functionality of intra-frequency handover

7/21/2019 Functionality of Intra-frequency Handover

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2/4/2558 Functionality of intra-frequency handover

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Functionality of intra-frequency handover

Intra-frequency handovers can be soft or hard handovers. The vast majority of intra-frequency handovers

in the Wideband Code Division Multiple Access (WCDMA)radio access network are soft handovers. The

following sections describe the algorithms involved in intra-frequency soft and hard handover. For the

signaling procedures involved, see Soft handover signalingand Intra-frequency hard handover signaling.

Functionality of soft handover

The handover decision algorithm of the Radio Network Controller (RNC)for intra-frequency handover is

based on the event-triggered measurement reports. When in active mode, the 3G User Equipment (UE)

continuously measures the Common Pilot Channel (CPICH)of the serving and neighboring cells

(indicated by the RNC) on the current carrier frequency. The measurement quantity is CPICH Ec/No

(received energy per chip divided by the power density in the band, that is, CPICH RSCP/UTRA Carrier

RSSI). The UE compares the measurement results with handover thresholds, which have been provided

by the RNC, and sends a measurement report to the RNC when the handover thresholds are fulfilled.

Filtering of CPICH Ec/No measurements is controlled with the RNP parameter EcNoFilterCoefficient.Based on the measurement report, the RNC orders the UE to add, replace or remove cells from its

active set, that is the set of cells participating in soft handover. The RNC limits the number of cellsparticipating in soft handover. The maximum size of the active set is three cells. When detected set

reporting is enabled in one or more active set cells, handover control takes into account the detected set

reporting quantities for soft handover decisions.

The handover decision algorithm of the RNC is fairly straightforward for soft (and softer) handover: the

algorithm accepts practically everything the UE suggests according to the measurement reporting

events.

The handover control of the RNC contains the following measurement reporting events and mechanisms

for modifying measurement reporting behavior:

reporting event 1A for adding cells to the active set

reporting event 1B for deleting cells from the active setreporting event 1C for replacing cells in the active set

event-triggered periodic intra-frequency measurement reporting

time-to-trigger mechanism for modifying measurement reporting behavior

cell individual offsets for modifying measurement reporting behavior

mechanism for forbidding a cell to affect the reporting range

reporting events 6F and 6G for deleting cells from the active set

When the channel type is DCH, the intra-frequency measurements are controlled by the intra-frequency

measurement control (FMCS) parameters of the best (according to CPICH Ec/No) active set cell

controlled by the serving RNC. During anchoring, if the Inter-frequency Handover over Iurand I-BTS

Sharingfeatures are disabled in the serving RNC, the intra-frequency measurements are controlled by

the FMCS parameters of the last serving RNC cell. The handover control of the RNC reselects the best

active set cell after each active set update procedure. The handover control of the RNC updates the intra-

frequency measurement control param ters to the UE if the FMCS parameter set changes along with the

best active set cell. In addition, the handover control of the RNC updates the intra-frequency

measurement control parameters to the UE if the FMCS parameter set changes when the service type

(RT/NRT/standalone SRB) or the channel type (DCH/HSDPA) changes during the RRC connection. The

FMCS parameter sets are identified on the servide type-by-type basis with the following parameters.

The RtFmcsIdentifierparameter identifies the measurement control parameter set (FMCS object)which controls the intra-frequency measurements of a user having a real time (RT) radio bearer

allocated on DCH.

The NrtFmcsIdentifierparameter identifies the measurement control parameter set (FMCSobject) which controls the intra-frequency measurements of a user having a non-real time (NRT)

radio bearer allocated on DCH.The SRBDCHFmcsIdparameter identifies the measurement control parameter set (FMCS object)which controls the intra-frequency measurements of a user having standalone SRB allocated on

DCH. If the value of this parameter is "Not defined" in the controlling cell or the value of the

FastHSPAMobilityEnabledparameter is "Disabled" in the controlling cell or the Fast HSPA Mobility


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feature is disabled in the SRNC, the RtFmcsIdentifierparameter identifies the FMCS parameterset for standalone SRB on DCH.

When the channel type is HSDPA/HSPA, the intra-frequency measurements are controlled by the intra-

frequency measurement control (FMCS) parameters of the serving HS-DSCH cell. For more information

on the FMCS parameter sets when the channel type is HSDPA/HSPA, see WCDMA RAN RRM HSDPA

and WCDMA RAN RRM HSUPA. The handover control updates the intra-frequency measurement

control parameters to the UE if the FMCS parameter set changes along with the serving cell change.

