Feature Introduction-MRO

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Contents
01 – MRO feature MAP
02 – Scenario identification
03 – Handover scenario Handling
04 – Activation

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MRO feature MAP

Premature Handover

Delayed Handover
Handover Scenario
Identification
Ping-Pong Handover

Coverage-induced
Abnormal Handovers
Intra-RAT MRO Principles

Preprocessing

Handover Scenario
Optimization Modes
Handling

MRO Against Premature

Intra-Frequency MRO
or Delayed Handovers

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MRO feature MAP
Overview
As mobile telecommunications technologies advance, networks continue to grow and incorporate multiple radio access technologies
(RATs), resulting in complicated network maintenance. To simplify maintenance, an LTE system must support self-organizing network
(SON) technology. Mobility robustness optimization (MRO) is used for self-optimization in a SON.
MRO identifies scenarios of abnormal handovers and automatically optimizes settings of handover-related parameters in these scenarios.
MRO processing consists of handover scenario identification, handover scenario handling, and result monitoring

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Contents
01 – MRO feature MAP
02 – Scenario identification
03 – Handover scenario Handling
04 – Activation

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 Handover Scenario Identification Intra-RAT MRO Principles
Handover Scenario
Identification
Premature
Handover

Premature Handover
Result of the
Scenario Handover to the Duration of Stay in the Target Cell RRC Reestablishment To Cause Applicable To
Target Cell
Intra-RAT MRO and
Type -1 Failed None Source cell Signal quality in the target cell is poor.
Inter-RAT MRO

The camping time is less than the value

Type -2 Succeeded Source cell Signal quality in the target cell is unstable. Intra-RAT MRO
of MRO.IntraRatHoTooEarlyTimeThd.

The camping time is less than the value The probability that the target cell meets the
Type -3 Succeeded Third-party cell Intra-RAT MRO
of MRO.IntraRatHoTooEarlyTimeThd. handover conditions is too high.

Type -1 Type -2 Type-3

Handovers of type 3 are also called handovers to a wrong cell. The counters measured in type 3 include L.HHO.HoToWrgCell.

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 Handover Scenario
Handover Scenario Identification
Intra-RAT MRO Principles Delayed Handover
Identification

Delayed Handover
In a delayed handover, a radio link failure (RLF) occurs in the source cell and then the RRC connection is reestablished in another cell. In this case, handover parameter
settings are too strict. As a result, the UE has moved out of the source cell but no handover is triggered. Table 4-2 describes delayed handover types.
Result of the Handover Duration of Stay in the
Scenario RRC Reestablishment To Cause Applicable To
to the Target Cell Target Cell
Handover parameter
settings are too strict. As
a result, the UE has Intra-RAT MRO and Inter-
Type-4 Not initiated None Target cell
moved out of the source RAT MRO
cell but no handover is
triggered.
Signal quality in the
target cell is unstable
and third-party cells
cannot meet the
Type-5 Failed None Third-party cell
handover conditions. As
Intra-RAT MRO
a result, the UE is
handed over to a wrong
cell.

Type-4 Type-5

Handovers of type 2 are also called handovers to a wrong cell. The counters measured in type 2 include L.HHO.HoToWrgCell.

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Handover Scenario Identification Intra-RAT MRO Principles
Handover Scenario
Identification
Ping-Pong
Handover

Ping-Pong Handover
Cell-Level Ping-Pong Handover

If the duration in which the UE stayed in the target cell is less than the value of MRO.PingpongTimeThd and the UE is handed over back to the source cell, the
handover is regarded as a ping-pong handover.

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Handover Scenario Identification Intra-RAT MRO Principles
Handover Scenario
Identification
Coverage-induced
Abnormal Handovers

Coverage-induced Abnormal Handovers

If the signal qualities of the source cell and target cell indicated in the RLF report are less than the values of MRO.ServingRsrpThd and MRO.NeighborRsrpThd,
respectively, the eNodeB determines that the RLF is a coverage-induced RLF and measures coverage-induced RLFs within the MRO period.
During an MRO period, if the proportion of coverage-induced abnormal handovers is greater than the value of MRO.CoverAbnormalThd and the number of coverage-
induced abnormal handovers is greater than the total number of abnormal handovers (including premature and delayed handovers), the eNodeB does not
perform MRO within the current MRO period.
The following formula is used to calculate the proportion of coverage-induced abnormal handovers:
Proportion of coverage-induced abnormal handovers = Number of coverage-induced abnormal handovers/(Number of premature handovers + Number of
delayed handovers)

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Contents
01 – MRO feature MAP
02 – Scenario identification
03 – Handover scenario Handling
04 – Activation

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Scenario Handling Intra-RAT MRO Principles
Handover Scenario
Handling
Preprocessing

Preprocessing
Handover Scenario Statistics
If the number of handovers is greater than the value of MRO.StatNumThd in the period specified by MRO.OptPeriod, the MRO procedure is triggered.

