3 Lte Eran6.0 Mro Feature Issue 1.00

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Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved.

LTE eRAN6.0 MRO Feature


Version Difference

eRAN3.0--Intra-freq LTE MRO

Intra frequency MRO arrives commercial standard

For intra-freq scenario, adjust CIO of cell-pairs as per

previous period's abnormal RLF rate

eRAN6.0--Intra-freq LTE MRO

Decrease ping-pong number for UE Level

Recognize and send anti-ping-pong CIO parameter to

ping-pong UEs.

Page3


Objectives

Upon completion of this course, you will be able to:

Describe the function of MRO

Detail feature and parameters of intra-RAT MRO

Detail feature and parameters of inter-RAT MRO

Page4


Contents

1. Overview

2. Intra-RAT MRO Management

3. Inter-RAT MRO Management

4. Related Features

5. Engineering Guidelines

6. MRO in M2000

Page5


Contents

1. Overview



4. Related Features


6. MRO in M2000

Page6


What is MRO?

MRO (Mobility Robust Optimization) is one

feature of SON

The MRO feature achieves self-optimization

functionality by automatically optimizing handover-

related parameters. This improves the handover

success rate and resource usage.

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MRO Processing Flow

Page8

Handover Scenario Identification

Handover Scenario Handling

Result Monitoring

X2

Handover processing


Contents

1. Overview



4. Related Features


6. MRO in M2000

Page9


Intra-RAT Handover Overview

Page10

Intra-Frequency Handover

Inter-Frequency Handover

Measurement trigger (Default)

Handover trigger (A3 event)

Measurement trigger (A2 event)

Handover trigger (A4 or A3 event)


Intra-RAT MRO Procedure

See Remark.

Page11


Classification of Intra-RAT MRO

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Intra-RAT MRO

Intra-frequency MRO

A3 CIO modification

Inter-frequency MRO

A3 or A4 CIO

modification

A2 threshold

modification


Identification of Premature Handover

Page15

UE movement

Source eNodeB Target eNodeB

Normal handover areaPremature handover area


Identification of Premature Handover (Cont.)

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eNB1 eNB2 UE

1. Measure Report(HO)

2. Handover Request

3. Handover Response

6. RLF In eNB1

8. if find UE ID in local cell UE Context, increase num_ho_too_early by 1

5. Handover Command

7. Re-establish (to old cell)


Identification of Delayed Handover

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Source eNodeB

UE movement

Target eNodeB

Normal handover area Delay handover area


Identification of Delayed Handover (Cont.)

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eNB1 eNB2 UE

1: Measure Control(HO)

3: Re-establish ( to new cell)

4: RLF Indication

2. RLF In eNB2

5: if find UE Id in local cell UE Context, increase num_ho_too_late by 1.


Classification of Delayed Handover

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Source

TargetSource Target

No A2 measurement

report

Gap Measurement command failure

Source Target

A2 measurement report

Measurement configuration failure

Source Target

A4 or A3 measurement report

Handover command failure

X2

Delayed intra-frequency handover Delayed inter-frequency handover related to event A2

Delayed inter-frequency handover related to event A2


Coverage-induced Delayed Handover In a delayed handover, a UE experiences an RLF in

cell A, the RRC connection is reestablished with

neighboring cell B, and cell B reports this

reestablishment event to cell A. This process may

occur in one of the following coverage areas:

Coverage hole in the overlapping area of the two cells

Coverage hole of cell A or B within their overlapping

area

Coverage hole or weak coverage area between cells A

and B that do not overlap

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Identification of Ping-Pong Handover

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Ping-Pong Handover: Period 2 < PingpongTimeThd

… Cell A

… Period 1

Period 1

Information on the UE

Cell A Cell B

… Cell A Cell B

… Period 1

Period 2

Period 2Information on the UE

Ping-pong handover decision


MRO Scenario Handling

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Check handover statistics periodically

Check whether the threshold is achieved

Premature handovers and delayed handover

optimization

Ping-Pong handover

optimization


Optimization of Premature & Delayed Intra-Frequency Handover Proportion of RLF-induced abnormal handovers >

RLF-induced abnormal handover threshold

Proportion of RLF-induced abnormal handovers ≤

RLF-induced abnormal handover threshold, and

Handover success rate ≤ MRO.NcellOptThd

(threshold for MRO between neighboring cells)

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http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/MRO-NcellOptThd.html


Optimization of Premature & Delayed Intra-Frequency Handover(Cont.) In either of the preceding scenarios, the eNodeB

reacts as follows:

If the proportion of premature handovers to the total

number of RLF-induced abnormal handovers is greater

than 70%, the eNodeB decreases the CIO for intra-

frequency event A3 by one step.

