls the

radio reso rces 4or the access networ .


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What are transparent mode ac#no"led%ed mode and !nac#no"led%ed mode?

I Trans0arent mode corres0onds to the lowest service o4 the @" layer, no controlsand no detection o4 missing data.

I *nac nowledged mode o44ers the 0ossibility o4 segment and concatenate o4 data b t no error correction or retransmission there4ore no g arantee o4 delivery.

I c nowledged mode o44ers, in addition to *: mode 4 nctions, ac nowledgemento4 transmission, 4low control, error correction and retransmission.

Which layer*s+ per&orm cipherin% &!nction?

" 4or ac nowledged mode 8 :9 and nac nowledged mode 8*:9.: " 4or trans0arent mode 8T:9.

What is ,@?

rthogonal Hariable #0reading Factor.

(o" many ,@ code spaces are availa$le?

I Total H#F codes 6 25&.I eserved! 1 #F&$ 4or #-""%" , 1 #F25& 4or "% 1.( 6 &( sers>cell.

Can a !ser have ,@ code as 93333:?

No, beca se J1111OK 825& times9 is sed by "%


15/27

I There4ore 25&+ chi0s>T# 7 15 T#>4rame 7 81+++ms>1+ms9 4rame>sec 6 ),($+,+++chi0>sec.

What is cell selection criterion?

"ell selection is based on!

a. Smean! the average #< o4 the target cell. b. S min! minim m re= ired #< .

c. %com0ensation ! a correction val e 4or di44erence *E classes.# 6 S mean - S min - %com0ensation

d. re4 ses admission re= ests based on the c rrent loadon the dedicated monitored reso rces and the characteristics o4 the re= est

"ongestion "ontrol! detects>resolves overload sit ations

What are the ma;or 6 -Is in propa%ation model t!nin% and typical accepta$leval!es?

The $ R%


16/27

Can "e assi%n same scram$lin% codes to sister sectors *sectors on same site+?

No, beca se scrambling code on the downlin is sed 4or cell identity. s a re= irement,scrambling codes have to maintain a sa4e se0aration to avoid inter4erence.

Are scram$lin% codes ortho%onal?

No, scrambling codes are not orthogonal since they are not synchroniCed at eachreceiver. They are 0se do random se= ences o4 codes.

Can "e assi%n scram$lin% codes 3 4 and 8 to sister sectors?

es.

In I,2 = "e have a -N re!se &actor *-N step si>e+ and there&ore cannot !se all =34-N codes "hy isn t it necessary &or UM), scram$lin% codes?

Beca se


17/27

#tatic analysis can only show #"% and Ec>No 4ail re 8"a0acity9.I ownlin Eb>No 4ail re 8 ange9.I *0lin Eb>No 4ail re.I @ow 0ilot #< .I Noise rise limit reached.I Etc.

What does 9tra&&ic spread: mean?

JTra44ic s0readK means s0reading tra44ic 8n mber o4 terminals9 in a cell coverage area.

Do yo! !se live tra&&ic or even2load tra&&ic in yo!r desi%n?

8 e0ends9.

What are the optimi>ation tools yo! !se?

rive test, analysis, othersU

Are ,ystem In&ormation Bloc#s *,IB+ transmitted all the time?


18/27

No, system in4ormation bloc is m lti0le/ed with synchroniCation channel.#ynchroniCation channel occ 0ies the 4irst time slot 8T#9 and #


19/27

I e14! a %rimary "%*@ thro gh0 t 4or %# ! 21+ b0s 4or loaded, 2$+ b0s 4or nloaded.

What is the typical UE transmit po"er?


20/27

Haries - most o4 the time below +dBm.

(ave yo!r !sed Ericsson )EM,? I& soation?

%lease e/0lain.

What is the typical event se !ence o& I0A) (andover &rom 81 to 41

I Event 2d entering into com0ressed mode meas rement o4 2? candidates Event )a Heri4ication o4 2? reso rces andover 4rom *T N "ommand4rom )? N" to *E

What are the possi$le ca!ses &or an I0A) @ail!re?

I :issing 2? relationsI Non availability o4 2? eso rces

I %oor 2? "overageI :issing )? elations

What is -a%in% ,!ccess 0atio? What is the typical -,0 that yo! have seen in aUM), net"or#?

I %# %aging es0onses to the %aging ttem0ts

I bo t '+

What are the possi$le ca!ses &or a lo"er -,0?


