Inter-frequency
LOAD BALANCING
OVERVIEW
› Description
ȫ Enables load distribution between
co-located and non-co-located
cells and is supported in both
intra and inter eNodeB
configurations
› Operator benefit
ȫ Creates better fairness between
users allocated to different LTE
frequencies
ȫ Improved end user performance
at high load and possibility to add
more users
Improves utilization of existing spectrum
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 2
INTRODUCED PARAMETERS
› cellSubscriptionCapacity
ȫ Normalized subscription capacity of the cell. The value
represents the total capacity of the cell.
ȫ MO: EUtranCellFDD
› qciSubscriptionQuanta Load measurement
ȫ Normalized subscription quantity associated with the
specific QCI. Specifies the subscription cost of a bearer
with this QCI profile.
ȫ MO: QciProfilePredefined
› loadBalancing
ȫ Indicates if inter-frequency load balancing is ALLOWED or
NOT_ALLOWED from the current cell and towards the cell Load information exchange
indicated by the cell relation.
ȫ MO: EUtranCellRelation
› lbThreshold
ȫ The minimum load (subscription ratio) difference to trigger
load balancing action.
ȫ MO: LoadBalancingFunction
› lbCeiling Load balancing action magnitude
ȫ The maximum load (subscription ratio) difference taken
into account in one load balancing cycle.
ȫ MO: LoadBalancingFunction
› a5Threshold1Rsrp
ȫ The Reference Signal Received Power (RSRP) threshold1
value for eventA5.
ȫ MO: ReportConfigEUtraInterFreqLb
› a5Threshold2Rsrp
ȫ The Reference Signal Received Power (RSRP) threshold2 UE selection for load balancing
value for eventA5.
ȫ MO: ReportConfigEUtraInterFreqLb action
› hysteresisA5
ȫ The hysteresis value for the eventA5 measurement.
ȫ MO: ReportConfigEUtraInterFreqLb
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 3
LOAD MEASUREMENT
› Each individual cell measures load.
› Load is represented by a subscription ratio:
∑qciSubscriptionQuanta
subscriptionRatio =
cellSubscriptionCapacity
ȫ Subscription Quanta value for each QCI is configured with the parameter
qciSubscriptionQuanta (MO: QciProfilePredefined).
ȫ Cell subscription capacity value for each cell is configured with the parameter
cellSubscriptionCapacity (MO: EUtranCellFDD).
MO PARAMETER VALUE Remark
QciProfilePredefined=qci6 qciSubscriptionQuanta 200 both 800 & 1800 cells
QciProfilePredefined=qci8 qciSubscriptionQuanta 200 both 800 & 1800 cells
EutranCellFDD cellSubscriptionCapacity 10000 800 cells Only
EutranCellFDD cellSubscriptionCapacity 20000 1800 cells Only
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 4
LOAD INFORMATION EXCHANGE
› Load information is exchanged between cells in order to balance load.
› Load balancing can be configured to be allowed (or not) on cell relation level
for each cell with the parameter loadBalancing (MO: EUtranCellRelation).
ȫ This may be used to allow load balancing in one direction only. Mobility
functionality is not affected by this.
ȫ In our strategy, IFLB is only allowed from 800 to 1800, thus only 1800 cell need to
report its load info to 800 cell.
MO PARAMETER VALUE
EUtranFreqRelation=1548,EUtranCellRelation loadBalancing 1
EUtranFreqRelation=6275,EUtranCellRelation loadBalancing 0
1800 cell
800 cell
800 cell
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 5
LOAD BALANCING ACTION
MAGNITUDE
› The LBA magnitude that a source cell determines for each target cell is done
by considering:
ȫ The load difference to each target cell
ȹ The minimum load difference to trigger load balancing action is configured with
the parameter lbThreshold (MO: LoadBalancingFunction).
ȹ The maximum load difference taken into account in load balancing action
during one load balancing cycle is configured with the parameter lbCeiling
(MO: LoadBalancingFunction).
ȫ The total off-loading from the source cell
ȹ The LBA magnitude for each target cell is moderated such that the source and
target cells all aim at the same resulting load level.
MO PARAMETER VALUE Remark
LoadBalancingFunction lbThreshold 30 both 800 & 1800 cells
LoadBalancingFunction lbCeiling 200 both 800 & 1800 cells
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 6
UE SELECTION FOR LOAD
BALANCING
› A UE is considered suitable for moving when it:
ȫ Supports the frequency of the target cell in question
ȫ Experiences acceptable coverage in the target cell.
› The trigger for the report of measurement results is an A5 event in L14B.