If the proportion of delayed handovers to the total

number of RLF-induced abnormal handovers is greater

than 70%, the eNodeB increases the CIO for intra-

frequency event A3 by one step.

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Optimization of Delayed Inter-Frequency Handover related to A2 Triggering condition: Inter-frequency MRO trigger has the

same conditions as intra-frequency, and with the

following additional conditions:

The proportion of delayed handovers related to event A2

≥ a specified threshold,

the threshold for event A2 < the threshold for the event

A1,

the handover is regarded as a delayed handover

related to event A2 and A2 threshold is increased

by one step.

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Proportion of delayed handovers

related to event A2

Number of delayed handovers related to event A2

Number of premature handovers

Number of delayed

handovers


Optimization of Premature or Delayed Inter-Frequency Handover unrelated to A2

If the proportion of delayed handovers related to

event A2 < the specified threshold, the handover

is regarded as a delayed handover unrelated

to event A2 or a premature handover: Number of premature handovers < Number of delayed

handovers, then A4 or A3 CIO of inter-frequency

neighbor cell is increased by one step.

Number of premature handovers > Number of delayed

handovers, then A4 OR A3 CIO of inter-frequency

neighbor cell is decreased by one step.

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Cell-Level MRO against Ping-Pong Handovers The eNodeB performs MRO against ping-pong handovers

by decreasing the CIO value between the cells by one

step if the following conditions are met:

Proportion of ping-pong handovers > MRO.MRO.

PingpongRatioThd

where, Proportion of ping-pong handovers = Number of ping-pong

handovers/Total number of successful handovers

Handover success rate ≥ MRO.MRO.NcellOptThd

Proportion of RLF-induced abnormal handovers < RLF-

induced abnormal handover threshold/2

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http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/MRO-PingpongRatioThd.html

http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/MRO-NcellOptThd.html


UE-Level MRO against Ping-Pong Handovers the number of consecutive ping-pong handovers<

MRO.UePingPongNumThd, the eNodeB does not

regard the UE as a ping-pong UE. The eNodeB

delivers the configured CIO value to the UE.

the number of consecutive ping-pong handovers=

MRO.UePingPongNumThd, the eNodeB regards

the UE as a ping-pong UE, decreases the configured

CIO value by 1 dB for the UE, and then delivers the

result to the UE.

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http://localhost:7890/pages/GZC0304J/Draft%20B/GZC0304J/Draft%20B/resources/lte/mml/ratL/para/MRO-UePingPongNumThd.html



UE-Level MRO against Ping-Pong Handovers(Cont.) MRO.UePingPongNumThd <the number of

consecutive ping-pong handovers< MRO.

UePingPongNumThd+2, the eNodeB regards the

UE as a ping-pong UE, decreases the configured CIO

value by 2 dB for the UE, and then delivers the result

to the UE.

the number of consecutive ping-pong handovers ≧ <

MRO.UePingPongNumThd+2, the eNodeB cannot

resolve ping-pong handovers for the UE and

increases the number of ping-pong handover

resolution failures by 1.Page29






Value Range for Intra-Frequency Handovers If operators expect that an intra-frequency handover

is triggered when the difference of the measured

signal quality between the neighboring and serving

cells falls into the range of A to B, the operators

should set CELLMRO.CioAdjLowerLimit and

CELLMRO.CioAdjUpperLimit according to the

following formulas:

CioAdjLowerLimit = Min(Off + Ofs + Ocs - Ofn + Hys -

B)

CioAdjUpperLimit = Max(Off + Ofs + Ocs - Ofn + Hys -

A)Page30

http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/CellMro-CioAdjLowerLimit.html

http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/CellMro-CioAdjUpperLimit.html


MML Command

Page31


Value Range for Inter-Frequency Handovers The entering condition for event A4 is as follows: Mn

+ Ofn + CIO - Hys > Thresh. It is generally agreed

that a neighboring cell can provide continuous

services only when Mn is higher than -110 dBm.

