nsn rno fi 191007 partiii

1 © Nokia Siemens Networks RNO / Wind 18/01/2008 - NMI

Confidential

RNO WindPart III

Confidential2 © Nokia Siemens Networks RNO / Wind 18/01/2008 - NMI

Part III - Content

Call Setup Time

UL Interference

PS Utilization

Cell Reselection


Call Setup Time


Call setup Time – Preamble PRACH

• During drive testing can be noted that there are call setup failures where the network does not seem to respond to RRC Connection Requests with RRC Connection Setup –message.These are problems due to the spiky UL noise and due to that the power ramping is not aggressive enough to provide high enough Tx power for the terminal during open loop PC

Downlink / BSDownlink / BS

Uplink / UEUplink / UEPreamble 1 Message part

…. ….

UEtxPowerMaxPRACH

Preamble n

PRACH_preamble_retrans: The maximum number of preambles allowed in one preamble ramping cycle

RACH_tx_Max: # of preamble power ramping cycles that can be done before RACH transmission failure is reported,

L1ACK/AICH

RACH

PowerOffsetLastPreamblePRACHmessage

PowerRampStepPRACHpreamble

PtxAICH

PRACHRequiredReceivedCI

Note: The power ramp-up process will continue until 1) A positive or negative AI is received from the network2) RACH_tx_MAX value is reached3) UE reaches UEtxPowerMaxPRACH value



Ptx = CPICHtransmissionPower-RSCP(CPICH) +RSSI(BS) + PRACHRequiredReceivedCI (-20dB)Example:CPICH = 33dBm (Parameter per Node-B)RSCP = -80dBm (Measured by UE)RSSI = -85 dBmUL_Required_C/I = -25 dB (Parameter per Node-B)UE PRACH First Preamble Power = 33 dBm – (-80 dBm) + (-85 dBm) + (-25 dB) = 8 dBm

The parameters affecting to open loop power control are, in brackets are the recommended values:• PRACH_preamble_retrans (7)• RACH_tx_Max (16) • PowerOffsetLastPreamblePRACHmessage (2 dB)• PowerRampStepPRACHpreamble (2dB)

The PRACHRequiredReceivedCI (-20dB) allow to calculate the UEpower for the fist preambleas in thefollowing:

The parameter PRACHRequiredReceivedCI can be set to -18…-20dB instead of the default -25dB (typically -20dB is enough)



100%

0% 0% 0%

88%

2% 5% 6%0%

20%

40%

60%

80%

100%

1 2 3 4

# RRC Connection Request Messages per call setup

%

PRACH req. C/I = -20dB PRACH req. C/I = -25dB

Clear improvement in number of needed RRC Connection Request messages per call. For –20dB 100% of established calls are setup with only 1 RRC Connection Request message

Clear improvement number of sent preambles per RRC Connection Request for –20dB case. For –20dB 50% of cases the needed number of preambles is <=4 where as for –25dB it is ~6.5

0%10%20%30%40%50%60%70%80%90%

100%

1 2 3 4 5 6 7 8

PRACH req. C/I = -25dB PRACH req. C/I = -20dB

There should be significant improvement also for call setup delay

Typical improvement passing from -25dB to -20dB:



The average number of acknowledged PRACH preambles during the RRI period can be calculated based on the KPI below

RACH load due to preamble can then be calculated by dividing the above further by the max number preambles can be received during RRI • For example if RRI period is 200ms the are 10 20ms RACH frames and in each 20ms RACH frame there are

15 RACH sub slots within each it is possible to receive and decode max 4 preambles -> therefore in 200ms it is possible to receive 15*4*10=600 preambles

BLES_ACK_PREAMDENOM_RACH M1000C177ESCK_PREAMBLSUM_RACH_A M1000C176

% 100*/600BLES_ACK_PREAMDENOM_RACH M1000C177ESCK_PREAMBLSUM_RACH_A M1000C176


Call Setup Time – SRB Rate

Why 13.6kbit/s? Use of 13.6 kbit/s SRB also in highly loaded networks Decreased setup times (PDP context activation minimum 0.7s lower) Improved Iub efficiency

Typical improvement passing from 3.4 to 13.6

0

1

2

3

4

5

6

7

3G-3G CS call setup PS call setup DCH allocation

Seco

nds

Nokia RAN1.5 (3.4 kbps) + M11

Nokia RAN04 (13.6 kbps) + M12Nokia RAN target


Call setup Time – KPIIn RN2.2 the following counters are available to monitor the Call Setup Time

