Lte IRAT Ericsson

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LTE Inter RAT Handover

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Introduction

•

• IRAT stands for Inter Radio Access Technology where UE can handoverIRAT stands for Inter Radio Access Technology where UE can handover

between two differen

between two different access t access technologies.technologies.

•

• In the current ATT project we are targeting IRAT’s between LTE & UMTS.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 primaryIRAT triggers on the basis of two events i.e. RSRP & RSRQ where primary

trigger is RSRP and secondary trigger is RSRQ.

•

• In AIn ATT project TT project the trigger value has the trigger value has been setbeen set – – for RSRP for RSRP & -19.5db for RSRQ.& -19.5db for RSRQ.

•

• It is not necessary that every time we will observe IRAT to be triggered at -It is not necessary that every time we will observe IRAT to be triggered at

-110dBm due to the

110dBm due to the HysteHysteresis that we resis that we set.set.

•

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

•

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Introduction

•

• IRAT stands for Inter Radio Access Technology where UE can handoverIRAT stands for Inter Radio Access Technology where UE can handover

between two differen

between two different access t access technologies.technologies.

•

• In the current ATT project we are targeting IRAT’s between LTE & UMTS.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 primaryIRAT triggers on the basis of two events i.e. RSRP & RSRQ where primary

trigger is RSRP and secondary trigger is RSRQ.

•

• In AIn ATT project TT project the trigger value has the trigger value has been setbeen set – – for RSRP for RSRP & -19.5db for RSRQ.& -19.5db for RSRQ.

•

• It is not necessary that every time we will observe IRAT to be triggered at -It is not necessary that every time we will observe IRAT to be triggered at

-110dBm due to the

110dBm due to the HysteHysteresis that we resis that we set.set.

•

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

•

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Lte mobility

•

• The LTE mobility can be divided into “IntraThe LTE mobility can be divided into “Intra--LTE mobility” and “InterLTE mobility” and “Inter-

-LTE mobility” (inter

LTE mobility” (inter-working with 2G/3G and CDMA 2000).-working with 2G/3G and CDMA 2000).

•

• It can It can be further divided be further divided into RRC_CONNECTED and RRC_IDLE modeinto RRC_CONNECTED and RRC_IDLE mode

mobility. IRAT-HO (Inter Radio Access Technology Handover) is one

type of “Inter

type of “Inter--LTE mobility” in RRC_CONNECTED mode while cellLTE mobility” in RRC_CONNECTED mode while cell

reselection is referred to as RRC_IDLE mode mobility.

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Selection procedure

• Like UMTS, LTE also follows to Selection Criterion S for cell selection. • Cell Selection criterion is fulfilled when

• where

• Where

Pcompensation = max (PEMAX – PPowerClass, 0) dB

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)

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

3GPP Ericsson Pcompensation pMaxServingCell

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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

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Parameter calculation

• Q rxlevmin (RSRP) is only considered here.

• Neglecting Q rxlevminoffset and Pcompensationfrom the equation.

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

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RESELECTION process

in lte BASED ON CELL

RESELECTION

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Reselection based on cell

priorities

• 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 inter-RAT frequencies that are given in system information and for which the UE has a priority provided.

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Intra-Freq and Equal priority If

Cell Reselection Criterion

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

• Where

• 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

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Parameter calculation

• 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)

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Measurement rules for Cell

Reselection

•

For E-UTRAN Inter-frequency or Inter-RAT frequency cell

Measurements:-• 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 Srxlev < 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

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Parameter calculation

• If Srxlev< SnonIntraSearch

• Qrxlevmeas < Qrxlevmin + SnonintraSearch

< -120 + 10 < - 110 dBm

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E-UTRAN IF and IRAT Cell

Reselection Criterion

• 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 Srxlev < ThreshServingLow and a cell of a lower

priority RAT/ frequency fulfils Srxlev > ThreshXLow during a time interval

TreselectionRAT;

3GPP Ericsson

TreselectionRAT TreselectionEUTRA (for LTE target frequency) TreselectionRAT TreselectionUTRA (for UMTS target frequency)

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High prio. LTE to Low prio.

