nccr

(E)GPRS Radio Networks NCCR Planning and Optimization Guidelines Version 1.0

2/35 CMO SBU MS Network & Service Optimization Capability Management

27/04/2009

Copyright 2007 Nokia Siemens Networks. All rights reserved.

DOCUMENT DESCRIPTION

Title and version (E)GPRS Radio Networks – Planning and optimization guidelines v1.0 Reference Target Group Radio, Tranmission, E2E Technology and SW release

GERAN - S13

Related Service Items

Service Item number

Author Pal Szabadszallasi Date Approver Villa Salomaa

CHANGE RECORD

This section provides a history of changes made to this document

VERSION DATE EDITED BY SECTION/S COMMENTS 1.0 27.04.2009. Pal Szabadszallasi

Copyright © Nokia Siemens Networks. This material, including documentation and any related computer programs, is protected by copyright controlled by Nokia Siemens Networks. All rights are reserved. Copying, including reproducing, storing, adapting or translating, any or all of this material requires the prior written consent of Nokia Siemens Networks. This material also contains confidential information which may not be disclosed to others without the prior written consent of Nokia Siemens Networks.


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Table of contents

1. Introduction....................................................................................... 4

1.1 Resource Allocation in BSS............................................................................................4

2. Functionality of MS controlled cell (re)-selection ............................... 5

2.1 C1, C2 and cell reselect hysteresis.................................................................................5

3. Functionality of Network Controlled Cell (Re)-selection..................... 8

3.1 NCCR Benefits ...............................................................................................................8 3.2 NCCR Functionality ........................................................................................................9 3.2.1 Commanding MS to network control (NC2 mode)...........................................................9 3.2.2 NCCR criteria ...............................................................................................................10 3.2.3 Target cell selection......................................................................................................11 3.2.4 Signaling flow ...............................................................................................................12 3.2.5 NCCR – Power Budget.................................................................................................13 3.2.6 NCCR – Quality Control................................................................................................13 3.2.6.1 Block Error Rate (BLER)...............................................................................................14 3.2.6.2 BLER Degradation Duration Counter............................................................................14 3.2.6.3 BLER Limits are Needed for the Quality Control Function in PCU2 ..............................15 3.2.6.4 Bitrate (BER) ................................................................................................................15 3.2.6.5 Bitrate per Radio Block Degradation Duration Counter .................................................16 3.2.6.6 Corrective Actions ........................................................................................................16 3.2.7 ISNCCR .......................................................................................................................17

4. NCCR planning and optimization .................................................... 20

4.1 Power budget ...............................................................................................................20 4.1.1 Example .......................................................................................................................20 4.1.2 Parameters...................................................................................................................22 4.1.3 OSS counter flow chart.................................................................................................22 4.1.4 Drive test measurement results ....................................................................................23 4.1.5 Summary......................................................................................................................31 4.2 Quality Control..............................................................................................................31 4.2.1 OSS counter flow chart.................................................................................................32 4.2.2 Parameters...................................................................................................................32

5. Cell (re)-selection measurements ................................................... 34

5.1 OSS measurements .....................................................................................................34 5.1.1 Cell re-selection Measurements (NC_0) .......................................................................34 5.1.2 Cell re-selection Measurements (NC_2) .......................................................................34 5.2 Drive tests ....................................................................................................................34


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1. Introduction It is important to allocate the users to the most appropriate layer for maximizing the user data rate (based on maximized RLC/MAC data rate).

The network resources are usually limited (capacity, coverage and interference limited); therefore the proper allocation of users among the resources is very important.

The terminal is firstly allocated to a cell, secondly to a BTS inside segment (if MultiBCF / CBCCH is used) and at the end the allocation is finally based on scheduling.

The (E)GPRS traffic is allocated among:

• Cells (Segments)

In some of the cases the resource allocations are based on simple and independent measurements (C1, C2). From S11.5 Network Controlled Cell Reselection (NCCR) can be used, where the user allocation is network controlled.

