Cell Reselection in NSN

Network-Controlled Cell Re-selection

dn0443664Issue 1-2 en

# Nokia CorporationNokia Proprietary and Confidential

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2003353Nokia BSC/TCSM S11.5 Update 1

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Contents

Contents 3

List of tables 4

List of figures 5

Summary of changes 7

1 Overview of Network-Controlled Cell Re-selection 9

2 Requirements for Network-Controlled Cell Re-selection 11

3 Technical description of Network-Controlled Cell Re-selection 13

4 Functionality of Network-Controlled Cell Re-selection 154.1 Cell change procedures in different mobile states 154.2 Network control modes 154.3 Ordering network control modes to MS 164.3.1 Broadcasting network control mode NC2 164.3.2 Network control mode NC2 Rel97/Rel99/Rel4 onwards 164.3.3 Ordering MS to NC0 mode 174.4 MS neighbour cell measurements 184.4.1 MS neighbour cell measurement reporting 184.4.2 MS neighbour cell measurement storing and averaging in the PCU 204.5 Quality Control cell change triggers 214.6 Algorithms and cell reselection criteria 214.6.1 Power budget criterion 224.6.2 Data transmission quality criterion 264.7 PACKET CELL CHANGE ORDER 294.8 Avoiding continuous cell changes between two cells 31

5 Effect of Network-Controlled Cell Re-selection on interfaces 33

6 User interface of Network-Controlled Cell Re-selection 35



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Contents

List of tables

Table 1. Software requirements for NCCR 11

Table 2. Hardware requirements for NCCR 11

Table 3. Quality Control corrective actions with default values 26




List of figures

Figure 1. Process for power budget NCCR criterion 23

Figure 2. Process for Quality Control NCCR criterion 27



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List of figures

Summary of changes

Summary of changes

Changes between document issues are cumulative. Therefore, the latest documentissue contains all changes made to previous issues.

Changes made between issues 1�2 and 1�1

Ordering MS to NC0 mode

The minimum period of time that the PCU waits for measurement reports fromthe MS has been updated.

Updated information about the cell change operation.

MS neighbour cell measurement storing and averaging in the PCU

The minimum period of time that the PCU waits for measurement reports fromthe MS has been updated.

PACKET CELL CHANGE ORDER

Updated information about the cell change operation.

Power budget criterion

Figure Process for power budget NCCR criterion has been updated to indicatethat the HCS and PBGT values are computed for all the serving cells as well asfor all the neighbouring cells.

User interface of Network-Controlled Cell Re-selection

NCCR_STOP_UL_SCHEDULING and NCCR_STOP_DL_SCHEDULINGparameters have been removed.

The HCS threshold (HCS) parameter has been added.

Changes made between issues 1�1and 1

Editorial changes.



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Summary of changes

1 Overview of Network-Controlled Cell Re-selection

Description

Network-Controlled Cell Re-selection (NCCR) gives to the network thepossibility to order a cell re-selection instead of the autonomous selection doneby the mobile station (MS) itself. With this feature, the network decides when theMS changes cell and what is the target cell.

Cell re-selection is a basic cellular radio network operation, where the MS'scontact point to network is changed during MS network connection. Cell re-selection is performed by the MS. The target cell of the cell re-selection can beselected by the network or autonomously by the MS.

Network-Controlled Cell Re-selection (NCCR) introduces the possibility for thenetwork to control timing and target cell selection in cell re-selection. WithNCCR there are the following cell reselection criteria:

. Power budget will push EGPRS capable MSs to EGPRS cells and non-EGPRS capable MSs to non-EGPRS capable cells.

. Quality Control triggers NCCR when the serving cell transmission qualitydrops even if the serving cell signal level is good.

NCCR is application software and requires a valid licence in the BSC. For moreinformation, see Licensing in BSC .



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Overview of Network-Controlled Cell Re-selection

Network�Controlled Cell Re-selection benefits

. Efficient allocation of EGPRS resources. When EGPRS TRXs areintroduced gradually in GSM networks, some cells will have EGPRSTRXs and others will not. The PCU will push EGPRS capable MSs toEGPRS cells and GPRS capable MSs to non-EGPRS capable cells bypower budget NCCR criterion.

. Cell attractiveness can be defined neighbour cell specifically also takinginto account each neighbour cell's capacities (for example CS-3/CS-4 orEQoS support).

. Quality criterion allows the NCCR when the serving cell quality dropseven if the signal level is good.

Compliance

Network Controlled Cell Re-selection complies with the following standards:

. 3GPP TS 23.060

. 3GPP TS 44.018

. 3GPP TS 44.060

. 3GPP TS 45.008

Related topics

. Requirements for Network-Controlled Cell Re-selection

. Technical description of Network-Controlled Cell Re-selection

. Functionality of Network-Controlled Cell Re-selection

. Effect of Network-Controlled Cell Re-selection on interfaces

. User interface of Network-Controlled Cell Re-selection

. Activating and testing Network-Controlled Cell Re-selection




2 Requirements for Network-ControlledCell Re-selection

Software requirements

Table 1. Software requirements for NCCR

Network element Software release required

BSC S11.5

Nokia UltraSite EDGE BTSs No requirements

Nokia MetroSite EDGE BTSs No requirements

Nokia 2nd Gen. BTSs No requirements

Nokia PrimeSite BTSs No requirements

Nokia InSite BTS No requirements

MSC/HLR No requirements

SGSN No requirements

Nokia NetAct OSS4

Hardware requirements

Table 2. Hardware requirements for NCCR

Network element Hardware requirements

BSC No requirements

BTS No requirements



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Requirements for Network-Controlled Cell Re-selection

Table 2. Hardware requirements for NCCR (cont.)