Therefore, Huawei eNodeB calculates the upper limit

of the CIO value range for event A4 as follows:

Min(Thresh + 110 - Ofn + Hys). The eNodeB takes -

24 as the lower limit.

In summary, the CIO value range for inter-frequency

event A4 is [-24, Min(Thresh + 110 - Ofn + Hys)].

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Adjustments for Cell-Level MRO Cell-Level Penalty Ping-pong adjustments of parameter settings may occur

between MRO periods. Huawei eNodeB monitors the last

three parameter adjustments made during MRO periods.

If the last value is identical to the first value, the eNodeB

considers that a ping-pong parameter adjustment

occurred. As a penalty, the eNodeB will not perform MRO

throughout the next two MRO periods, each specified by

MRO.OptPeriod.

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1

2

0

No optimization

No optimization

OptimizationPing-Pong

Optimization

http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/MRO-OptPeriod.html


Adjustments for UE-Level MRO UE-Level Penalty When a UE-level ping-pong handover MRO period (4

hours) approaches its end, the eNodeB calculates the

proportion of RLFs due to delayed handovers caused by

UE-level MRO as follows:

Proportion of RLFs due to delayed handovers caused by UE-

level MRO against ping-pong handovers = Number of such

delayed handovers/(Number of times the CIO value is

decreased by 1 dB + Number of times the CIO value is

decreased by 2 dB)

If the proportion of RLFs due to delayed handovers

caused by UE-level MRO against ping-pong handovers

exceeds 1/20 (fixed), the eNodeB postpones the UE-level

ping-pong handover MRO for two periods.Page34


MML Command

Page35


MML Command (Cont.)

Page36


Contents

1. Overview



4. Related Features


6. MRO in M2000

Page38


Inter-RAT Handover Overview

Page39

Inter-RAT Handover

Measurement trigger (A2 event)

Handover trigger (B1 event)


Inter-RAT Handover Classification

Page40

Inter-RAT MRO

Delayed handover

A2 related delayed

handover

Optimization A2 triggering threshold for

QCI

A2 non-related delayed

handover

Optimization of hysteresis

for B1

Premature handover

Optimization of hysteresis for B1


Identification of Delayed Inter-RAT Handover related to event A2 - type 1

Page42

Triggering conditions:

The eNodeB does not or fails to deliver the gap

measurement configuration, and does not receive

intra-RAT premature or delayed handover indication

The source cell has valid inter-RAT neighboring cells

and the inter-RAT neighboring cells support the

ongoing services of the UE

The source cell deletes the UE context due to timer

expiration.


Optimization of Delayed Inter-RAT Handover related to event A2 - type 1

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MRO handling conditions: Proportion of delayed handovers in type 1 ≥ Proportion

threshold for delayed handovers related to event A2 Threshold for event A2 < Threshold for event A1

the handover is regarded as a delayed Inter-RAT handover related to event A2 and A2 threshold is increased by one step (for the corresponding QCI)


in type 1

Number of delayed inter-RAT handovers in type 1

Number of premature inter-RAT handovers

Number of delayed inter-RAT handovers


Identification of Delayed Inter-RAT Handover related to event B1 - type 2

Page44

Triggering conditions:

The eNodeB receives a measurement configuration for

event A2 and successfully delivers a measurement

configuration for setting up a measurement gap.

The eNodeB does not or fails to deliver a handover

command, and does not receive intra-RAT premature or

delayed handover indication.

The source cell has valid inter-RAT neighboring cells

and the inter-RAT neighboring cells support the

ongoing services of the UE.

The source cell deletes the UE context due to timer

expiration.