RRC Setup TimeM1001C221/M1001C222

RAB Setup TimeM1001C223 / M1001C224 for CSM1001C235 / M1001C236 for DATA BACKGR

In detail we have:

M1001C221 - SUM OF RRC SETUP TIMES Sum of RRC setup times. This counter divided by the DENOMINATOR - M1001C222 gives the averageRRC setup time. RRC setup time is defined as the time between the RRC: RRC CONNECTION REQUESTmessage and the RRC: RRC CONNECTION SETUP COMPLETE message.

M1001C223/235 - SUM OF RAB SETUP TIMES FOR CS VOICE/FOR DATA BACKGRSum of RAB setup times. This counter divided by the DENOMINATOR - M1001C224/236 gives the averageRAB setup time. RAB setup time is defined as the time between the RANAP: RAB ASSIGNMENTREQUEST and RANAP: RAB ASSIGNMENT RESPONSE messages during RAB establishment.


Call setup Time – Annex1

MO-UE MT-UEMobile-to-mobile CS call setup on common channelsDelay CumulativeRRC connection request UE RNC 0 0RRC connection setup RNC UE 40 40RRC connection setup completeUE RNC 100 140CM service request UE CS 200 340Security mode command RNC UE 100 440Security mode complete UE RNC 200 640Setup UE CS 300 940Call proceeding CS UE 100 1040 Paging RNC UE 400 1340Radio bearer setup RNC UE 100 1140 RRC connection request UE RNC 50 1390Radio bearer setup complete UE RNC 300 1440 RRC connection setup RNC UE 40 1430

RRC connection setup completeUE RNC 100 1530Paging response UE CS 100 1630Security mode command RNC UE 100 1730Security mode complete UE RNC 200 1930Setup CS UE 300 2230Call confirmed UE CS 100 2330Radio bearer setup RNC UE 100 2430Radio bearer setup complete UE RNC 300 2730

Alerting CS UE 250 2980 CS UE 250 2980

Parallel RB setup for MO-UE and paging of MT-UE

(CS core feature)

<3.0 s mobile-to-mobile AMR call setup time

Average paging delay

of 320 ms assumed (640

ms paging cycle)

RA

CH

/FA

CH

RA

CH

/FA

CH

Typical value for CS Call Setup Time


Call setup Time – Annex2

RRC + PDP on common channels Delay CumulativeRRC connection request UE RNC 0 0RRC connection setup RNC UE 40 40RRC connection setup complete UE RNC 100 140GPRS service request UE PC 200 340Security mode command RNC UE 100 440Security mode complete UE RNC 200 640PDP context activation request UE PC 250 890Radio bearer setup RNC UE 150 1040Radio bearer setup complete UE RNC 300 1340PDP context activation accept PC UE 200 1540

Common channels used for setup to

avoid slow synchronized

reconfigurations later

Parallel RB setup and RL/AAL2 setups (or pre-

reserved Radio links)

RA

CH

/FA

CH

<1.6 s PS call setup time

Initial bit rate DCH allocated directly together

with SRB

Typical value for PS Call Setup Time


UL Interference


What’s Interference?

Any working point turned off from the expected load curve can be considered as interference.Interference can be internal or external.Internal interference can be caused by not appropriate dimensioning, planning or commissioning External is usually referred to mobile or other RF sources

Prx Target [dB]

PrxTarget [dB] + PrxOffset [dB]Overload Area

Marginal Load Area

Feasible Load Area

Own cell load factor

Wid

eba n

d po

wer

lev e

l Ito

tal

LRT UnloadedRT and LNRT UnloadedNRT

Unloaded Area


Load vs. Power

Typical mismatch among load and Power can be easily found in a live network.Above is reported a qualitative behaviour in class_1 power for some Wind WBTSs that are experiencing a 1<rt_load<2 (rt_load relative value from 0 to 4) and the related nrt_load and Prx_power.The nrt load added to rt can not give sense of the Prx spike

