idle mode parameter opti

5/27/2018 Idle Mode Parameter Opti

1/331 Nokia Siemens Networks Presentation / Author / Date

For internal use

Slowing Down the Inter RAT Cell Reselections;Parameter Tuning & Monitoring GuideVersion 1.0

23.09.2007 Reunanen Jussi



For internal use

Agenda

Treselection

Hysteresis between 3G->2G and 2G->3G cell reselections PRACHRequiredReceivedCI and

PowerRampStepPRACHpreamble

PrxAlpha

PrxTarget



For internal use

Treselection Introduction

Treselection: how long the reselection conditions must be fulfilled

before reselection is triggered Impacts all cell reselections : Inter RAT, intra frequency and inter

frequency

The UE reselects the new cell, if the cell reselection criteria (R-criteria, see next slide) are fulfilled during a time interval

Treselection



For internal use

Treselection Introduction

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

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

Rn (GSM) > Rs (WCDMA)And

Rxlev (GSM) >QrxlevMin

YesNo

Cell re-selectionto GSM

Neighbour WCDMA or GSM

cell calculation with offsetparameter

Serving WCDMA cellcalculation, with

hysteresis parameter

UE starts GSM measurements ifCPICH Ec/No < qQualMin+ sSearchRAT

SintraSearch

SinterSearch

SsearchRAT

CPICH EcNo

qQualMin

Second ranking only for WCDMAcells based on CPICH Ec/No

Rs = CPICH Ec/No + Qhyst2Rn=CPICH_Ec/No(n)-Qoffset2

Cell re-selection toWCDMA cell of highest

R value



For internal use

Treselection Recommended Values

As this parameter impacts on all the cell reselections too long Treselection timermight cause problems in high mobility areas but too short timer causes too fast cellreselections and eventually causes also cell reselection ping pong

Recommended value 1s should work in every conditions i.e. enough averaging tomake sure that correct cell is selected

However careful testing is needed to check the performance of different areas

(Dense) Urban area, slow moving UEs with occasional need for fast andaccurate (to correct cell) reselections e.g. outdoor to indoor scenarios or cityhighwaysin 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 workloadis considered as well

Highways, fast moving UEs must reselect correct celltypically 1s works thebest (however occasionally also 0s might be needed in fast speed outdoor toindoor 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 poortypically 1s works the best

Location Area Borders, usually the coverage is fairly poortypically 1s worksthe best but sometimes to reduce location area reselection ping pong 1s is usedwhen going from LA1 to LA2 and 2s from LA2 to LA1



For internal use

Treselection KPIs and Analysis

RRC connection request amount for inter RAT cell reselection ratio to all RRCConnection request causes

When Treselection is increased this KPI should decrease

RRC connection request amount for registrations ratio to all RRC Connectionrequest causes

When Treselection is increased this KPI should decrease

TP_ATTRRC_CONN_SM1001C0

_ATTSELL_RE_SELINTR_RAT_CM1001C42


ON_ATTSREGISTRATIM1001C46



For internal use


At the same time the CSSR and especially the RRC Connection Setup andAccess Complete must be monitored

The KPIs below should remain the same despite the Treselectionmodification or even get better

If the CSSRs or RRC Connection Setup and Access Complete decrease theTreselection value should be decreased

RNC_94d: RRC Setup and Access Complete Ratio from network point of

view RNC_565e: CSSR CS Voice (RAS05.1) or RNC_565d : CSSR CS Voice

(RAS05)

The RRC Connection Setup attempts should decrease

M1001C0 RRC_CONN_STP_ATT



For internal use


Following RRC Connection Setup failure causes should decrease as theamount of RRC Connection setup attempts is decreasing

M1001C3 RRC_CONN_STP_FAIL_AC

M1001C4 RRC_CONN_STP_FAIL_BTS

M1001C5 RRC_CONN_STP_FAIL_TRANS

M1001C530 RRC_CONN_STP_FAIL_IUB_AAL2

Above indicate saved resources and more detailed analysis can be donebased on counters below BTS CE : RAS05.1