Network element Hardware requirements

TCSM No requirements

SGSN No requirements

End-user equipment

NCCR is supported by NC2 capable mobile terminals.

Frequency band support

NCCR is supported by the following frequency bands:

. GSM 800

. GSM 900

. GSM 1800

. GSM 1900

For an overview, see Overview of Network-Controlled Cell Re-selection .




3 Technical description of Network-Controlled Cell Re-selection

Interworking

Common BCCH Control in BSC and Multi BCF Control in BSC

If transmission quality is poor on the serving BTS, the MS may be reallocatedfirst to another BTS in the cell and the NCCR performed later. For moreinformation, see Quality Control in (E)GPRS in BSC .

Double BCCH Allocation List

If there is no PBCCH in the cell and a BCCH Allocation List (BA list) is used,the MS does not send Packet Enhanced Measurement Report messages but onlyPacket Measurement Report messages to the BSC. This is because GPRS BSICDescription is not broadcast if a BA list is used.

For more information, see Double BCCH Allocation List .

Enhanced Quality of Service (EQoS)

EQoS Quality Control (QC) may trigger NCCR as one of the corrective actionsafter detecting degradation in the quality of the serving cell.

NCCR streaming TBF offset functionality of power budget NCCR is availableonly if EQoS is in use.

EQoS target cell admission control is used in intra-PCU cell changes to avoidcommanding MSs to change to highly loaded cells.

For more information on EQoS, see Enhanced Quality of Service .

Inter-System NCCR (ISNCCR)

ISNCCR enables the BSC to initiate cell re-selection from a GSM cell to aWCDMA cell. The activation of NCCR is a prerequisite for activating ISNCCR.NCCR does not require ISNCCR to be active in the BSC.



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Technical description of Network-Controlled Cell Re-selection

For more information on ISNCCR, see Inter-System Network-Controlled Cell Re-selection .

IMSI-Based Handover (IBHO)

IMSI is not taken into account with NCCR.

Network�Assisted Cell Change (NACC)

After the PCU has determined a new cell for the MS, the PCU sends dataconcerning the target cell to the MS in order to make the cell change faster.Currently NACC is supported for intra-BSC cell changes.

For more information, see Network�Assisted Cell Change .

PCU overload protection

NCCR enhances the PCU overload protection in two ways. In a lower level PCUoverload situation, NCCR reduces the PCU load by ignoring every secondmeasurement report sent by the NCCR-controlled MSs. In a higher level PCUoverload situation, NCCR moves the MSs from network-controlled toautonomous cell reselection. This is done one by one as measurement reports arereceived from the MSs.

For an overview, see Overview of Network-Controlled Cell Re-selection .




4 Functionality of Network-Controlled CellRe-selection

4.1 Cell change procedures in different mobile states

MM Dedicated state

The handover procedure is used for mobiles that are in MM Dedicated state. TheMS is in MM Dedicated state when there is an ongoing circuit-switched call.

MM Idle state

In MM Idle state, the MS can be in MM GPRS IDLE , MM STANDBY or MMREADY state. NCCR is applicable in MM READY state only. In other states theMS uses autonomous cell re-selection.

In MM GPRS IDLE state , the MS performs autonomous cell re-selection basedon the BCCH broadcast parameters defining C1 and C2 criteria.

In MM STANDBY state , the MS performs autonomous cell re-selection basedon the BCCH broadcast parameters defining C1 and C2 criteria, or if the PBCCHexists, the cell re-selection is based on the PBCCH broadcast parameters definingC1, C31 and C32 criteria.

In MM READY state , the MS is either in RR packet transfer mode or RR packetidle mode. NCCR is applied in both modes. If NCCR is enabled, the MS selects anew cell as ordered by the network. If NCCR is not enabled, the MS performs anautonomous cell re-selection as in MM STANDBY state.

4.2 Network control modes

The network control mode defines how the cell re-selection is performed. The3GPP standards define the following three network control modes:



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Functionality of Network-Controlled Cell Re-selection

NC0 The MS will perform an autonomous cell reselection.

NC1 The MS sends neibhbour cell measurements to the networkand performs an autonomous cell re-selection.

NC1 is not supported by Nokia BSC.

NC2 The MS sends neighbour cell measurements to the networkand the network commands the MS to perform cell re-selection.

The network control mode is broadcast in the NETWORK_CONTROL_ORDERparameter in the SI13 and SI2quater messages on BCCH, or in case PBCCH isused, in the PSI5 message. The PSI5 message is sent only if the value NC2 isbroadcast. Sending of PSI5 is determined by the MEASUREMENT ORDERfield in PSI1.

Alternatively, the NETWORK_CONTROL_ORDER parameter can be sent in aPACKET MEASUREMENT ORDER message on PCCCH or PACCH to aparticular mobile station.

