07 LTE Mobility Mngmnt GC

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LTE Functionalities and Overview
Random Access
LTE Mobility Management
LTE Measurements Management
LTE Intra Frequency Coverage Handover
LTE Inter Frequency Handover
Intra-LTE handover via S1
CS Fallback to UTRAN or GSM via Redirect
UE measurements
CQI measurements
eNB measurements
Non standardized (vendor specific): TA, Average RSSI, Average SINR, detected PRACH preambles, transport channel BLER
Standardized: DL RS Tx Power, Received Interference Power, Thermal Noise Power
Measurements from LTE to other systems
UE measurements are mainly intended for handover.
UTRA FDD: CPICH RSCP, CPICH Ec/No and carrier RSSI
GSM: GSM carrier RSSI
CDMA2000: 1xRTT Pilot Strength, HRPD Pilot Strength
List of detected preambles: The eNB shall report a list of detected PRACH preambles to higher layers. Higher layer utilize this info for the RACH procedure
Transport BLER: The ACK/ NACKs for each transmission of the HARQ process are reported to the MAC. Based on these ACK/NACKs the higher layers compute the BLER for RRM issues.
TA: The eNB needs to measure the initial timing advance (TA) of the uplink channels based on the RACH preamble
Average RSSI: Measured in UL by eNB. It can be used as a level indicator for the UL power control. The RSSI measurements are all UE related and shall be separately performed for ( TTI intervals)
· UL data allocation (PUSCH)
· UL control channel (PUCCH)
Sounding reference signal (SRS)
Average SINR: In UL the eNB measures SINR per UE. The average SINR can be used as a quality indicator for the UL power control
UE Measurements: RSRP and RSRQ
RSRP (Reference Signal Received Power)
Average of power levels (in [W]) received across all Reference Signal symbols within the considered measurement frequency bandwidth.
UE only takes measurements from the cell-specific Reference Signal elements of the serving cell, this makes RSRP results load and MIMO/diversity independent.
If receiver diversity is in use by the UE, the reported value shall not be lower than the corresponding RSRP of any of the individual diversity branches
Received Signal Strength Indicator (RSSI)
RSSI comprises the linear average of the total received power (in [W]) observed only in OFDM symbols containing reference symbols for antenna port 0, in the measurement bandwidth, over N number of resource blocks by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc.
RSRQ (Reference Signal Received Quality)
Defined as the ratio N×RSRP/(E-UTRA carrier RSSI), where N is the number of RBs of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator shall be made over the same set of resource blocks
Cell Selection Procedure
1) UE creates a candidate list of potential cells to camp on. Two possible search procedures:
• Initial Cell Selection UE scans all RF channels to find a suitable cell. On each carrier, the UE searches for the strongest cell and reads its system information. Once the UE has found the suitable cell for the selected PLMN, the UE creates a candidate list consisting of this cell and its neighboring cells as received in measurement control information.
• Stored Information Cell Selection (optionally) This procedure requires information stored from previously received measurement control information elements (cell parameters, carrier frequencies, etc). After the UE has found a suitable cell for the selected PLMN, candidate list is created same as the initial cell selection process.
2) Each cell on the candidate list is evaluated according to the selection criteria S
3) After selecting a suitable cell (S criterion fulfilled) for camp on, UE reports this event to NAS for registration procedures. If the registration is successful, the UE enters into "camped normally“ state.
Initial Selection
- Carrier 1:
strongest cell
- Carrier 2:
strongest cell
- Carrier i …..
- Previous information
- Previous detections
CELL SELECTION
Upon PLMN selection, UE uses “cell selection” for fast cell searching to camp on. To
receive system information UE tunes to the control channels. This procedure is
known as "camping on the cell”.
The UE will then register its presence in the registration area of the chosen cell by
NAS (Non Access Stratum) registration procedure.
NAS registration procedure means the upper layer information is transmitted from UE
to CN via AS (Access Stratum). The NAS offers the E-UMTS service to the users.
The cell will be decided as suitable if it fulfils the cell selection criteria.
The purpose of camping on a cell is:
• To enable UE reception of system information from the selected PLMN
• To allow UE an RRC connection, accessing the network on the cell control
channel.
• To receive paging and respond to paging messages on a tuned control channel in
the registration area. The PLMN knows the tracking area of the cell in which the
registered UE is camped.
PLMN SELECTION
UE scans RF channels in the eUTRAN band according to its capabilities to find available PLMNs.
On each carrier, the UE searches for the strongest cell
If the UE can read the PLMN identity (from SIB), the PLMN and the measured signal strength is reported to the NAS
After selecting a PLMN, the cell selection process starts where the UE selects a suitable cell and the radio access mode based on idle mode measurements and cell selection criteria.