Class1_Prx/Load

-5000

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0 50 100 150 200 250

WBTS

Rel

. Am

plitu

de

ave_lrt_class_1 ave_lnrt_class_1 ave_prxtot_class_1


NSN Load Areas & Class of Power

CLASS AREA INCREMENTED IF

CLASS 0 Unloaded (Lrt=<UnloadedRT) AND (Lnrt=<UnloadedNRT)

CLASS 1 Feasible_Load_Area_1 (PrxTarget -PrxOffset >= PrxTotal ) AND ((Lrt>UnloadedRT) OR (Lnrt>UnloadedNRT))

CLASS 2 Feasible_Load_Area_2 (PrxTarget > PrxTotal > PrxTarget -PrxOffset) AND ((Lrt>=UnloadedRT) OR (Lnrt>= UnloadedNRT))

CLASS 3 Marginal_Load_Area (PrxTarget + PrxOffset > PrxTotal >=PrxTarget) AND ((Lrt>UnloadedRT) OR(Lnrt> UnloadedNRT))

CLASS 4 Overload_Area (PrxTotal >= PrxTarget + PrxOffset) AND ((Lrt>UnloadedRT) OR (Lnrt>UnloadedNRT))

Prx Target [dB]

PrxTarget [dB] + PrxOffset [dB]

Overload Area

Marginal Load Area

Feasible Load Area_1

Own cell load factor

Wid

eba n

d po

wer

lev e

l Ito

tal

LRT UnloadedRT and LNRT UnloadedNRT

Unloaded Area

Feasible Load Area_2

Class4

Class3Class2

Class1

Class0

PrxTarget [dB] - PrxOffset [dB]


UL Interferece Detection Method

Different approach can be applied to detect UL interference.

Mainly we have:- Field measurement - Counters Analysis

Using the Counters Analysis approach dedicate counters are available for UL Interfernce detection as MAXPrxNoise and MINPrxNoise (M1000C12 and M1000C13)The UL interference severity can be estimated by analysing: MAXPrxNoise – MINPrxNoise, but these counters are incremented only when cell is unloaded.

Here we propose a line for a method that approximately return the WBTS interfered.The method takes the basis from the autotuning algorithm and use the value of Prx returned to detect the interfered cell.The first step is the localization of reference point for each classThen different kind of statistical model can be applied for evaluating the drawn from themFinally a w.w.w concept is used to derive information from space and time recurrenceSome help could come from counters that trigger downgrade or release bocause of interference (e.g. M1000C147RB_DOWNGR_DUE_PBS_INTERF M1000C159RB_RELEASE_DUE_PBS_INTERF if PBS is enabled)


Prx Autotuning

Prx Target_t0 [dB]

Overload Area

Marginal Load Area

Feasible Load Area 1

Time

Wid

eba n

d po

wer

lev e

l Ito

tal

Unloaded Area

t0 t1

Prx Target_t1 [dB]

The auto-tuning algorithm moves the reference point of the load curve and this means that all the areas can be shifted up and down during the day this means that a certain value of PrxTotal (which is measured by the bts) may trigger different areas during the day. For example the sample 4 triggers in the first case the class 2 while in the second case the class 1, but it’s the same value of power!

Feasible Load Area 2 4 4

Main idea is to use this gap to detect interference


Permanence in Class1>45min

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

WBTS

Prx

Rel.

Ampl

itude

Class Power Reference PointIt is not an easy task to find the expected value of Prx in each class.Different masking effect are present either for the granularity of the measurement available that are not appropriate for this kind of analysis or for the inherent difficulty in evaluating the real load experienced.Here a shot for class1 considering the stay time in the class is attempted

Permanence in Class1<15min

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 74 147 220 293 366 439 512 585 658 731 804 877 950 1023 1096 1169 1242 1315

WBTS

Prx

Rel.

Ampl

itude

The spike are more accentuated for low permanence and diluited for the high one

An average can be attempted filtering off the spike and the default value

Prx Displacement

Prx Displacement


Power Class Distribution Function

Here a Prx Distribution over the all WCELs is presented. Typical value of the reference point are represented individuating areas where interference can be detected.The different shape of the curve of the Feasible_Load_Area_2 and the Marginal_Load_Area_2 respect to the Class_0, Class_1 and Class_4 seems due to the different behaviour of the algorithm.The step visible in C2 and C3 could be due to the strict margin in term of Power Budget to react to the load increase. The overshoot of the C0 curve over the C1 is due to to the different triggering condition that for C0 is load based instead of Power Level driven. Finally C1 having a greater budget maintain a smoother shape.