For more information, see Base Station Controller Parameter Handling in BSC(EEM command).

4.3 Ordering network control modes to MS

The use of Network-Controlled Cell Re-selection is controlled with the NCCRcontrol mode parameter.

4.3.1 Broadcasting network control mode NC2

Network control mode NC2 is broadcast as described in Network control modes .

4.3.2 Network control mode NC2 Rel97/Rel99/Rel4 onwards

Network control mode NC0 is broadcast, but NC2 is ordered by sending aPACKET MEASUREMENT ORDER message to a particular mobile station.

Although support for Network-Controlled Cell Re-selection has been mandatoryfor the MS since 3GPP Rel97, it is possible that some MS vendors have not hadthe chance to test their products in actual networks and that their products maynot work properly when ordered into NC2 mode.




Therefore, in all cases NC0 is broadcast, but individual MSs are ordered into NC2mode based on their 3GPP release support. If the value of NCCR control modeis 'NC2 Release 97 Onwards', PACKET MEASUREMENT ORDER is sent to allmobiles. If the value is 'NC2 Release 99 Onwards', PACKET MEASUREMENTORDER is sent to mobiles that are Release 99 or later. If the value is 'NC2Release 4 Onwards', PACKET MEASUREMENT ORDER is sent to mobiles thatare Release 4 or later.

The MS support for 3GPP Rel99 is indicated in the Revision Level Indicationfield in the MS RAC IE. If any of the fields under Additions in Release 4 arepresent in the MS RAC IE, the MS supports the 3GPP Release 4.

The PCU receives the MS RAC at TBF establishment. If the MS RAC is notreceived (one phase uplink access or DL-UNITDATA PDU without MS RACIE), the MS remains in NC0 mode. If the PCU receives the MS RAC during TBF,the PCU checks the MS 3GPP release support and sends a PACKETMEASUREMENT ORDER if needed.

Ordering MS to NC2 mode in RR packet transfer mode

If the MS is in RR packet transfer mode, the PCU sends a PACKETMEASUREMENT ORDER message on the PACCH. The PCU polls for aPACKET CONTROL ACKNOWLEDMENT. If the MS does not send anacknowledgement, the PACKET MEASUREMENT ORDER is transmittedagain. If the MS still does not acknowledge the polling, the PCU considers theMS to be in NC0 mode.

Ordering MS to NC2 mode in RR packet idle mode

If Inter-System Network-Controlled Cell Re-selection (ISNCCR) is not enabled,the PCU does not order a MS that is in RR packet idle mode to NC2 with thePACKET MEASUREMENT ORDER message.

For more information, see Inter-System Network-Controlled Cell Re-selection .

4.3.3 Ordering MS to NC0 mode

In some situations that have resulted from abnormal procedures, the PCU mayorder the MS from NC2 mode to NC0 mode by sending a PACKETMEASUREMENT ORDER. This happens in the following situations:



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. The PCU has not received measurement reports from a MS that is in packettransfer mode. The PCU waits for the reports for three and a half times thelength of the reporting period or at least 15 seconds.

. The PCU receives a measurement report when NCCR is not enabled.

. The PCU overload protection is triggered. For more information, seeTraffic administration in (E)GPRS in BSC.

Ordering MS to NC0 mode in RR packet transfer mode

If the MS is in RR packet transfer mode, the PCU sends a PACKETMEASUREMENT ORDER message on the PACCH. The PCU does not poll fora PACKET CONTROL ACKNOWLEDMENT.

Ordering MS to NC0 mode in RR packet idle mode

If the MS is in RR packet idle mode and the PCCCH exists, the PCU sends aPACKET MEASUREMENT ORDER message on the PCCCH. The PCU doesnot poll for a PACKET CONTROL ACKNOWLEDMENT.

If the MS is in RR packet idle mode and the PCCCH does not exist, the PCU firstassigns a single downlink block to the MS with an IMMEDIATE ASSIGNMENTmessage on the CCCH assuming the MS to be in non-DRX mode. The PCU thensends the PACKET MEASUREMENT ORDER in the assigned block.

4.4 MS neighbour cell measurements

4.4.1 MS neighbour cell measurement reporting

The Network-Controlled Cell Re-selection uses cell adjacencies that are definedby the operator (using the command class EA ). Alternatively, if the doubleBCCH Allocation List is in use, the NCCR uses adjacencies that are included inBA list defined by operator (using the command class EB ). For moreinformation, see Double BCCH Allocation List . Only GPRS-enabled neighbourcells are valid.

If the PBCCH exists, the cell adjacency information is delivered to the MS in thePSI3/PSI3bis messages. If the PBCCH does not exist, the information isdelivered in the SI2/SI2bis/SI2ter/SI2quater messages.




There are two types of measurement reports: PACKET MEASUREMENTREPORT (PMR) and PACKET ENHANCED MEASUREMENT REPORT(PEMR). The PEMR enables the MS to report more neighbours and offers bettercontrol on multiband/multirat reporting. The operator can select which type ofmeasurement report to use with the PRFILE parameterNCCR_MEAS_REPORT_TYPE . PEMR is not supported by all mobiles.