S – Criterion Cell Selection
UE selects a eUTRA cell if the S (selection) criteria is fulfilled:
Srxlev = Qrxlevmeas – (Qrxlevmin* + Qrxlevminoffset**) - Pcompensation
UE measurement
SIB1 Parameter
*** PEMAX = LNCEL: pMaxOwnCell
qrxlevmin
Srxlev > 0
LNCEL; 2..16dB; 2dB; -
34 dBm default means not used
Please note that cell selection consists of UE searching for the strongest cell on all supported carrier frequencies of each supported RAT untill finding a suitable cell.
It should not take a long time which is challenging with many frequencies and RATs.
The NAS may speed up by indicating the RATs supported for the selected PLMN
Srxlev > 0
Qrxlevminoffset is an offset which may be configured to prevent ping pong between PLMNs which may occur due to fluctuating radio conditions. The offset is only considered when performing a periodic search for a higher priority PLMN when camped on a suitable cell on a VPLMN
Parameters broadcasted in SIB 1
pMaxOwnCell - The P-Max is used to limit the UE's uplink transmission power on a carrier frequency; it is also used to calculate the parameter P-compensation defined in TS 36.304 .
Corresponds to parameter PEMAX in TS 36.101.
The UE transmit power should not exceed the minimum of this value (in dBm), if provided, and the maximum UE power for the UE power class, PUMAX, as specified in TS 36.101
Qrxlevmin in both SIB1 and SIB 3 – what is the reason for this redundancy?
S – Criterion Cell Selection

Cell Re-Selection Procedure – Measurements
UE is not continuously measuring neighbour cells in search of a better cell to camp on
UE only performs these measurements when the criterias below are met for the different type of cells:
Intra - Frequency:
Srxlev <= Sintrasearch
Inter - Frequency:
2dB
Cell reselection between frequencies and RATs is primarily based on priorities
LTE configures priorities for each frequencies of each RAT
Cell specific priorities are provided via system information
Of the frequencies allowed for cell reselection the UE considers only those for which it has priorities
Equal priorities are not aplicable for inter- RAT cell reselction
The UE can reselect to a cell on a higher priority only if the S-value of the target cell is fulfilled
The UE can reselect on a cell on a lower priority if the S-value of the serving cell is below a certain threshold
If there is still more than one candidate then and only then the R criterion may be applied
Cell reselection is based primarily on absolute priorities -> UE first evaluates the frequencies of all RATs based on their priority
Secondly the UE compares the cells on the relevant frequencies based on radio link quality using a ranking criterion
Finally before reselection the UE check cells availability
Measurements rules: which frequencies/ RATs to measure:
High priority
Cell Re-Selection Procedure - R- Criterion
Once the measurements for neighbour cells have been triggered the UE will rank the measured cells which fulfill the S- Criterion according to the R- Criterion.
Intra-frequency / equal priority case
Best Rank(Highest R)
Note:
n – indicates the candidate neighbour cell.
qHyst
LNCEL; 0dB (0), 1dB (1), 2dB (2), 3dB (3), 4dB (4), 5dB (5), 6dB (6), 8dB (7), 10dB (8), 12dB (9), 14dB (10), 16dB (11), 18dB (12), 20dB (13), 22dB (14), 24dB (15); - ; 1 dB
qOffsetCell (IAFIM)
IAFIM; -24 dB (0), -22 dB (1), -20 dB (2), -18 dB (3), -16 dB (4), -14 dB (5), -12 dB (6), -10 dB (7), -8 dB (8), -6 dB (9), -5 dB (10), -4 dB (11), -3 dB (12), -2 dB (13), -1 dB (14), 0 dB (15), 1 dB (16), 2 dB (17), 3 dB (18), 4 dB (19), 5 dB (20), 6 dB (21), 8 dB (22), 10 dB (23), 12 dB (24), 14 dB (25), 16 dB (26), 18 dB (27), 20 dB (28), 22 dB (29), 24 dB (30); - ; 0 dB(15); 2 dB
Rn > Rs “cell reselection“
Qhyst is the hysteresis to avoid ping-pong effects
Qoffset is an offset value to control different frequency specific characteristics (e.g. propagation properties of different carrier frequencies) or cell specific characteristic
Cell Re-Selection Procedure - R- Criterion
The UE shall reselect the new cell, if the following conditions are met:
The new cell is better ranked than the serving cell during a time interval tReselection
More than 1 second has elapsed since the UE has camped on the current serving cell.
Intra-frequency / equal priority case
- ; 1 dB
0dB (15) ; 2 dB
Mobility States & Scaling Factors
The evaluation of the cells measured when the S-criterion is fulfilled depends on whether HCS (Hierarchical Cell Structure) is employed
HCS enables the differentiation of high, medium and normal mobility speed UE’s.
For faster moving UEs the procedure alters - speed dependent scaling rules are applied.
UE state detection:
If the number of (different cells) cell reselections during the past time period tEvalulation exceeds nCellChgHigh, high mobility has been detected.
If the number exceeds nCellChgMed, and not nCellChgHigh, medium mobility has been detected.