Neighbor cell parameters are defined on an intra-frequency neighboring cell-by-cell basis by attaching a

specified HOPS parameter set to a specified intra-frequency neighbor cell. The HOPS parameter setdefines the handover path from the active set cell to the intra-frequency neighbor cell in question. The

HOPS parameter sets are identified on the service type-by-type basis with the following parameters:

The RtHopsIdentifierparameter defines the HOPS parameter set which controls the intra-frequency handover path to the intra-frequency neighbour cell when a real time (RT) radio

bearer is allocated on DCH.

The NrtHopsIdentifierparameter defines the HOPS parameter set which controls the intra-frequency handover path to the intra-frequency neighbour cell when a non-real time (NRT) radio

bearer is allocated on DCH.

TheAdjdRTHopsIdparameter defines the HOPS parameter set which controls the intra-frequency handover path to the additional intra-frequency neighbour cell when a real time (RT)

radio bearer is allocated on DCH.

TheAdjdNRTHopsIdparameter defines the HOPS parameter set which controls the intra-frequency handover path to the additional intra-frequency neighbour cell when a non-real time

(NRT) radio bearer is allocated on DCH.

The SRBHopsIdentifier parameter identifies the HOPS parameter set which controls the intra-frequency handover path to the intra-frequency neighbor cell when standalone SRB is allocated

on DCH. If the value of this parameter is "Not defined" or the value of the

FastHSPAMobilityEnabled parameter is "Disabled" in the controlling cell or the Fast HSPA Mobilityfeature is disabled in the SRNC, the ADJS parameter RtHopsIdentifier identifies the HOPS

parameter set when the standalone SRB is allocated on DCH.

TheAdjdSRBHopsIdparameter identifies the HOPS parameter set which controls the intra-frequency handover path to the additional intra-frequency neighbor cell when standalone SRB is

allocated on DCH. If the value of this parameter is "Not defined" or the value of theFastHSPAMobilityEnabled parameter is "Disabled" in the controlling cell or the Fast HSPA Mobilityfeature is disabled in the SRNC, theAdjdRTHopsIdparameter identifies the HOPS parameter setwhen the standalone SRB is allocated on DCH.

The admission control of the RNC may overrule the handover algorithm decision because of capacity reasons. For moreinformation, see Radio resource management functions and Function in abnormal conditions.

Reporting event 1A for adding cells to the active set

Reporting event 1A is controlled with the following parameters:

Active Set Weighting Coefficient (ActiveSetWeightingCoefficient)

Addition Time (AdditionTime)Addition Window (AdditionWindow).CPICH Ec/No Offset (AdjsEcNoOffset)Maximum Active Set Size (MaxActiveSetSize)

For a description of the parameters, see WCDMA Radio Network Configuration Parameters.

Reporting event 1A is used for adding cells in the active set. The UE sends the event 1A-triggered

measurement report when a cell enters the reporting range as defined by the following formula:

Figure 36: Formula for calculating the UE measurement report on event 1A

The variables in the formula are defined as follows:

Variable Description

MNew Measurement result of the cell


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entering the reporting range

Mi Measurement result of a cell in theactive set, not forbidden to affect thereporting range

NA Number of cells not forbidden toaffect the reporting range in thecurrent active set

MBest Measurement result of the strongest

cell in the active set, not forbidden toaffect the reporting range and nottaking into account any cell

individual offset

W Active Set Weighting Coefficient(ActiveSetWeightingCoefficient)parameter sent from the RNC to the

UE

R Addition Window (AdditionWindow)parameter sent from the RNC to theUE

H1a Hysteresis, which is zero for event1A

CIOnew CPICH Ec/No Offset

(AdjsEcNoOffset)parameter of theneighbor cell entering the reportingrange

Table 10: Variables for measurement report on event 1A

A time-to-trigger mechanism can be used to modify the measurement reporting behavior of event 1A. If

the time-to-trigger mechanism is used, the cell must continuously stay within the reporting range for a

given period of time before the UE can send the event 1A-triggered measurement report to the RNC.

The length of this period is controlled by the RNP parameter Addition Time (AdditionTime).Measurement event 1A can be triggered by monitored set cells and detected set cells. Detected set cells

are only taken into account if detected set reporting is enabled in one or more of the active set cells.

Reporting event 1B for deleting cells from the active set

Reporting event 1B is controlled with the following parameters:

Active Set Weighting Coefficient (ActiveSetWeightingCoefficient)Drop Time (DropTime)Drop Window (DropWindow)CPICH Ec/No Offset (AdjsEcNoOffset)

For a description of the parameters, see WCDMA Radio Network Configuration Parameters.Reporting event 1B is used for deleting cells in the active set. The UE sends the event 1B-triggered

measurement report when a cell leaves the reporting range as defined by the following formula:

Figure 37: Formula for calculating the UE measurement report on event 1B

The variables in the formula are defined as follows:


MOld Measurement result of the cellleaving the reporting range

Mi Measurement result of a cell in the

active set, not forbidden to affect thereporting range


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NA Number of cells not forbidden toaffect the reporting range in thecurrent active set

MBest Measurement result of the strongestcell in the active set, not forbidden toaffect the reporting range and nottaking into account any cellindividual offset.