Prx_Dist. function

0

0.2

0.4

0.6

0.8

1

0 200 400 600 800 1000 1200 1400 1600 1800

WBTS

Rel.

Ampl

itude c2

c1

c0

c3

c4

Probable InterferedWCEL

Probable InterferedWCEL


W.W.W. Approach

A single interfernce event can not raise any relevant bother. A statistical analysis is needed. The Who? When? Where? approach is used to derive information and troubleshoot the probable interferer source. The space-time diagram has to be intended as a recurrence indicator for the interference event. In the left side of the F_space axis are reported occurences not adjoined in space. Same concept for F_time.

F_space

F_tim

e

+

+

-

-

stable interference for a adjacent cluster of cell

periodical spot interference

Fixed Ext. SourceCommissioning /Dimensioning

Mobile Ext. Source

Adj missing


Class 0

Class0 can act as the third dimension of the WWW Approach diagram.Considering Class0 as the unlaoded class in the sense that the unloaded limit for RT and NRT (1% and2% respectively) is not exceeded the interference detection in this class can have two advantages:

a) More interference sentivity because of low loadb) Easier discrimination between internal and external interference

The first point is assured by the triggering condition and can be strenghtened superimposing a secondcondition over the load. Imposing the LoadRT = 0 and LoadNRT = 0 we have more reliable result for interference This condition triggered mainly during the nigh-time returns the possibility to have an easiertroubleshooting


PS Utilization


Traffic Mix KPI

The KPI provides an indication of the percentage of CS voice, CS data, PS data RAB establishment attempts relative to the total number of RAB establishment attemptsThe KPI is meaningful for cluster/cell level and on day/hour basis. Same KPI can be obtained using RAB ACC COMPThese KPI are intended to provide a high level indication of the traffic profile loading the network:• CS_VOICE• CS_CONV• CS_STREA• PS_CONV• PS_STREA• PS_INTER• PS_BACKG

Example for CS_VOICE:

T_PS_BACKGRAB_STP_AT T_PS_INTERRAB_STP_AT T_PS_STREARAB_STP_AT T_PS_CONVRAB_STP_AT T_CS_STREARAB_STP_AT T_CS_CONVRAB_STP_AT T_CS_VOICERAB_STP_ATT_CS_VOICERAB_STP_AT

BACKGPSSTPRABINTERPSSTPRABSTREACSSTPRABCONVCSSTPRABVOICECSSTPRABVOICECSSTPRAB

__________________

Traffic Mix

51%

1%

32%

16%

Voice

Data Conv

PS Inter

PS Backg

To take into consideration that PS might cause many attempts in each call another option is to consider the

duration counters!


Traffic Mix KPIFor each traffic class there are counters for RAB Holding time (incremented when the RAB is released only on the cell that was the reference when the RAB is released)

If a distribution on cell level is required the RAB_HOLD_TIME_IN_REF_CELL can be usedFor NRT traffic classes (inter and backg) there are also counters for DCH Holding time (incremented when the RAB is released only on the cell that was the reference when the RAB is released)

)(100/_____

_____ sINTERPSTMHLDRABDENOM

INTERPSTMHLDRABAVG

)(100/_____

_____ sINTERPSTMHLDDCHDENOM

INTERPSTMHLDDCHAVG

For each Traffic Class

Only for NRT Traffic Class

RAB Holding Time [s]

20406080100120140160180200More

DCH Holding Time [s]20406080100120140160180200More


From Cell_DCH to Cell_FACH

CELL_

FACH

CELL_

DCH

UE

RLC

buff

er p

aylo

adRL

C bu

ffer

pay

load

(tra

nspo

rt c

hann

el t

raffi

c vo

lum

e)(t

rans

port

cha

nnel

tra

ffic

volu

me)

CELL_FACH state

CELL_DCH state

InactivityTimerUL(DL)DCH

After the inactivity timer expires the RRC radio bearer reconfiguration–procedure is performed.RRC sends an RRC: RADIO BEARER RECONFIGURATION message to the UE.UE acknowledges by sending the RRC: RADIO BEARER RECONFIGURATION COMPLETE –message to theRRC signaling entity of the RNC which starts L2 reconfiguration (as well as PS is informed about thecell state change).Radio link and AAL2 resources are then released and UE is changed to CELL_FACH state.In case the UE is having RT RB which has become inactive and at the same time it is having inactiveNRT RB then RADIO BEARER RELEASE procedure is used (instead of RADIO BEARER RECONFIGURATION).