• BTSs inside segments

The right BTS (with the maximized TSL data rate and territory) must be selected if MultiBCF or CBCCH are used. So the GPRS capable mobiles can be allocated to BTS with GPRS, while the EGPRS capable terminals are allocated to the EGPRS capable BTS inside the segment.

If EDGE and non-EDGE TRXs are mixed in same BTS, BB Hopping requires segment solution and own hopping groups. (EDGE cannot move to non-EDGE TRX).

• The resource allocation among TSLs is based mainly on PCU algorithm (load

calculations), as well as in case of QoS scheduling.

The calculation of the load of TSLs is done by the PCU and based on the Priority based QoS parameters and different penalties given to the TSLs (PACCH, timeslot type and GPRS/EGPRS multiplexing).

In BSS network further bottlenecks can limit the access to the resources, like EDAP and PCU limitations.

1.1 Resource Allocation in BSS So the resource allocation is based on the following items below:

• Cell-Reselection

• BTS selection and TSL allocation

• Scheduling


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2. Functionality of MS controlled cell (re)-selection First step in resource allocation procedure is the cell selection (and re-selection in mobility). The cell selection and re-selection is based on C1, C2, NCCR and NACC.

Three network control order parameters are defined, which determine the measurement reporting and network control on the MS.

• NC0: MS controlled cell reselection, no measurement reporting;

• NC1: MS controlled cell reselection, MS sends measurement reports;

• NC2: Network controlled cell reselection, MS sends measurement.

NSN in BSS is supporting NC0 and NC2.

NCM is modified with MML command ZEEM.

2.1 C1, C2 and cell reselect hysteresis The Nokia BSS supports network control order NC0, and therefore there are no network controlled cell (re)-selections in (E)GPRS, the cell is selected autonomously by the mobile using the existing path loss criteria C1 and cell reselection parameter C2.

The network broadcasts on the BCCH the Modified system info 3 and System info 13 parameters related to mobility management, which the (E)GPRS mobiles utilize to ensure that they are camped on the cell offering best service in each area.

MS PCU

cell update

FLUSH - LL

SGSN

C1, C2, Criterion triggers

MS PCU

cell update

FLUSH - LL

SGSN

NCCR triggers

PACKET ENHANCED MEASUREMENT REPORT

PACKET CELL CHANGE ORDER

Autonomous MS cell reselection

Network controlled cell reselection


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The MS calculates the value of C1 and C2 for the serving cell and will re-calculate C1 and C2 values for the neighboring cells every 5 seconds. The MS will then check whether:

• The path loss criterion (C1) for current serving cell falls below zero for a period of 5 seconds. This indicates that the path loss to the cell has become too high.

• The calculated value of C2 for a non-serving suitable cell exceeds the value of C2 for the serving cell for a period of 5 seconds.

If, however, in the case of the new cell being in a different location area or, for a (E)GPRS MS, in a different routing area or always for a (E)GPRS MS in ready state, the C2 value for the new cell shall exceed the C2 value of the serving cell by at least CELL_RESELECT_HYSTERESIS (dB).

The idea is that the MS compares field strength levels of different cells defined in the idle mode BA list and selects the most appropriate using the C1 criteria:

C1 = (a-Max(B,0))

A= received level Average – p1

B= p2-maximum RF Power of the Mobile Station

p1= Rxlevel access min

p2= MS TXPower MAX CCH

All values are expressed in dBm. POWER_OFFSET is not used.

In C1 the following parameters must be observed:

Rxlev Access Min (RXP)MS TXPWR Max CCH (TXP1)MS TXPWR Max CCH1x00 (TXP2)

The too low RXP will generate high retransmission, but probably less unexpected TBF release.

TXP1 is used for 800/900 MHz, while TXP2 is used for 1800/1900 MHz.

The C2 parameter can be utilized together with the C1 parameter to provide the operator with greater traffic management capability. The C2 parameter was introduced in GSM phase two and designed for use in layered-architecture networks (micro/macro cell/Dual Band).

