Lte IRAT Ericsson

LTE Inter RAT Handover

Introduction •

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IRAT stands for Inter Radio Access Technology where UE can handover between two different different access technologies. In the current ATT project we are targeting IRAT’s between LTE & UMTS.

IRAT triggers on the basis of two events i.e. RSRP & RSRQ where primary trigger is RSRP and secondary trigger is RSRQ. In ATT ATT project the trigger value has been set – for RSRP & -19.5db for RSRQ. It is not necessary that every time we will observe IRAT to be triggered at 110dBm due to the Hyste Hysteresis resis that we set.

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In absence of UMTS network one can see IRAT IRAT happening to the GSM

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Network.

Introduction •

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IRAT stands for Inter Radio Access Technology where UE can handover between two different different access technologies. In the current ATT project we are targeting IRAT’s between LTE & UMTS.

IRAT triggers on the basis of two events i.e. RSRP & RSRQ where primary trigger is RSRP and secondary trigger is RSRQ. In ATT ATT project the trigger value has been set – for RSRP & -19.5db for RSRQ. It is not necessary that every time we will observe IRAT to be triggered at 110dBm due to the Hyste Hysteresis resis that we set.

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In absence of UMTS network one can see IRAT IRAT happening to the GSM

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Network.

Lte mobility •

The LTE mobility can be divided into “Intra-LTE mobility” and “InterLTE mobility” (inter-working with 2G/3G and CDMA 2000).

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It can be further divided into RRC_CONNECTED and RRC_IDLE mode mobility. IRAT-HO (Inter Radio Access Technology Handover) is one type of “Inter-LTE mobility” in RRC_CONNECTED mode while cell

reselection is referred to as RRC_IDLE mode mobility.

Flow chart- irat handover

Call flow irat

Selection procedure •

Like UMTS, LTE also follows to Selection Criterion S for cell selection.

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Cell Selection criterion is fulfilled when

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where

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Where Pcompensation = max (PEMAX – PPowerClass, 0) dB

3GPP Pcompensation

POWER CLASS

MAXIMUM OUTPUT POWER

Power class 1

33dBm (2W)

Power class 2

27dBm (0.5 W)

Power class 3

24dBm (0.25 W)

Power class 4

21dBm (0.125 W)

Ericsson pMaxServingCell At this moment we wouldn’t be considering Squal in AT&T Networks

Selection procedure - Continued

The signalled values Q r x l e v m i n o f f s e t   and Q q u a l m i n o f f s e t  are only applied when a cell is evaluated for cell selection as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN 

Parameter calculation •

Q rxlevmin (RSRP) is only considered here.

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Neglecting Q rxlevminoffset and Pcompensation from the equation.

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 UE is able to select eUTRAN cell from where it is receiving at least -120dBm signal strength.

RESELECTION process in lte BASED ON CELL RESELECTION PRIORITIES

Reselection based on cell priorities •

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Priority values in the range [0..7] are used, where 0 indicates lowest priority and 7 indicates highest priority. Equal priorities between different RATs are not supported All parameters based on cell reselection priority are broadcasted on SIB5, SIB6,SIB7 and SIB8 for Inter LTE freq, UMTS, GSM and CDMA respectively. UE performs cell reselection evaluation for E-UTRAN frequencies and interRAT frequencies that are given in system information and for which the UE has a priority provided. UE doesn’t consider any black listed cells as candidate for cell reselection.

Intra-Freq and Equal priority If Cell Reselection Criterion •

Ranking Criterion applies to both Intra frequency cells and Inter frequency cells with equal priorities.

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Where

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  Qoffsetfrequency:- Frequency specific offset for equal priority E -UTRAN Frequencies

In all cases, the UE shall reselect the new cell, only if the following conditions are met: •

New cell is better ranked than the serving cell during a time interval TreselectionEUTRA;

Parameter calculation •

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Rs = Q rxlevmeas + Q Hyst =

- 113 + 4

=

- 109 dBm

Rn = Q rxlevmeas – Q offset =

-107 – 0

=

-107 dBm

If Rn > Rs, for TreselectionEUTRA (2 Sec)

All the parameter values are calculation purpose only. They are not golden parameter values

Measurement rules for Cell Reselection •

For E-UTRAN Inter-frequency or Inter-RAT frequency cell Measurements:•

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If Srxlev > SnonIntraSearchP and Squal > SnonIntraSearchQ  then the UE shall search for inter-frequency and Inter-RAT layers of higher priority at least every Thigher_priority_search If the serving cell fulfils S rxlev < SnonIntraSearchP and Squal < SnonIntraSearchQ , the UE may choose to perform measurements of E-UTRAN inter-frequencies or inter-RAT frequency cells of equal or lower priority.

NOTES: The UE shall search every layer of higher priority at least every Thigher_priority_search = (60 * Nlayers) seconds, where Nlayers is the total number of configured higher priority E-UTRA, UTRA FDD, UTRA TDD, CDMA2000 1x and HRPD carrier frequencies and is additionally increased by one if one or more groups of GSM frequencies is configured as a higher priority.