UMTS

Time Starts measuring IF or IRAT freq T reselectionUTRA Signal strength

Threshxlow (UMTS)

Snonintrasearch(LTE)

Threshservinglow (LTE)

LTE (High priority) signal UMTS (Low priority) signal

LTE (High priority) signal

C o n d i t _i o n 1 C o n d i t _i o n 2 Satisfied Case 1 Reselection to UMTS

Qrxlevmin (LTE or UMTS)

Signal strength

Reselection to UMTS

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High prio. LTE to Low prio.

UMTS

Time Starts measuring IF or IRAT freq TreselectionUTRA Signal strength

Threshxlow (UMTS)

Threshservinglow (LTE)

LTE (High priority) signal UMTS (Low priority) signal

LTE (High priority) signal

C o n d i t _i o n 1 C o n d i t _i o n 2 Satisfied Case 2 Reselection to UMTS

Qrxlevmin (LTE or UMTS)

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Parameter calculation

• If Srxlev (serving LTE)< ThreshServingLow

• Qrxlevmeas < Qrxlevmin +ThreshServingLow < - 120 + 8

< - 112 dBm

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

• Qrxlevmeas > Qrxlevmin +ThreshxLow > -119 + 6

> -113 dBm

• For TreselectionRAT (2 Sec)

Parameter Tech MO Class Value Unit Range Resolution

Qrxlevmin LTE EUtranCellFDD-ETRANFreqRelation -120 dBm -140..-44 1

Qrxlevmin LTE EUtranCellFDD-UTRANFreqRelation -119 dBm -119..-25 1

ThreshXLow LTE EUtranCellFDD-ETRANFreqRelation 6 dB 0..62 2

TreselectionEutra LTE EUtranCellFDD-ETRANFreqRelation 2 sec 0..7 1

TreselectionUtra LTE SIB6 struct in the MO c lass EUtranCellFDD 2 sec 0..7 1

ThreshXLow LTE EUtranCellFDD-UTRANFreqRelation 6 dB 0..62 2

Thres hServingLow LTE SIB3 struct in the MO c lass EUtranCellFDD ₈_dB _0..62 ₂

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E-UTRAN if and IRAT Cell

Reselection Criterion -

Continued

• 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 TreselectionRAT; and

• More than 1 second has elapsed since the UE camped on the current

serving cell.

3GPP Ericsson

TreselectionRAT TreselectionEUTRA (for LTE target frequency) TreselectionRAT TreselectionUTRA (for UMTS target frequency)

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low prio. LTE to High prio.

UMTS

Time Starts measuring

IF or IRAT freq TreselectionRAT Signal strength

ThreshxHigh (UMTS)

UMTS (High priority) signal

LTE (Low priority) signal

Condition Satisfied

Case 1

Reselection to UMTS

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low prio. LTE to High prio.

UMTS

Time Starts measuring IF or IRAT freq TreselectionRAT Signal strength

ThreshxHigh (UMTS)

UMTS (High priority) signal

LTE (Low priority) signal

Case 2

Condition Satisfied

Reselection to UMTS

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Parameter calculation

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

• Qrxlevmeas > Qrxlevmin +ThreshxHigh > -119 + 6

> -113 dBm

• For TreselectionRAT (2 Sec)

Qrxlevmin LTE EUtranCellFDD-ETRANFreqRelation -120 dBm -140..-44 1

Qrxlevmin LTE EUtranCellFDD-UTRANFreqRelation -119 dBm -119..-25 1

ThreshXhigh LTE EUtranCellFDD-ETRANFreqRelation 6 dB 0..62 2

TreselectionEutra LTE EUtranCellFDD-ETRANFreqRelation 2 sec 0..7 1

TreselectionUtra LTE SIB6 struct in the MO class EUtranCellFDD ₂_{sec 0..7} ₁

ThreshXhigh LTE EUtranCellFDD-UTRANFreqRelation 6 dB 0..62 2

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SIb6

•

Parameters for reselection towards WCDMA is supplied

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UMTS TO LTE RESELECTION BASED ON CELL

RESELECTION PRIORITIES

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Reselection from UMTS to LTE

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

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Reselection for IRAT E-UTRA

cells

with given Absolute Priorities

•

Two different mechanisms for cell reselection are supported in

WCDMA:

• 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

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Reselection for IRAT E-UTRA

cells

with given Absolute Priorities

• 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.