If NC2 mode is broadcast, the report type is indicated in the PSI5 message (incase PBCCH exists) or the SI2quater message (in case PBCCH does not exist). Ifthe control mode indicates NCCR support for part of the 3GPP release MSs only(in other words, if the value is �NC2 Release97/99/04 Onwards�), the report typeis sent to the appropriate mobiles in the PACKET MEASUREMENT ORDERmessage.

In the PACKET MEASUREMENT REPORT, the MS reports the RXLEV valuesfor the serving cell and six strongest neighbour cell carriers for which the BSIChas successfully been decoded and is allowed. If the MS is a multiband MS, itreports the strongest BCCH carriers, the number of which is indicated by themultiband cell reporting parameter.

In the PACKET ENHANCED MEASUREMENT REPORT, the MS reports theRXLEV values for the serving cell and as many cells (successfully decoded andallowed by the BSIC) as it can include in the message. When the SCALE bit is setto 1, the PCU adds 10 dBs to each GSM neighbour cell RXLEV value beforeusing it in NCCR algorithms. The BSC broadcasts the BSIC information in thePSI3/PSI3bis messages (in case PBCCH exists) or the SI2quater message (in casePBCCH does not exist).

The MS reports neighbour cells according to the following multiband andmultirat parameters

. serving band reporting (SBR)

. 900 reporting offset (R9)

. 900 reporting threshold (RT9)









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Furthermore, with the scale ord (SCO) parameter the BSC controls whetherthe MS should scale the GSM RXLEV values by 10 dB.

The parameters listed above are either broadcast in the PSI5 message (in casePBCCH exists) or the SI2quater message (in case PBCCH does not exist), ordelivered to individual mobiles in PACKET MEASUREMENT ORDERmessages.

The MS reports neighbour cell measurements using a reporting period assignedby the BSC. These periods are defined with the parameters NCCR idle modereporting period (NIRP) and NCCR transfer mode reportingperiod (NTRP) .

When the MS is in RR packet idle mode and has a measurement report to send, itmakes a channel request (in case PBCCH does not exist) or a packet channelrequest (in case PBCCH exists) for a single block and sends the measurementreport in the assigned block. If the MS is in RR packet transfer mode and has adownlink TBF, it sends the measurement report instead of PACKETDOWNLINK ACK/NACK message. If the MS in RR packet transfer mode hasan uplink TBF, it sends the measurement report on the PACCH. The MS sendsRLC/MAC blocks withe the following order of priority:

1. RLC/MAC control blocks containing a Packet Cell Change Notificationmessage

2. other RLC/MAC control blocks, except Packet Uplink Dummy ControlBlocks

3. RLC data blocks

4. RLC/MAC control blocks containing Packet Uplink Dummy ControlBlocks

4.4.2 MS neighbour cell measurement storing and averaging in the PCU

Segment-level parameters NCCR rxlev transfer mode window size andNCCR rxlev idle mode window size define the number of serving cell andneighbour cell RXLEV value samples received from the PACKET(ENHANCED) MEASUREMENT REPORT that are averaged in RR packettransfer mode and RR packet idle mode, respectively.

The latest measurement reports are used for averaging. At the beginning of anaveraging session, the available number of measurements are used in theaveraging until the window size is fulfilled. In other words, the average iscounted already from the first measurement report.




A zero is entered as a measurement result for the adjacent cells that are missingfrom the measurement sample. A segment-level parameter NCCR number ofzero results indicates the maximum number of zero results from GSM cellsthat are omitted when the measurement results of the adjacent cells are averaged.

In order to know which power budget and data transmission quality criteriathreshold parameters to use, the PCU must know the MS EGPRS capability. If thePCU receives a measurement report from a MS whose EGPRS capability it doesnot know, it requests the MS Radio Access Capabilities (RAC) information fromthe SGSN using Radio Access Capability Update procedure. For moreinformation, see Radio Access Capability Update in BSC-SGSN InterfaceSpecification BSS GPRS Protocol (BSSGP).

The MS stops sending measurement reports when it enters the MM STANDBYstate, that is, when its MM READY timer expires. Even though the PCU does notknow the value of this timer, it considers that it can stop monitoring the MS afterthe MS has not sent a measurement report in RR packet idle mode for a certainperiod of time. This period of time is three and a half times the reporting period(defined by parameter NCCR idle mode reporting period ) or at least 15seconds.

4.5 Quality Control cell change triggers

Quality Control measures the MS-specific radio interface block error ratio(BLER) and bitrate per timeslot quantities that are used as cell change criteria.For more information on Quality Control functionality, BLER and bitrate pertimeslot monitoring, see (E)GPRS in BSC .

With Enhanced Quality of Service, the Quality Control also monitors the PFC-specific radio interface throughput that is used as a cell change criterion. For moreinformation on throughput monitoring, see Quality Control in Enhanced Qualityof Service.

4.6 Algorithms and cell reselection criteria

Network-Controlled Cell Re-selection uses two criteria: power budget and datatransmission quality.

The power budget criterion is based on the RXLEV values received in themeasurement reports sent by the MS. The PCU runs power budget algorithmevery time it receives new measurement report. The operator can adjust thereporting periods as described in MS neighbour cell measurements .



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The PCU Quality Control monitors the transmission quality and triggers theNCCR in case the monitored quality degrades. Target cell selection is performedwhen the Quality Control NCCR criterion triggers and after that, if needed,always when a new PACKET (ENHANCED) MEASUREMENT REPORTmessage is received.

