LTE Mobility

MOBILITY

Event A3 - Neighbor becomes amount offset better than serving.

Event A2 - Serving becomes worse than absolute threshold

Events for IRAT HO

Cell Selection CriterionThe cell selection criterion (the S criterion) is based on the measured Reference Signal Received Power (RSRP) level in the cell, normalized with respect to the minimum required receive signal level in the cell and certain compensations.The cell selection criterion is fulfilled if: Srxlev > 0where:Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminoffset) - PcompensationThe UE obtains the Srxlev value using the following measurements and parameter values:Qrxlevmeas -Measured RSRP value in the cell (dBm)Qrxlevmin - Required minimum RSRP level in the cell (dBm)Qrxlevminoffset - Offset to Qrxlevmin taken into account in the Srxlev evaluation as a result of a periodic search for a higher priority PLMN (not provided in the current release of the LTE Basic). Value 1000 means the parameter is not included in system information Default value: 0 (dBm)Pcompensation - Compensation [max (PEMAX - PUMAX, 0)] if the maximum power according to the UE capability(PUMAX) is less than the maximum UE power to be used in the cell (PEMAX).

Parameter DescriptionEUtranCellFDD qRxLevMin (-120 dbm) -Required minimum RSRP level in the E-UTRA cell. EUtranCellFDD pMaxServingCell (1000 )- - Maximum UE power to be used in the cell. If absent, the UE applies the maximum power according to UE capability.

Measurements Performed by UEThe UE in idle mode measures the RSRP level of the E-UTRA cells on the current frequency. These measurements are performed in the camped normally and camped on any cell states, dependingon parameters broadcast in system information. The results from these measurements are used in the cell reselection evaluation process.The amount of measurements the UE performs may impact UE battery performance. A trade-off between cell reselection and UE battery performance is required when setting configuration parameter values to control thesemeasurements.

Measurements on intra-frequency cells are performed if SServingCell ≤ Sintrasearch

If SServingCell > SIntrasearch, the UE does not need to perform these measurements.

Parameter Description EUtranCellFDD systemInformationBlock3 sIntraSearch (62) - Threshold for intra-frequency measurements. Corresponds to parameter Sintrasearch in the document 3GPP TS 36.304. EUtranCellFDD systemInformationBlock3 sNonIntraSearch (10 / 4) - Threshold for inter-frequency and inter-RAT measurements on frequencies of equal or lower priority. EUtranCellFDD systemInformationBlock3 threshServingLow (10) - Threshold for the signal strength of the serving cell, below which the UE performs cell reselection towards a lower priority inter-frequency or inter-RAT frequency.

When camped on an E-UTRA cell, the UE performs a ranking of neighboring E-UTRA cells on the same frequency, taking into account the cells satisfying the cell selection criteria The cell ranking isbased on the RSRP measurement quantities of the serving cell (Qmeas,s) and the neighboring cells (Qmeas,n).The UE applies the cell ranking criterion Rs on the serving cell, and the cell ranking criterion Rn on the intra-frequency cells: Rs = Qmeas,s + Qhyst Rn = Qmeas,nWhen a neighboring cell is ranked as better than the serving cell (that is, Rn > Rs) during a time interval TreselectionEUTRA, the UE performs a cell reselection to the better-ranked cell.

Parameter DescriptionEUtranCellFDD systemInformationBlock3 qHyst (4 db) -Cell reselection parameter that defines the hysteresis value in the intra-frequency cell ranking criteria.EUtranFreqRelation tReselectionEutra (2 sec) - Cell reselection timer value for an E-UTRA frequency.qRxLevMin -(neighboring cells) Required RSRP level in the intra-frequency neighboring cells.EUtranFreqRelation pMax (23)- Maximum UE power to be used in neighboring cells on the E-UTRA frequency. If absent, the UE applies the maximum UE power for the UE power class.

Parameters for Intra-Frequency Cell Reselection

Priority-Based Cell Reselection

A cell reselection priority is configured for the E-UTRA frequency of the serving cell.cellReselectionPriority - Absolute cell reselection priority for the E-UTRA frequency. The cellReselectionPriority parameter can be configured but is useful only when there are inter-frequency carriers and/or inter-RAT frequencies defined in system information.

