Nokia Academy
LTE Radio Parameters 2 [FL15a]
Idle Mode Mobility
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Module Objective
After completing this learning element, the participant should be able to describe
discuss and analyze:
•Parameters associated to idle mode mobility load balancing
Index
•Idle Mode Mobility Load Balancing
•Load triggered Idle Mode Mobility Load Balancing
•Measurement based Idle Mode Load Balancing
Index
•Idle Mode Mobility Load Balancing
•Load triggered Idle Mode Mobility Load Balancing
•Measurement based Idle Mode Load Balancing
Idle Mode Mobility Load Balancing
Load Balancing Features Overview
Intra-Frequency
Inter-Frequency
Intra-LTE
Inter-RAT
Idle Mode Load Balancing Features
LTE487 – Idle Mode Load Balancing (RL50/RL35TD/RL50FZ)
LTE1677 – Idle Mode Load Balancing Extensions (RL60/RL45TD)
LTE2050 – Load Triggered Idle Mode Load Balancing (RL70/RL55TD)
LTE2051 – Measurement Based Idle Mode Load Balancing (FL15A/TL15A)
LTE 487 Idle Mode Mobility Load Balancing
RL50
LTE1677 Idle Mode Mobility Load Balancing Extensions
RL60
A percentage of UEs switching from connected to idle state are provided dedicated cell
reselection priorities for different frequency layers and RATs via RRC Release message
Percentage of UEs
33%
4. UEs uses the
IMMLB priorities for
reselection
1. UEs connected to
Freq1
Dedicated Cell Reselection
Priorities
Broadcasted Cell Reselection
Priorities
Freq 1
High
Freq 2
Low
Low
Freq 2
High
Low
Freq 2
High
2. UEs are released by
the cell
Broadcasted Cell
Reselection Priorities
Dedicated Cell Reselection
Priorities
Freq 1
Freq 1
Freq1
3. Selected UEs are
sent IMMLB priorities
Freq 1
High
Freq 2
Low
Broadcasted Cell
Reselection Priorities
Freq 1
High
Freq 2
Low
Freq2
LTE 487/LTE1677 Idle Mode Mobility Load
Balancing/Extensions
Candidate UE selection

Each time a UE is released without redirection, the ratio of RRC connection release
messages with idlemodemobilityConfigInfo IE configured with RRC connection release
messages is compared with the configured idleLBPercentageOfUe

This is done at the object level (LNCEL, MOPR or MODPR) selected by the IMMLB algorithm
Check assumes
that UE to be
released is sent
idleModeMobility
ControlInfo
# of RRC connection release
messages with
idleModeMobilityControlInfo
idleLBPercentageOfUe
# of RRC connection release
messages

If the condition is met, the RRC connection release message is configured to include the
idleModeMobilityControlInfo IE and UE would use dedicated IMMLB priorities in cell
reselection

Otherwise, the RRC connection release would be constructed without the
idleModeMobilityControlInfo IE and UE would use SIB priorities in cell reselection
Idle mode mobility balancing extensions
LTE1677 – Idle Mode Mobility Load Balancing Extensions (RL60)
-
Weighted Round Robin (WRR)
-
In RL60 the Cell does not have configured the absolute dedicated priorities, instead a
weighting factor is set and available alternative layers chosen at random via WRR and
dedicated priority for this layer is then set =max.
EXAMPLE
•
•
Random value from the range [0;1] is generated.
