WCDMA Selection and Reselection

 

UMTS Knowledge Acquisition Presentation Overview  %d&ance / 'i&e Netor! Netor! / Performance

asic / ac!ground / "#eor$

Measurement fundamentals (Spreading and De-spreading, Ec/No, RSCP, RSSI)

E %ccess and Idle Mode e#a&ior  Cell Selection * Reselection

Call Setup R%C+/Paging procedure

+ando&er E&ents * IR%"

Poer Control

R Data * +SDP%

Netor! design and planning o&er&ie

0% and "raining netor! test results

 %dmission Control Radio Resource Management Capacit$ management Statistical Performance and 0ault anal$sis .PIs, Counters Parameters (+, %dmission11) No!ia SS CM Editor, .PI Monitor, ptimier  M"S ptimiation Routine 2M "as!s

Ne

Dri&e Data %nal$sis

Completed

Cluster %cceptance

  Draft

 

Cell Selection and Reselection

 

 

Objectives At the end of this module, you will be able to • Understand the cell syncronisation s yncronisation pro process cess

• List the motivations for cell selection and reselection

• Understand the cell selection criterion S

• Outline the measurement rules • Explain the rankin criterion !

 

 

Cell Synchronisat Synchronisation ion "hen a UE is switched on, it starts to monitor the radio interface i nterface to #nd a suitable cell to camp on$ %ut it has to determine, whether there is a "&'(A cell nearby$ )f a "&'(A cell is available, the UE has to be synchronised to the downlink transmission of the system information i nformation * transmitted on the physical channel +&&+&- * before it can make a decision, in how far the available cell is suitable to camp on$ )nitial cell selection is not the only reason, why a UE wants to perform cell synchronisation$ .his process is also re/uired for cell reselection and the handover procedure$ &ell synchronisation is achieved with the Synchronisation Channel (SC!$$ (SC!  

 

Synchronisation Channel (SC! 3

"#e Synchron Synchronisation isation Channel Channel (SC+)  (SC+) is a donlin! signal used for cell searc#1 "#e SC+ consists of to su4 c#annels, t#e Primar$ and Secondar$ Sec ondar$ SC+1 "#e 56 ms radio frames fram es of t#e Primar$ and Secondar$ are di&ided into 57 slots, eac# eac # of lengt# 8796 c#ips1 Picture 4elo illustrates t#e structure of SC+ t#e SC+ radio frame1 "#e Primary SCH consists SCH consists of a modulated code of lengt# 879 c#ips, t#e primar$ s$nc#roniation code (PSC) is transmitted once e&er$ slot1 "#e PSC is t#e same for e&er$ cell c ell in t#e s$stem1 "#e Secondary SCH consists SCH consists of repeatedl$ transmitting a lengt# 57 se:uence of modulated codes of lengt# 879 c#ips, t#e Secondar$ S$nc#ronisation Codes (SSC), transmitted transm itted in parallel it# t#e Primar$ SC+1 "#e SSC is denoted csi,! in figure, #ere i  ;  ; 6, 5, PMABD +!

)n order to access a cell, the UE has to use the common channel +!A&-$  .he operator determines determines the the maximum cell radius radius by limitin the maximum .C power level, a UE can use on the +!A&-$ .his is the UEI.C+"!I(ACI!A&- 9d%m:$ UEI.C+"!I(ACI!A&- can rane * accordin to the speci#cations  between *G7 d%m and JJ d%m$ On the other hand, there is the UE8s maximum !? output power, iven by +I(AC 9d%m:$

 

 

Cell Selection Criterion S &ell siHe de#nin parameters0 •  @rxlevmin • @/ualmin ) am outsid e 



) am inside, but have not enouh power Pco*"ensation < *a9(U7TBP2MAB2AC *a9(U7TBP2MAB2A C > PMABD +!  