W Active Set Weighting Coefficient(ActiveSetWeightingCoefficient)parameter sent from RNC to UE

R Drop Window (DropWindow)parameter sent from RNC to UE

H1b Hysteresis, which is zero for theevent 1B

CIOnew CPICH Ec/No Offset(AdjsEcNoOffset)parameter of theneighbor cell entering the reporting

range

Table 11: Variables for measurement report on event 1B

A time-to-trigger mechanism can be used to modify the measurement reporting behavior of event 1B. If

the time-to-trigger mechanism is used, the cell must continuously stay outside the reporting range for a

given period of time before the UE can send the event 1B-triggered measurement report to the RNC. The

length of this period is controlled by theDrop Time (DropTime)RNP parameter.

The RNC does not remove a cell from the active set if it is the only cell in the active set which has uplink physical layersynchronization.

Reporting event 1C for replacing cells in the active set

Reporting event 1C is controlled with the following parameters:

Maximum Active Set Size (MaxActiveSetSize)Replacement Time (ReplacementTime)Replacement Window (ReplacementWindow).CPICH Ec/No Offset (AdjsEcNoOffset)


Reporting event 1C is used for replacing cells in the active set. The UE sends the event 1C-triggered

measurement report when the number of cells in the active set is equal to the Maximum Active Set Size

(MaxActiveSetSize) parameter and a cell that is not included in the active set becomes better than a cellin the active set as defined by the following formula:

Figure 38: Formula for calculating the UE measurement report on event 1C


MNew Measurement result of the cell notincluded in the active set

MInAS Measurement result of the cell in theactive set which has the lowest

measurement result in the active set

MBest Measurement result of the strongestcell in the active set, not forbidden to

affect the reporting range

H1c Replacement window parameter


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sent from the RNC to the UE

CIONew CPICH Ec/No Offset(AdjsEcNoOffset)parameter of thecell not included in the active set

CIOinAS CPICH Ec/No Offset(AdjsEcNoOffset)parameter of thecell in the active set

R1b FMCS DropWindowparameter sent

from RNC to UE

Table 12: Variables for measurement report on event 1C

The RNC does not add the monitored/detected cell (that has triggered the reporting event 1C) into the

active set if the monitored/detected cell and the active set cells are controlled by the same LCG (Local

Cell Group) of the WCDMA BTS.

In the following figure, cells 1, 2 and 3 are in the active set, but cell 4 is not (yet) in the active set.

Figure 39: A cell tha t is not in the active set beco mes bett er than a cell in a full active set

A time-to-trigger mechanism can be used to modify the measurement reporting behavior of event 1C. If

the time-to-trigger mechanism is used, the cell must continuously stay within the triggering condition for

given period of time before the UE can send the event 1C-triggered measurement report to the RNC.

The length of this period is controlled by the Replacement Time (ReplacementTime)RNP parameter.The cell (not included in the active set) leaves the triggering condition if it again becomes worse than the

cells in the active set as defined by the following formula:

Figure 40: Formula for calculating the UE measurement report on event 1C

The RNC might add the monitored/detected cell (that has triggered the reporting event 1C) into the active

set and remove the active set cell whose combined measurement result and cell individual offset

(MInAS+CIOInAS) is the lowest if the monitored/detected cell satisfies the following equation:

If the monitored/detected cell does not satisfy the preceding equation, the RNC checks whether some cell

(or cells) are to be removed from the active set. The RNC removes all those active set cells from the

active set which does not satisfy the following condition:

Measurement event 1C can be triggered by monitored set cells and detected set cells. Detected set cells

are only taken into account if detected set reporting is enabled in one or more of the active set cells.

The RNC does not replace a cell in the active set if it is the only cell in the active set which has uplink physical layer


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synchronization.

Event-triggered periodic intra-frequency measurement reporting

The reporting period is controlled with the following parameters:

Addition Reporting Interval (AdditionReportingInterval)Replacement Reporting Interval (ReplacementReportingInterval)Drop Reporting Interval (DropReportingInterval)


When a cell enters the reporting range and triggers event 1A, 1B or 1C, the UE transmits a

MEASUREMENT REPORT message to the RNC to update the active set.

The UE reverts to periodical measurement reporting if the RNC does not update the active set after the

transmission of the measurement report. The RNC can be unable to add the cell to the active set

because of capacity shortage, for example. If the reported cell is not added to or removed from the activ

set, the UE continues reporting by changing to periodical measurement reporting. This is illustrated in

Figure Periodic reporting triggered by event 1Abelow.