From Cell_FACH to Cell_DCH

In uplink direction the need for the capacity is detected by the MAC of UE.UE requests dedicated capacity by sending an RRC: MEASUREMENT REPORT message on RACH to theRRC signaling entity of RNCAfter the procedure, data transmission on DCH can begin and UE is in CELL_DCH state.In downlink direction the capacity need is detected by the UE MAC entity of RNC.PS requests the RRC signaling entity of RNC to start transport channel reconfiguration –procedureThe RRC signaling entity sends an RRC: TRANSPORT CHANNEL RECONFIGURATION message to the UEon FACH, which is acknowledged with an RRC: TRANSPORT CHANNEL RECONFIGURATION COMPLETEAfter the procedure, data transmission on DCH can begin and UE is in CELL_DCH state.

CELL_

FACH

CELL_

DCH

UE

RLC

buff

er p

aylo

adRL

C bu

ffer

pay

load

(tra

nspo

rt c

hann

el t

raffi

c vo

lum

e)(t

rans

port

cha

nnel

tra

ffic

volu

me)

TrafVolThresholdDL(UL)Low(WCEL)

CELL_FACH state

CELL_DCH

state TrafVolThresholdDL(UL)High


Cell-DCH/Cell-FACH KPIs

Percentage of time in cell dch:

NRT RB data transfer activeNRT RB inactivity timer running

Downlink DCH

Uplink DCH

CELL_FACH CELL_DCH CELL_FACH

%100__________

INTERPSTMHLDRABAVGINTERPSTMHLDDCHAVG

DCH Time %10%20%30%40%50%60%70%80%90%100%More

Similar KPI giving the ratio between FACH and DCH can be constructed starting fromM1006C90 SUM OF UE OPERATING TIME IN CELL_FACHM1006C87 SUM OF UE OPERATING TIME IN CELL_DCH

Dividing per the number of UE is possible to have average time for user:M1006C90 SUM OF UE OPERATING TIME IN CELL_FACH/M1006C92 NUM OF UE MEASURED IN CELL_FACHM1006C87 SUM OF UE OPERATING TIME IN CELL_DCH / M1006C89 NUM OF UE MEASURED IN CELL_DCHThe number of transition can be monitored as well:M1006C45 CELL DCH STATE TO CELL FACHM1006C46 CELL FACH STATE TO CELL DCH


Measuring the RACH/FACH ChannelThe RACH channel average throughput for both data and signaling can be measured by the following KPI

kbps /1000_3RACH_DENOM M1000C61

THROUGHPUTAVE_RACH_ M1000C60

The FACH Total throughput means all the user related data (FACH-u) and signalling (FACH-c) for a SCCPCHincluding PCH can be measured by the follwing KPI

Load KPI are available as well using the following countersM1000C64 AVE SCCPCH INC PCH LOADM1000C65 SCCPCH LOAD DENOM 0When the throughput approach the maximum allowed or the load the 100% for the actual configuration aparameter tuning to avoid the starvation in CCH or an expansion of RACH and FACH channel is required. Thedecision outcomes from different input:

DCH resources availableMarketing Strategy

bit/s ENOM_0TOT_TPUT_DFACH_USER_ M1000C67

SCCP_PCH_TOT_TPUT_AVE_FACH_U M1000C66


Cell Reselection


Cell Reselection List

GSM MS starts WCDMA measurements if :RLA_C< F(Qsearch_I) for 0<Qsearch_I<=7

orRLA_C> F(Qsearch_I) for 7<Qsearch_I<=15

If, for suitable UMTS cell & for a period of 5 s:

CPICH RSCP > RLA_C + FDD_Qoffset

CPICH Ec/No FDD_Qmin

and

WCDMA cellreselection

BCCH: FDD_Qmin, FDD_Qoffset

Cell Reselection 2G -> 3G

Startmeasurement


Depending on operator´s 2G – 3G interworking strategy parameter Q_search_I should planned accordingly.