The speed-dependent scaling of cell reselection criteria is used to influence the cell reselection criteria for fast moving UE. It helps the UE to respond more quickly to cell changes when moving at high speed. A UE may enter three different mobility states:• Normal• Medium• High mobilityThe usual TreselectionEUTRA and Qhyst parameters are used in the normal mobility state for the evaluation of cell reselection criteria.In the medium and high mobility states, the UE applies a scaling factor, decreasing the value of the TreselectionEUTRA parameter. In that way, the evaluation period of cell reselection criteria is reduced.

In addition, a negative offset is added to the Qhyst hysteresis value in the cell ranking criteria. It lowers the threshold for the reselection of intra-frequency cells. A sliding time window is used. The parameter TCRmax determines the duration of the sliding time window. The parameters NCR_M (medium mobility) and NCR_H (high mobility) determine the number of cell reselections the UE performs within the sliding time windowto enter the medium and high mobility states. Once in the medium or high mobility state, the UE re-enters the normal mobility state when the number of cell reselections during the sliding time window (TCRmax) stays below the parameter NCR_M and NCR_H values during a period equal to the additional time period. The parameter TCRmaxHyst determines the duration of the additional time period.

Speed-Dependent Scaling of Cell Reselection Criteria

Parameters to Set Entry Criteria for Mobility StatesEUtranCellFDD tEvaluation (240 Sec)- Duration for the evaluation of the entering criteria to the mobility states. Corresponds to 3GPP parameter TCRmax.EUtranCellFDD tHystNormal (240 Sec) - Additional duration for the evaluation of the reentering criteria to the normal mobility state. Corresponds to 3GPP parameter TCRmaxHyst.EUtranCellFDD nCellChangeMedium (16) - Number of cell changes to enter the medium mobility state. Corresponds to 3GPP parameter NCR_M.EUtranCellFDD nCellChangeHigh (16) - Number of cell changes to enter the high mobility state.Corresponds to 3GPP parameter NCR_H.

Parameters to Set Speed-Dependent Scaling of Intra-Frequency Cell Reselection Criteria :

EUtranCellFDD qHystSfMedium (0 dB) - Reduction of the Qhyst parameter applied in medium mobilitystate. Corresponds to 3GPP parameter sf-Medium of Speed dependent ScalingFactor for Qhyst.EUtranCellFDD qHystSfHigh (0 dB) - Reduction of the Qhyst parameter applied in high mobility state. Corresponds to 3GPP parameter sf-High of Speed dependent ScalingFactor for Qhyst.EUtranFreqRelation tReselectionEutraSfMedium (100) -Scaling of the TreselectionEUTRA parameter in medium mobility state. The attribute t-ReselectionEUTRA is multiplied with this factor if the UE is in medium mobility state Corresponds to 3GPP parameter sf-Medium of Speed dependent ScalingFactor for TreselectionEUTRA. Value mapping:25 = 0.2550 = 0.575 = 0.75100 = 1.0Unit: 1 %Resolution: 25 EUtranFreqRelation tReselectionEutraSfHigh (100) Scaling of the TreselectionEUTRA parameter in high mobilitystate. Corresponds to 3GPP parameter sf-High of Speed dependent ScalingFactor for TreselectionEUTRA.

LTE-UMTS Interworkingidle and active mode

AGENDA• Idle Mode Reselection from LTE to WCDMA (SIB3 / SIB6)

• Idle Mode Reselection from WCDMA to LTE (SIB19)

• Connected Mode from LTE to UMTS• Optimization Discussion• OSS Configuration

Overview

Connected Mode

Reselection Session Continuity

Blind Measured

Idle Mode

Blind session continuity redirection

based on A2 event.

Measured session continuity redirection based on A2/B2 event.