During periodical reporting, the UE transmits measurement report messages to the RAN at pre-defined

intervals. The reports include information on the active, monitored and detected (if applicable) cells in th

reporting range.

Figure 41: Periodic reporting triggered by event 1A

Event-triggered periodic measurement reporting is terminated either when there are no more active,

monitored or detected (if applicable) cell(s) within the reporting range or when the RNC has updated the

active set so that it includes the optimal cells.

Time-to-trigger mechanism for modifying measurement reporting behavior

The value of the time-to-trigger is controlled separately for each event with the following parameters:

Addition Time (AdditionTime)Drop Time (DropTime)Replacement Time (ReplacementTime)


A time-to-trigger parameter can be connected with reporting events 1A, 1B and 1C.

When the time-to-trigger mechanism is applied, the report is triggered only after the conditions for the

event have existed for the specified time. In the following example, cell 3 enters the reporting range

(event 1A), but it is not reported until it has been within the range for the time indicated by the Addition

Time (AdditionTime) parameter.


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Figure 42: Time-to-trigger limits the number of measurement reports

Identification of an intra-frequency cell

Handover control identifies an intra-frequency cell which is reported in the RRC: MEASUREMENT

REPORT message by comparing the scrambling code of the Primary CPICH of the reported cell with:1. the primary CPICH scrambling code of the cells included in the combined intra-frequency cell list2. the primary CPICH scrambling code of those intra-frequency neighbor cells of the active set cells that have been left out from

the full combined intra-frequency cell list3. the primary CPICH scrambling code of additional intra-frequency neighbo r cells of the active set cells

When detected set reporting based soft handover is enabled in one or more active set cells, handover

control proceeds step-by-step in the identification process from the 1st step to the 3rd step until it

identifies the reported cell. Handover control does not execute the steps 2 and 3 if detected set reporting

or the detected set reporting based soft handover is disabled in all active set cells.

The reported intra-frequency cell can be an active, monitored or detected set cell:1. an active set cell included in the combined intra-frequency cell list2. a monitored set cell included in the combined intra-frequency cell list3. an intra-frequency neighbor cell defined in the RNW databa se object ADJS which has been left out from the full combined

intra-frequency cell list4. an additional intra-frequency neighbor cell which is defined in the RNW database object ADJD and not included in the intra-

frequency cell list

If the scrambling code of the Primary CPICH of the reported cell matches with more than one relevantintra-frequency neighbor cells, handover control associates the reported neighbor cell to the active set cel

with the higher CPICH Ec/No measurement result. If the scrambling code of the Primary CPICH of the

reported cell does not match with any relevant intra-frequency cell, the reported intra-frequency cell

remains an unidentified cell.

Soft handover based on detected set reporting

Detected set reporting is based on a 3GPP feature that allows the UE to measure and report any intra-

frequency cell which is outside the intra-frequency cell list of the UE. This capability removes the limitatio

on the length of the intra-frequency cell list. In addition to the active and monitored set cells that are

included in the intra-frequency cell list of the UE, the UE can include any detected intra-frequency cell in

the event evaluation and reporting:

The UE sends an event 1A/1C triggered measurement report to the RNC when a cell, that is not

included in the intra-frequency cell list of the UE, enters the reporting range.

The Primary CPICH scrambling code identifies the detected set cell that has triggered the event

1A/1C measurement report.

The RNC adds the detected set cell into the active set if it is possible to identify the detected set cell, tha

is the primary CPICH scrambling code of the detected set cell equals to the primary CPICH scrambling

code of an intra-frequency neighbor cell. The RNC is not able to identify the detected set cell during

anchoring. Detected set reporting is available for all supported bearer services.

The Soft Handover based on Detected Set Reportingfeature needs to be enabled on RNC level. For

more information on license management (applicable only for the RNC solution) see License

Management Principles.

When the feature is enabled on RNC level, it can be activated and deactivated on a cell-by-cell basis by

modifying the value of the FMCS parameter DSRepBasedSHO.

Handover control activates the detected set reporting for an RRC connection if the Soft Handover Based


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on Detected Set Reportingfeature is enabled on RNC level and either of the following conditions is true:

Detected set reporting is enabled in one or more active set cells by the FMCS parameter

DSRepBasedSHO(value of the parameter is 1). Detected set reporting without soft handover isused to collect statistics on the missing intra-frequency neighbor cell definitions.

Detected set reporting based soft handover is enabled in one or more active set cells by the

FMCS parameter DSRepBasedSHO(value of the parameter is 2).