Configuration 1RLA_C<

F(Qsearch_I) ( 0<Qsearch_I<=6 )

GSM 3G

Configuration 2RLA_C> F(Qsearch_I) ( 7<Qsearch_I<=15 )

In the best case, 3G cell measurements are restricted to the condition: RLA_C level > –78 dBm

GSM3G

In the best case, 3G cell measurements are possible when RLA_C level < –74 dBm

GSM

3G

Configuration 3RLA_C< (always).

(Qsearch_I=7)

2G -> 3G Measurement


2G -> 3G Cell Re-selection Parameters Qsearch_I and Qsearch_P define the threshold for non-GPRS/GPRS (respectively) capable UEs to measure 3Gneighbour cells when a running average of the received downlink signal level (RLA_C) of the serving cell below (0-7) or above (8-15) the threshold

Value 0 1 … 6 7 8 9 10 … 14 15

dBm -98 -94 … -74 Always -78 -74 -70 … -54 Never

FDD_Qoffset and FDD_GPRS_Offset the non-GPRS/GPRS (respectively) capable UEs add this offset to theRLA_C of the GSM cells. After that the UE compares the measured RSCP values of 3G cells with signal levelsof the GSM cells

Value 0 1 2 3 … 8 … 14 15

dBm Always -28 -24 -20 … 0 … 24 28

Always select irrespective of RSCP value Reselect in case RSCP >

GSM RXLev (RLA_C) +28dB

If RLA_C < -94 UE starts 3G measurements

UE always measures 3G cells

If RLA_C > -70 UE starts 3G measurements

FDD_Qmin, defines minimum Ec/No threshold that a 3G cell must exceed, in order the UE makes a cell reselection from 2G to 3G.


Cell Re-selection Example-Weaker WCDMANon GPRS case

t

Serving GSM Cell

Neighbour WCDMA Cell

Ec/NoRSCP/RLA_C

5 sec.

Cell re-selection to WCDMA

FDD_Qmin=0(-20 dB)

FDD_Qoffset =6 (-8 dB)

Qsearch_I=0 (-98 dBm)

RLA_C

Measurements starts (serving cell)

Minimum Quality Requirement for WCDMA

Ec/N0

RSCP


Cell Re-selection Example-Weaker WCDMAGPRS case

t

Serving GSM Cell (Best)

Neighbour WCDMA Cell

Ec/NoRSCP/RLA_C

5 sec.

Cell re-selection to WCDMA

FDD_Qmin=-20 dB

FDD_GPRS_Qoffset =10 (8 dB)Qsearch_P=0(-98 dBm)

RLA_P

Measurements starts (serving cell)

Minimum Quality Requirement for WCDMA

Ec/N0

RSCP


Cell Reselection 3G -> 2GWhilst camping in a 3G cell the UE performs intra-frequency, inter-frequency, and inter-systemmeasurements based on the measured CPICH EcNo.Serving cell parameters Sintrasearch, Sintersearch and SsearchRAT are compared with Squal (CPICH Ec/No – Qqualmin) in S-criteria for cell re-selection

1 - None (Squal > Sintrasearch ) 2 - WCDMA intra-frequency (Sintersearch < Squal Sintrasearch)3 - WCDMA intra- and inter- frequency, no inter-RAT cells (SsearchRAT < Squal Sintersearch) 4 - WCDMA intra- and inter-frequency and inter-RAT cells (Squal SsearchRAT )

Sintrasearch Sintersearch SsearchRAT

WCDMACELL

1234



First ranking of all the cells based on CPICH RSCP (WCDMA) and RSSI (GSM)

Rs = CPICH RSCP + Qhyst1Rn= Rxlev(n) - Qoffset1

Rn (GSM) > Rs (WCDMA)And

Rxlev (GSM) >QrxlevMin

YesNo

Cell re-selection to GSM

Neighbour WCDMA or GSM cell calculation with offset

parameter

Serving WCDMA cell calculation, with

hysteresis parameter

UE starts GSM measurements if CPICH Ec/No =< qQualMin + sSearchRAT

SintraSearch

SinterSearch

SsearchRAT

CPICH EcNo

qQualMin

Second ranking only for WCDMA cells based on CPICH Ec/No

Rs = CPICH Ec/No + Qhyst2Rn=CPICH_Ec/No(n)-Qoffset2 Cell re-selection to

WCDMA cell of highest R value



UE ranks the serving cell and the measured neighboring cells to find out if reselection should be made• All the measured suitable cells (S-criteria) are included in the ranking. • Criteria for a suitable cell (S-criteria) is defined as

– WCDMA intra-frequency neighbour cell: CPICH Ec/No > AdjsQqualmin and CPICH RSCP > AdjsQrexlevmin

– WCDMA inter-frequency cell: CPICH Ec/No > AdjiQqualmin and CPICH RSCP > AdjiQrexlevmin

– GSM cell:Rxlev > Qrxlevmin

Ranking is done using Criteria R, and the UE reselects to the cell with highest R-criteria. R-criteria is definedas:• For serving cell: Rs = Qmeas,s + Qhysts • For neighboring cell Rn = Qmeas,n – Qoffsetts,n

Qmeas is CPICH Ec/No for WCDMA cell and RxLev for GSM cell


How to avoid ping pong ?

When phone is camped on 3G, GSM measurements can start when CPICH Ec/Io of serving cell is below Ssearch_RAT + QqualMin.When phone is camped on GSM, cell reselection to 3G is possible if CPICH Ec/Io of the candidate is above FDD_Qmin.Therefore, to avoid ping pongs between 3G and GSM the following condition should be met:

FDD_Qmin >= QqualMin + Ssearch_RAT

QqualMin=-18 dB

Ssearch_RAT=4 dB

CPICH Ec/Io

FDD_Qmin >= -12 dB

QqualMin +Ssearch_RAT

t

Camping on 3G Measure GSM Camping on 3G


How to avoid ping pong ?

Parameters for cell reselections

• Qqualmin = -18dB Ssearch_RAT =2dB -> the 3G->2G cell reselection starts when Ec/No hits -16dB• FDDQmin(GPRSFDDQmin) = -14dB (6) and QsearchP/QsearchI = always

The cell reselection paramters 3G -> 2G and 2G -> 3G provide only 2dB hysteresis which is not enough and should be noticed from the RNC statistics as high amount of INTR_RAT_CELL_RE_SEL_ATTS from all the RRC Connection Setup Attempts

• Recommendation is to adjust the FDDQmin from -14dB to -10dB (or even up to -8dB) to provide 6 to 8 dB hysteresis between 3G to 2G cell reselection and 2G to 3G cell reselection

• Another parameter to tune is Qrxlevmin

On top of Treselection the above parameters will slow down further the 2G to 3G and 3G to 2G cell reselections


TreselectionHow long the reselection conditions must be fulfilled before reselection is triggered?Treselection

Impacts all cell reselections : Inter RAT, intra frequency and inter frequencyThe UE reselects the new cell, if the cell reselection criteria (R-criteria, see next slide) are fulfilled during a time

intervalTreselectionAs this parameter impacts on all the cell reselections too long Treselection timer might cause problems in high mobility areas but too short timer causes too fast cell reselections and eventually causes also cell reselection ping pongRecommended value 1s should work in every conditions i.e. enough averaging to make sure that correct cell is selectedHowever careful testing is needed to check the performance of different areas• (Dense) Urban area, slow moving UEs with occasional need for fast and accurate (to correct cell) reselections e.g.

outdoor to indoor scenarios or city highways – in some cases cell by cell parameter tuning is performed to find most optimal value between 0s and 2s but typically 1s is optimal value when workload is considered as well

• Highways, fast moving UEs must reselect correct cell – typically 1s works the best (however occasionally also 0s might be needed in fast speed outdoor to indoor cell reselections e.g. tunnels)

• Rural areas, slow or fast moving UEs need very often reselect between different RATs and make proper cell reselections even when the coverage is poor – typically 1s works the best

• Location Area Borders, usually the coverage is fairly poor – typically 1s works the best but sometimes to reduce location area reselection ping pong 1s is used when going from LA1 to LA2 and 2s from LA2 to LA1


Cell Reselection KPIs

RRC connection request amount for inter RAT cell reselection ratio to all RRC Connection request causes• When hysteresis is increased this KPI should decrease

RRC connection request amount for registrations ratio to all RRC Connection request causes• When hysteresis is increased this KPI should decrease

TP_ATTRRC_CONN_SM1001C0_ATTSELL_RE_SELINTR_RAT_C M1001C42

TP_ATTRRC_CONN_SM1001C0ON_ATTSREGISTRATI M1001C46

nsn rno fi 191007 partiii

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