Else Normal Mobility is considered
.
tEvaluation
LNCEL; 30s (0), 60s (1), 120s (2), 180s (3), 240s (4) ; - ; 60s
nCellChgHigh
LNCEL; 1..16; 1; -; 1
Mobility States & Scaling Factors
For High and medium mobility states the UE , cell ranking criteria will be modified to consider a scaling factor:
High mobility:
Multiply Qhyst by "Speed dependent ScalingFactor for Qhyst for high mobility state“ (qHystSfHigh)
Multiply tReselection by "Speed dependent ScalingFactor for TreselectionRAT for high mobility state for RAT cells. (RAT = EUTRAN, UTRAN, GERAN). (celResTiFHM)
Medium mobility:
Multiply Qhyst by "Speed dependent ScalingFactor for Qhyst for medium mobility state“ (qHystSfMed)
Multiply tReselection by "Speed dependent ScalingFactor for TreselectionRAT for medium mobility state for RAT cells. (RAT = EUTRAN, UTRAN, GERAN). (celResTiFMM )
qHystSfHigh
LNCEL; -6 dB (0), -4 dB (1), -2 dB (2), 0 dB (3); - ; -4dB
qHystSfMed
LNCEL; -6 dB (0), -4 dB (1), -2 dB (2), 0 dB (3); - ; -4dB
celResTiFHM
LNCEL; 0.25 (0), 0.5 (1), 0.75 (2), 1 (3); - ; 0.5 (1)
celResTiFMM
LNCEL; 0.25 (0), 0.5 (1), 0.75 (2), 1 (3); - ; 0.5 (1)
Cell Re-Selection Procedure - R-Criterion
If UE camps longer than 1 sec in the serving cell and:
A higher priority neighbour fulfills (during TreselectionRAT) :
SnonServingCell,x > Threshhigh
SServingCell < Threshserving,low
Threshhigh > Threshx,low > Thresserving,low
LTE f1
UE reselects to WCDMA f1 when:
SservingCell (RSRP) is < than
UFFIM; 0..62dB; 2dB; -
LTE f1
LTE f1 RSRP is <= LNCEL: sNonIntrsearch
UE reselects to WCDMA f1 when:
SnonservingCell > UFFIM: utraFrqThrH
UFFIM; 0..62dB; 2dB; -
Broadcast of SIB 4 is optional – no need to broadcast any intra-frequency neighbour cells
UE is able to complete cell re-selection with SIB3 information
eUTRAN SIB4 informs about LTE idle mode neighbours
Physical Cell Identifier (PCI) of neighbour cell can be broadcast
cell (neighbour) individual re-select offset can be broadcast
SIB4 also informs about blacklisted cells (BC)
A UE is not allowed to re-select a blacklisted cell
Up to 16 groups of cells (PCIs) can be blacklisted
UE will not measure BC cells in connected mode
UE will never be instructed from eNB to handover to a blacklisted cell
New parameter object introduced: IAFIM
IAFIM = Intra Frequency Idle Mode
Idle Mode Mobility LTE Intra-Frequency
Blacklisted Cell
Neighbour Cell
regular neighbour
BC neighbour
black-listed cell
physCellIdNcl
PCI is a unique cell identification in a neighboring cell list
IAFIM; 0…503; 1; -
qOffsetCell
IAFIM; -24 dB (0), -22 dB (1), -20 dB (2), -18 dB (3), -16 dB (4), -14 dB (5), -12 dB (6), -10 dB (7), -8 dB (8), -6 dB (9), -5 dB (10), -4 dB (11), -3 dB (12), -2 dB (13), -1 dB (14), 0 dB (15), 1 dB (16), 2 dB (17), 3 dB (18), 4 dB (19), 5 dB (20), 6 dB (21), 8 dB (22), 10 dB (23), 12 dB (24), 14 dB (25), 16 dB (26), 18 dB (27), 20 dB (28), 22 dB (29), 24 dB (30); 0dB (15)
PCI = Physical Cell Id.
physCellIdNcl
qOffCell
Black Listed Cells –> the feature prohibit UE to camp on group of cells
UE shall not consider Black Listed Cells to camp on
Operator can control Black Cell List
Range of blacklisted cells must be consecutive
Range can be defined with parameter IAFIM: rangeIntraPci
Start of range can be defined with parameter IAFIM: startIntraPci
PCI is Physical Cell Identifier
0
503
startIntraPci
rangeIntraPci
IAFIM; n4 (0), n8 (1), n12 (2), n16 (3), n24 (4), n32 (5), n48 (6), n64 (7), n84 (8), n96 (9), n128 (10), n168 (11), n252 (12), n504 (13), Not Used (14) ;-
intrFrBCList (structure – 2 parameters)
startIntraPCI Indicates the lowest PCI in the range
intrFrNCList (structure – 2 parameters)
physCellIdNcl The Physical Cell Identifier is a unique cell identification in a Neighbouring Cell List
qOffsetCell The parameter defines a cell-specific offset (in dB) that is used in the cell reselection procedure.