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Measurement rules for iRAT

(e-UTRA Cells) with given Absolute Priorities

•

The rate of these measurements may vary depending on whether

S

rxlev

and S

qual

of the serving cell are above or below S

prioritysearch1

and

S

prioritysearch2.

•

If S

rxlevServingCell

> S

prioritysearch1

and/or S

qualServingCell

> S

prioritysearch2

then

the UE shall search for E-UTRA layers of higher priority at least every

T

higher_priority_search.

•

If S

rxlevServingCell

<= S

prioritysearch2

or S

qualServingCell

<= S

prioritysearch2

the UE

shall search and measure E-UTRA frequency layers of higher or lower

priority in preparation for possible reselection.

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.

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Parameter calculation

• If SrxlevServingCell <= Sprioritysearch1

• Qrxlevmeas < Qrxlevmin +Sprioritysearch1

< -119 + 16 < -103 dBm

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Reselection for IRAT E-UTRA

cells

with given Absolute Priorities - Continued

•

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

• the SrxlevnonServingCell of a cell on an evaluated higher absolute priority layer is greater than

Threshhigh during a time interval Treselection

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Parameter calculation

• For Low priority UMTS cell  High priority LTE cell

• Reselection occurs if SrxlevnonServingCell> Threshhighfor Treselection (2sec)

Q rxlevmeas > Q rxlevmin + Threshhigh

> -120 + 12 > -108 dBm

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Reselection for IRAT E-UTRA

cells

with given Absolute Priorities - Continued

•

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

• SrxlevServingCell < Threshserving,low or SqualServingCell < 0 and the SrxlevnonServingCell of a cell on an

evaluated lower absolute priority layer is greater than ThreshLow during a time interval Treselection

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Parameter calculation

• For High priority UMTS cell  Low priority LTE cell

• Reselection occurs if SrxlevServingCell<Threshserving,low

Q rxlevmeas< Q rxlevmin + Threshserving,low

< -119 + 4

< -115 dBm

• And SrxlevnonServingCell> Threshlow

Q rxlevmeas> Q rxlevmin + Threshlow

> -120 + 14 > -106 dBm

Threshhigh WCDMA UtranCell-ETRANFreqRelation 12 dB 0..62 2

absPrioCellRes.ThreshServingLow WCDMA UTRANCell 4 dB 0..62 2

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For high priority LTE and low

priority UMTS

• UE starts its measurements when Srxlev < SnonIntraSearch

Q rxlevmeas < Q rxlevmin + SnonintraSearch

< -120 + 10 < - 110 dBm

• UE reselects to UMTS if Srxlev (serving LTE)< ThreshServingLow

Q rxlevmeas < Q rxlevmin + ThreshServingLow

< - 120 + 8 < - 112 dBm

• And if Srxlev (non-serving IF LTE or IRAT)> ThreshXLow for TreselectionRAT (2 Sec)

Q rxlevmeas > Q rxlevmin + ThreshxLow

> -119 + 6 > -113 dBm

• UE in UMTS system starts its LTE measurements if Srxlev (ServingCell) <= Sprioritysearch1

Q rxlevmeas < Q rxlevmin + Sprioritysearch1

< -119 + 16 < -103 dBm

• UE reselects to LTE if Srxlev (nonServingCell) > Threshhigh for Treselection (2sec)

Q rxlevmeas > Q rxlevmin+ Threshhigh

> -120 + 12 > -108 dBm

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For low priority LTE and high

priority UMTS

• UE starts its measurements when Srxlev < SnonIntraSearch

Q rxlevmeas < Q rxlevmin + SnonintraSearch

< -120 + 10 < - 110 dBm

• UE reselects to UMTS if Srxlev (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 SrxlevServingCell <= Sprioritysearch1

Q rxlevmeas < Q rxlevmin + Sprioritysearch1

< -119 + 16 < -103 dBm

• UE reselects to LTE if Srxlev (ServingCell) < Threshserving,low

Q rxlevmeas < Q rxlevmin + Threshserving,low

< -119 + 4 < -115 dBm

• And SrxlevnonServingCell > Threshlow

Q rxlevmeas > Q rxlevmin + Threshlow

> -120 + 14 > -106 dBm

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