The C2 feature brings new parameters:

• penaltyTime (20 ... 640 s) describes the time delay before the final comparison is made between two cells.

• temporaryOffset (0 ... 70 dB) describes how much field strength could have been dropped during this penalty time,

• cellReselectOffset (0 ... 126 dB) describes an offset to cell reselection. C2 cell reselection is calculated by equation


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C2 = C1 + cellReselectOffset - temporaryOffset x H(penaltyTime-T) when penaltyTime < 640

or

C2 = C1 - cellReselectOffset when penaltyTime=640

C2 parameters are used to push slow moving users to the cells with less cell size but probably better signal level, C/l and capacity, so the user data rate can be increased (because of higher TSL RLC/MAC data rate and bigger territory) on micro and pico cells.

M a c ro 9 0 0 “ A "

M a c ro 9 0 0 “C ”

M ic ro 9 0 0 “ D ”

M a c ro 1 8 0 0 “B ”

1. Figure C2 parameters’ usage in multilayer networ k environment

The allocation decision is always based on received level average (RLA_P) for each of the carriers in BA list.


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3. Functionality of Network Controlled Cell (Re)-selection

Target cell to which the cell reselection is done, can be selected by the MS itself or by the network.

In earlier releases Nokia implemented only MS controlled cell reselection without measurement reports, which is basically commanded by Network Control Order 0 (NC0). In NC0, cell reselection is controlled by MS in both MM Ready and MM Standby states whether MS is in Packet Idle Mode or Packet Transfer Mode.

When there is NCCR is enabled, then the cell (re)-selection in MM Ready state is controlled by the network. When MSs go back to MM Stand By state, cell reselection is done by MS as in NC0.

NCCR support is indicated by setting the Network Control Order to NC2.

PBCCH is not needed for NCCR.

NCCR can be enabled for Release97 mobiles onward.

NCCR (Network Controlled Cell Reselection) enables the network to control the resource allocation when the MS performs the cell reselection.

NCCR is an optional feature. Operator can enable/disable the feature on BSC level.

3.1 NCCR Benefits Benefits that Network Controlled Cell (Re)-selection introduces:

o Efficient allocation of EGPRS resources. Some operators introduce EGPRS TRXs gradually in GSM networks. Some cells have EGPRS TRXs and some have not. EGPRS resources will be scarce and will need to be allocated efficiently. PCU will push EGPRS capable MSs to EGPRS cells and GPRS capable MSs to non-EGPRS capable cells by power budget NCCR criterion. Cell attractiveness can be defined neighbour cell specifically also taking into account each neighbour cell’s capacities (e.g. CS-3/CS-4 support).

o Quality criterion allows NCCR when the serving cell quality drops even if the signal level is good.

o Quality Control may trigger NCCR. It means that QoS can trigger NCCR to make cell selection.

o Service based NCCR is possible (SGSN UTRAN CCO BSSGP procedure) in the later releases.

o Possibility to select WCDMA network as soon as it is available or when GSM coverage ends, depending on operator choice.

NCCR is an optional feature. Operator can set the feature on/off on BSC level, and decide whether NCCR to WCDMA FDD cells is allowed.


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3.2 NCCR Functionality

3.2.1 Commanding MS to network control (NC2 mode)

The operator has to set cell adjacencies, NCCR algorithm parameters, Network Control Order (NCO) mode and MS reporting period parameters.

Cell adjacencies and NCO mode are broadcast to MS. Depending on the operator parameter the MS may be commanded to send neighbour cell measurements by broadcasting the command to all MSs or by commanding individual MSs during TBF.

Once commanded to report neighbour cell measurements MS will send neighbour cell measurements to PCU in a frequency defined by the reporting period parameters. MS sends neighbour cell measurements in MM ready state, i.e. RR packet transfer and packet idle modes.

