Interfrequency Load Balancing Lte

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LTE Review

Inter Frequency Load Balancing

Analysis

Paulo Campolina Paulo Campolina Sr. RF Engineer / June, 2016 Sr. RF Engineer / June, 2016

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• IntroductionIntroduction

The description given on the next pages can be applied to Ericsson,

The description given on the next pages can be applied to Ericsson, Nokia or other vendorNokia or other vendor. It is . It is alwaysalways

needed to verify the associated features per Vendor and the associated “Golden Paramet

needed to verify the associated features per Vendor and the associated “Golden Parameters List” ers List” andand

strategy per operators. strategy per operators.

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• RequirementsRequirements

For E/// LTE network, the

For E/// LTE network, the following must be fulfilled at following must be fulfilled at featurfeature activation:e activation:

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• A license key must be activated to operate these features:A license key must be activated to operate these features:

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• Coverage-Triggered Inter-FrequeCoverage-Triggered Inter-Frequency ncy Handover Handover featurefeature •

• Inter-frequInter-frequency ency Load Balancing Load Balancing featurfeaturee

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• The cell relations where load balancing is desired must be configured to allow load balancing actionsThe cell relations where load balancing is desired must be configured to allow load balancing actions and reporting. The

and reporting. The loadBalancingloadBalancing parameter is set toparameter is set to ALLOWE ALLOWEDD in the desiredin the desired EUtranCellRelationEUtranCellRelationMO.MO.

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• Load balancing between cells in diffeLoad balancing between cells in different RBS nodes rrent RBS nodes requires an X2 connection betequires an X2 connection between the RBSween the RBS nodes.

nodes.

More information about this feature and related topics

More information about this feature and related topics can be found in can be found in the following documentation:the following documentation:

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• 3GPP TS 36.300, Overall description; Stage 23GPP TS 36.300, Overall description; Stage 2 •

• 3GPP TS 36.331, Radio Resource Control (RRC); Protocol Specification3GPP TS 36.331, Radio Resource Control (RRC); Protocol Specification •

• 3GPP TS 36.423, X2 Application Protocol (X2AP)3GPP TS 36.423, X2 Application Protocol (X2AP)

Inter

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• Subscription Ratio Definition

The IFLB feature uses a model for the assessment of traffic load in a cell, wherein the expected load of each E-RAB is quantified based on the QoS class to which it belongs as follows:

• AqciSubscriptionQuanta value is associated with each E-RAB, and it is an estimate of the

expected traffic activity for an E-RAB of the particular QoS class.

• The assessment of traffic load in a cell is made in terms of a ‘‘subscription ratio’’ value;

• ThecellSubscriptionCapacity value is an estimate of the total amount of qciSubscriptionQuanta

values the cell is expected to accommodate at full system load.

• A configuration of the qciSubscriptionQuanta and the cellSubscriptionCapacity values is

required to obtain the desired load balancing behavior.

• It enables the Inter-frequency Load Balancing feature to perform load balancing between cells

with different mix of UE population and between cells with different traffic capacity.

• The exchange of cell load information is performed over X2 private messages.

• Each cell may receive load reports from one or more other cells in the same RBS or in the

remote RBS.

• The selection of target cells is controlled with the loadBalancing parameter.

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In practice, the following recommendations are made:

• TheqciSubscriptionQuanta parameter for a GBR type of E-RAB is chosen in proportion to the typical

‘‘guaranteed downlink bit rate’’ (in kbps) for the particular QCI:

• QCI=1 (conversational voice) the value depends on the typical voice codec in use.

• Other GBR types of E-RAB (QCI=2..4, …) the value depends on the type of streaming media. The

qciSubscriptionQuanta parameter for a non-GBR type of E-RAB is chosen in proportion to what

is considered an acceptable downlink bit rate (in kbps) for UE in connected mode in LTE RAN at high load: The ‘‘default’’ non-GBR types of E-RAB are activated whenever the UE enters

connected mode, irrespective if they are going to be used; conservative values should be chosen, reflecting an expected low or moderate duty rate on these E-RABs.

• QCI=5 (default for IMS signaling), the expected bit rate is typically very low (not exceeding 3

kbps).

• for a default Internet Service Provision (ISP) E-RAB, a suitable value can be based on the typical

UE data consumption over a longer time period in relation to the time spent in connected mode over the same time period; the value should focus on the conditions in LTE RAN at high load.

• For on-demand non-GBR types of E-RAB, values should be chosen based on the typical

minimum QoS requirements of the intended applications.