Iub : AAL2 Path Average Reserved Bandwidth % : RAS05

E_DLMAX_USED_CM5001C3

CE_ULMAX_USED_M5001C4

E_DLMIN_USED_CM5001C5CE_ULMIN_USED_M5001C6

E_DLAVG_USED_CM5001C7

E_ULAVG_USED_CM5001C8

RATEGUAR_CELL_AAL2_PATH_M550C0

SNBR_SAMPLEM550C7ATEVED_CELL_RSUM_RESERM550C1

100%


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9 Nokia Siemens Networks Presentation / Author / Date

For internal use

Hysteresis Between 3G->2G and 2G->3G CellReselections Introduction & Recommended Values

Parameters for cell reselections

Qqualmin = -18dB Ssearch_RAT =2dB -> the 3G->2G cell reselection startswhen Ec/No hits -16dB

FDDQmin/GPRSfddQmin = -14dB (6) and QsearchP/Qsearch = always

The cell reselection paramters 3G -> 2G and 2G -> 3G provide only 2dB hysteresiswhich is not enough and can been noticed from the RNC statistics as high amountof INTR_RAT_CELL_RE_SEL_ATTS from all the RRC Connection Setup Attempts

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

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


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For internal use

Hysteresis Between 3G->2G and 2G->3G CellReselections Introduction & Recommended ValuesHowever careful testing is needed to check the performance of different areas

UEs must reselect correct cell in case of 3G outdoor to certain 2Gin thesecases adjacency based parameterAdjqoffset1 can be used to prioritize certain2G neighbor

Impacts the R-criteria as shown below

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

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


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For internal use

Hysteresis Between 3G->2G and 2G->3G CellReselections KPIs and Analysis

RRC connection request amount for inter RAT cell reselection ratio to all RRCConnection request causes

When hysteresis is increased this KPI should decrease

RRC connection request amount for registrations ratio to all RRC Connectionrequest causes

When hysteresis is increased this KPI should decrease


_ATTSELL_RE_SELINTR_RAT_CM1001C42


ON_ATTSREGISTRATIM1001C46


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For internal use


At the same time the CSSR and especially the RRC Connection Setup andAccess Complete must be monitored

The KPIs below should remain the same despite the hysteresis modificationor even get better

If the CSSRs or RRC Connection Setup and Access Complete decrease thehysteresis value should be decreased

RNC_94d: RRC Setup and Access Complete Ratio from network point of

view RNC_565e: CSSR CS Voice (RAS05.1) or RNC_565d : CSSR CS Voice

(RAS05)

The RRC Connection Setup attempts should decrease



13/33


For internal use


Following RRC Connection Setup failure causes should decrease as theamount of RRC Connection setup attempts is decreasing





Above indicate saved resources and more detailed analysis can be done

based on counters below BTS CE : RAS05.1

Iub : AAL2 Path Average Reserved Bandwidth % : RAS05

E_DLMAX_USED_CM5001C3

CE_ULMAX_USED_M5001C4

E_DLMIN_USED_CM5001C5CE_ULMIN_USED_M5001C6

E_DLAVG_USED_CM5001C7

E_ULAVG_USED_CM5001C8

RATEGUAR_CELL_AAL2_PATH_M550C0

SNBR_SAMPLEM550C7ATEVED_CELL_RSUM_RESERM550C1

100%


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For internal use

CLUSTER JBK09

0%

20%

40%

60%

80%

100%

50% of all RRCsetups for Inter RAT cell reselection

Hysteresis Between 3G->2G and 2G->3G CellReselections KPI Analysis Example

Hysteresis from 2dB -> 6dB


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For internal use

PRACHRequiredReceivedCI andPowerRampStepPRACHpreamble Introduction

During drive testing it is usually noted that there are call setup failures where thenetwork does not seem to respond to RRC Connection Requests with RRC

Connection Setupmessage

These are problems due to the spiky UL noise and due to that the powerramping is not aggressive enough to provide high enough Tx power for theterminal during open loop PC