 

(1nitial! Cell Selection Process  .here exist exist two cell selection procedur procedures0 es0 • 1nitial Cell Selection  .he UE has to #nd #nd a suitable suitable cell of the +L +L(1$ (1$ . .o o do so, the mobile phone scans all radio fre/uency carriers of U.!A$ U.!A$ -ereby, the UE focuses its cell search to the stronest cell on each carriers$ As soon as the mobile phone has found a suitable cell, it selects it$ )n contrast to the initial cell selection procedure =qual*in : + Sr9lev < =r9lev*eas ) =r9lev*in = r9lev*in > Pco*"ensation Pco*"ensation : + 1nitial Cell Selection (scan 2? channel!

or

Stored 1nor*ation Cell Selection

  1 have to

 

@nd a suitable cell

 

4o5ia Para*eters or Cell Selection • "&EL0 =r9levMin  .he minimum re/uired !C level in the cell$ .his parameter is part of S)% J$ KFFG $$$ *BG d%m, step B d%m2 default0 FFG d%m$ • "&EL0 =qualMin =qualMin    .he minimum re/uired /uality /uality level in the cell 9Ec1o:$ .his parameter is part of S)% J$ KB5 $$$ 7 d%, step F d%, default0 F6 d%$ • "&EL0 U7t9PowerMa9P2AC  .his parameter de#nes the maximum transmission power level a UE can use on +!A +!A&-$ &-$ .he value of the parameter also e;ects the cell selection and reselection procedures$ .he value of the parameter is sent to UE in the &ell selection and reselection of S)% J and 5 of the servin cell$ 'efault0 BF d%m • K$$  

 

Cell 2eselection

After Af ter a mobile phone camps on a cell, it periodically look for a better cell to camp on$ %ut what is a =better= cell> On the %&&-, parameters for cell reselection are broadcasted$ )f a cell meets the cell selection criteria of these parameters, it is a better cell to camp on$ .he cell re selection may result in the chane of the U.!A carrier or even the !A.$ )f the UE camps normally on a cell, it is responsib responsible le to • monitor the %&&- and to obtain the system information2 to its pain channel and its pain channel resource2 • • listen perform servin cell measurements measurements periodically2 • perform neihbourin neihbourin cell measurements as far as this is re/uired by the cell re selection evaluation procedure2 procedure2 • conduct the cell reselection evaluation procedure, when %&&- information has chaned or internal threshold measures indicate it$2 • ex execute ecute a cell reselection, if a better cell has been found after the cell reselection evaluation process2 • (ove the UE to the internal state Any cell selection, if no suitable cell can be found$  .he UE performs performs its measurements measurements based on the %&&%&&-$$ .he % %&&&&- also delivers th the e neihbourhood neihbou rhood list to the UE$ Diven this information, the UE decides, on which !A.s and fre/uency bands it has to perform its measurements which cells are candidate cells for f or measurements within one fre/uency band and

 

!A. !A . 99-&S:, -&S:, and  

Cell 2eselection# Measure*ent 2ules  .he operator has has to determine the thr threshold eshold values, which trier the cell reselection process by the UE$ 1ntra)?requency *easure*ent threshold Sintrasearch   )f this parameter is not sent in the servin cell, the UE must always perform intrafre/uency measurements$ )f it is transmitted and S9 : Sintrasearch , the UE does not perform intrafre/uency measurements$ )f S9 F< Sintrasearch, it performs intrafre/uency measurements$ • 1nter)?requency *easure*ent threshold Sintersearch )f this parameter is not sent in the servin cell, the UE must always perform intrafre/uency measurements$ )f it is transmitted and S9 : Sintersearch , it must perform interfre/uency measurements, but if S9 F< Sintersearch , there is no need to perform this type o off measurement$ measurement$ • 1nter)2AT *easure*ent threshold Ssearch2AT *  )f this parameter is not sent in the servin cell, the UE must always perform intrafre/uency measurements$ )f it is transmitted and S9 : Ssearch2AT *, it won8t conduct measurements measurements on cells of radio access technoloy 3m3$ %ut if S9 F< Ssearch2AT *, it has to do these measurements$  

Sintrasearch , Sintersearch , and Ssearch2AT * can et inteer values ranin from *JB  

Cell 2eselection# Measure*ent 2ules S9 ?or that, a cell)ran5ing criterion 2 was 2 was speci#ed0 9for the servin cell: • 2s < =*easDs G =hysts • 2n < =*easDn ) =oHsetsDn 9for candidate neihbourin cells for cell reselection:  .he servin cell cell and the candidate candidate cells are ranked ranked accordin accordin to criterion !$ .he cell ranked ranked with the hihest value ! is tthe he best cell for the UE to camp on$