UE Triggered: LTE UMTS Network Triggered: LTE UMTS

LTE to UMTS ReselectionUMTS to LTE Reselection

L11 L12

Inter-working scenario/PriorityLTE devices are to camp on LTE networkDownward mobility from LTE layer to existing UMTS network is directed towards the intended carrier based on DL UARFCN priority (usually on best coverage)Mobility between UMTS frequencies can be based on existing neighbor strategies

Movement between UMTS and LTESystem Information Blocks (SIBs) are used to broadcast parameters for Idle-Mode Cell Reselection•LTE SIB3 contains parameters for evaluating serving LTE cells•LTE SIB6 contains parameters for evaluating non-serving UMTS cells•UMTS SIB19 contains information for LTE

Basic Principle for Idle Mode•Search for higher priority layer

Reselect if new (LTE) is above a threshold• Search for lower priority layer:

Reselect if serving (LTE) is below a threshold & New (UMTS) is above a threshold

At release from connected mode, specific priority information may be sent to the UE

Reselection

UE in idle mode (UE triggered)

Reselection

Idle Mode

UE Triggered: LTE UMTS

Cell reselection, LTE to UMTS

1. Measurement of UMTS cells begins when LTE RSRP falls below sNonIntraSearch+qRxLevMin

2. LTE unsuitable when LTE RSRP falls belowthreshServingLow+qRxLevMin

3 UMTS suitable when UMTS CPICH RSCP is abovetheshXLow+qRxLevMin

4. Reselection occurs when LTE remains unsuitable AND UMTS remains suitable for the duration t-ReselectionUTRA

Cell reselection, LTE to UMTS

Current:Reselection from LTE ≤ -110 dBm to UMTS ≥ -119 dBmTo Change:Reselection from LTE ≤ -112 dBm to UMTS ≥ -119 dBm

SNonIntraSearch change to 8 threshServingLow change to 8

2 sec10+(-120)

10+(-120)

-120

0+(-119)= -119

-119 dBm

SIB3 – Where to get values• Transmitted every 320 ms – Parameters must be configured• Contains cell re-selection information common for intra-frequency, inter-frequency and/ or

inter-RAT cell re-selection mainly for the serving cell.

TEMS Discovery

OSS

SIB6 – Where to get values• Transmitted every 640 ms - must be mapped.• Contains cell re-selection information common for cell re-selection towards UMTS.

1 2

SIB6 Parameters Description

Cell reselection, UMTS to LTE

1. More regular measurement (every 6.4 secs) of LTE cells begins when WCDMA rxlev falls below sPrioritySearch1 (note that a UE camping on WCDMA will still measure periodically on LTE anyway. 3GPP requirement: 60 secs)

2. LTE suitable than qRxLevMin + threshHigh

3. Reselection occurs when LTE remains suitable for time t-ReselectionEUTRA

Cell reselection, UMTS to lte

Current:Reselection from UMTS to LTE ≥ -104 dBmTo Change:Reselection from UMTS to LTE ≥ -106 dBm

threshHigh change to 14

16+(-120)= -104

-120 dBm

2 sec

16+(-119)= -103

SIB19 – Where to get values› Contains cell re-selection information common for cell re-selection towards LTE

LTE EUTRA Frequency (8 max)

UMTS Priority (0…7, 7 is highest)

LTE Priority

Cell reselection occurs when LTE cell Srxlev > this value for duration treSelection (SIB3). 2dB increments. qRxLevMin + threshHigh = -120 + 16 = -104dBm

Srxlev limit in UMTS below which UE may perform reselection to LOWER priority RATNot used here.

Minimum required Rx level for reselection, used as reference. 2db increments so -60 = -120dBm

Allows UE to alert subscriber that LTE coverage is detected

Connected Mode

CONNECTED MODEA1/A2/A3/A5/B2 functionality

• Purpose: – Allows the UE to make measurements on neighbors and report measurement to eNB for handover/redirection.