Note that the E-DCH active set does not affect the procedure. Detected set reporting might increase

signaling on Uu interface because an UE reverts to periodical measurement reporting if detected set

reporting based soft handover is not enabled or if the RNC cannot add the detected cell to the active setbecause of the missing neighbor cell definition. Increased signaling on Uu interface may cause slight

degradation of quality. If a dominant neighbor cannot be added to the active set, serious UL interference

is caused to the surrounding cells and the call can eventually drop because of poor EbNo.

In the handover decision process, handover control handles detected set cells according to the value of

the FMCS parameter DSRepBasedSHO:

Detected set cells are excluded from the decision when the value of FMCS parameter

DSRepBasedSHOis 0 (DSR is not allowed) or 1 (DSR is enabled but SHO to detected cell is notallowed).

Detected cells are taken into account in addition to the active and monitored set cells when the

value of FMCS parameter DSRepBasedSHOis 2 (DSR based SHO is enabled). This applies to

detected cells which are defined in the ADJS object but are left out from the full combined intra-frequency cell list.

Unknown reported cells are excluded from the handover decision process.

If a detected set cell is added to the active set as a result of the handover decision procedure, handover

control adds this new active set cell (ex-detected set cell) and its neighboring cells into the combined

intra-frequency cell list which is sent to the UE in the RRC: MEASUREMENT CONTROL message.

If an inter-RNC soft/softer handover is not possible, the handover control initiates an inter-RNC intra-

frequency hard handover to the detected set cell as soon as the measurement results of the detected se

cell satisfy the required conditions.

Detected set reporting may increase signalling on Uu interfacebecause of UE reverts to periodical

measurement reporting if detected set reporting based soft handover is not enabled or if the RNC canno

add the detected cell to the active set because of the missing neighbor cell definition. Increasedsignalling on Uu interface might cause slight degradation of quality. If a dominant neighbor cannot be

added to the active set, serious uplink interference is caused to the surrounding cells and the call can

eventually drop because of poor EbNo.

Softer handover between cells within one base station

The handover control of the CRNC (controlling RNC) determines the soft handover type for the intra-BTS

intra-frequency handover on the basis of the LCG (Local Cell Group) information. The CRNC receives the

CId (Cell Identifier) - LCG ID mapping information from the BTS in the NBAP: AUDIT RESPONSE and

NBAP: RESOURCE STATUS INDICATION messages. The possible soft handover types for the intra-

BTS intra-frequency handover are:

Intra-BTS softer handover: Intra-frequency handover between cells within one LCG of the BTS.

It is performed if the UE already has an existing radio link in the LCG where the target cell

belongs to.

Intra-BTS soft handover: Intra-frequency handover between cells which belong to different LCG

within one BTS. It is performed if the UE does not have any radio link in the LCG where the

target cell belongs to.

The decision procedure is the same in the serving and drifting RNCs.

Soft handover between Local Cell Groups or base stations within one RNC

Soft handover can take place between cells which belong to different LCGs (Local Cell Groups) within

one BTS (intra-BTS soft handover, see Softer handover between cells within one base stationfor moreinformation) or between cells which belong to different BTSs (inter-BTS soft handover).

Inter-RNC soft and softer handover

The handover control of the DRNC (drifting RNC) determines the soft handover type for the inter-RNC


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intra-frequency handover on the basis of the BTS, cell and LCG (Local Cell Group) information. Thepossible soft handover types of the inter-RNC intra-frequency handover are:

Inter-RNC softer handover: Intra-frequency handover between cells within one Local Cell Group

(LCG) of the BTS controlled by the same DRNC. It is performed if the UE already has an

existing radio link in the LCG where the target cell belongs to.

Inter-RNC soft handover: Intra-frequency handover between cells which belong to different

LCGs within one BTS or different BTSs controlled by the same DRNC. It is performed if the UE

does not have any radio link in the LCG where the target cell belongs to.

The decision procedure is the same in the serving and drifting RNCs.

Cell individual offsets for modifying measurement reporting behavior

Individual offsets can be controlled with the CPICH Ec/No Offset (IntraFreqNcellEcNoOffset) parameter.For a description of the parameter, see WCDMA Radio Network Configuration Parameters.

The individual offset mechanism can be used to change the reporting of an individual cell, and as a

result, to move the cell border. For each cell that is monitored, an offset value can be defined which the

UE adds to the measurement result (CPICH Ec/No) of the neighbor cell before it compares the Ec/No

value with the reporting criteria. The offset can be either positive or negative.

In the following example, an offset is added to the measurement result of cell 3, and the dotted curve is

used in evaluating if an event occurs. Measurement reports from the UE to the RNC are thereforetriggered when the cell including the corresponding offset (the dotted curve) leaves and enters the

reporting range.

When positive offset is used, as in the following example, the UE sends measurement reports as if the

cell (CPICH) is offset x dB better than what it really is. Therefore, cell 3 is included in the active set

earlier than should have been the case without the positive offset. The cell in question can reside in an

area where it often becomes good very quickly (because of street corners, for instance).

