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.
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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
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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 $reathin%: and "hy?
The cell coverage shrin s as the loading increases, this is called cell breathing.
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2. in# layer 8@29! is s0lit into 2 s b-layers :edi m ccess "ontrol 8: "9and adio @in "ontrol 8 @"9.Q : "! res0onsible 4or m lti0le/ing data 4rom m lti0le a00lications onto
0hysical channels in 0re0aration 4or over-the-air transmit ion.
Q @"! segments the data streams into 4rames that are small eno gh to betransmitted over the radio lin .
). Upper layer 8@)9! vertically 0artitioned into 2 0lanes! control 0lane 4orsignaling and ser 0lan 4or bearer tra44ic.Q 00C 8 adio eso rce "ontrol9 is the control 0lan 0rotocol! controls the
radio reso rces 4or the access networ .
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What are transparent mode ac#no"led%ed mode and !nac#no"led%ed mode?
I Trans0arent mode corres0onds to the lowest service o4 the @" layer, no controlsand no detection o4 missing data.
I *nac nowledged mode o44ers the 0ossibility o4 segment and concatenate o4 data b t no error correction or retransmission there4ore no g arantee o4 delivery.
I c nowledged mode o44ers, in addition to *: mode 4 nctions, ac nowledgemento4 transmission, 4low control, error correction and retransmission.
Which layer*s+ per&orm cipherin% &!nction?
" 4or ac nowledged mode 8 :9 and nac nowledged mode 8*:9.: " 4or trans0arent mode 8T:9.
What is ,@?
rthogonal Hariable #0reading Factor.
(o" many ,@ code spaces are availa$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 "%
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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%
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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
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#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?
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No, system in4ormation bloc is m lti0le/ed with synchroniCation channel.#ynchroniCation channel occ 0ies the 4irst time slot 8T#9 and #
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I e14! a %rimary "%*@ thro gh0 t 4or %# ! 21+ b0s 4or loaded, 2$+ b0s 4or nloaded.
What is the typical UE transmit po"er?
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Haries - most o4 the time below +dBm.
(ave yo!r !sed Ericsson )EM,? I& soation?
%lease e/0lain.
What is the typical event se !ence o& I0A) (andover &rom 81 to 41
I Event 2d entering into com0ressed mode meas rement o4 2? candidates Event )a Heri4ication o4 2? reso rces andover 4rom *T N "ommand4rom )? N" to *E
What are the possi$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$le ca!ses &or a lo"er -,0?
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I Non-contin o s F "overage *E going in and o t o4 coverage area4re= ently
I Hery igh Y%eriodic @ocation *0date TimerD Ree0ing *Es in H@ long timea4ter it moved o t o4 coverage
I @ower %aging "hannel %ower
I ccess "hannel %arameter "N Bo ndaries
What are the possi$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
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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
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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>
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*@ 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.
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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 $et"een GAlertin% and the &irst 00CConnection 0e !est *Call Initiation+ messa%es.
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What is pre2synchroni>ed handover?
A pre2synchroni>ation method in "hich the so!rce cell chooses a si%nat!re &or the!ser mo$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
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