• Event based triggering– Event A2 - Serving becomes worse than threshold

• UE perceives bad coverage– Event A3 – Neighbor becomes offset better than the serving cell

• IntraLTE handover (eNB to eNB)– Event A5 – Serving cell becomes worse than threshold1 and neighbor becomes better than threshold2

• Interfrequency LTE redirection or handover– Event B2 - Serving becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2

• IRAT Redirection (LTE to 3G/2G)– Event A1 - Serving becomes better than threshold, stop measurements

• UE enters good coverage

MEASUREMENT REPORT(Event A2)

RRC CONN RECONFIGURATION (Event A2, A3)

RRC CONN RECONFIGURATION (Event A1/A5/B2)

MEASUREMENT REPORT(Event A5/B2)

MEASURE

RRC CONNECTION RELEASE(REDIRECT INFO)

RRC CONN RECONFIGURATION COMPLETE

RRC CONN RECONFIGURATION COMPLETE

MEASURE

eNBUE

MEASUREMENT REPORT(Event A3)

IRAT REDIRECTION

› Blind: Triggered by the serving ENB based on serving cell threshold (A2 event)

› Measured: Triggered by the serving ENB based on serving cell threshold (A2 event) and B2

Event

Connected Mode

IRAT/ Session Continuity

Blind Measured

Blind IRAT handover based on A2 event.

Measured IF handover based on A2/B2

event.

Network Triggered: LTE UMTS

Event A2 (LTE Redirection)serving cell becomes worse than threshold

RSRP / RSRQ

Time

HysteresisA2Prim

timeToTriggerA2Prim

reportAmountA2Prim(0 = continual during event)

EnterEvent A2

Measurement ReportsreportIntervalA2Prim

Cell A

sMeasure(based on

RSRP only)

Filtering can be appliedto measurements before

Reports are sent to the RBS

LeaveEvent A2

HysteresisA2Prim

a2ThresholdRsrpPrimOr

a2ThresholdRsrqPrim

S S E

E

S Start measuring serving cellEnd measuring serving cell

E

1. Measurement of serving LTE cell begins when LTE RSRP falls below sMeasure

2. UE enters event A2 when

RSRP < a2thresholdRsrpPrim – HysteresisA2Prim

3. 1st Measurement report after entering event A2 is sent by the UE to eNB after a duration timeToTriggerA2Prim

4. After 1st measurement report is sent, UE sends measurement reports till it either leaves event A2, redirects to UMTS or drops every reportIntervalA2Prim

5. UE is released and redirected to UMTS.

6. UE leaves event A2 when

RSRP > a2thresholdRsrpPrim + HysteresisA2Prim

Event A2 (LTE Redirection)

•sMeasure: 0 - Disabled•a2ThresholdRsrpPrim: -110dBm, to change: -112dBm•HysteresisA2Prim: 1dBm•timeToTriggerA2Prim: 640ms•reportIntervalA2Prim: 480ms•filterCoefficientEUtraRsrp: 9

Time

RSRP / RSRQ

HysteresisA2Prim

timeToTriggerA2Prim

reportAmountA2Prim(0 = continual during event)

EnterEvent A2

Measurement Reports

reportIntervalA2Prim

Cell A

sMeasure(based on

RSRP only)

Filtering can be appliedto measurements before

Reports are sent to the RBS

LeaveEvent A2

HysteresisA2Prim

a2ThresholdRsrpPrimOr

a2ThresholdRsrqPrim

S S E

E

S Start measuring serving cellEnd measuring serving cell

E

0

640ms

9 480ms

1dBm1dBm

-110dBm

-19.5(-110)+1= -109(-110)-1= -111

RRCConnectionReconfiguration Parameters

• Parameters sent by the serving RBS to the UE. • The bad coverage evaluation parameters that are contained in the RRCConnectionReconfiguration are shown in table 1• RSRP is used in the handover evaluation process.

Table 1

Session Continuity Paramters in OSS

Optimization Discussion

Why Optimize?

Some scenarios:- Move user to UMTS earlier to improve customer throughput experience- IRAT is currently a Blind HO (release and redirect). Optimization required if there are drops in LTE -> UMTS transition- Situations of terrain limitation where UE experiences sudden loss of LTE coverage (need to HO to UMTS quicker for success)- Site has good KPIs and in good coverage but high IRAT Rate. Optimize to keep user on LTE longer.