Figure 43: A positive offse t is app lied to cell 3 befo re even t evalua tion in the UE

The cell individual offset can be seen as a tool to move the cell border. It is important to note that theoffset is added before triggering events, i.e. the offset is added by the UE before evaluating if a

measurement report should be sent as opposed to offsets that are applied in the network and used for

the actual handover evaluation. Note that the UE does not include the cell individual offset in the

measurement result which is reported to the RNC.

During soft/softer handover, the handover control of the RNC sets the cell individual offsets, which are

transmitted to the mobile station, as follows:1. The handover control sets the cell individual offsets for the intra-frequen cy neighbor cells of the best (according to CPICH

Ec/No) active set cell. Note that an intra-frequency neighbor cell of the best active set cell can be itself an active set cell.2. The handover control sets the cell individual offsets for those intra-frequency neighbor cells of the second best active set cell

which are not neighbor cells of the best active set cell. Note that an intra-frequency neighbor cell of the second best active setcell can be itself an active set cell.

3. The handover control sets the cell individual offsets for those intra-frequency neighbor cells of the third best active set cellwhich are not neighbor cells of the best or second best active set cell. Note that an intra-frequency neighbor cell of the third

best active set cell can be itself an active set cell.

The handover control of the RNC updates the cell individual offsets to the UE, if needed, after each active

set update procedure.

Mechanism for forbidding a cell to affect the reporting range


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The mechanism for forbidding cells to affect the reporting range is controlled with the following parameter:

Disable Effect on Reporting Range (AdjsDERR) indicates whether or not the neighbor cell isforbidden to affect the reporting range (addition/drop window) calculation, if it belongs to the

active set.

For a description of the parameter, see WCDMA Radio Network Configuration Parameters.

The Addition Window (AdditionWindow) and Drop Window (DropWindow) parameters affect reportingevents 1A and 1B. The reporting ranges of events 1A and 1B are relative to the measurement results of

those cells in the active set which are not forbidden to affect the reporting range.

In the following figure, cell 3 is forbidden to affect the reporting range, for example, because it is very

unstable in a specific area.

Figure 44: Cell 3 is forbidden to affect the reporting range

The UE ignores the mechanism if all cells in the active set are forbidden to affect the reporting range.

Reporting events 6F and 6G for deleting cells from the active set

UE Rx-Tx time difference measurement is controlled with the following parameters:

Upper Rx-Tx Time Difference Threshold (UpperRxTxTimeDiff)determines the upper threshold

which is used by the UE to trigger the reporting event 6F because of UE Rx-Tx time difference.

Lower Rx-Tx Time Difference Threshold (LowerRxTxTimeDiff)determines the lower threshold

which is used by the UE to trigger the reporting event 6G because of UE Rx-Tx time difference.

The RNC ignores the reporting event 6F and 6G when the size of the active set is one cell. The RNC

configures the reporting event 6F and 6G for the RRC connection when the size of the active set

becomes larger than one cell for the first time by sending an RRC: MEASUREMENT CONTROL

message to the UE (the RNC does not remove the reporting event 6F and 6G even if the size of the

active set returns to one cell later on).


When the UE Rx-Tx time difference for a cell included in the active set becomes larger than the

threshold defined by the parameter Upper Rx-Tx Time Difference Threshold (UpperRxTxTimeDiff), theUE sends an event 6F-triggered measurement report message to the RNC and the RNC deletes the cell

from the active set. Similarly, the RNC deletes the cell from the active set if the UE sends an event 6G-

triggered measurement report message to the RNC when the UE Rx-Tx time difference for the cell has

become smaller than the threshold defined by the Lower Rx-Tx Time Difference Threshold

(LowerRxTxTimeDiff)parameter.

Function in abnormal conditions

This section describes the functioning of the RNC in case of an unsuccessful soft handover and radio link

failure. In abnormal conditions, the RNC can release the RRCconnection or order the UE to move to

CELL_FACH state to avoid excessive uplink interference. If the conditions for the RRC connection

release and the intra-frequency hard handover are met simultaneously, the hard handover has the higher

priority.