System Information Block 4
Black Cell List
8 PCIs are blacklisted
RL20 supports idle mode mobility from LTE to LTE
This is intra-RAT, inter-frequency cell reselection from LTE f1 to LTE f2
Could be imagined as additional LTE layer for capacity reason
3GPP defines so called „priority layer“ concept
Parameters provided to UE controlling reselection to a frequency layer
rather than cell individual neighbour relationsships
8 frequency layers within LTE can be defined
candidates for cell re-selection (16 per frequency layer)
blacklisted cells – no valid candidates for cell re-selection (16 per frequency layer)
Frequency layer specific reselection parameters used
Cell individual re-selection offsets supported
New parameter object introduced: IRFIM
Inter Frequency Idle Mode configuration (for LTE inter-frequency)
Please note (Holma page 151):
The priority parameter introduced in LTE (release 8 concept applied also to UMTS)
eNodeB can provide a priority per LTE frequency and per RAT in SIBs or RRC connection release message
In case the UE is camping on a cell on the highest priority frequency the UE does not need to measure cells in other frequencies or RAT as long as the signal strength of the serving cell is above a certain threshold
If the UE is camped on a cell in the lower priority layer it should measure other cells under higher priority frequencies or RAT
Question: there are in total 16x8= 128 neighbours which could be broadcasted – very many neighbours ??
3GPP Priority Layer concept:
No Cell individual neighbour releationships defined
Priority Layer (expressed by RF frequency, bandwidth and priority) is defined
up to 8 UTRA Frequency layers can be defined
LTE f2
Idle Mode Mobility LTE Inter-Frequency
irfimId
IRFIM; 0…8; 1; -
Max. allowed bw. for neighbours
IRFIM; 0 (6mbw), 1 (15mbw), 2 (25mbw), 3 (50mbw), 4 (75mbw), 5 (100mbw) ; -
For the neighbour LTE frequencies (IRFIM)
Offset parameter to control re-selection
Used for equal priority frequency layers
Frequency layer bias for cell re-selection
qOffFrq
Frequency specific offset for equal priority EUTRAN frequencies
IRFIM; -24 dB (0), -22 dB (1), -20 dB (2), -18 dB (3), -16 dB (4), -14 dB (5), -12 dB (6), -10 dB (7), -8 dB (8), -6 dB (9), -5 dB (10), -4 dB (11), -3 dB (12), -2 dB (13), -1 dB (14), 0 dB (15), 1 dB (16), 2 dB (17), 3 dB (18), 4 dB (19), 5 dB (20), 6 dB (21), 8 dB (22), 10 dB (23), 12 dB (24), 14 dB (25), 16 dB (26), 18 dB (27), 20 dB (28), 22 dB (29), 24 dB (30); 0dB (15)
eutCelResPrio
IRFIM; 0…7; 1; -
LNCEL; 0…7; 1; -
Start inter-frequency NB list measurements
no need to measure any other frequency layer if serving cell is good
better for UE battery capacity
Evaluate the cell re-selection criteria
based on network planning parameters for cell re-selection
Execute cell re-selection
UE applies timer to check re-selection criteria before cell re-selection is triggered
rangeInterPci
startInterPci
physCellIdNcl
qOffCell
interFrqThrH
interFrqThrL
x 16
x 16
interTResEut
RL20 supports idle mode mobility from LTE to WCDMA
This is inter-RAT cell reselection from LTE to WCDMA
Inter-RAT cell reselection from WCDMA to LTE is supported in later release
Similar procedure to LTE interfrequency cell reselection (only differences presented here)
3GPP defines so called „priority layer“ concept
Parameters provided to UE controlling reselection to a frequency layer
rather than cell individual neighbour relationsships
32 frequency layers within WCDMA can be defined
16 x FDD, 16 x TDD
Frequency layer specific reselection parameters used
No individual cells can be specified – e.g. no scrambling code parameter
New parameter object introduced: UFFIM
UTRAN FDD/TDD Frequency Idle Mode Configuration
SIB6
LNBTS
LNCEL
UFFIM
tResUtra UTRA cell reselection timer
tResUtraSF (structured – 2 parameters)
utrResTiFHM The field t-ReselectionUTRA is multiplied by this factor if the UE is in the high mobility state as defined in 36.304.
utrResTiFMM The field t-ReselectionUTRA is multiplied by this factor if the UE is in the medium mobility state as defined in 36.304.
x 1
dlCarFrqUtra Contains the downlink frequency (Nd).
pMaxUtra UTRA maximum allowed transmit power.
qQualMinUtra This specifies the minimum required quality level in the cell in dB.
qRxLevMinUtra This specifies the minimum required RX level in the cell in dBm.
uCelResPrio Absolute priority of the UTRA carrier frequency.
utraFrqThrH This specifies the threshold used by the UE when reselecting towards a higher priority frequency X than the current serving frequency.
utraFrqThrL This specifies the threshold used in reselection towards the frequency X priority from a higher priority frequency.