-
[0;0.5] then frequency f 1 will be chosen as a main target for IMMLB; Dedicated Cell Reselection Priority for f1  7
-
(0.5;0.75] then frequency f3 will be chosen as a main target for IMMLB; Dedicated Cell Reselection Priority for f3  7
-
(0.75;1] then frequency f4 will be chosen as a main target for IMMLB; Dedicated Cell Reselection Priority for f4  7
Please note that frequency/layer configured with the highest IMMLB weight (in this example f1) in relation to
other frequency/layers has the highest probability of being selected as a main target for IMMLB
•
IMMLB weights are used only to determine which frequency will be selected as main target for IMMLB
Generated value 0.76 means that f4 will get priority 7 in IMMCI
Example: Value 0.76 was randomly generated
p1WRR(f1) = 0.5
0
p2WRR(f3) = 0.25
0.5
f1 = [0;0.5]
0.5
0.75
f3 = (0.5;0.75]
p3WRR(f4) = 0.25
0.75
f4 = (0.75;1]
1
LTE 487/LTE1677 Idle Mode Mobility Load
Balancing/Extensions
Parameters
•
•
actIdleLB
idleLBPercentageOfUes
balancing
moimpId
modimpId
T320
For MODIMP, MOIMP, LNCEL
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Activation of idle mode load balancing (IdleLB)
MODPR, MOPR, LNCEL Percentage of UE for idle mode load
Idle mode mobility profile identifier
Idle mode mobility default profile identifier
LNCEL Timer T320
dlCarFrqEut
EUTRA carrier freq for IMMLB
utrFddCarFrq
UTRA-FDD carrier frequency for IMMLB
cdmaRttBdCl
CDMA 1xRTT band class for IMMLB
cdmaHRPDBdCl
CDMA HRPD band class for IMMLB
g eranB andInd
GERAN carrier frequency band for IMMLB
g eranC arFrqIdleModeL
GERAN carrier frequency list for IMMLB
idleLBCellReSelPWeight
Cell Reselection Priority for IMMLB (LNC E L only)
idleLBEutCelResWeight
EUTRA carrier frequency priority for IMMLB
idleLBUtraFddCelResWeight
UTRA-FDD carrier frequency priority for IMMLB
idleLBRttCelResWeight
CDMA 1xRTT band class priority for IMMLB
idleLBHrpdCelResWeight CDMA HRPD band class priority for IMMLB
idleLBGeranCelResWeight GERAN carrier frequency priority for IMMLB
Index
•Idle Mode Mobility Load Balancing
•Load triggered Idle Mode Mobility Load Balancing
•Measurement based Idle Mode Load Balancing
LTE2050 Load Triggered Idle Mode Load Balancing
•
Idle Mode Mobility Load Balancing (IMMLB) refers to the inclusion of Dedicated Priorities
within the RRC Connection Release message
•
Load balancing is achieved by allowing:
•
•
some UE’s use the Dedicated Priorities broadcast within the SIB
•
some UE’s use Dedicated Priorities included within their RRC Connection Release
IMMLB has evolved with each software release
RL40
•
•
Load balancing across
LTE carriers
RL50 – LTE487
•
Introduction of interRAT capability
RL60 – LTE1677
•
Introduction of Absolute
Priority Weights
RL70 introduces the capability to trigger IMMLB only when the load becomes high
•
rather than always triggering the feature
LTE2050 Load Triggered Idle Mode Load Balancing
• The load threshold used to trigger Idle Mode Mobility Load Balancing is configured
using the idleLBCapThresh parameter
• This parameter defines a percentage Composite Available Capacity (CAC)
• CAC = 100 % corresponds to an unloaded cell
• CAC = 0 % corresponds to a fully loaded cell
• Configuring a value of 100 % provides the same functionality as RL60, i.e. the feature i s
always triggered
LNCEL; idleLBCapThresh
Idle mode load balancing capacity threshold 0
to 100 %,
Default: 100
LTE2050 Load Triggered Idle Mode Load Balancing
Composite Available Capacity (CAC)
•
Triggering based upon load uses the
Composite Available Capacity (CAC)
•
load balancing is triggered when CAC <
idleLBCapThresh
•
CAC is calculated from the downlink GBR,
non-GBR and PDCCH loads
•
The calculation is completed in 3 steps