When Quality Control indicates quality degradation, power budget criterionalgorithm is run before data transmission quality criterion target cell selection.

4.6.1 Power budget criterion

The power budget criterion ensures that the MS is always commanded to performcell re-selection to a cell with the minimum path loss. Furthermore, power budgetcriterion can be used to allocate EGPRS resources efficiently. The BSC can forceEGPRS MSs to select EGPRS-capable cells as well as keep GPRS MSs in non-EGPRS-capable cells.

The power budget criterion includes the C31 and C32 criteria of 3GPP TS45.008. The operator can prefer intra-PCU cell re-selections. The operator canalso set the BSC to avoid cell re-selections for MSs that have streaming trafficclass PFCs.

The figure below describes the power budget NCCR criterion process.




Figure 1. Process for power budget NCCR criterion

The power budget criterion is evaluated each time the BSC receives ameasurement report from the MS. The algorithm is applied to those neighbourcells that have been reported in any measurement report and that have effectivemeasurements available after the measurement report averaging. For moreinformation on measurement report averaging, see MS neighbour cellmeasurement storing and averaging in the PCU .

The meaning of the variables and parameters that take part in the algorithm is asfollows:

PBGT(n)

PBGT(n) = (AV_RXLEV_NCELL(n) - AV_RXLEV_SERV ) +(GPRS_MS_TXPWR_MAX_CCH - GPRS_MS_TXPWR_MAX_CCH (n) ) -TO(n) * ( 1 - L(n) )

Is HCS> 0 true for some cell?YES

YES

NO*

NO

* The cell under investigation is left out of calculations

Compute HCS & PBGT values for all cells(for serving cell and reported neighbours)

Measurement report processing

NO*

NO*

YES

AV_RXLEV_NCELL(n) >RxLevMinCell(n) + Max(0, Pa)

PBGT(n) >PGBT_margin(n)

Search for the reported neighbouring cell withhighest PBGT(n)-PBGT_margin(n) value


Select the cell that has the highestPBGT(n)-PBGT_margin(n) valueamong those cells that have thehighest PRIORITY_CLASS amongthose that fulfil HCS >0

Trigger NCCR to cell (n)

YESIs selected cell serving cell?

YES

NO



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. AV_RXLEV_SERVand AV_RXLEV_NCELL(n) are the average RXLEVvalues measured on the BCCH channel for the serving cell and neighbourcell n. There is one AV_RXLEV_NCELL parameter for each of the cellsthat are being reported by a certain MS.

. GPRS_MS_TXPWR_MAX_CCH is the maximum allowed transmitpower of the MS in the serving cell defined by the BTS parameterMsTxPwrMaxGPRS (if the serving cell is GSM 900 or GSM 800) orMsTxPwrMaxGPRS1x00 (if the serving cell is GSM 1800 or GSM1900)

. GPRS_MS_TXPWR_MAX_CCH(n) is the maximum allowed transmitpower of the MS in the neighbour cell defined by the ADJ parameterMsTxPwrMaxGPRS(n) (if the adjacent cell is GSM 900 or GSM 800) orMsTxPwrMaxGPRS1x00(n) (if the adjacent cell is GSM 1800 or GSM1900)

TO(n) = TEMPORARY_OFFSET_NCCR(n) * H(PENALTY_TIME_NCCRS(n)- T(n))

. TEMPORARY_OFFSET_NCCR(n) applies a negative offset to PBGT(n)for the duration of PENALTY_TIME_NCCR(n) after a timer T has startedfor that cell. T is a timer implemented for each cell in the list of strongestcarriers. T is started from zero when the cell is placed by the MS on the listof strongest carriers, in other words, TEMPORARY_OFFSET_NCCR(n)is applied until cell n has been included in as many continuousmeasurement reports as defined by the timer T(n).

The TO(n) parameter prevents, for instance, the network from ordering afast-moving MS a cell change to a neighbouring microcell.TEMPORARY_OFFSET_NCCR(n) and PENALTY_TIME_NCCR(n) aredefined by parameters GPRS temporary offset and GPRS penaltytime respectively.

H(x) =0 for x < 0, and 1 for x >= 0

L(n) =0 if PRIORITY_CLASS(n) = PRIORITY_CLASS(s) , and 1 ifPRIORITY_CLASS(n) <> PRIORITY_CLASS(s)

. PRIORITY_CLASS(s) is the HCS (Hierarchical Cell Structures) priorityfor the serving cell defined by the BTS parameter priority class

. PRIORITY_CLASS(n) is the HCS (Hierarchical Cell Structures) priorityfor the neighbour cell defined by the ADJ parameter priority class




. If the neighbour cell is in a different routing area, the hysteresis valuedefined by the BTS parameter ra reselect hysteresis issubtracted from the PBGT value.

. If the MS has an active TBF for streaming traffic class PFC, the offsetvalue determined by the BTS parameter NCCR streaming TBF offsetis subtracted from the PBGT value. For more information on PFC, seePacket Flow Context management in Enhanced Quality of Service.

. If the neighbour cell is not under the control of the same PCU as theserving cell, the offset value determined by the new segment levelparameter NCCR other PCU cell offset is subtracted from thePBGT value.