Idle Mode Mobility LTE to WCDMA
SIB6
Idle Mode Mobility LTE to GERAN
SIB7
LNBTS
LNCEL
GFIM
GNFL
tResGerSF (structured 2 parameters)
GFIM Parameter Object:
gCelResPrio Absolute priority of the GERAN carrier frequency
gerArfcnVal Each ARFCN value explicitly listed
gerFrqThrH GERAN inter-frequency threshold high
gerFrqThrL GERAN inter-frequency threshold low
gnflId GERAN neighbour frequency configuration identifier
nccperm NCC permitted bitmap
SIB7
x 16
How GSM BCCH Frequencies can be presented in LTE SIB7:
2 different Priority Layers defined in example below:
a) ARFCN 15 – 47
b) ARFCN 81 – 102
For SrxLev calculation of GERAN target cell, UE needs minimum required level of neighbour frequency layer:
15
ARFCN
47
81
102
bandInd
Indicator to distinguish the GERAN frequency band in case of ARFCN values associated with either GSM 1800 or GSM 1900 carriers
GNFL; 0 (gsm1800), 1 (gsm 1900); -
qRxLevMinGer
hrpdArfcn the carrier frequency within a CDMA2000 Band.
hrpdCellId the CDMA "Physical cell identity".
tResHrpd CDMA2000 HRPD cell reselection timer
Idle Mode Mobility LTE to CDMA2000
SIB8
tResHrpdSF (structured – 2 parameters)
hrpResTiFHM The field t-ReselectionHrpd is multiplied by this factor if the UE is in the high mobility state
hrpResTiFMM The field t-ReselectionHrpd is multiplied by this factor if the UE is in the medium mobility state
hrpdBdClList (structured – 4 parameters)
hrpdBdClBcl Identifies the CDMA2000 HRPD Frequency Band in which the CDMA2000 Carrier can be found
hrpdCResPrio Absolute priority of the Bandclass of CDMA2000 HRPD
hrpdFrqThrH specifies the high threshold used in reselection towards CDMA2000 HRPD
hrpdFrqThrL specifies the low threshold used in reselection towards CDMA2000 HRPD
Idle Mode Mobility LTE to CDMA2000
SIB8
Handovers in LTE are:
Hard handovers: resources are prepared in the target cell before the UE is commanded to move to the target cell
Lossless: Packets are forwarded from the source to the target.
Network controlled: The target cell is selected by the network not by the UE. The handover control is in the e-UTRAN not in the Core network
UE-assisted: Measurements are made and reported by the UE to the network although it is the network (eNodeB) which triggers those measurements
Late path switch: Only when the inter eNodeB handover is successful, the packet core is involved (X2 required)
Intra-LTE (or Intra-RAT) handovers:
Intra frequency handovers, that is, handovers within the same frequency band. There are two scenarios:
Intra-eNodeB handover (i.e. inter sector)
Inter-eNodeB handover (i.e. inter site)
Inter e-NodeB HO can happen via the X2 interface or via the S1 interface (supported in RL20).The downlink data forwarding over X2 is applied for lossless data path switching.
Inter-frequency handovers that allow service continuity for LTE deployments in different frequency bands and also for LTE deployments within one frequency band but with different centre frequencies. Currently supported in RL20
Handover Types
Inter-RAT handovers:
These are the handovers to other radio access technologies (RAT) to provide continuous PS coverage:
LTE HO to/from WCDMA
LTE HO to/from GSM
LTE HO to/from HRPD (3GPP2)
Inter-RAT handover from WCDMA to LTE is not supported yet (RU 20 ...)
RSRP and RSRQ as event-triggering & reporting quantity
Resulting configurable events for reporting to E-UTRAN
Event A2/A1: Serving cells RSRP down/upcrossing certain RSRP threshold
Event A3: Neighbor cell’s RSRP is a predefined offset better than serving cell’s RSRP
Event A5: Serving cell’s RSRP downcrossing certain threshold, while neighbor cell’s RSRP upcrossing an other threshold
RSRP
If UE supports event A5, A5 event-triggered measurement
to monitor serving cell’s RSRP downcrossing Th3 (or Th3_InterFreq) while a neighbor’s RSRP upcrossing Th3a (or Th3a_InterFreq)
Redirect trigger: A2 event-triggered measurement
to monitor serving cell’s RSRP downcrossing Th4
Th4
Th3
Th3a
Only serving cell measurements. No neighbor measurements, and no reporting when above Th1.