21/27

I Non-contin o s F "overage *E going in and o t o4 coverage area4re= ently

I Hery igh Y%eriodic @ocation *0date TimerD Ree0ing *Es in H@ long timea4ter it moved o t o4 coverage

I @ower %aging "hannel %ower

I ccess "hannel %arameter "N Bo ndaries

What are the possi$le ca!ses &or a Drop Call on a UM), net"or#?

I %oor "overage 8 @ > *@9I %ilot %oll tion > %ilot #0illover

I :issing Neighbor I #" "ollisionsI elayed andoversI No reso rce availability 8"ongestion9 4or and inI @oss o4 #ynchroniCationI Fast FadingI elayed < T TriggersI ardware


22/27

I @oss o4 #ynchroniCationI Fast FadingI %ilot %oll tion > #0illover iss es

What is (ard (andover in UM),? When "ill it happen?

I ard andover in *:T# is a brea be4ore ma e ty0e andover

or ccess "hannel %aging > ccess %arameters

What is ,o&t (andover verhead? What is the typical val!e in UM), net"or#?

I #o4t andover verhead is calc lated in two ways. 19 verage ctive #et #iCe TotalTra44ic > %rimary Tra44ic. 29 #econdary > Total Tra44ic

Ty0ical Hal es are li e 1.3 8 vg ctive #et #iCe9 or )5 8#econdary > Total 9


23/27

What "ill happen to the ,o&t (andover verhead "hen yo! apply CN, on thenet"or#? And Why?

I ith "N#, the inter4erence 8load9 increases. This leads to red ction in Ec>


24/27

*@ 0 E0IC,, N EF-E0IENCED+ What is the ,ystem 0e&erence -oint at "hichall the -o"er evels are meas!red in Ericsson NodeB?

I #ystem e4 %oint 4or E>>> NodeB is at the o t0 t o4 T: 8Between T: and ntenna9

What are the typical val!es &or Greportin%ran%e3a and Greportin%ran%e3$ ?

I ) dB and 5 dB res0ectively.

What "ill $e the impact "hen yo! chan%e Greportin%ran%e3a &rom 8 to 6 dB andGtimetotri%%er3a 3'' to 84' ms "itho!t chan%in% any other parameters?

I ed ction in n mber o4 Event1a

elayed Event1a trigger ed ction in verage ctive #et #iCe

elay in Event1a co ld increase @ inter4erence, which co ld lead to a dro0 callor increase in verage %ower %er *ser 8red ction in cell ca0acity9

What is Admission Control?

I dmission "ontrol is an algorithm which controls the eso rce llocation 4or a

new call and additional reso rce allocation 4or an e/isting call.


25/27

I "ongestion "ontrol monitors the dynamic tiliCation o4 s0eci4ic cell reso rces and

ins res that overload conditions do not occ r. ation Codes that can $e allocated &or(, as per 81-- standard?

I 15 codes o4 #F 1&.

What is GCode M!ltiple in% in (,D-A?

,harin% the (, Channeli>ation Codes amon% more than one (, !sers "ithin the4ms ))I period.

*@ 0 E0IC,, N EF-E0IENCED+ In Ericsson ,ystem ho" is the -o"er allocated&or (,D-AH

Power unutilized by 99 PS, CS and Common Channels, is used for HS (P HS = P max -hsPowerMargin - P non-HS)

What are Events that can tri%%er the (,D-A Cell Chan%e?

I Event 1d # "hange o4 Best "ell in the ctive #et

Event 1b or Event 1c emoval o4 the Best "ell 4rom the ctive #et

(o" is typically the Call ,et!p )ime o& a C, call calc!lated in UM), !sin% 8messa%es?

C,) is calc!lated as the time di&&erence $et"een GAlertin% and the &irst 00CConnection 0e !est *Call Initiation+ messa%es.


26/27

What is pre2synchroni>ed handover?

A pre2synchroni>ation method in "hich the so!rce cell chooses a si%nat!re &or the!ser mo$ile to !se in the tar%et cell &or 0AC( access and instr!cts the!ser mo$ile to per&orm 0AC( access and ret!rn to the c!rrent cell$e&ore a handover command *$rea# command+ is iss!ed. )his ca!sesparallel e ec!tion o& the U synchroni>ation process "ith the conte ttrans&er process amon% the t"o $ase stations

Brie& descri$e the advanta%es and disadvanta%es o& so&t handover?

Advanta%es

,peech !ality

important wcdma technical question answer

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