MAJOR ROADS INNER & OUTER BLOCKED COUNT

BREAKDOWN

No Immediate

Assignment, 1

No Radio

Bearer Setup

Complete, 2No Alerting or

Connect, 1

N-300 and T-

300 expiry, 4

No Setup, 1

RRC Connection

Reject, 3


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For internal use

PRACHRequiredReceivedCI andPowerRampStepPRACHpreamble Introduction

The parameters affecting to open loop power control are, in brackets are the recommendedvalues:

PRACH_preamble_retrans (7) RACH_tx_Max (16)

PowerOffsetLastPreamblePRACHmessage (2 dB)

PowerRampStepPRACHpreamble (2dB)

Downlink

BS

L1 ACK / AICH

Uplink

MS Preamble1

Not detected

Message partPreamble2

PreamblePRACH_preamble_retrans

# PRACH preambles transmitted during onePRACH cycle without receiving AICH response

UEtxPowerMaxPRACH

RACH_tx_Max# preamble power ramping cycles that can be

done before RACH transmission failure is

PowerRampStepPRACHpreamble

PowerOffsetLastPreamblePRACHmessage

Ptx = CPICHtransmissionPower-RSCP(CPICH)

+RSSI(BS) + PRACHRequiredReceivedCI (-20dB)


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For internal use

PRACHRequiredReceivedCI andPowerRampStepPRACHpreamble Recommended Values

Typically the parameter PRACHRequiredReceivedCI is set to -18-20dBinstead of the default -25dB (typically -20dB is enough)

Also the parameter PowerRampStepPRACHpreamble is adjusted in case theproblem of missed MT calls or call setup failures due to missing RRCConnection Setup still persists (default 2dB usually works the best but in somenetworks also 3dB is used)

Check also the values for RACH_tx_Max and PRACH_preamble_retrans

They should be set accordingly as: PRACH_preamble_retrans (7)

RACH_tx_Max (16)

Also the parameters should all be set in line as below:

PowerOffsetLastPreamblePRACHmessage (2 dB)

PowerRampStepPRACHpreamble (2dB)

PRACHRequiredReceivedCI (-20dB)

PRACH_preamble_retrans (7)

RACH_tx_Max (16)

C C


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For internal use

PRACHRequiredReceivedCI andPowerRampStepPRACHpreamble Recommended Values

If for example PowerRampStepPRACHpreamble is set to 3dB then otherparameters should be adjusted with extra care to avoid unnecessary UL noise

spikes Current defaults are tested to work properly without excessive increase in UL

noise

PRACHR i dR i dCI d


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For internal use

PRACHRequiredReceivedCI andPowerRampStepPRACHpreamble KPIs and Analysis

The impact of this parameter has to be tested with drive testing (as in case thePRACH preambles are not heard and therefore the RRC Connection Request is

not heard by the BTS/RNC no RRC connection setup attempt counter isincremented)

From the network statistics following should be monitored RNC_177b Noise Floor of the System

RNC_101b Average Uplink load Related to above the M1001C3 RRC_CONN_STP_FAIL_AC should not increase (if do then load

level reduction actions are needed, explained in PrxAlpha tuning section)

Secondary KPIs to follow If the CSSRs or RRC Connection Setup and Access Complete decrease the hysteresis

value should be decreased

RNC_94d: RRC Setup and Access Complete Ratio from network point of view

RNC_565e: CSSR CS Voice (RAS05.1) or RNC_565d : CSSR CS Voice (RAS05)

The RRC Connection Setup attempts should increase but the failures should not increase(especially AC rejections which are related to UL noise increase / Average UL load)





PRACHR i dR i dCI d


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For internal use

PRACHRequiredReceivedCI andPowerRampStepPRACHpreamble KPI Analysis Example

Two values for PRACHRequiredReceivedCI tested (drive testing)

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 RRCConnection Request messages per call. For

20dB 100% of established calls are setup withonly 1 RRC Connection Request message

Clear improvement number of sent preamblesper RRC Connection Request for20dB case.

For20dB 50% of cases the needed number ofpreambles is


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For internal use


Clear improvement in call setup delay for20dBcase. ~65% of the established calls are throughwith only 3.53.7s delay and the >5.5s delaytail disappears (in this case).

Two values for PRACHRequiredReceivedCI tested (drive testing) -20dB

-25dB

UL interference conditions are at the same level(reported in SIB 7 for both cases)

96.2%

100.0%

94%

95%

96%

97%

98%

99%

100%

-25dB -20dB

Call Setup Success Rate

0.0%

20.0%

40.0%

60.0%80.0%

100.0%

120.0%

5.

5s

Call Setup Delay (seconds) RRC Conn. Req. to Alerting

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

PRACHRequiredReceivedCI and


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For internal use


AMR Voice Before 1stdrive 2nddrive

Average Preamble Counts 2.40 2.01 1.617Average RACH_TX_Pwr -9.11 -7.09 -6.581

average UL interference -102.42 -102.07 -101.53

Video Before 1stdrive 2nddrive

Average preamble count 2.84 1.77 1.933

Average RACH_TX_Pwr -6.95 -6.45 -6.888average UL interference -102.46 -102.15 -101.33

1. The number of resend for PRACH (Preamble Count) has reduced after the parameterschanging, that mean shorter time to build the radio link. 1stdrive is afterPRACHRequiredReceivedCIbeen changed (-25dB -> -20dB), while 2nddrive is afterRACH_tx_maxbeen changed (8 -> 16)

2. Meanwhile the RACH_TX_Pwr for both AMR and Video services is increased, which mean morepower is consumed by the UE .

3. The slighlty increased UL interference can be tried to be reduced by taking the alpha trimmedmean filter into use to filter the Prx measurements in BTS

PRACHRequiredReceivedCI and


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For internal use


AMR (MOC) Before 1stdrive 2nddriveAverage CS call setup time (MOC) 2.36s 2.44s 2.38sCall Setup Success Rate 97.87% 99.30% 100.00%

PrxAlpha Introduction


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For internal use


In case the indicators below have increased due to the open loop PC parametermodifications

RNC_177b Noise Floor of the System RNC_101b Average Uplink load

Or in generally if there are high amount of rejections due to following rasons


M1001C80 RAB_STP_FAIL_CS_VOICE_AC

M1001C85 RAB_STP_FAIL_CS_CONV_AC

The BTS PrxTotal filtering parameters can be modified i.e. how the BTS averagesthe PrxTotal measurements before sending the results to the RNC in RadioResource Indication messages



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For internal use


Frame mean of Prx_total is pre-calculated using arithmetic mean ofthe slot values (15 slots)

Averaged frames are sorted based on PrxMeasAveWindowframes

Filtered values are calculated by taking arithmetic frame meanvalues which are between ALPHA and (1-APLHA) defined byPrxAlpha

N x lowest and highest measurements removed N x (1- 2) measurements remain

Av. Frame measurements

Prx PrxMeasAveWindow= 10 & PrxAlpha= 0.2

Frame averages are calculated for 10 frames

2 max. & 2 min. values excluded : 6 valuesremaining

Final average Prx_total is calculated on the 6values



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For internal use


RADIO RESOURCE INDICATION (RRI)

messagePrx Total is reported to the RNC for LC, AC andPS usage, on every RRIindicationperiod (200ms)

The BTSismeasuring:Prx Total

BTS sends the LASTESTaveraged measurementresult to RNC every RRIperiod

RNC is calculatinga sliding windowaveraged valueover the valuesgiven by RRImessages

Frame measurements

Prx

RRIxRRIx+1RRIx+2RRIx+n

Sliding window averageresult on every RRIperiod

WinAcRabSetupUI

m

j

jntotalrx Totalxm

P1

_ _Pr1

BTS usesALPHA TRIMMED MEANFILTER

PrxAlpha

PrxMeasAvWindow

PrxAlpha Recommended Values & Example


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For internal use

PrxAlpha Recommended Values & Example

PrxAlpha=0.1

PrxMeasAveWindow=10

RRIPeriod=200ms

PrxAlpha=0PrxMeasAveWindow=10

RRIPeriod=200ms

Clearly some impact when changingthe PrxAlpha-> suggests that the

interference conditions aresomewhat spiky and the PrxTotalvalues could be further reducedadjusting the PrxAlpha

The PrxAlpha parameter valueshould be adjusted in 0.1 step

intervals and KPIs monitored foreach parameter value

PrxAlpha KPIs and Analysis


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For internal use

PrxAlpha KPIs and Analysis

Following indicators should be monitored for each PrxAlpha value

RNC_177b Noise Floor of the System

RNC_101b Average Uplink load




PrxTarget Introduction


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For internal use

PrxTarget Introduction

If the received Non-controllable power (RT) + the estimated powerincrease caused by the to be established RAB is above the

PrxTarget, the RT RAB setup is rejectedIf the received Non-controllable power (RT) is above the PrxTargetlimit then the RRC Connection Setup is rejected

However note that for the following RRC Connection Requestcause values the AC limits are not used (in UL nor in DL)

Emergency call Registration

Detach

Originating High Priority Signaling

Terminating High Priority Signalling

Inter-RAT cell re-selection Inter-RAT cell change order

PrxTarget Recommended Values & Example


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For internal use

PrxTarget Recommended Values & Example

TOTAL NUMBER OF RRC CONN STP FAIL AC

0

1000

2000

3000

4000

5000

6000

6/1/2007

6/2/2007

6/3/2007

6/4/2007

6/5/2007

6/6/2007

6/7/2007

6/8/2007

6/9/2007

6/10/2007

6/11/2007

6/12/2007

6/13/2007

6/14/2007

6/15/2007

6/16/2007

6/17/2007

6/18/2007

6/19/2007

6/20/2007

6/21/2007

6/22/2007

6/23/2007

6/26/2007

6/27/2007

6/28/2007

6/29/2007

6/30/2007

7/1/2007

Total Moving Avg

WCELL Name (All) Batch 4th Batch

Sum of RRC_CONN_STP_FAIL_AC

Date

In case the PrxAlpha tuning does not reduce the AC rejections thenthe PrxTarget can be increased to reduce the AC rejections

Typically just 2dB increase provides significant reduction on the ACrejections

Starting 16 June 2007PtxTarget modified 4dB -> 6dB

PrxTarget Recommended Values


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For internal use


First the following counters should be checked


The above should be compared with the parameter value PrxNoise (WCEL) Max(RNC_177b, PrxNoise) = A

RNC_101b Average Uplink load

M1000C0 AVE_PRXTOT_CLASS_0, M1000C1 PRXTOT_DENOM_0


M1000C4 AVE_PRXTOT_CLASS_2, M1000C5 PRXTOT_DENOM_2 M1000C6 AVE_PRXTOT_CLASS_3, M1000C7 PRXTOT_DENOM_3




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For internal use


First the following counters should be checked

The PrxTotal distribution should be calculated from above and the needed

PrxTarget distribution and average Average needed PrxTarget; ARNC101b

Distribution can be calculated the same way A-AVE_PRXTOT_CLASS_X and the %of samples for each class PRXTOT_DENOM_X/(PRXTOT_DENOM_1+PRXTOT_DENOM_2+ PRXTOT_DENOM_3+ PRXTOT_DENOM_4+PRXTOT_DENOM_5)

Then the PrxTarget parameter tuning should be performed in steps of 2dBtowards the highest calculated PrxTotal value

Max PrxTarget value should not exceed 10dB (in normal conditions without anyspecial interferer)

PrxTarget KPIs and Analysis


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For internal use

a get s a d a ys s

When the PrxTarget is modified following KPIs should be monitored


RNC_101b Average Uplink load M1001C3 RRC_CONN_STP_FAIL_AC








RNC_94d: RRC Setup and Access Complete Ratio from network point of view

RNC_565e: CSSR CS Voice (RAS05.1) or RNC_565d : CSSR CS Voice(RAS05)

idle mode parameter opti

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