When below Th1, start intra frequency neighbor measurement
RSRP (reported)
Th3 < Th3a
Th3_InterFreq < Th3a_InterFreq
Th2a
(Th3a_InterFreq)
(Th3_InterFreq)
LNCEL: threshold1 defines the absolute RSRP level for UE
intra-frequency measurement activation and de-activation
RSRP of
serving cell
UE does not measure nor report intra-frequency neighbor list
UE measures intra-frequency neighbor list and reports A3 or A5 if respective condition(s) are met
140 dBm
Absolute power level: -140 dBm + threshold1
Example: if threshold 1 = 55dB -> RSRP = -140dBm + 55 dB = -85 dBm
LNCEL: threshold2InterFreq defines the absolute RSRP level for UE inter-frequency measurement activation
RSRP of
serving cell
time
threshold2InterFreq
UE measures inter-frequency neighbors and reports A3 or A5 if respective condition(s) are met
140 dBm
LNCEL; 0ms..5120ms; -; -
a2TimeTo Trigger
LNCEL: threshold2a defines the absolute RSRP level for UE inter-frequency measurement de-activation
RSRP of
serving cell
LNCEL; 0..5120ms; -; -
a1TimeTo Trigger
Better Cell Handover
Better Cell Handover aims to keep the UE always on best cell
(measured by RSRP)
Event A3 defines relative offset LNCEL: a3-offset
Timer to Trigger LNCEL: a3-TimeToTrigger
Reporting Interval LNCEL: a3-ReportInterval
Better Cell Handover can be enabled / disabled:
enableBetterCellHo
RSRP at serving cell + a3Offset < RSRP at neighbor cell
A3 condition met
reporting condition met
LNCEL; -15..15dB; 0.5dB; - ; ; 4 dB
The actual value is the parameter value multiplied by 0.5 dB -> 4*0.5 = 2dB
a3TimeToTrigger
LNCEL; 0ms (0), 40ms (1), 64ms (2), 80ms (3), 100ms (4), 128ms (5), 160ms (6), 256ms (7), 320ms (8), 480ms (9), 512ms (10), 640ms (11), 1024ms (12), 1280ms (13), 2560ms (14), 5120ms (15); - ;
320 ms (8)
a3ReportInterval
LNCEL; 120ms (0), 240ms (1), 480ms (2), 640ms (3), 1024ms (4), 2048ms (5), 5120ms (6), 10240ms (7), 1min (8), 6min (9), 12min (10), 30min (11), 60min (12); - ; 1024 ms (4)
Coverage Handover
Coverage Handover is used to HO to other eUTRA cell in case
serving cell RSRP gets below an abolute threshold and (&&)
neighbour cell RSRP gets better than an abslolute threshold
Based on 3GPP reporting event „A5“:
3GPP „ThresholdEUTRA“ used to define absolute RSRP level for
serving cell: LNCEL: threshold3 and
neighbour cell: LNCEL: threshold3a
Reporting Interval LNCEL: a5-ReportInterval
Better Cell Handover can be enabled / disabled:
3GPP event A5 is UE optional; eNB knows from feature group bits
enableCovHo
RSRP at serving cell < threshold3
AND
LNCEL: a5TimeToTrigger: Time during which the specific criteria for the
measurement event must be met in order to trigger a measurement report
LNCEL: a5Report Interval: Time spacing between measurement reports
a5ReportInterval
LNCEL; 120ms (0), 240ms (1), 480ms (2), 640ms (3), 1024ms (4), 2048ms (5), 5120ms (6), 10240ms (7), 1min (8), 6min (9), 12min (10), 30min (11), 60min (12); - ; 240 ms (1)
threshold3
threshold3a
AND (&&)
threshold3a
threshold3
a5TimeToTrigger
LNCEL; 0ms (0), 40ms (1), 64ms (2), 80ms (3), 100ms (4), 128ms (5), 160ms (6), 256ms (7), 320ms (8), 480ms (9), 512ms (10), 640ms (11), 1024ms (12), 1280ms (13), 2560ms (14), 5120ms (15); -
threshold3
UE needs to support both bands and inter-frequency HO
Service continuity for LTE deployment in different frequency bands as well as for LTE deployments within one frequency band but with different center frequencies
The UE performs the measurements as configured by eNodeB: eutraCarrierInfo parameter specifies the inter-frequency band
eutraCarrierInfo
LNHOIF; 0..65535; 1; -
LNBTS; disabled (0), enabled (1); -; enabled (1)
Overview-LTE55 Intra LTE inter-frequency HO
This feature allows to hand over a UE in RRC_Connected mode between two LTE cells operating on different carriers (frequencies/bands).
The trigger for this procedure is:
better neighbor cell (frequency) coverage (A3, RSRP)
better neighbor cell (frequency) quality (A3, RSRQ)
limited serving cell (frequency) and sufficient neighbor cell (frequency) coverage (A5)
Measurement gaps
if needed then gap pattern 0 is used (6ms gap each 40ms)
actIfHo
LNBTS; disabled (0), enabled (1); -; enabled (1)
A3 event based Handover
Mn – hysA3OffsetRsr(p/q)InterFreq > Ms + a3OffsetRsr(p/q)InterFreq
Event A3 condition fullfilled,
UE sends measurement report
measQuantInterFreq
LNHOIF; RSRP, RSRQ; both; RSRP
Name
Range
Default
Description
-
Margin for RSRP for better cell HO. Used in measurement event type A3 where the event is triggered when the inter frequency neighbour cell becomes A3 offset better than the serving cell.