Parameters for optimization

1. a2ThresholdRsrpPrim – as a first option. Current typical used values: -110/-112

2. filterCoefficientEUtraRsrp – may be used in terrain challenged areas. Gold standard = 9. Values of 4 have been used based on pre-launch trial results.

1. a2ThresholdRsrpPrim – reduce IRAT drops

A2 event NOT followed by a “rel redirected succ” event

a2ThresholdRsrpPrim setting found in rrcConnReconfig msg

A2 events followed by drop and reselection to UMTS

UE triggers A2 but no “rel and redirect” msg seen. Try changing parameter -112 to -110 to trigger Irat earlier and reduce drops during redirect.

poor coverage areA in hilly terrain with missing LTE sites.UE travels around a bend and quickly loses LTE coverage. Not enough time to successfully IRAT to UMTS and call drops.

2. filterCoefficientEUtraRsrp – terrain challenged

Filter coefficient info

Filter coefficient values (k) used in pre-launch trial: 9,11,4.This value allows UE to give various weighting to past measurements compared to new measurements. The higher the FC used, the more weighting given to previous measurements which smooths out the measurement values and helps to counteract fast fading and sudden fluctuations in received signal.Changing FC from 9 (gold standard) to 4 gives more weighting to new measurements which could help with faster IRAT.

filter coefficient (k)

% old measurement

% new measurement

9 79 21.02

11 85.13 14.87

4 50 50

Check points - Mobility

• Handover failure • No dominant server• Interference between neighbors• Licensing issues

Handover preparation failure - Due to parameter imbalances - Feature disabled (ANR, IntraLteHO, InterFrequencyHO, Irat...) Handover execution failure - Due to existing overload in the eNodeB - Due to marginal RF

• Degrading RF conditions• Different propagation environments in source and target

• Coverage holes • Due to large cell areas

• Identifying potential over shooters

Radio link Monitoring

Supervision of UE in RRC connected mode

INTRA-LTE MOBILITY

• RRC_CONNECTED mode mobility• In LTE, network controlled UE assisted handovers with context transfer between eNB’s are used to support UE mobility. An

intra- LTE handover can be executed either via the X2 or via the S1 interface.

Intra-LTE HO (within one MME pool).

Inter MME handover

Intra LTE Handover (within one MME-pool).

• If the target RBS is unable to accept the handover attempt then it will send the HANDOVER PREPARATION FAILURE message to the serving RBS. When this occurs the serving RBS reevaluates the handover candidate list and attempts to set up the handover to the next best candidate RBS.

• If no suitable handover candidate cell exists then the call continues on the serving cell.• By default, user equipment in the LTE network detect suitable neighbor cells without the

assistance of a list of neighbor cells sent by the serving RBS. User equipment are expected to blindly detect suitable handover candidates and the subsequent handover evaluation is undertaken using generic offset values. The exception to this occurs when specific handover offset values are defined between neighboring cells by the network operator. When specific cell offset relationships exist, this information is sent to the user equipment in RRCConnectionReconfiguration messages by the RBS.

• The RRCConnectionReconfiguration message can also contain a list of cells for which handover is not allowed.

MobilityHO success Rate (Intra) %= 100 * ( pmHoPrepSuccLteIntraF / pmHoPrepAttLteIntraF) *

(pmHoExeSuccLteIntraF / pmHoExeAttLteIntraF)

IRAT RATE % = 100 * (pmUeCtxtRelSCCdma + pmUeCtxtRelSCGsm + pmUeCtxtRelSCWcdma) /

pmUeCtxtEstabSucc

Two types of HO :Intra-frequency LTE S1 Handover (HO) and Intra-Frequency LTE X2 HO .

The number of Session continuity RRC Connection Release with redirect to UTRA FDD

The total number of Initial Context Setup Establishment successes.

Handover Pairs

Incoming Handover Failure

ITK Report View

The number of Incoming Handover Preparation Failure messages sent by the target eNB due to lack of license for handover

The number of Handover Preparation Failure messages sent by the target eNB due to license for connected users being exceeded.