RRC connection release because of unsuccessful soft handover


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When an intra-frequency neighbor cell enters the reporting range and triggers either event 1A (cell

addition) or event 1C (cell replacement), the UE transmits a measurement report to the RNC to add the

neighbor cell to the active set. If the soft handover branch addition is unsuccessful, the RNC may release

the RRC connection or order the UE to move to CELL_FACH state. This is to avoid excessive uplink

interference because of non-optimum fast closed loop power control as the UE is not linked to the

strongest cell any more when the requested handover branch is clearly the strongest branch or would

become the strongest branch. The RRC connection release and state transition to CELL_FACH because

of unsuccessful branch addition procedure are performed according to the following rules:

emergency calls: The RNC does not release emergency call in any case.AMR + NRT PS multi services: The RNC releases the NRT DCH and retries the branch addition

for the AMR service immediately after the NRT DCH is mapped to DCH/DCH 0/0 kbit/s. If there

are several NRT DCHs, the RNC releases one NRT DCH and retries the branch addition for the

AMR service and the remaining NRT PS data services. If the retry is unsuccessful, the RNC

aborts the ongoing branch addition procedure. The RNC can start another branch addition

immediately after the reception of the next event 1A/1C triggered measurement report.

NRT PS data services: The RNC may order the UE to move to CELL_FACH state when the

requested handover branch is clearly the strongest branch. The EnableRRCReleaseparameter ofthe intra-frequency handover path indicates whether the state transition to CELL_FACH state is

allowed because of non-optimum fast closed loop power control. In case of RT/NRT multi

services, the RNC uses the HOPS parameter set which is defined for real time (RT) radio

bearers.CS AMR or data services and AMR + RT PS data multi services: the RNC may release the RR

connection when the requested handover branch is clearly the strongest branch. The

EnableRRCReleaseparameter of the intra-frequency handover path indicates whether the RRCconnection release (excluding emergency calls) is allowed because of non-optimum fast closed

loop power control.

The parameters related to handling of RRC connection release because of an unsuccessful soft handove

are:

CPICH Ec/No Averaging Window (EcNoAveragingWindow) determines the number of eventtriggered periodic intra-frequency measurement reports from which the RNC calculates the

averaged CPICH Ec/No values.

Enable RRC Connection Release (EnableRRCRelease) determines whether RRC connectionrelease (excluding emergency calls) is allowed in situations when soft handover branch addition

(or replacement) fails.

Release Margin for Average Ec/No (ReleaseMarginAverageEcNo) determines the maximumallowed difference between the averaged CPICH Ec/No of the neighbor cell and the averaged

CPICH Ec/No of the best cell in the active set in situations when the RNC is not able to perform

a soft handover between these cells. If the difference between the averaged CPICH Ec/No

values exceeds the value of the parameter, the RNC releases the RRC connection or orders the

UE to move to CELL_FACH state (in case of streaming and NRT PS data services) in order to

avoid excessive uplink interference because of non-optimum fast closed loop power control.

Release Margin for Peak Ec/No (ReleaseMarginPeakEcNo) determines the maximum alloweddifference between the CPICH Ec/No of the neighbor cell and the CPICH Ec/No of the best cell

in the active set in situations when the RNC is not able to perform a soft handover between

these cells. If the difference between CPICH Ec/No values exceeds the value of the parameter,

the RNC releases the RRC connection or orders the UE to move to CELL_FACH state (in case

of streaming and NRT PS data services) in order to avoid excessive uplink interference because

of non-optimum fast closed loop power control.


The UE proceeds to the periodic measurement reporting if the RNC cannot add the requested cell into

the active set. If the forced RRC connection release or state transition to CELL_FACH is allowed, the

RNC makes the decision on the release or state transition to CELL_FACH on the basis of the CPICH

Ec/No of the best cell in the active set, the CPICH Ec/No of the requested neighbor cell and the Release

Margin for Average Ec/Noand Release Margin for Peak Ec/No control parameters.

The RRC connection release or state transition to CELL_FACH is required when the measurement

results of the requested neighbor cell satisfies one of the following equations:

AveEcNoDownlink + ReleaseMarginforAveEc/No (n) < AveEcNoNcell (n)

or


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EcNoDownlink + ReleaseMarginforPeakEc/No (n) < EcNoNcell (n)

The measurement results in the equations are defined as follows:


AveEcNoDownlink averaged CPICH Ec/No of the bestcell in the active set

AveEcNoNcell(n) averaged CPICH Ec/No of theneighboring cell

EcNoDownlink CPICH Ec/No of the best cell in theactive set

EcNoNcell(n) CPICH Ec/No of the neighboring cell

Table 13: Criteria for enabling the RRC connection release

The RNC calculates the averaged values from a specified number of periodic intra-frequency

measurement reports. Averaging is controlled with the CPICH Ec/No Averaging Window

(EcNoAveragingWindow) parameter.

Radio link failure

When a radio link in the active set loses uplink physical layer synchronization, the RNC deletes the radio

link (cell) from the active set if the uplink physical layer remains out of synchronization for a period of

time which is specified by an internal constant. After the radio link deletion procedure, the UE can start

sending reporting event 1A to the RNC to return the cell back to the active set.