ȫ The A5 event represents acceptable coverage for load balancing.
ȫ The A5 event is configured with the parameters a5Threshold1Rsrp,
a5Threshold2Rsrp and hysteresisA5(MO: ReportConfigEUtraInterFreqLb).
› Reporting UEs are off-loaded until each LBA magnitude is reached.
› The off-loading is realized by inter-frequency handover.
MO PARAMETER VALUE Remark
ReportConfigEUtraInterFreqLb a5Threshold2Rsrp -109 800 cells Only
ReportConfigEUtraInterFreqLb hysteresisA5 10 800 cells Only
ReportConfigEUtraInterFreqLb a5Threshold1Rsrp -44 800 cells Only
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 7
CHANGES IN PARAMETERS FOR
LB
› In L14B, Event A5 is introduced for UE selection to trigger IFHO to off load UE
as replacement of Event A4 in early versions before L14B.
MO L14B Before L14B
ReportConfigEUtraInterFreqLb a5Threshold2Rsrp a4ThresholdRsrp
ReportConfigEUtraInterFreqLb hysteresisA5 hysteresisA4
ReportConfigEUtraInterFreqLb a5Threshold1Rsrp
› Event A5 parameters are configured for both IFHO and IFLB and they are
located under different MOs as in below table.
Event A5 for IFLB Event A5 for IFHO
MO PARAMETER MO PARAMETER
ReportConfigEUtraInterFreqLb a5Threshold2Rsrp ReportConfigA5 a5Threshold2Rsrp
ReportConfigEUtraInterFreqLb hysteresisA5 ReportConfigA5 hysteresisA5
ReportConfigEUtraInterFreqLb a5Threshold1Rsrp ReportConfigA5 a5Threshold1Rsrp
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 8
BASELINE SETTINGS
MO PARAMETER VALUE Remark
QciProfilePredefined=qci6 qciSubscriptionQuanta 200 both 800 & 1800 cells
QciProfilePredefined=qci8 qciSubscriptionQuanta 200 both 800 & 1800 cells
LoadBalancingFunction lbThreshold 30 both 800 & 1800 cells
LoadBalancingFunction lbCeiling 200 both 800 & 1800 cells
EUtranFreqRelation=1548,EUtranCellRelation loadBalancing 1
EUtranFreqRelation=6275,EUtranCellRelation loadBalancing 0
EutranCellFDD cellSubscriptionCapacity 10000 800 cells Only
EutranCellFDD cellSubscriptionCapacity 20000 1800 cells Only
ReportConfigEUtraInterFreqLb a5Threshold2Rsrp -109 800 cells Only
ReportConfigEUtraInterFreqLb hysteresisA5 10 800 cells Only
ReportConfigEUtraInterFreqLb a5Threshold1Rsrp -44 800 cells Only
The new introduced A5 parameters are colored by blue
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 9
TEST CASE
› Let us suppose this scenario：
› There is a LTE site: L3696A
and its LB related parameters 17 users
Cell: 436961
follow our baseline.
› Currently, there are 17 users ……
in cell 436961 and 12 users in
cell 436964 ……
› For each user, one bearer is Site: L3696A
established for traffic. Cell: 436964 12 users
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 10
TEST CASE CONTD..
› Load measurement:
ȫ For cell 436961: 17 1 200
subscriptionRatio = = 0.17
20000
ȫ For cell 436964:
12 1 200
subscriptionRatio = = 0.24
10000
› Load information exchange
ȫ 436961 send 436964 msg to request its load info and 436964 give a
response to 436961 with its suscriptionRatio via intra-eNB msg.
pmLbMeasuredUe in Eutranfreqrelation MO can be verified for optimization
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 11
TEST CASE CONTD..
› Load balancing action magnitude
ȫ Load difference can be calculated:
Load Difference = subscriptionRatio(436964) − subscriptionRatio(436961)
= 0.24 − 0.17 = 0.07
ȫ Load difference(0.07) is larger than the minimum load difference
setting: lbThreshold(0.03), so LB is triggered;
ȫ Load difference(0.07) is smaller than the maximum load difference
setting: lbCeiling (0.2), so load can be balanced in one LB cycle;
ȫ If one UE off loaded from 800 to 1800, load in 800 cell will decrease
0.02, meanwhile load in 1800 cell will increase 0.01, that would
reduce load difference by 0.03 between these two cells.
ȫ In this case, total 0.06 load difference should be balanced, so two
UEs should be selected to off load
pmLbQualifiedUe from EutranCellRelation MO can be verified for optimization
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 12
TEST CASE CONTD..