•
Relative Load = Measured Load / Target
Load
•
Available Capacity = 100 % - Relative
Load
•
Composite Available Capacity =
Min(Available Capacities)
Available
Capacity
calculated for
GBR, non-GBR
and PDCCH
Loadsettings; mlbEicicOperMode
Mode for calculating the CAC in load bal. and
eICIC
nonGbrOnly (0), nonGbrPdcch (1), allUes (2)
Default : AllUes
LTE2050 Load Triggered Idle Mode Load Balancing
Triggering
• load balancing is triggered when
CAC < idleLBCapThresh
LNCEL; idleLBCapThresh
Idle mode load balancing capacity
threshold
0..100%
Default: 100%
Cell load max
100%
Target load
60%
Rel load 100%
CAC
50%
CAC 50% < idleLBCapThresh 90%
therefore IMLB = True
idleLBCapThresh 90%
LTE2050 Load Triggered Idle Mode Load Balancing
•
Triggering based upon load uses some of the parameters from the loadSettings
parameter structure
•
The relevant parameters are:
nomNumPrbNonGbr
• targetLoadGbrDl
• targetLoadNonGbrDl
• targetLoadPdcch
•
New object for common
load balancing parameters
LNCEL - loadSettings
cellCapClass
mlbEicicOperMode
nomNumPrbNonGbr
targetLoadGbrDl
targetLoadNonGbrDl
targetLoadPdcch
ulCacSelection
ulStaticCac
Index
•Idle Mode Mobility Load Balancing
•Load triggered Idle Mode Mobility Load Balancing
•Measurement based Idle Mode Load Balancing
LTE2051: Measurement based Idle Mode Load Balancing
• LTE2051 is an extension of IMMLB algorithm
FL/TL15A
• From FL/TL15A onwards eNB may validate if selected
main target frequency layer has sufficient power
(RSRP) and/or quality (RSRQ)
• Starting from FL/TL15A it is possible to avoid
steering UEs to worse cells in terms of RSRP as well
as avoid reselections to congested cells (RSRQ)
• Selected main target frequency layer is checked
against absolute configurable thresholds as well as
against serving cell RSRP/RSRQ
• LTE2051 can be used together with LTE2050, but
LTE2050 is not a prerequisite
LTE2051: Measurement based Idle Mode Load Balancing
Load Triggered Idle Mode Load Balancing
•
The feature is split into 5 f unctions;
1) Load supervision and CAC calculation:
•
Measurements of source cell DL CAC (CAC S)
2) Check if IMMLB should be triggered
•
Source cell CAC is compared with configured load threshold
(LNCEL:idleLBCapThresh) that defines an IMMLB trigger point
3) IMMLB Objects Selection
•
According to configuration, proper IMMLB object is selected, from which
percentage of UEs as well as IMMLB weights are taken
4) Candidate UE selection
•
Connected
For each UE that is being released, it is verified if IMMCI should be added
5) IMMCI creation
•
WRR (selection of main target frequency layer) [LTE487/LTE1677]
•
Main target validation (A4 measur ements of main target) [LTE2051]
•
IMMCI is filled up with frequency layers and assigned dedicated
priorities [LTE487/LTE1677]
Load supervision and
CAC calculation
Check if IMMLB
should be triggered
L
T
E
2
0
5
0
IMMLB Objects
Selection
Candidate UE
Selection
IMMCI creation
LTE2051
Idle
L
T
E
4
8
7
/1
6
7
7
I
d
l
e
M
o
d
e
M
o
b
il
i
ty
L
o
a
d
B
a
l
a
n
c
in
g
LTE2051: Measurement based Idle Mode Load Balancing
5) IMMCI* Creation
• Overview of enhanced Idle LB procedure is illustrated below (LTE2051 part is included)
START
1.UE is a candidate for LB
2.IMMLB object(s) is/are selected for UE, IMMLB weights can
be derived from proper structure
STEP 2
STEP 1
STEP 4
STEP 3
STOP = NO IMMCI is sent to
UE
No
STEP 5
List of frequency
layers, based on
selected IMMLB
object is created. This
is done for the Main
target frequency
selection
Is there
any
frequency
on list?
Weighted Round Robin
Algorithm is used to
determine the main
target for IMMLB
Yes
Main target validation
RSRP/RSRQ of cells of
main target are checked
All criteria
fulfilled?