At this moment we wouldn’t be considering Squal in AT&T Networks Ericsson doesn’t support SnonIntraSearchQ at this time

Parameter calculation •

If Srxlev < SnonIntraSearch

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Qrxlevmeas < Qrxlevmin + SnonintraSearch <

-120 + 10 <

- 110 dBm

E-UTRAN IF and IRAT Cell Reselection Criterion •

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For High priority LTE cell to Low priority LTE inter frequency or Inter-RAT frequency If ThreshServingLow is provided in SystemInformationBlockType3, cell reselection would perform if •

The serving cell fulfils S rxlev < ThreshServingLow and a cell of a lower priority RAT/ frequency fulfils S rxlev > ThreshXLow during a time interval TreselectionRAT ;

3GPP

Ericsson

TreselectionRAT

TreselectionEUTRA (for LTE target frequency)

TreselectionRAT

TreselectionUTRA (for UMTS target frequency)

High prio. LTE to Low prio. UMTS Case 1 Signal strength

UMTS (Low priority) signal Reselection to UMTS

Snonintrasearch(LTE) Threshservinglow (LTE) Threshxlow (UMTS) LTE (High priority) signal

Qrxlevmin  (LTE or UMTS)

Time Starts measuring IF or IRAT freq

 C   o n  d  i    t   i    o n 1 

 C   o n  d  i    t   i    o n 2 

Satisfied

TreselectionUTRA

High prio. LTE to Low prio. UMTS Case 2 Signal strength

UMTS (Low priority) signal

TreselectionUTRA Reselection to UMTS

Snonintrasearch(LTE) Threshservinglow (LTE) Threshxlow (UMTS) LTE (High priority) signal

Qrxlevmin  (LTE or UMTS)

Time Starts measuring IF or IRAT freq

 C   o n  d  i    t   i    o n 1 

 C   o n  d  i    t   i    o n 2 

Satisfied

Parameter calculation •

If Srxlev (serving LTE)< ThreshServingLow •

Qrxlevmeas < Qrxlevmin + ThreshServingLow

<

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And if Srxlev (non-serving IF LTE or IRAT)> ThreshXLow •

Qrxlevmeas > Qrxlevmin + ThreshxLow

> > •

- 120 + 8 < - 112 dBm

-119 + 6 -113 dBm

For TreselectionRAT (2 Sec)

Parameter Qrxlevmin Qrxlevmin ThreshXLow TreselectionEutra TreselectionUtra ThreshXLow Thres hServingLow

Tech LTE LTE LTE LTE LTE LTE LTE

MO Class EUtranCellFDD-ETRANFreqRelation EUtranCellFDD-UTRANFreqRelation EUtranCellFDD-ETRANFreqRelation EUtranCellFDD-ETRANFreqRelation SIB6 struct in the MO c lass EUtranCellFDD

EUtranCellFDD-UTRANFreqRelation SIB3 struct in the MO c lass EUtranCellFDD

All the parameter values are calculation purpose only. They are not golden parameter values

Value -120 -119 6 2   2 6   8

Unit dBm dBm dB sec sec dB dB

Range -140..-44 -119..-25 0..62 0..7 0..7 0..62 0..62

Resolution 1 1 2 1 1 2 2

E-UTRAN if and IRAT Cell Reselection Criterion -

Continued

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For Low priority LTE cell to High priority LTE inter frequency or Inter-RAT frequency If ThreshServingLow is provided in SystemInformationBlockType3, cell reselection would perform if A cell of a higher priority Inter RAT/ frequency fulfils Srxlev > ThreshXHigh during a time interval T reselectionRAT ; and More than 1 second has elapsed since the UE camped on the current serving cell. •

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3GPP

Ericsson

TreselectionRAT

TreselectionEUTRA (for LTE target frequency)

TreselectionRAT

TreselectionUTRA (for UMTS target frequency)

low prio. LTE to High prio. UMTS Case 1 Signal strength UMTS (High priority) signal

Reselection to UMTS

Snonintrasearch(LTE)

ThreshxHigh (UMTS) LTE (Low priority) signal

Time Starts measuring IF or IRAT freq

TreselectionRAT

Condition Satisfied

low prio. LTE to High prio. UMTS Case 2 Signal strength UMTS (High priority) signal

Snonintrasearch(LTE)

Reselection to UMTS

ThreshxHigh (UMTS) LTE (Low priority) signal

Time TreselectionRAT Starts measuring IF or IRAT freq Condition Satisfied

Parameter calculation •

If Srxlev (non-serving IF LTE or IRAT) > ThreshXHigh •

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Qrxlevmeas > Qrxlevmin + ThreshxHigh

>

-119 + 6

>

-113 dBm

For TreselectionRAT (2 Sec)

Parameter Qrxlevmin Qrxlevmin ThreshXhigh TreselectionEutra TreselectionUtra ThreshXhigh

Tech LTE LTE LTE LTE LTE LTE

MO Class EUtranCellFDD-ETRANFreqRelation EUtranCellFDD-UTRANFreqRelation EUtranCellFDD-ETRANFreqRelation EUtranCellFDD-ETRANFreqRelation SIB6 struct in the MO class EUtranCellFDD

EUtranCellFDD-UTRANFreqRelation

All the parameter values are calculation purpose only. They are not golden parameter values

Value -120 -119 6 2   2 6

Unit dBm dBm dB sec sec dB

Range -140..-44 -119..-25 0..62 0..7 0..7 0..62

Resolution 1 1 2 1 1 2

SIb6 •

Parameters for reselection towards WCDMA is supplied through SIB 6.