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(every 15 seconds)

1. Determine cell load status

2. Exchange and compare load status with target relations

3. If own cell has higher load than target, select offload candidate UEs

4. If target has good RSRP, then send UEs to target to balance load

5. New own cell load status

Inter Frequency Load Balancing

Flow Overview

Inter-Frequency Load Balancing feature handles uneven distribution of traffic in the Shared RAN network. For cells that have load relations established, the high-level behavior is:

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Every load balancing cycle, each cell determines its load status.

The ratio load based is based on total sum of

qciSubscriptionQuanta overcellSubscriptionCapacity

– Subscription quanta is weighted based on QCI and represents a generic cost of each

bearer.

› The value for each QCI is configured with the

parameter qciSubscriptionQuanta

(QciProfilePredefined / QciProfileOperatorDefined).

Cell subscription capacity represents an estimate of the total cell capacity.

The value for each cell is configured with the parameter cellSubscriptionCapacity (EUtranCellFDD / EUtranCellTDD).

› Average subscription ratio is observed with the counters pmLbSubRatioSum and pmLbSubRatioSamp

(EUtranCellFDD / EUtranCellTDD)

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This is done based on the following:

(a) Load difference to each target cell. Source and target cells exchange load info and the difference in load are checked against minimum and maximum offload thresholds.

(b) Minimum load difference, lbThreshold , to trigger load balancing action.

Total off-loading from the source cell. If multiple target cells exist, the total off-loading is split between those.

(c) Maximum load difference, lbCeiling, taken into account in one round of load balancing action.

Inter Frequency Load Balancing

Info Exchange

(a) (b) (c)

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• If the difference in load subscriptionRatio(a) is grater than lbThreshold (b)the load balancing

Load_Balance_Magnitude (c) is calculated.

• The amount of UEs to load balance is determined and the maximum amount of UE’s is limited by

lbCeiling.

• UEs are randomly selected and requested to reconfigure for a A4 Measurement report.

• The following checks are performed before the UE is requested to perform the A4 Measurement

report.

• Not in an emergency call *

• Not in bad coverage in the source cell # • Support the frequency of the target cell

• UE is not restricted by the Handover Restriction List (HRL) to measure the target frequency. • If the UE successfully reports the A4 Measurement, a final check is done to see if load balancing

amount has been met before the UE is then sent for IFHOUE’s that report the A4 Measurement have

acceptable coverage in the target cell

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• Increasing the value of the lbThresholdparameter may reduce the rate of load balancing actions back

and forth between cells as a result of random variation of the traffic load up and down.

• However, certain degree of UE shuffling between the cells may be useful, as it reduces the risk of UE

segregation due to differences in traffic behavior.

• An increase of the lbThreshold parameter may also increase the ‘‘burstiness’’ of load balancing

actions (all at once rather than a sequence of small steps).

• A reduction of the lbCeilingparameter may help to distribute a sudden large amount of load

balancing action over a period of time.

• However, care is required to ensure the lbCeiling parameter is configured large enough to outbalance

any systematic drift in the load balance; for example, due to poor coverage triggered mobility or due to mobility between neighbor cells on particular carrier frequencies.

• The lbThresholdparameter can be configured greater than the lbCeilingparameter. The effect may be

that the load gap between the cells is not entirely closed.

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• If the UE has reported the target cell as the best server and has met all verifications , it UE will be

sent for a regular Inter-Frequency Handover to the target cell.

• A UE can only be balance to its reported best server.

• The cell will continue the load balancing process until the 15sec lbCycle has finished. At this time, the

cell will have its new load balancing status and the new lbCycle will start.

• The a5Threshold1Rsrp, a5Threshold2Rsrpand hysteresisA5parameters are configured for each

source cell for the inter-frequency event A5 measurement reporting in the UE selection for load balancing action.

• To ensure that the UE is able to stay in the target cell after a load balancing action, the

a5Threshold2Rsrpparameter should be configured with a value above the ‘‘Event A2 Poor Coverage’’

threshold in the target cell.

• If QCI dependent thresholds are applied in the target cell, the a5Threshold2Rsrpparameter should be

configured with a value above the maximum of those.

• The a5Threshold1Rsrpparameter can be used to exclude UEs in very good radio environment from

load balancing.

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• pmLbSubRatioSum

This PM records the subscription ratio as the result of the traffic load assessment at every load balancing cycle.