HCS(n)

HCS(n) = AV_RXLEV_NCELL(n) - HCS_THR(n) - TO(n) * L(n)

. AV_RXLEV_NCELL(n), TO(n) and L(n) as in the PGBT(n) formulaabove

. HCS_THR(n) is the signal threshold for applying HCS GPRS reselection.It is determined by the ADJ parameter HCS signal level threshold.

AV_RXLEV_NCELL(n) > RxLevMinCell(n) + Max(0, Pa)

. AV_RXLEV_NCELL(n) as in the PBGT(n) formula above

. RxLevMinCell(n) is the minimum received signal level at the MS requiredfor access to the system. RxLevMinCell(n) is defined by the ADJparameter GPRS rxlev access min .

. Max(0, Pa) takes into account the maximum transmission powercapabilities of different MSs types so that the uplink connection issuccessfully established in all candidate cells.

Pa = GPRS_MS_TXPWR_MAX_CCH(n) - P

. GPRS_MS_TXPWR_MAX_CCH(n) as in the PBGT(n) formula above

. P is the MS maximum GMSK RF output power on the band of the cell n.

PBGT(n) > PBGT_margin(n)

. PBGT_margin(n) is the value that the PBGT variable of the neighbouringcell 'n' has to exceed before a cell re-selection to that cell can be performed.



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PBGT_margin is defined by the ADJ parameter NCCR EGPRS PBGTmargin (if the MS is EGPRS capable) or NCCR GPRS PBGT margin(if the MS is non-EGPRS capable)

Note

Due to separate thresholds for EGPRS-capable and non-capable MSs, thiscriterion cannot be used before the MS EGPRS capability is known. For moreinformation on MS RAC, see MS neighbour cell measurement storing andaveraging in the PCU.

4.6.2 Data transmission quality criterion

Quality Control monitors that a PFC of an MS is given the negotiated QoS level.The monitored items are PFC throughput, TBF BLER and the radio channelquality. For more information on Quality Control, TBF BLER monitoring andradio channel quality monitoring, see (E)GPRS in BSC. For more information onthroughput monitoring, see Enhanced Quality of Service.

When Network-Controlled Cell Re-selection is enabled, Quality Control mayalso trigger NCCR as a corrective action. The BSC parameter QC ActionTrigger threshold defines the number of radio block periods that thequality degradation has to last before cell re-selection is triggered.

Table 3. Quality Control corrective actions with default values

Action Block periods

Re-allocation 25

Network-Controlled Cell Re-selection 100

Quality of Service re-negotiation* 200

Drop* 400

* requires Enhanced Quality of Service application software

Target cell selection is performed when the QC NCCR criterion triggers and afterthat, if needed, always when a new PACKET (ENHANCED) MEASUREMENTREPORT message is received until




. MS NCCR context is deleted,

. TBF is released, or

. Quality in the serving cell gets better, that is, conditions for qualitydegradation end.

The BSC selects the NCCR target cell by the following process.

Figure 2. Process for Quality Control NCCR criterion

The meaning of the variables that take part in the algorithm is as follows:

YES

NO*

NO*

YES

Quality Control NCCR trigger

Measurement report processing

Search for the neighbouring cell withhighest AV_RXLEV_NCELL(n)

AV_RXLEV_NCELL(n) >AV_RXLEV_SERV +Quality_Margin(n)

Trigger NCCR to cell (n)


* The cell under investigation is left out of calculations



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. AV_RXLEV_SERVand AV_RXLEV_NCELL(n) are the average RXLEVvalues measured on the BCCH channel for the serving cell and neighbourcell 'n'. There is one AV_RXLEV_NCELL parameter for each of the cellsthat are being reported by a certain MS.

. RxLevMinCell(n) is the minimum received signal level at the MS requiredfor access to the system. RxLevMinCell(n) is defined by the ADJparameter GPRS rxlev access min .

. Max(0, Pa) takes into account the maximum transmission powercapabilities of different MSs types so that the uplink connection issuccessfully established in all candidate cells.

Pa = GPRS_MS_TXPWR_MAX_CCH(n) - P

. GPRS_MS_TXPWR_MAX_CCH(n) is the maximum allowed transmitpower of the MS in the neighbour cell defined by the ADJ parameterMsTxPwrMaxGPRS(n) (if the adjacent cell is GSM 900 or GSM 800) orMsTxPwrMaxGPRS1x00(n) (if the adjacent cell is GSM 1800 or GSM1900).

. P is the maximum GMSK RF output power on the band of the cell n.

. Quality_Margin(n) is the margin for EGPRS MS by which the signal levelAV_RXLEV_NCELL(n) of the neighbour cell (n) must exceed the signallevel AV_RXLEV_SERV of the serving cell before cell re-selection ispossible. Quality_Margin(n) is defined by the ADJ parameter NCCREGPRS quality margin (if the MS is EGPRS-capable) or NCCRGPRS quality margin (if the MS is non-EGPRS capable)

Note

Due to separate thresholds for EGPRS-capable and non-capable MSs, thiscriterion cannot be used before the MS EGPRS capability is known. For moreinformation on MS RAC, see MS neighbour cell measurement storing andaveraging in the PCU.