Yes
No
STEP 7
IMMCI list is filled up:
STOP = NO IMMCI is sent to
UE
1)Main target frequency layer is
added with assigned priority 7
2)All frequencies from STEP 6 with
SIB priority lowered by one
3)t320 timer is added
LTE2051
STEP 6
1)Second list containing
frequency layers configured
in selected IMMLB object is
created.
2)Main target frequency is
removed (if present)
3)Frequency layers that not
configured for SIB broadcast
are removed
STOP
LTE2051: Measurement based Idle Mode Load Balancing
5) IMMCI Creation
-
STEP 4: Main target validation (LTE2051)
When LTE2051 is activated (LNBTS:actMeasBasedIMLB = true), eNB considers
RSRP/RSRQ validation of the main target frequency layer, provided that:
•Selected main target frequency layer is inter-frequency LTE layer
-
If serving cell`s frequency layer is selected as main target or frequency layer that belongs to different RAT, quality
check (RSRP/RSRQ) for the primary target is not done (IMMCI with dedicated priorities is sent according to
LTE487/LTE1677 rules)
•Selected LTE target frequency layer is configured to be measured (IRFIM:enableA4IMLB = true)
FL/TL15A
Only primary target that is an inter-frequency
LTE layer may be validated with LTE2051
LTE2051: Measurement based Idle Mode Load Balancing
5) IMMCI Creation
-
STEP 4: Main target validation (LTE2051)
Idle LB algorithm is working just before RRC Connection Release message is built for UE
•LTE2051 requires A4 measurements to be done
before RRC Connection Release is sent to UE
•A4 measurements are possible only in RRC
Connected state
•To facilitate A4 measurements for Idle LB needs,
prolonged RRC Connected state is required
-
•
e
t
a
t
s
C
R
R
RRC Connected
1
A4 supervision timer (LNBTS:reportTimerIMLBA4)
is controlling both prolonged RRC Connected state
as well as A4 measurement period
2
3
RRC Idle
time
Normal data activity (signalling or user data) can
happen in prolonged RRC Connected state
Just before RRC Connection Release with or without
IMMCI is sent, eNB has to verify inactivity state again.
If any activity was recorded, RRC Connection Release
procedure is stopped
Note:
1 InactivityTimer is running (LNCEL:InactivityTimer)
2 RRC Connected phase is prolonged as A4 supervision
timer is running
3 RRC Connection Release with or without IMMCI,
depending on Idle LB algorithm decision
LTE2051: Measurement based Idle Mode Load Balancing
5) IMMCI Creation
-
STEP 4: Main target validation (LTE2051)
Once A4 MR is received, TCL is created
•Cells belonging to TCL are checked against RSRP and/or RSRQ thresholds:
-If RSRP parameters are configured (IFRIM:minRsrpIMLB, IRFIM:minDeltaRsrpIMLB):
•RSRP of potential target (RSRPT) is checked against absolute RSRP threshold IFRIM:minRsrpIMLB
•RSRP of each potential target (RSRPT) is checked against serving cell RSRP (RSRPS), i.e. whether
RSRPT > RSRPS + IRFIM:minDeltaRsrpIMLB
-If RSRQ parameters are configured (IFRIM:minRsrqIMLB, IRFIM:minDeltaRsrqIMLB):
•RSRQ of potential target is checked against absolute RSRQ threshold IFRIM:minRsrqIMLB
•RSRQ of each potential target (RSRQT) is checked against serving cell RSRQ (RSRQS), i.e. whether
RSRQT > RSRQS + IRFIM:minDeltaRsrqIMLB
-
STEP 5: Main target validation (LTE2051)
If all abovementioned criteria are met for at least one cell, IMMCI will be added to RRC Connection release,
otherwise RRC Connection release is sent without dedicated priorities
Note: If IMMCI is not sent after the primary target validation , #of RRC Connection Release message s with idleModeMobilityControlInfo is not decremented!