If all radio links in the active set lose uplink synchronization, the RNC initiates either an RRC Connection

Re-establishment or an RRC Connection Release procedure. For more information, see WCDMA RAN

packet data transfer states.

Restart of intra-frequency CPICH Ec/No measurement without detected set reporting

If the handover control receives an RRC: MEASUREMENT CONTROL FAILURE message from the UE

upon the request to report detected set cells, the handover control restarts the intra-frequency CPICH

Ec/No measurement without the detected set reporting.

Functionality of intra-frequency hard handover

Intra-frequency hard handover is required to ensure handover between cells controlled by different

RNCs in situations when an inter-RNC soft handover is not possible, for example, because of Iur

congestion. Furthermore, the Enable Inter-RNC Soft Handover (EnableInterRNCsho) RNP parameterdetermines whether the inter-RNC handover from the serving cell to a specified neighbor cell is

performed as a soft handover or as a hard handover. Exceptions with regards to the HSPA inter-RNC

cell change have been described in HSDPA mobility handlingin.

The intra-frequency hard handover is controlled with the following RNP parameters:

Enable Inter-RNC Soft Handover (EnableInterRNCsho) determines whether or not the neighborcell can participate in a soft handover if it is controlled by an RNC other than the local RNC.

CPICH Ec/No Averaging Window (EcNoAveragingWindow) determines the number of event-triggered periodic intra-frequency measurement reports from which the RNC calculates the

averaged CPICH Ec/No values.

HHO Margin for Average Ec/No (HHOMarginAverageEcNo) determines the maximum alloweddifference between the averaged CPICH Ec/No of the neighboring cell and the averaged CPICH

Ec/No of the best active cell in situations when an inter-RNC soft handover is not possible

between these cells.

HHO Margin for Peak Ec/No (HHOMarginPeakEcNo) determines the maximum allowed differencebetween the CPICH Ec/No of the neighbor cell and the CPICH Ec/No of the best active cell in

situations when an inter-RNC soft handover is not possible between these cells.


The RNC makes the intra-frequency hard handover decision on the basis of event-triggered periodic

intra-frequency measurement reports, which are usually applied to soft handover, and the above-

mentioned control parameters. The UE proceeds to the periodic measurement reporting if the RNC

cannot add the requested cell into the active set.


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The handover decision is based on the downlink Ec/No of the best cell in the active set, downlink Ec/No

of the neighbor cell and handover margins which are used as a threshold to prevent repetitive hard

handovers between cells. The measurement results of the neighbor cell must satisfy one of the following

two equations before the intra-frequency hard handover is possible:

AveEcNoDownlink + HHOMarginForAverageEcNo (n) < AveEcNoNcell (n)

or

EcNoDownlink + HHOMarginForPeakEcNo (n) < EcNoNcell (n)

The measurement results in the equations are defined as follows:


AveEcNoDownlink Averaged downlink Ec/No of the bestcell in the active set

AveEcNoNcel l(n) Averaged downlink Ec/No of the

neighbor cell (n)

EcNoDownlink Downlink Ec/No of the best cell in theactive set

EcNoNcell(n) Downlink Ec/No of the neighbor cell

Table 14: Measurement result criteria for intra-frequency hard handover

The RNC calculates the averaged Ec/No values from a specified number of periodical intra-frequency

measurement reports. Averaging is controlled with the CPICH Ec/No Averaging Window

(EcNoAveragingWindow). The maximum allowed difference between the averaged or peak CPICH powerlevel of the neighboring cell (n) and that of the best active set cell is defined with a parameter in situations

when the RNC cannot perform an inter-RNC soft handover between these cells. If the difference in the

averaged or peak Ec/No values exceeds the value of the relevant parameter, the RNC performs an intra-

frequency hard handover to avoid excessive uplink interference because of fast closed loop power control

that is no longer optimal.

Time interval between hard handover attemptsThe RNC does not set any limit for the minimum interval between the inter-RNC intra-frequency hard

handovers. However, to prevent repetitive unsuccessful inter-RNC intra-frequency hard handover

attempts to the same target cell, the RNC determines a time interval during which an intra-frequency

hard handover to the cell in question is not allowed. The length of the interval is fixed 2 seconds for

emergency calls. Otherwise the length of the interval depends on the number of unsuccessful hard

handover attempts related to the same target cell during the same RRC connection. This interval

increases 2 seconds per unsuccessful hard handover attempt (to the same target cell during the same

RRC connection), up to the maximum of 10 seconds. The RNC determines the interval in the following

way:

TIME_INTERVAL = min (10 seconds, NUMBER_OF HHO_FAILS * 2 seconds)

Related information

Descriptions

Handover control

Types of handovers

DN03471612 Id: 0900d805809836c6 2013 Nokia Siemens Networks

functionality of intra-frequency handover

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