4.7 PACKET CELL CHANGE ORDER

Whenever one of the NCCR criteria is triggered and an appropriate target cellfound, the PCU sends a PACKET CELL CHANGE ORDER (PCCO) message tothe MS. If the MS has a TBF, PCCO is sent on the PACCH channel, and if it doesnot have a TBF, PCCO is sent on the PCCCH channel or in the assigned singleblock (in case PCCCH does not exist).

When Network Assisted Cell Change (NACC) application software is activatedand the MS has a TBF, the PCU sends target cell system information to the MSbefore sending the PCCO message. For more information, see Network-AssistedCell Change .

MS in RR packet idle mode

On CCCH, the PCU assigns one downlink block using IMMEDIATEASSIGNMENT. The PACKET CELL CHANGE ORDER message is then senton the assigned block. On PCCCH, the PACKET CELL CHANGE ORDERmessage is sent directly on PCCCH.

The PCU does not poll for PACKET CONTROL ACKNOWLEDGEMENT.When the PCU receives FLUSH, it considers the cell change successful.

The PCU assumes the MS to be in non-DRX mode.NCCR_NON_DRX_PERIOD defines the time that the MS stays in non-DRXmode after sending the PACKET (ENHANCED) MEASUREMENT REPORT.The parameter is either broadcast on SI2quater (in case PBCCH does not exist) orPSI5 (in case PBCCH exists), or told to individual MSs with the PACKETMEASUREMENT ORDER message. The value for theNCCR_NON_DRX_PERIOD is defined by the PRFILE parameterNCCR_NON_DRX_PERIOD .

Note

It is possible that the PCU has to perform Radio Access Capability updateprocedure between receiving the PACKET (ENHANCED) MEASUREMENTREPORT message and sending the PACKET CELL CHANGE ORDER message.The value for NCCR_NON_DRX_PERIOD parameter should be set high enoughin order to take this into account.



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MS in RR packet transfer mode

The PCU sends the PACKET CELL CHANGE ORDER to the MS and polls for aPACKET CONTROL ACKNOWLEDGEMENT. If the MS does not respond tothe polling, the PACKET CELL CHANGE ORDER is retransmitted once(without polling).

After sending PACKET CELL CHANGE ORDER, the PCU lets the MScontinue operations in the old cell. When the PCU receives FLUSH, it considersthe cell change successful.

GSM target cell operation

The NETWORK_CONTROL_ORDER field in the PACKET CELL CHANGEORDER message is set to the RESET value, indicating the MS to use thebroadcast value.

Failure to change cell

If the MS fails to connect to the target cell, it sends a PACKET CELL CHANGEFAILURE message to the PCU. If the MS does not have data to send, it requests asingle block in the source cell and sends the PACKET CELL CHANGEFAILURE message in the block. If the MS had an uplink TBF prior to the cellchange order, it establishes a new uplink TBF and sends the PACKET CELLCHANGE FAILURE message on this TBF. In case the MS does not even try toconnect to the target cell, it can send the PACKET CELL CHANGE FAILUREmessage on the PACCH of the existing TBF.

If the cause of the failure indicated in the PACKET CELL CHANGE FAILUREmessage is 'Ongoing CS connection', 'MS in GMM Standby state', or 'Forced tothe Standby state', and the MS is in RR packet idle mode, the PCU deletes the MSNCCR context. In all other cases, the PCU assumes that the MS stays in NC2network control mode and prepares to start receiving measurement reports fromthe MS.

When the PCU receives a PACKET CELL CHANGE FAILURE message from aMS, the PCU does not initiate any further cell re-selections for that MS to aneighbour cell defined by the ARFCN and BSIC in the PACKET CELLCHANGE FAILURE message for a certain period of time. The length of thisperiod of time is defined with the parameter NCCR neighbour cellpenalty (NNCP) .




4.8 Avoiding continuous cell changes between twocells

Continuous cell changes between two cells would cause delays and degradeperformance. They are avoided by using two timers.

Whenever a MS is ordered to select another cell, a timer for the MS is started inthe source cell. The value of this timer is defined with NCCR return to oldcell time (NOCT) parameter.

If the MS returns to a cell where the timer is still running, another timer is started.Only after this timer has expired can the MS be commanded to the same targetcell. The value of the second timer is defined with the NCCR target cellpenalty time (NTPT) parameter.

The timers described above are maintained separately for each MS NCCRcontext.

For an overview of NCCR, see Overview of Network-Controlled Cell Re-selection .



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5 Effect of Network-Controlled Cell Re-selection on interfaces

Radio interface

The following new messages have been introduced due to NCCR:

. PACKET MEASUREMENT REPORT

. PACKET ENHANCED MEASUREMENT REPORT

. PACKET MEASUREMENT ORDER

. PACKET CELL CHANGE ORDER

. PACKET CELL CHANGE FAILURE

. PACKET SYSTEM INFORMATION TYPE 5

There have been changes to the following messages due to NCCR:

. SYSTEM INFORMATION TYPE 13

. SYSTEM INFORMATION TYPE 2QUATER

. PACKET SYSTEM INFORMATION TYPE 1

. PACKET SYSTEM INFORMATION TYPE 3QUATER

Abis interface

No effect.

A interface

No effect.