=hysts ives a hysteresis value to make the servin cell more attractive and thus delay the cell reselection$ )t exists in two versions0 )f the /uality measure is based on &+)&- Ec1o, @hystBs is used in 9?'' cell only:2 otherwise the hysteresis value @hystFs is used 9if the /uality measure measur e for ?'' cells is i s based on &+)&- !S&+, for .'' cells and DS( cells:$ )t ranes between 7 and 57 9step siHe B:$  

 

Cell 2eselection# 2)Criterion 1 a neighbouring cell was ran5ed with the highest value 2D will the U7 start the cell re)selectionI )f it is a DS( or .'' cell, then indeed the UE performs the cell reselection process process to this cell$ )f it is an ?'' cell, it depends on the used /uality measure$ .here ar are e two options0 &+)&- !S&+ or &+)&- Ec1o$ .he UE learns from the system information, which /uality measure to use$ )f the /uality measure &+)&- !S&+ is used, the UE U E perform the cell reselection$ )f the /uality measure Ec1o is used, the UE has to make a second rankin based on the same measurement /uantity$ .he UE performs cell reselection to the ?'' cell, which was ranked ranked best in the second rankin process$

1s the cell re)selection initiated ini tiated i**ediately ater the U7 ran5s a neighbouring cell ato be the bestI )f so, we could face pinpon e;ect * a UE often performin cell reselection between two neihbourin cells$ .o avoid this, the operator uses the time interval value Treselection Treselection,, whose value ranes between 7 and JF seconds$ Only when a cell was ranked .reselection seconds better then the servin cell, a cell reselection to this cell takes place$ )n addition to this, a UE must camp at least $ second on second on a servin cell, before the next cell c ell reselection may take place$ $

   

Cell 2eselection# 2)Criterion 2s < =*easDs G =hysts 2n < =*easDn ) =oHsetsDn     s     a     e     *

2  : 2   0 and Srxle > 0 !here" Squal # $qualmeas % $qualmin Srxle # $rxlemeas % $rxlemin - Pcompensation

S&riterion ful#lled "#e cells are ran!ed using t#e ran!ing criterion R Rs # $meas&s ' $hysts Rn # $meas&n - $offsets&n

A neihbor cell is selected if 

3 (t is ran)ed higher than the sering cell for a time greater than *reselection

3*he +, has been  camped on the current sering cell for atleast one second  

4o5ia Para*eters or Cell 2eselection

• "&EL0 =hyst$ (=hyst%! @hystF is used for .'' and DS( cells, and for ?'' cells when cell selection and reselection /uality measure measure is set to CPICH RSCP (CPICH Ec/No) 9  9=hyst$ =hyst$s =hyst%s:$ .his parameter is part of S)% J$ K7 $$$ 57 d%, step B d%, default0 5 d%$ • -O+S0 Adjs=oHset$ (Adjs=oHset%!  .his parameter is used used in the cell cell reselection and rankin between "&'(A cells$  .he value of this this parameter is su subtracted btracted from the the measured CPICH RSCP (CPICH t he intrafre/uen intrafre/uency cy neihbour cell before the UE compares the /uality Ec/No) of the measure with the cell reselectionran reselectionrankin kin criteria$ KG7 $$$ G7 d%, default0 7 d%$ -O+D0 Adjg=oHset$  .his parameter is used in the cell reselectio reselection n and rankin rankin between "&'(A "&'(A and DS( cells$ .he value of this t his parameter is subtracted from the measured DS( carrier the neihbou neihbourin rin before the UE compares the /uality measure with the!SS) cell of reselectionran reselectionrankin kincell criteria$  .his parameter is part of System )nfor )nformation mation %lock FFNFB$ *G7$$$G7 d%, step F d% 'efault0  d% • "&ELL0 Treselection  .he UE triers the the reselection of a new cell if the the cell reselection reselection criteria ar are e ful#lled durin the time interval .reselection$ .his parameter is part of S)% J$ 7s:: K7 $$$ JF seconds, default0 B seconds$ 91ote0 91ote0 ?or hihways consider 7s

   