a3OffsetRsrqInterFreq (LNHOIF)
-
Margin for RSRQ for better cell HO. Used in measurement event type A3 where the event is triggered when the inter frequency neighbour cell becomes A3 offset better than the serving cell.
hysA3OffsetRsrp InterFreq (LNHOIF)
-
Related Hysteresis of Handover Margin for Better Cell Handover of Inter-Frequency
hysA3OffsetRsrq InterFreq (LNHOIF)
-
Related Hysteresis of Handover Margin for Quality Handover of Inter-Frequency
Name
Range
Default
Description
a3TimeToTriggerRsrpInterFreq (LNHOIF) a3TimeToTriggerRsrqInterFreq (LNHOIF)
0ms (0), 40ms (1), 64ms (2), 80ms (3), 100ms (4), 128ms (5), 160ms (6), 256ms (7), 320ms (8), 480ms (9), 512ms (10), 640ms (11), 1024ms (12), 1280ms (13), 2560ms (14), 5120ms (15), notUsed (16)
notUsed (16)
Time for which the specific criteria for the inter frequency measurement event A3 with quantity RSRP/RSRQ must be met in order to trigger a measurement report.
Name
Range
Default
Description
a3ReportIntervalRsrpInterFreq (LNHOIF) a3ReportIntervalRsrq InterFreq (LNHOIF)
120ms (0), 240ms (1), 480ms (2), 640ms (3), 1024ms (4), 2048ms (5), 5120ms (6), 10240ms (7), 1min (8), 6min (9), 12min (10), 30min (11), 60min (12), notUsed (13)
notUsed (13)
Defines the interval with which measurement reports are repeatedly sent as long as the specific criteria for the inter frequency measurement event A3 with quantity RSRP/RSRQ is met
Ms + hysThreshold3InterFreq < threshold3InterFreq
Name
Range
Default
Description
-
Threshold for RSRP of serving cell. If RSRP of serving cell smaller than Th3 and RSRP of inter frequency-neighbor cell greater Than Th3a then handover is triggered.
threshold3aInterFreq (LNHOIF)
-
Threshold for RSRP of serving cell. If RSRP of serving cell smaller than Th3 and RSRP of inter frequency-neighbor cell greater Than Th3a then handover is triggered.
hysThreshold3InterFreq (LNHOIF)
-
Related Hysteresis of Handover Margin for Coverage Handover of Inter-Frequency.
Name
Range
Default
Description
a5TimeToTriggerInterFreq (LNHOIF)
-
Time for which the specific criteria for the inter frequency measurement event A5 must be met in order to trigger a measurement report.
Name
Range
Default
Description
a5ReportIntervalInterFreq (LNHOIF)
-
Defines the interval with which measurement reports are repeatedly sent as long as the specific criteria for the inter frequency measurement event A5 is met.
S1 based handover is only applicable for inter-eNB handover
LTE inter-eNB handover can be executed without X2 interface usage in following scenarios:
No X2 connectivity existing between Source and Target eNB (or blacklisted by operator)
MME or S-GW change required when routing via Core Network
User data traffic and signaling messages are indirectly send via core nodes (MME and S-GW)
For UE there is no difference whether HO is executed via X2 or S1 interface
S1
S1
MME
SAE-GW
This is a basic S1 handover utilizing the same MME.
The source eNB configures the UE measurement procedures with an RRC RECONFIGURATION
2. UE is triggered to send MEASUREMENT REPORT to the source eNB. It can be event triggered or periodic
3. Source eNB makes handover decision based on UE report + load and service information
4. The source eNB issues a S1 HANDOVER REQUIRED to the MME
5. MME identifies Target eNB and sends a S1 HANDOVER REQUEST.
6. The target eNB performs admission control
RRC Reconfiguration Complete
7. HO Request Ack
The target eNB configures resources and sends a S1 HO REQUEST ACK.
Various GTP signalling is used to update S-GW and create forwarding tunnel.
MME forwards the HO information to the source eNB in a S1 HANDOVER COMMAND.
Source eNB generates the RRC RECONFIGURATION towards UE informing it to move to the target cell.
Source eNB starts forwarding packets to target eNB via S1 (Indirect Forwarding).
UE performs the final synchronisation to target eNB and accesses the cell via RACH procedure.
DL pre-synchronisation is obtained during cell identification and measurements.
Target eNB gives the uplink allocation and timing advance information.
9. HO Command
10. RRC Reconfiguration
13. UL allocation and timing advance
In order to achieve Lossless HO’s packets are forwarded from the source to the target.
Depending on each bearer's QoS profile, the eNodeB shall decide whether data forwarding should be applied to it during the handover or not.
The GTP-U message End Marker is used for ever EPS bearer which is subject to a HO.
The End Marker is an indication of the last DL T-PDU (i.e. user data SDU) to source eNB is expected from the EPC.