In the early phase of network deployment, the number of handovers within an MRO period cannot reach the value of MRO.StatNumThd in many cells. However, RLFs
frequently occur in these cells. In this situation, the MRO procedure cannot be triggered in these cells if the current parameter settings are retained. If users change the
value of MRO.OptPeriod or MRO.StatNumThd to increase the probability of triggering MRO in these cells, incorrect MRO adjustment is more likely to occur. MRO is
performed as follows:
✓ If the number of handovers between the pair of neighboring cells reaches the value of MRO.StatNumThd within the first MRO period, the MRO procedure is triggered in
these cells.
✓ If the number of handovers between the pair of neighboring cells does not reach the value of MRO.StatNumThd within the first MRO period, the eNodeB retains the
number of handovers. The MRO procedure is triggered in these cells at the end of any of the 30 periods as long as the cumulative number of handovers reaches the
value of MRO.StatNumThd.
✓ If the cumulative number of handovers within 30 MRO periods does not reach the value of MRO.StatNumThd, the eNodeB resets the number to 0 and does not perform
the MRO procedure in these cells.

MRO Evaluation
The eNodeB does not perform MRO but resets the cumulative number of handovers to 0 at the end of an MRO period if users manually performed either of the following
modifications using MML commands within this MRO period:
✓ Adjusting the CIO or other handover-related parameters (such as the hysteresis, threshold, offset, time-to-trigger, and filtering coefficient)
✓ Modifying the blacklist attributes of cells in neighboring cell pairs
In the next MRO period, the eNodeB will perform MRO based on the manual modifications.

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Scenario Handling Intra-RAT MRO Principles
Handover Scenario
Handling
Optimization
Modes

Optimization Modes
The MRO optimization mode is specified by the MRO.MroOptMode parameter.

✓ If MRO.MroOptMode is set to FREE, the eNodeB determines parameters to be optimized based on handover scenarios and optimizes the parameter settings when
the MRO period approaches its end.

✓ In free mode, if EutranIntraFreqNCell.CtrlMode or EutranInterFreqNCell.CtrlMode is set to MANUAL_MODE, the parameter optimization advice cannot be delivered to
the eNodeBs. In this case, change the value to AUTO_MODE.

• If MRO.MroOptMode is set to CONTROLLED, the eNodeB reports the parameter optimization advice to the MAE-Access when the MRO period elapses. After
maintenance personnel confirm the advice, the MAE-Access executes this advice. Maintenance personnel can manually change the suggested parameter values.

✓ When MRO.MroOptMode is set to CONTROLLED, the MAE-Access provides the following information :
▪ MRO optimization advice
▪ Tracking area codes (TACs) of the affected local and neighboring cells for users to check whether the cells are in a certain area
▪ Indicator statistics used in the execution of the MRO optimization advice. The following table lists these indicators. The statistics help determine whether
the MRO optimization advice is proper.
Indicator Description
Total Handover numbers Total number of outgoing handovers between specific neighboring cells

Success Handover numbers Number of successful handovers between specific neighboring cells

Too early Handover numbers Number of premature handovers between specific neighboring cells

Too late Handover numbers Number of delayed handovers between specific neighboring cells

A2 Related Too late Handover numbers Number of A2-related delayed handovers between specific neighboring cells

Pingpong Handover numbers Number of ping-pong handovers between specific neighboring cells

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Scenario Handling Intra-RAT MRO Principles
Handover Scenario
Handling
MRO Against Premature
or Delayed Handovers
Intra-Frequency MRO