Cell 2eselection# Measure*ent 2equire* -ow often are measurements conducted for cell reselection evaluation> "hat happens, if the criterion S is no loner lo ner ful#lled for the cell, the UE camps on> • Serving Cell At least once  once every '!C cycle, the UE must  measure the &+)&- Ec)o and &+)&- !S&+ level of the servin cell and  evaluate the S criterion$ )f the servin cell is not ful#llin the cell selection criterion S for 4serv  consecutive '!C cycles, the UE has to start measurements on all all   neihbourin cells$ .he 4serv is known by the UE with the '!C cycle lenth$ .he UE has to #nd a suitable cell within FB seconds$ )f it fails, and the UE is in the !!& idle mode, it initiates the cell selection procedures procedures for the selected +L(1$ )f it fails to #nd a suitable cell wit within hin FB seconds, it is considered to be =out of service area=$

   

Cell 2eselection# Measure*ent 2equire*ents > Serving Cell DRX  

cycle

S

 

S

 

S

S

start measurement on  

all neihbourin cells

4serv $% seconds

DRX cycle

At least one • &+)&- Ec)o measurement • &+)&- !S&+ measurement

if UE RRC idle

UE initiates cell selection procedures for the selected +L(1

if still no suitable cells UE =out of service areaP

• S criterion

 

 

Cell 2eselection# Measure*ent 2equire* • inter)2AT JSM cells )f interDS( measurements are re/uired accordin the the measurement rules, the UE measures the !SS) of DS( %&&- carriers$ .hese measurements are conducted at least every T*easureJSM$ A runnin averae of 5 measurements for each DS& %&&- carrier is calculated by the UE$ )n addition to that, the UE must determine the %S)& * which is carried on the S&- of each DS( %&&- carrier * at least every J7 seconds for the four stronest DS( neihbourin cells$ Also rankin in accordance to the cell reselection rules must be done for these cells every J7 seconds$ %ut what happens, if the UE detects a %S)&, which was not named in the neihbourhood neihbour hood list of the servin cell> .hen, this cell is not considered as candidate cell for And what does thecell UEreselection$ with a neihbourin cell, where it is not capable to ain the %S)& value> .his cell, too, is not rearded rearded as candidate for cell reselection$

   

EAercise  Cell reselection scenarios

3

0igure s#os a cell and t#e associated 4roadcast parameter &alues for :ualmin, rAle&min and E"FPGRM%FR%C+1 It also s#os &alues for :ualmeas and rAle&meas for t#ree positions in t#e cell, %,  and C1

51

0or 0or p pos osit itio ion n %,  and and C ca calc lcul ulat ate e #e #et# t#er er t#e t#e c cel elll se sele lect ctio ion nc cri rite teri ria aa are re fulfilled for a poer class > E(85 dm)

81

0or 0or p pos osit itio ion n %,  and and C ca calc lcul ulat ate e #e #et# t#er er t#e t#e c cel elll se sele lect ctio ion nc cri rite teri ria aa are re fulfilled for a poer class = E(8> dm)

=1

G#at G#at mig# mig#tt $ou $ou ad adHu Hust st to en ensu sure re t#at t#at t#e t#e cel celll a app ppea ears rs suit suita4 a4le le for for 4 4ot ot# # t$pes of E in all locations

   

$qualmin # -12 d. $rxlemin # -5 d.m +,8*9P:R8;98RCH # 24 d.m

compensation   Pcompensation

Class / +, # 24 % 24 # 0

 

Class 4 +, # 24 % 21 # /



:ualmeas ; - d rAle&meas ; -J> dm

C .

:ualmeas ; -55 d rAle&meas

C/ Squal # - - - 12 # /   Srxle # -34 - - 5 # 21 C4 Squal # - - - 12 # /   Srxle # -34 - - 5 - / # 16

:ualmeas ; -56 d rAle&meas ; -K dm C/ Squal # -10 - - 12 # 2   Srxle # -6 - - 5 # 7

 C4 Squal Srxle##-10 -6--- -12 5#- 2/ # /



 ; -= dm C/ Squal # -11 - - 12 # 1   Srxle # -/ - - 5 # 2 C4 Squal # -11 - - 12 # 1   Srxle # -/ - - 5 - / # -1

   

2eerences ?orr this module, followin JD++ speci#cations were used0 ?o • .S • .S • .S • .S

BJ$FBB BG$FJJ BG J75 BG$JJF

QJ$76$7 QJ $76$7 QJ$FF$7 QJ$FF$7 QJ$FF$7 QJ$FF$7 QJ$FB$7 QJ$FB$7

1okia "&'(A !A1B$B +arameter 'ictionary 9refer to 1E' or 1OLS: