Inter-frequency Load Balancing

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CAPITALS

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Inter-frequency Load balancing

FAJ 1213009

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Measurement Report: LTE Events

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Feature process flow

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IFLB functional overview

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Determine Load Status

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QCI Subscription Quanta, Cell Subscription capacity

Subscription quanta/capacity are recommended to be

configured according to “Downlink Bit Rate Analogy”

qciSubscriptionQuanta:

– QCI subscription quanta is configured to represent the minimum

acceptable downlink bit rate for the QoS class. In units of kbps.

e.g. QCI8 = 100Kbps = 100 (Default Value 1)

cellSubscriptionCapacity:

– Cell subscription capacity is configured to represent the achievable

downlink bit rate of the cell (at maximum load). In units of kbps.

e.g. For 5MHz site= 8000 and 20MHz site = 16000 (Default Value 1000)

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Exchange Load Info

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Load Balancing Action Magnitude

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Select Candidates

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Load Balancing Action

> The trigger for the report of measurement results is an A4 event.

-- The A4 event represents acceptable coverage for load balancing.

-- The A4 event is configured with the parameters a4ThresholdRsrp and hysteresisA4 (MO:

ReportConfigEUtraInterFreqLb).

-- Observed with the counter pmLbQualifiedUe (MO: EUtranCellRelation)

> If a UE reports more than one target cell, the UE is only allowed to be off-loaded to the best

reported cell.

> Reporting UEs are off-loaded until each LBA magnitude is reached.

Observed with pmHoPrepAttLteInterFLb, pmHoPrepSuccLteInterFLb,

pmHoExeAttLteInterFLb and pmHoExeSuccLteInterFLb.

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› Load Balancing calculation (example):

› 1900 Band , 30 QCI9 E-RABs (Source)

› 800 Band , 10 QCI9 E-RABs (Target)

Parameter setting

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Load_Diff = SubRatio_Source - SubRatio_target.

Load_Diff = {30(100/8000)} - {10(100/8000)}

= 0.375 - 0.125 = 0.25

Load_Balance_Magnitude = {min ( 0.3 , 0.25)} / {1+1}

= 0.25 / 2 = 0.125

No. of ERAB candidates for IFLB = 0.125*(8000/100) = 10 ERAB.

Conclusion: 10 ERAB from 1900 will be shifted to 800 for load balancing.

Load Balancing calculation

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IFLB Activation Threshold

L14B

FAJ 121 3058

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› Inter-Frequency Load Balancing is triggered as soon as the

load difference between the serving and target cell is

above a threshold (lbThreshold) Background.

› Feature INTRODUCTION IFLB

IFLB background

If, Load_Diff > Load Difference Threshold (lbThreshold)

Then, Trigger Inter Frequency Load Balancing

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› The main disadvantage of IFLB is that as soon as the Inter

Frequency Load Balancing is triggered, many unnecessary

UE measurements are ordered even WHEN SOURCE CELL

LOAD IS QUITE LOW.

IFLB background:

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› The optional feature IFLB Activation Threshold, FAJ 121 3058

introduces a load threshold towards the target frequency that governs

activation of Inter Frequency Load Balancing actions.

› The feature provides an activation threshold lbActivationThreshold

for the Inter Frequency Load Balancing (IFLB) feature, which can be

used to reduce the number of load balancing actions taken by IFLB

› The main benefits of IFLB Activation Threshold are:

– UE measurements and handovers for IFLB are reduced.

– Operator has better control of when IFLB is triggered

IFLB ACTIVATION THRESHOLD (feature description):

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›

› InterFrequencyOffload

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› The feature reuses solution for “load measurement” and introduces new methods for “LBA magnitude” and “UE selection”

› “Load information exchange” is not required

Feature process:

Load measurement Determine traffic load in each individual cell

Load information exchange Request and exchange load information between cells

Load balancing action magnitude Determine the amount of off-loading needed to manage load between cells

UE selection for load balancing action Determine and off-load suitable UEs

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› To prevent overloading the UTRAN target cells, the RNC may reject

handover preparation for offload

› The eNB temporarily stops offload from the source E-UTRA cell to the

UTRAN target cells whereto the handover preparations are rejected

– The backoff time is controlled with the parameter lbUtranOffloadBackoffTime

› Depending on UTRAN deployment:

– The RNC may apply a specific admission policy for incoming offload handover preparation

IROW Backoff Mechanism:

Inter-frequency Load Balancing

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