› UE selection for load balancing action
ȫ UE support target freq;
ȫ UE which RSRP meet Event A5 configured in MO:
ReportConfigEUtraInterFreqLb
UE met above conditions will be randomly selected and moved to 436961
via IFHO.
› After LB
ȫ 19(17+2) users in 436961,
19 1 200
subscriptionRatio = = 0.19
20000
ȫ 10(12-2) users in 436964,
101 200
subscriptionRatio = = 0.20
10000
ȫ Load difference is 0.01 less than the minimum load difference , LB will not
be triggered and load get balanced.
Introduction about IFLB Baseline Setting | Ericsson Internal | 2015-04-08 | Page 13
DISADVANTAGE
❑The main disadvantage here 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. For
Example, with the current implemented settings:
• The subscription ratio calculated in each cell is a tool for monitoring the traffic load in the cell.
• Current values:
• Serving cell load: 3 UEs with QCI9 bearers each, Subscription Ratio = (3x100)/8000 = 0.0375 = 3.75%
• Target cell load: 0 UE, Subscription Ratio = 0
• Load Difference: Serving cell load – Target cell load = 3.75%
• Since, Load Difference > lbThreshold, IFLB will be triggered even with a low serving cell load of 3 UEs/bearers.
Feature DESCRIPTION
› 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 threshold
can be configured per EUtranFreqRelation.
› IFLB towards a cell triggered only if: load in source cell is above the preconfigured load threshold for
the frequency of the target cell and if the load difference is larger than the load difference threshold.
› 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
Feature DESCRIPTION CONTD..
IFLB NOT Triggered
Since, Load_Serving_Cell <
3 QCI9 bearers 0 bearers lbActivationThreshold_Target1 +
Serving Frequency Target Frequency
lbThreshold
lbActivationThreshold +
lbThreshold
› Here:
lbThreshold = 30 (Unit = 0.001) = 0.030 or 3%
lbActivationThreshold = 100 (Unit = 0.001) = 0.1 or 10% or Equal to 8 QCI9 bearer load
cellSubscriptionCapacity = 8000
qciSubscriptionQuanta = 100 (QCI9)
IFLB Activation Threshold Feature State: ACTIVATED
IFLB Activation Threshold | Ericsson Internal | 2014-03-20 | Page 16
Feature DESCRIPTION CONTD..
› CALCULATIONS INVOLVED:
- Number of QCI9 bearers attached on Serving Frequency = 3
- Number of QCI9 bearers attached on Target Frequency = 0
Load = Subscription Ratio =
Load Serving Freq. = (3 x 100)/8000 = 300/8000 = 0.0375 = 3.75%
Load Target Freq. = 0
Condition: Load_Serving_Freq > lbActivationThreshold for Target Frequency + Load
Difference Threshold (lbThreshold)
=> 0.0375 < 0.1 + 0.03
=> 0.0375 < 0.13 OR 3.75% load < 13% total threshold
Therefore, CONDITION for IFLB is not met and IFLB is not triggered.
IFLB Activation Threshold | Ericsson Internal | 2014-03-20 | Page 10
Feature DESCRIPTION CONTD..
IFLB Triggered
Load_Diff
Since, Load_Serving_Cell >
16 QCI9 bearers 0 bearers
Target Frequency
lbActivationThreshold_Target1 +
Serving Frequency
lbThreshold
lbActivationThreshold lbActivationThreshold +
lbThreshold
› Here:
lbThreshold = 30 (Unit = 0.001) = 0.030 or 3%
lbActivationThreshold = 100 (Unit = 0.001) = 0.1 or 10% or Equal to 8 QCI9 bearer load
cellSubscriptionCapacity = 8000
qciSubscriptionQuanta = 100 (QCI9)
IFLB Activation Threshold Feature State: ACTIVATED
IFLB Activation Threshold | Ericsson Internal | 2014-03-20 | Page 18
Feature DESCRIPTION
› CALCULATIONS INVOLVED:
- Number of QCI9 bearers attached on Serving Frequency = 12
- Number of QCI9 bearers attached on Target Frequency = 0
Load = Subscription Ratio =
Load Serving Freq. = (16 x 100)/8000 = 1600/8000 = 0.20 = 20%
Load Target Freq. = 0
Condition 1: Load_Serving_Freq > lbActivationThreshold for Target Frequency + Load
Difference Threshold (lbThreshold)
=> 0.20 > 0.1 + 0.03
=> 0.20 > 0.13 OR 20% load > 13% total threshold
Therefore, CONDITION for IFLB is met and IFLB HOs are triggered.
IFLB Activation Threshold | Ericsson Internal | 2014-03-20 | Page 19