Optimization of Delayed Inter-RAT Handover related to event B1 - type 2

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MRO handling conditions:

Proportion of delayed handovers in type 1 < Proportion

threshold for delayed handovers related to event A2

Number of premature handovers < Number of delayed

handovers in type 2

the handover is regarded as a delayed Inter-RAT

handover related to event B1 and B1 threshold is

decreased by one step (for the corresponding QCI)


Optimization of Premature Inter-RAT Handover

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is defined similarly as the intra-RAT premature handover

Triggering conditions: Proportion of delayed handovers in type 1 < Proportion

threshold for delayed handovers related to event A2 Number of premature inter-RAT handovers > Number

of delayed inter-RAT handovers in type 2 the handover is regarded as a premature and the

hysteresis for event B1 is increased by one step.


in type 1

Number of delayed inter-RAT handovers in type 1

Number of premature inter-RAT handovers

Number of delayed inter-RAT handovers


Contents

1. Overview



4. Related Features


6. MRO in M2000

Page47


Related Features

MRO is closely related to mobility management in

connected mode. MRO is performed based on all the

parameter values initially set for mobility

management in connected mode, and the parameter

adjustments by MRO affect mobility management in

connected mode.

If RAN sharing is deployed, only the primary operator

can modify handover parameters.

Page48


Contents

1. Overview



4. Related Features


6. MRO in M2000

Page49


Intra-RAT MRO

Use intra-frequency MRO only after RF optimization

is performed. Use intra-frequency MRO continuously

during routine eNodeB maintenance because MRO

can automatically identify scenarios with no MRO

gains and avoid parameter adjustments.

When intra-frequency MRO is enabled, it is

recommended that the MRO.StatNumThd

parameter be set to 1000 and the MRO.OptPeriod

parameter be set to 1440, which indicates a day.

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http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/MRO-StatNumThd.html

http://localhost:7890/pages/GEC02288/Draft%20B/GEC02288/Draft%20B/resources/lte/mml/ratL/para/MRO-OptPeriod.html


Intra-RAT MRO (Cont.)

Use inter-frequency MRO when either of the

following conditions is met:

The number of intra-RAT RRC connection

reestablishments is higher than expected.

The number of premature, delayed, or ping-

pong handovers between two inter-frequency

cells is higher than expected.

Page51


Contents

1. Overview



4. Related Features


6. MRO in M2000

Page52


Intra-Frequency MRO Activation Observation

Page53

This section describes

how to use SON logs

to verify all types of

MRO.

If a switch is turned on

in a MRO Switch

Setting event, the

corresponding type of

MRO has been

activated.


Collecting and Analyzing MRO Data Choose Configuration > MRO Management and

choose “Log Statistics” tab.

Page54


Performance Monitoring

To monitor the performance of intra-RAT MRO,

observe the following counters:

Page55

Counter Name Description

L.HHO.Ncell.PingPangHoNumber of ping-pong handovers between a specific pair of cells

L.HHO.NCell.HoToolateNumber of delayed intra-RAT

handovers

L.HHO.NCell.HoTooearlyNumber of premature intra-RAT

handovers


Performance Monitoring(Cont.)

To monitor the performance of inter-RAT MRO,

observe the following counters:

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Description Description

L.IRATHO.E2W.PrepAttOutNumber of handover attempts from E-UTRAN to UTRAN

L.IRATHO.E2W.ExecSuccOutNumber of successful handovers from E-UTRAN to UTRAN

L.IRATHO.E2G.PrepAttOutNumber of handover attempts from E-UTRAN to GERAN

L.IRATHO.E2G.ExecSuccOutNumber of successful handovers from E-UTRAN to GERAN


Questions

What are the abnormal HO scenarios?

How to optimize the premature & delayed intra-

frequency handover?

Page57


Glossary

CIO: Cell Individual Offset

MRO: Mobility Robust Optimization

SON: Self-Organizing Network

RLF: Radio Link Failure

PCI: Physical Cell Identifier

CGI: Cell Global Identifier

RAT: Radio Access Technology

Page58

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3 Lte Eran6.0 Mro Feature Issue 1.00