Stepped at reception of traffic measurement report indicating a better cell due to Event A3,

Sample Case Study

a2ThresholdRsrpPrim changed from -110 to -112 dbm

are worst cell having high IRAT rate at

IRAT Rate

IRAT Rate Reduces significantly after trail

Case 2 .HO Preparation Failures: Disabled termpointtoMME

AFTER

BEFORE

Case 3 . Overshooting Case

There is only one way relation from ILL04322_7H_1_D to ILL0286_7A_1 and all executions are failed .

Need to set "isHOAllowed & isRemovedallowed"=false

Between relation

ILL04322_7H_1_D -> 310410-210286-15

MAL02247_7B_1 Worst HO Success Rate

time object Source Cell Target CellpmHoExeAttL

teIntraFpmHoExeSuccL

teIntraFpmHoPrepAt

tLteIntraFpmHoPrepSuccLteIntraF

2011W47 MAL02247_7B_1_310410-62261-17 MAL02247_7B_1 MAL02261_7C_1 3174 3067 3174 31742011W46 MAL02247_7B_1_310410-62261-17 MAL02247_7B_1 MAL02261_7C_1 2045 1960 2046 20452011W46 MAL02247_7B_1_310410-62226-15 MAL02247_7B_1 MAL02226_7A_1 25 20 25 252011W46 MAL02247_7B_1_310410-62224-16 MAL02247_7B_1 MAL02224_7B_1 4 0 4 4

Worst EUTRAN relations

MAL02261 is not on air

Target Cell MAL02261_7C_1 is not declared on air and has very High UL RSSI . Most of the HO drops with this cell.

Problem at Execution stage not in Preparation phase

Source Cell

object 11/14/2011 11/15/2011 11/16/2011 11/17/2011 11/18/2011 11/19/2011 11/20/2011 11/21/2011 11/22/2011 11/23/2011 11/24/2011 11/25/2011 11/26/2011 11/27/2011 11/28/2011

MAL02027_7A_1 85.88 91.07 84.62 85.11 90.28 93.53 94.07 83.01 94.25 96.98 96.00 87.88 98.59 100 99.59Worst EUTRAN relations

MAL02027_7A_1 Worst HO Success Rate

time object Source Cell Target CellpmHoExeAttL

teIntraFpmHoExeSuccL

teIntraFpmHoPrepAt

tLteIntraFpmHoPrepSuccLteIntraF

2011W46 MAL02027_7A_1_310410-62171-15 MAL02027_7A_1 MAL02171_7A_1 236 154 236 2362011W47 MAL02027_7A_1_310410-62171-15 MAL02027_7A_1 MAL02171_7A_1 134 86 134 1342011W46 MAL02027_7A_1_310410-62020-16 MAL02027_7A_1 MAL02020_7B_1 80 74 80 802011W47 MAL02027_7A_1_310410-62020-16 MAL02027_7A_1 MAL02020_7B_1 78 74 78 782011W47 MAL02027_7A_1_310410-62178-15 MAL02027_7A_1 MAL02178_7A_1 248 245 248 2482011W46 MAL02027_7A_1_310410-62178-15 MAL02027_7A_1 MAL02178_7A_1 200 198 200 200

Source MAL02027_7A_1 is overshooting and Added faraway neighbors through ANR. Attempts from MAL02027_7A_1 to MAL02171_7A_1 is very high comparatively to others.

Source Cell

Target cells

Observation: It is found that actual E tilt is not equal with Planned data.

DXL23002

DXL00221

DXL03002

DXL03040

DXL20221

DXL23040DXL20567DXL00567

DXL03162DXL23162

Date EUtranCellFDD EUtranCellRelation pmHoPrepSuccLteIntraF pmHoPrepAttLteIntraF HOPrepFails5/27/2011 DXL23040_2C DXL23040_2B 3 367 364

Date UTC Hour EUtranCellFDD EUtranCellRelation pmHoPrepSuccLteIntraF pmHoPrepAttLteIntraF HOPrepFailures5/27/2011 19:00 DXL23040_2C DXL23040_2B 1 365 364

› HO Prep failures occurred to DXL23040 as the IntraLTEHandover feature had been disabled

case 1.HO Preparation failures : Due to Disabled feature