Gb interface

The Radio Access Capability Update procedure is used with NCCR:



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Effect of Network-Controlled Cell Re-selection on interfaces

. RA-CAPABILITY-UPDATE

. RA-CAPABILITY-UPDATE-ACK





6 User interface of Network-Controlled CellRe-selection

Parameters

New BSC radio network object parameters used by NCCR:

. NCCR control mode (NCM)

. NCCR idle mode reporting period (NIRP)

. NCCR transfer mode reporting period (NTRP)

. NCCR return to old cell time (NOCT)

. NCCR target cell penalty time (NTPT)

. NCCR neighbour cell penalty (NNCP)

. QC reallocation action trigger threshold (QCATR)

. QC NCCR action trigger threshold (QCATN)

. NACC enabled (NACC)

New SEG-specific BTS radio network object parameters:

. NCCR rxlev transfer mode window size (NRTW)

. NCCR rxlev idle mode window size (NRIW)

. NCCR number of zero results (NNZR)

. NCCR streaming TBF offset (NSTO), for PCU2 only

. NCCR other PCU cell offset (NOPO)

. QC GPRS DL RLC ack throughput threshold (QGDRT)

. QC GPRS UL RLC ack throughput threshold (QGURT)

. QC EGPRS DL RLC ack throughput threshold (QEDRT)

. QC EGPRS UL RLC ack throughput threshold (QEURT)



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Old SEG-specific BTS radio network object parameters that are used by NCCR:

. GPRS MS txpwr max cch (GTXP1)

. GPRS MS txpwr max cch1x00 (GTXP2)

. priority class (PRC)

. scale ord (SCO)

. multiband cell reporting (MBR)

. RA reselect hysteresis (RRH)

. routing area code (RAC)

. GPRS rxlev access min (GRXP)

. max BLER in Acknowledge Mode (BLA)

. max BLER in Unacknowledge Mode (BLU)

. HCS threshold (HCS)

New adjacent GSM cell (ADJC) radio network object parameters:

. NCCR EGPRS PBGT margin (EPM)

. NCCR GPRS PBGT margin (GPM)

. NCCR GPRS quality margin (GQM)

. NCCR EGPRS quality margin (EQM)

Old adjacent GSM cell (ADJC) radio network object parameters that are used byNCCR:

. GPRS MS TX pwr max CCH (GTXP1)

. GPRS MS TX pwr max CCH1x00 (GTXP2)

. GPRS temporary offset (GTEO)

. GPRS penalty time (GPET)

. priority class (PRC)

. HCS signal level threshold (HCS)

. GPRS rxlev access min (GRXP)

. BCCH frequency (FREQ)

. network colour code (NCC)




. BTS colour code (BCC)

. routing area code (RAC)

. location area code of reference cell (LAC1-LAC5)

. cell identification of reference cell (CI1-CI5)

New adjacent WCDMA RAN cell (UADJC) radio network object parameter:

. ISNCCR FDD Quality Threshold (FQT)

Old adjacent WCDMA RAN cell (UADJC) radio network parameters that areused by NCCR:

. WCDMA Downlink Carrier Frequency (FREQ)

. downlink transmission diversity (DIV)

. scrambling code (SCC)

. cell identification (CI)

. radio network controller identifier (RNC)

Old Handover (HOC) radio network object parameters that are used by NCCR:

. serving band reporting (SBR)









. number of measured FDD cells (FDMR)

New PRFILE parameters that are used by NCCR:

. NCCR_NON_DRX_PERIOD

. NCCR_MEAS_REPORT_TYPE



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. BSSGP_T5

. BSSGP_RAC_UPDATE_RETRIES

. PCU_LOAD_LOWER_LIMIT

. PCU_LOAD_UPPER_LIMIT

For more information on radio network parameters, see BSS Radio NetworkParameter Dictionary.

For more information on PRFILE parameters, see PRFILE and FIFILE ParameterList.

MMLs

Base Station Controller Parameter Handling in BSC (EE )

The following existing MML commands are used to handle NCCR:

. EEM

. EEO

Base Transceiver Station Handling in BSC (EQ )

The following MML command is introduced due to NCCR:

. EQN

The following MML command is also used:

. EQO

Adjacent Cell Handling (EA )


. EAC

. EAM

. EAO

. EAP

. EAX

. EAE




. EAH

. EAI

Base Transceiver Station Alarms Handling (EO )


. EOO

. EOM

Handover Control Parameter Handling (EH )


. EHC

. EHN

. EHO

GSM Measurement Handling (TP )


. TPI

. TPM

. TPS

Parameter Handling (WO )


. WOC

. WOI

. WOA

. WOS

Counters

A new measurement type is introduced:



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. 27 GPRS Cell Reselection Measurement

. 28 GPRS RX level and Quality Measurement

There are changes to the following measurements:

. 72 Packet Control Unit Measurement.

Alarms

The following new alarms are introduced due to NCCR/ISNCCR:

. 3261 FAILURE IN UPDATING BSC SPECIFIC PARAMETERS TOPCU

. 7769 FAILURE IN UPDATING CELL SPECIFIC PARAMETERS TOPCU

For a detailed description of the alarms, see Failure Printouts (2000 - 3999) andBase Station Alarms (7000 - 7999).





Cell Reselection in NSN

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