UMTS TO LTE RESELECTION BASED ON CELL RESELECTION PRIORITIES

Reselection from UMTS to LTE •

Reselection from UMTS to LTE is only supported for UEs in idle mode and URA_PCH mode

Reselection for IRAT E-UTRA cells withgivenAbsolutePriorities •

Two different mechanisms for cell reselection are supported in WCDMA: •

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Legacy (or ranking based) cell reselection. This mechanism applies for intra-frequency cell reselection and inter-frequency cell reselection within WCDMA as well as for cell reselection from WCDMA to GSM. Priority based cell reselection. This mechanism applies for cell reselection from WCDMA to LTE.

Both legacy based- and priority based cell reselection can be active at the same time. If both these criterion come up with two cells from two different technologies, ranking criterion applies on top of it.

Reselection for IRAT E-UTRA cells withgivenAbsolutePriorities •

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The LTE frequencies and the parameters for priority based cell reselection is sent on the broadcast channel in System Information Block type 19 (SIB19). If the UE detects a neighboring LTE cell with higher priority than the serving WCDMA cell it will attempt a cell reselection even if the measured signal strength is lower for the LTE cell compared to the WCDMA cell. The signal strength must however be above a minimum threshold. A maximum of 8 EARFCNs can be listed in SIB19. A maximum of 9 black listed cells per UTRAN cell can be used to speed up the cell reselection procedure in border areas if different operators use the same LTE frequencies.

Measurement rules for iRAT

(e-UTRA Cells)

withgivenAbsolutePriorities •

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The rate of these measurements may vary depending on whether Srxlev and Squal of the serving cell are above or below Sprioritysearch1 and Sprioritysearch2. If SrxlevServingCell > Sprioritysearch1 and/or SqualServingCell > Sprioritysearch2 then the UE shall search for E-UTRA layers of higher priority at least every Thigher_priority_search. If SrxlevServingCell  -120 + 12 > -108 dBm

Reselection for IRAT E-UTRA cells withgivenAbsolutePriorities-Continued •

For High priority UMTS cell to Low priority LTE Inter-RAT frequency •

SrxlevServingCell < Threshserving,low or SqualServingCell < 0 and the S rxlevnonServingCell of a cell on an evaluated lower absolute priority layer is greater than ThreshLow during a time interval Treselection

Qrxlevmin  (LTE or UMTS)

Parameter calculation •

For High priority UMTS cell  Low priority LTE cell •

Reselection occurs if S rxlevServingCell < Threshserving,low Q rxlevmeas Threshlow Q rxlevmeas > Q rxlevmin + Threshlow > -120 + 14 > -106 dBm

Parameter Tech Threshhigh WCDMA absPrioCellRes.ThreshServingLow WCDMA

MO Class UtranCell-ETRANFreqRelation UTRANCell

All the parameter values are calculation purpose only. They are not golden parameter values

Value 12 4

Unit dB dB

Range 0..62 0..62

Resolution 2 2

For high priority LTE and low priority UMTS •

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UE starts its measurements when S rxlev < SnonIntraSearch Q rxlevmeas < Q rxlevmin + SnonintraSearch < -120 + 10 < - 110 dBm UE reselects to UMTS if S rxlev (serving LTE)< ThreshServingLow Q rxlevmeas < Q rxlevmin + ThreshServingLow < - 120 + 8 < - 112 dBm •

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And if Srxlev (non-serving IF LTE or IRAT)> Thresh XLow for TreselectionRAT  (2 Sec) Q rxlevmeas > Q rxlevmin + ThreshxLow > -119 + 6 > -113 dBm

UE in UMTS system starts its LTE measurements if S rxlev (ServingCell)  Threshhigh for Treselection (2sec) Q rxlevmeas > Q rxlevmin + Threshhigh > -120 + 12 > -108 dBm

All the parameter values are calculation purpose only. They are not golden parameter values

For low priority LTE and high priority UMTS •

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UE starts its measurements when S rxlev < SnonIntraSearch Q rxlevmeas < Q rxlevmin + SnonintraSearch < -120 + 10 < - 110 dBm UE reselects to UMTS if S rxlev (non-serving IF LTE or IRAT) > ThreshXHigh for TreselectionRAT  (2 Sec) Q rxlevmeas > Q rxlevmin + ThreshxHigh > -119 + 6 > -113 dBm UE in UMTS system starts its LTE measurements if S rxlevServingCell  Threshlow Q rxlevmeas > Q rxlevmin + Threshlow > -120 + 14 > -106 dBm

All the parameter values are calculation purpose only. They are not golden parameter values

Requirements