Intra-Frequency MRO Inter-Frequency MRO

Handover Reselection
Reselection parameter optimization is enabled by selecting
Handover parameter optimization is enabled by selecting
the IntraFreqReselOptSwitch option of CellAlgoSwitch.MroSwitch.
the IntraFreqMroSwitch option of CellAlgoSwitch.MroSwitch.
When both the IntraFreqMroSwitch and IntraFreqReselOptSwitch options are
This optimization is triggered if the following conditions are met
selected, during each MRO period specified by MRO.OptPeriod, the eNodeB
within the period specified by the MRO.OptPeriod parameter:
checks each pair of intra-frequency neighboring cells whose CIOs need to be
adjusted:
Number of handovers from the serving cell to an intra-frequency
If a pair of cells meet condition 1, the eNodeB does not optimize cell reselection
neighboring cell ≥ MRO.StatNumThd
parameters.
If a pair of cells do not meet condition 1, the eNodeB attempts to optimize cell
Proportion of RLF-related abnormal handovers
reselection parameters. The eNodeB attempts to change the value
> MRO.IntraRatAbnormalRatioThd
of CellQoffset for the cells to meet both conditions 2 and 3. If the cells would not
meet condition 2 or 3, the eNodeB does not change the value of CellQoffset for
optimization.
MRO.IntraRatTo
CIO degrease
greater oEarlyHoRatioT Condition 1 Qhyst + CellQoffset < Min(Ocs + Off + Hys – Ocn)
by 1
proportion of premature hd
handovers to all RLF-related Condition 2 Qhyst + CellQoffset = Min(Ocs + Off + Hys – Ocn)
abnormal handovers CIO increase by
greater MRO.IntraRatTo 1
oLateHoRatioT Condition 3 Qhyst + CellQoffset ≥ 1
hd

Proportion of RLF-related abnormal handovers = (Number of premature handovers + Number of delayed handovers)/(Number of
premature handovers + Number of delayed handovers + Number of successful handovers – Number of ping-pong handovers)

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Scenario Handling Intra-RAT MRO Principles
MRO Against Ping-
Cell-Level MRO

Pong Handovers
UE-Level MRO

MRO Against Ping-Pong Handovers(cell level)

If within an MRO period an eNodeB has performed MRO against premature or delayed handovers between a local cell and the target neighboring cell,
the eNodeB does not perform MRO against ping-pong handovers between the cells in this period. If the eNodeB has not performed MRO against
premature or delayed handovers, the eNodeB checks conditions for performing MRO against ping-pong handovers between the cells in this period.

Handover
The eNodeB performs MRO against ping-pong handovers by decreasing the CIO for the neighboring cell by one step if all the following
conditions are met
• Number of outgoing handovers to the neighboring cell ≥ MRO.StatNumThd
• Proportion of ping-pong handovers > MRO.PingpongRatioThd
• Intra-frequency or inter-frequency handover success rate > MRO.NcellOptThd
• Proportion of RLF-related abnormal handovers < MRO.IntraRatAbnormalRatioThd/2

Reselection
The reselection parameter optimization involves only the intra-frequency reselection parameter CellQoffset. The optimization principle is
the same as that for intra-frequency MRO.

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Contents
01 – MRO feature MAP
02 – Scenario identification
03 – Handover scenario Handling
04 – Activation

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Activation
Activation
//Enabling intra-frequency MRO
MOD MRO: MroOptMode=FREE;
MOD EUTRANINTRAFREQNCELL: LocalCellId=0, Mcc="460", Mnc="20", eNodeBId=255, CellId=2, CtrlMode=AUTO_MODE;
MOD CELLALGOSWITCH: LocalCellId=0, MroSwitch=IntraFreqMroSwitch-1&IntraFreqReselOptSwitch-0;
MOD CELLMRO: LocalCellId=0, CioAdjLimitCfgInd=CFG, CioAdjUpperLimit=dB1, CioAdjLowerLimit=dB-2;

Deactivation

//Disabling intra-frequency MRO

MOD CELLALGOSWITCH: LocalCellId=0, MroSwitch=IntraFreqMroSwitch-0&IntraFreqReselOptSwitch-0;

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Activation and Results verification

Results verification
The performance of intra-RAT MRO can be monitored by observing KPIs such as the handover success rate and service drop rate.
In addition, you are advised to observe the following counters

Counter Name
L.HHO.PingPongHo
L.HHO.HoToWrgCell
L.HHO.HoTooearly
L.HHO.HoToolate
L.HHO.Ncell.PingPongHo
L.HHO.NCell.HoToolate
L.HHO.NCell.HoTooearly
L.Traffic.User.Avg

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 Thank you
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