The values are accumulated during each ROP, allowing the average subscription ratio to be presented for each period.

• pmLbSubRatioSamp

The number of load balancing cycles during the ROP. This together with the counter pmAvSubRatioSum can be used to calculate an average subscription ratio.

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• pmLbMeasuredUe

Records the number of UEs selected for

measurements qualifying for load balancing action towards cells on the related frequency.

These values are accumulated each ROP.

It is used to calculate the LB measurement success rate for the related cells.

• pmLbQualifiedUe

Records the number of UEs qualified for load balancing action towards the related cell. These values are accumulated each ROP.

It is used to calculate the LB measurement success rate for the related cell.

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• pmHoPrepAttLteInterFLb

The number of attempts to start outgoing intra LTE inter frequency handover preparation due to load balancing. Sub-counter to pmHoPrepAttLteInterF (legacy)

• pmHoPrepSuccLteInterFLb

The number of successful outgoing intra LTE inter

frequency handover preparations that was performed for load balancing reasons. Sub-counter to

pmHoPrepSuccLteInterF (legacy)

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• pmHoExeAttLteInterFLb

The number of outgoing intra LTE inter frequency

handover execution attempts due to load balancing.Sub-counter to pmHoExeAttLteInterF (legacy)

• pmHoExeSuccLteInterFLb

The number of successful outgoing intra LTE inter frequency HO that was performed for load balancing reasons. Sub-counter to pmHoExeSuccLteInterF (legacy)

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According to 3GPP **, the UE shall:

1) consider the entering condition for this event to be satisfied when

2) consider the leaving condition for this event to be satisfied when

where:

• Ms is the measurement of the serving cell, not taking into account any offsets.

• Mn is the measurement of the neighboring cell, not taking into account any offsets. • Ofn is the frequency offset corresponding to the frequency of the neighbor cell. • Ocn is the cell specific offset of the neighbor cell.

• Hys is the hysteresis parameter for this event .

• Thresh1 is the threshold parameter for this event (i.e. a5-Threshold1). • Thresh2 is the threshold parameter for this event (i.e. a5-Threshold2). • Mn, Ms are expressed in dBm in case of RSRP, or in dB in case of RSRQ. • Ofn, Ocn, Hys are expressed in dB.

• Thresh1 is expressed in the same unit as Ms. • Thresh2 is expressed in the same unit as Mn.

** 3GPP 36331 – RRC Protocol Specification, Measurement Report Triggering, Event A5 (Serving becomes worse than threshold1 and neighbour becomes better than threshold2)

Inter Frequency Load Balance

Event A5 Description

2 Thresh Hys Ocn Ofn Mn    Thresh Hys Ms  Thresh Hys

Ms  MnOfnOcn Hys Thresh₂ **

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Inter Frequency Load Balance

Event A5 Description

** *

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Inter Frequency Load Balancing

Settings Plan

The Inter Frequency LB will be applied and it’s parameters will be updated according to:

• The feature should be applied per cell in a vertical relation (i.e. alpha 800 <-> alpha 1900 (1)&(2)) • IFLB parameters will follow the GPL setting

• A5 event thresholds will be the same for IFLB and for coverage trigger • The feature will be applied as need according to CFR caused by load • Test Site: zzz

• According to GPL, the following parameters must be updated: • lbActivationThreshold: Not active from 8321 to 8665

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Inter Frequency Load Balancing

Settings Plan

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Inter Frequency Load Balancing

Inter Freq HO GPL

-120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 1900 MHz 800 MHz _{2500 MHz} Serving 800 MHz Site A1A2S A5 1 -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 A5 2 + Offset freq 0 dB -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 A5 2 A5 2 + Offset freq +5 dB -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 1900 MHz 800 MHz _{2500 MHz} Serving 1900 MHz Site A1A2S A5 1 -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 A5 2 + Offset freq 0 dB -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 A5 2 8665 A5 2 + Offset freq -2 dB -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 1900 MHz 800 MHz _{2500 MHz} Serving 2500 MHz Site (TDD) A1 A2 A5 1 -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 A5 2 + Offset freq -24 dB -120 -118 -116 -114 -112 -110 -108 -106 -104 -102 -100 -98 -96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72 -70 -68 -66 -64 -62 -60 A5 2 A5 2 + Offset freq +10 dB 2 Thresh Hys Ocn Ofn Mn    A5 2 8321

Needs update from Nokia

Thresh Hys

Ms  

In: Out: Ms HysThresh MnOfnOcn HysThresh2