PCU sets MS NCCR context for each MS, which has been commanded, to NCO when first TBF is set for such MS or when first measurement report from such MS is received. PCU performs averaging for the measurements and applies NCCR algorithm to averaged measurements. The NCCR algorithm is based on operator set threshold values, so when certain threshold triggers NCCR is started.

So NC mode is always included in SI messages.

The broadcast value is defined by parameter Broadcast network control mode.

When NC2 is broadcast, all MSs in MM Ready state will be under network control

When NC0 is broadcast, MSs are commanded to NC2 mode by PACKET MEASUREMENT ORDER message depending on the MS 3GPP release support (found from MS RAC) and parameter NCCR control mode (NCM) setting (NCM->3) (see TN_BSC_SW_2006_839)

Network control includes whole MM ready state (MS NCCR context created)

Overload Control: Number of controlled MSs (MS NCCR contexts) is limited by internal PRFILE parameter Max number of MS NCCR contexts

• PACKET MEASUREMENT ORDER commanding extra MSs to NC0 mode is needed to keep service for all MSs

So PCU orders MS to send measurement reports by PACKET MEASUREMENT ORDER message on PACCH.

TBF

time

TBF

Network Control

ready timer

RR Packet Transfer mode RR Packet Idle mode


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New TBF

DL-UNITDATA during TBF

Is there MS RAC included ?

MS RAC received ?

Is PMO(NC2) needed based on mobile’s 3GPP release?

Send PMO(NC2)

No

Yes

No

Yes

measurement report from MS

Execute NCCR algorithms for the MS

Yes

No

STOP

3.2.2 NCCR criteria

S13 includes following NCCR criteria:

• Power budget NCCR

• Quality Controlled NCCR

• Coverage reason ISNCCR

The later BSS releases will introduce the following NCCR types:

• EQoS Quality Control

When serving cell cannot provide the guaranteed throughput or the transmission quality is below operator set threshold, NCCR may be tried to offer better service.

Target cell selection is performed when the QC NCCR trigger comes and always when new PACKET (ENHANCED) MEASUREMENT REPORT message is received until:


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• MS NCCR context is deleted

• TBF is released, or

• QC cancels the NCCR trigger.

• Service based ISNCCR

3.2.3 Target cell selection

The target cell evaluation is based on an RXLEV threshold algorithm, see block diagram bellow. It is shown the algorithm that the BSC would apply for an EGPRS MS. For GPRS MSs the algorithm is the same except for the Rx level margin comparison, which is:

AV_RXLEV_NCELL(N) > AV_RXLEV_SERV + CellReselMarginQualforGPRSMS(n)

for GPRS MS.

Due to separate thresholds for EGPRS capable and non-capable MSs, this criterion cannot be used before the MS EGPRS capability is known.


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Measurement report processing

Is reported BLER over

BLER_THRESHOLD?

Search for the neighbouring cell with

highest AV_RXLEV_NCELL(n)

NO

YES

NO

YES

AV_RXLEV_NCELL(n) >

AV_RXLEV_SERV +

CellReselMarginQualforEGPRSMS(n)

NOYESTrigger NCCR to cell (n)

NCCR successful

NO

YES

AV_RXLEV_NCELL(n) >

RxLevMinCell(n) + Max(0, Pa)

Erase the cell where the failure

occurred from target candidate cell

list until timer

T_NCELL_PENALTY expires

If NCCR is used then the following parameters are taken into account in C1 decision:

• GPRS RXLEV ACCESS MIN (GRXP) instead of RXLEV ACCESS MIN (RXP)

• GPRS MS TXPWR MAX CCH (GTXP1) instead of MS TXPWR MAX CCH (TXP1)

• GPRS MS TXPWR MAX CCH 1X00 (GTXP2) instead of MS TXPWR MAX CCH 1X00 (TXP2)

3.2.4 Signaling flow

The signaling flow of NCCR can be seen below:


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Uplink Packet Data transfer

PACCH

Packet (Enhanced) Measurement Report

MS Serving cell

PACCHPacket Cell Change Order

Measurement and NCCR information regarding target cell

T3174 startsTarget cell

PBCCH

Current TBF on serving cell is aborted!