The end marker is a special GTP-U PDU which carries no data.
UE sends RRC RECONFIGURATION COMPLETE to target eNB.
The source eNB sends a eNB STATUS TRANSFER carrying PDCP status information towards the MME for relaying to the target eNB.
MME uses a MME STATUS TRANSFER to pass PDCP status information to target eNB.
The target eNB informs the MME that the handover has been successful using HANDOVER NOTIFICATION.
The MME informs the source eNB to release the UE context using a UE CONTEXT RELEASE COMMAND.
The source eNB confirms with a UE CONTEXT RELEASE COMPLETE.
Following S1 based handover, if the Tracking Area had changed, the UE performs a Tracking Area Update.
16. MME Status Transfer
20.
Intra-LTE handover via S1 (LTE54)
The intra-LTE handover functionality via S1 can be enabled / disabled via O&M for all cells of the eNodeB
Priority indicator between X2-HO & S1-HO
Interface specific blacklists (Operator can force a S1-based handover by blacklisting neighbour-cells for X2-based handover via O&M Configuration)
New MOC LNADLP introduced for operator defined S1 handover target cells
actLTES1Ho
prioTopoHO
Define priorities between the 3 topology options for intra LTE handover
LNBTS; all equal (0), intra eNB HO prior inter eNB HO (1), intra prior X2 prior S1 (2), low prio S1 (3); all equal (0)
blacklistTopo
Allow blacklisting for X2-Handover only other HO variants are still allowed
LNCEL; allEqual (0), onlyX2 (1); all equal (0)
lnAdlpId
LNADLP; 0,…,31;1 ; -
LNCEL; - ;- ; -
RRC connection release with redirect
In case serving cell coverage by RSRP is on lower end of
scale, eNB can redirect the call to other frequency layer or
other RAT – this is no handover !
3GPP event A2 is used to define an absolute threshold
LNCEL: threshold4 (3GPP: ThresholdUTRA)
Risk of loosing the signaling connection with UE due to bad coverage
Once UE sends event triggered measurement report A2
eNB sends RRC:rrcConnectionRelease with target RAT
information to UE
Redirect feature can be enabled on LNBTS level:
[..]
LNCEL: threshold4 defines the absolute RSRP level of serving
cell for eNB to trigger RRC connection release with redirection.
RSRP
time
threshold4
a2TimeToTriggerRedirect
LNCEL; 0ms (0), 40ms (1), 64ms (2), 80ms (3), 100ms (4), 128ms (5), 160ms (6), 256ms (7), 320ms (8), 480ms (9), 512ms (10), 640ms (11), 1024ms (12), 1280ms (13), 2560ms (14), 5120ms (15); - ; 256ms (7)
Target RAT for redirection can be defined on cell level:
LNBTS
LNCEL
REDRT
redirRat
REDRT; eutra (0), geran (1), utraFDD (2), cdma2000HRPD (3), cdma20001xRTT (4), utraTDD (5); -
Depending on REDRT: redirRAT parameter setting (prev. slide), target RAT parameters must be set in REDRT pars:
redirBandCdma - Specifies the cdma2000 band class
redirFreqCdma - Specifies the cdma2000 ARFCN
redirFreqEutra - Specifies the eUTRA frequency
redirFreqUtra - Specifies the UTRA frequency
redirGeranArfcnValueL - List of GERAN ARFCN values
redirGeranBandIndicator - Indicator to distinguish the GERAN frequency band
in case of ARFCN values associated with either GSM 1800 or
GSM 1900 carriers.
redirGeranStartingArfcn - The first ARFCN value in the set of GERAN ARFCNs in
the GERAN carrier frequencies list.
This feature introduces service-based redirection of multimode UE from E-UTRAN to CS capable cell (UTRAN or GERAN) whenever CS voice call is to be established
Required when there is no Conversational Voice support on LTE side
E-UTRAN coverage must be overlapped by GERAN or UTRAN coverage
Both mobile originated and mobile terminated scenarios are supported
EPC must support CS inter-working for mobility management and paging
actCSFBRedir
csFallBPrio
REDRT; 1,…,6; 1 ; -
REDRT; 0,…,5; 1 ; -
Redirection by RRC connection release message with a RedirectedCarrierInfo Information Element that enforces the UE to search for any cell first at the highest priority UTRA carrier or within BCCH carrier set for GSM
E-UTRAN coverage must be overlapped by GERAN or UTRAN coverage
Having terminated CS call, the UE may either stay in current RAT or go back to E-UTRAN using existing mechanisms
PS services may be provided in parallel to the CS call depending on the DTM capability of the UE and target RAT
Evolved Packet Core (EPC) must support CS inter-working for mobility management and paging
SGs interface between MME and MSC server is needed
interworking between SGSN and MME and PDN-GW is realized via pre-Rel.8 Gn interface
CS domain must support CS Fallback, i.e. MSC must support SGs interface to MME

Documents

07 LTE Mobility Mngmnt GC