LTE2051: Measurement based Idle Mode Load Balancing
5) IMMCI Creation
-
STEP 6: Gathering frequency layers that will fulfill the IMMCI
If IMMCI is still to be sent, i.e. the primary target layer is already determined [verified by measurements or not],
second list of frequency layers is created
•
CASE A: Selected objects MOPR + MOIMPs (the same approach for MODPR + MODIMPs)
-
Serving cell frequency layer is included in Frequency List only if it is configured in MODIMP/MOIMP
•
CASE B: LNCEL+(LNCEL,IRFIM) or LNCEL+(LNCEL,IRFIM,UFFIM,CDFIM,GFIM) [when
LNBTS:actIdleLB = true]
-
When LNCEL is selected as IMMLB object for UE, then serving cell frequencyis always included in the Frequency List
Frequency List
MOPR
OR
MOIMP-1
MOIMP-X
FREQ
SIB PRIO
f1
3
f3
5
f5
2
f6
6
LNCEL
GFIM
CDFIM
UFFIM
IRFIM
STEP 4: Frequency List contains all
frequencies and priorities for SIB broadcast
configured in IMMLB object(s), excluding:
• frequency that is selected as main target
for LB
• frequencies not supported by UE
• frequencies that have not configured Cell
Reselection Priority for SIB broadcast
STEP 6
LTE2051: Measurement based Idle Mode Load Balancing
5) IMMCI Creation
-
STEP 7: IMMCI is filled up
•
Main target frequency layer is added to IMMCI with the highest
priority 7
•
Frequencies from Frequency List (created in STEP 6) with SIB priority
FREQ
SIB PRIO
of main target that could appear (priority value 7 in SIB will be
f1
3
changed into 6), however hierarchy of priorities is kept
f3
5
If configured absolute priority broadcasted in SIB is equal to 0, it is not
f5
2
f6
6
lowered by 1 are placed into IMMCI list
•
-
(STEP 4) Frequency
List
Lowering of SIB priorities while creating IMMCI prevents duplication
lowered. Value of 0 is kept
Main target frequency is
added with the highest prio
-1
…
…
-1
Dedicated Cell
Reselection
Priorities (IMMCI
list)
f4
7
f1
2
f3
4
f5
1
f6
5
LTE2051: Measurement based Idle Mode Load Balancing
5) IMMCI Creation
-
STEP 7: IMMCI is filled up
•
Timer t320 is added to IMMCI
-
t320 defines how long dedicated priorities take precedence over
SIB priorities
•
timer t320 is configurable (LNCEL:t320)
IE/ Group Name
RRCConnectionRelease
> rrc-TransactionIdentifier
> releaseCause
> redirectedCarrierInfo
>
idleModeMobilityControlI
nfo
> cellInfoList-r9
Need
ON
Source
RRC
RRC
eNB/RRC
eNB/RRC
OP
OP
eNB/RRC
eNB/RRC
IE/Group Name
idleModeMobilityControlInfo
> freqPriorityListEUTRA
>> carrierFreq
>> cellReselectionPriority
> freqPriorityListGERAN
>> carrierFreq
>> cellReselectionPriority
> freqPriorityListUTRA-FDD
>> carrierFreq
>> cellReselectionPriority
> freqPriorityListUTRA-TDD
>> carrierFreq
>> cellReselectionPriority
> bandClassPriorityListHRPD
>> bandClass
>> cellReselectionPriority
> bandClassPriorityList1XRTT
>> bandClass
>> cellReselectionPriority
> t320
Presence
M
OP
M
M
OP
M
M
OP
M
M
OP
M
M
OP
M
M
OP
M
M
OP
LTE2051: Measurement based Idle Mode Load Balancing
Configuration management
Abbrev
Description
MO
actMeasBasedIMLB
Activate measurement-based Idle mode load
balancing
LNBTS
minRsrpIMLB
Target cell minimum RSRP for idle mode load
balancing
IRFIM
inDeltaRsrpIMLB
Target cell min delta RSRP for idle mode load
balancing
IRFIM
minRsrqIMLB
Target cell minimum RSRQ for idle mode load
balancing
IRFIM
minDeltaRsrqIMLB
Target cell min delta RSRQ for idle mode load
balancing
IRFIM
enableA4IMLB
Enable A4 event for idle mode load balancing
IRFIM
reportTimerIMLBA4
Idle mode load balancing supervision timer for
A4 event
LNBTS