PBCCH

PBCCH of target cell is received

Waits until PSI1 ocurrence in B0

PBCCHPSI messages

• data transmission is resumed in target cell after all the relevant PSI messages have been received

•The service outage is 2-5 sec

Packet Channel Request

Packet Uplink Assignment

PRACH

PAGCH

T3174 stops

Uplink Packet Data transfer

PACCH

Packet (Enhanced) Measurement Report

MS Serving cell

PACCHPacket Cell Change Order

Measurement and NCCR information regarding target cell

T3174 startsTarget cell

PBCCH

Current TBF on serving cell is aborted!

PBCCH

PBCCH of target cell is received

Waits until PSI1 ocurrence in B0

PBCCHPSI messages

• data transmission is resumed in target cell after all the relevant PSI messages have been received

•The service outage is 2-5 sec

Packet Channel Request

Packet Uplink Assignment

PRACH

PAGCH

T3174 stops

3.2.5 NCCR – Power Budget

With NCCR Power Budget parameters it is possible to:

• Push EGPRS capable MSs to EGPRS cells

• Push non-EGPRS capable MSs to non-EGPRS capable cells

• Delay MSs entrance into a cell

• Avoid moving MSs unnecessary entrance into cells they only briefly pass

NCCR EGPRS PBGT margin (EPM) and NCCR GPRS PBGT margin (GPM) can be used to effectively allocate EDGE and GPRS capable MSs on different cells.

GPRS temporary offset (GTEO) and GPRS Penalty Time (GPET) can be used to avoid unnecessary cell reselection from moving MS to cells they briefly pass. E.g. Pico cells.

Priority Class (PRC) and HCS signal level threshold (HCS) should be used carefully! Preferably not used at all! Wrongly used they can increase ping-ponging and decrease network performance.

3.2.6 NCCR – Quality Control

The purpose of Quality Control (QC) in BSS11.5 onwards is to monitor and detect degradation periods in service quality, and to perform corrective actions to remove the service degradation. The possible actions in BSS11.5 include TBF reallocation and network controlled cell reselection.

NCCR is triggered only if the NCCR feature is active. NCCR activity is controlled by a BSC level parameter NCCR control mode.


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The Quality Control shall maintain statistics about BLER for each TBF as well as bitrate per radio block for each TBF in RLC ACK mode. QC uses this information for monitoring radio link performance and delay.

The monitored samples are filtered. The filtering is based on appropriate threshold values:

• For BLER sample filtering, the threshold value is operator parameter maximum BLER in acknowledged mode (BLA) or maximum BLER in unacknowledged mode (BLU), depending on the RLC mode of the TBF.

• For bitrate per radio block sample filtering, the threshold value is one of the four operator parameters QC GPRS DL/UL RLC Ack Throughput Threshold or QC EGPRS DL/UL RLC Ack Throughput Threshold, depending on the type and mode of the TBF, multiplied with e.g. 1.2 in order to have a safety margin of some degree during the first calculation cycles.

3.2.6.1 Block Error Rate (BLER)

RLC shall report to QC the BLER statistics - number of correctly transmitted RLC data blocks and number of RLC data blocks actually needed to transmit the correct blocks - for all TBFs, independently for UL and DL, and RLC ACK and UNACK mode. Based on BLER information provided by RLC, QC shall calculate and maintain the actual BLER values for each RAT, independently for UL and DL, and RLC ACK and UNACK mode.

The BLER definition in GPRS is straightforward, as the RLC block reception is an independent event. Thus, the BLER in GPRS is the probability of any RLC block received incorrectly. On the contrary in EGPRS with Incremental Redundancy, the reception of a retransmitted RLC block is not an independent event, but depends on the previous receptions of the same block. Thus, the BLER definition in EGPRS must be more general. However, the following formula is justified in both cases:

,1_

_

onstransmissineeded

blockscorrect

N

NBLER −=

where blockscorrectN _ is the number of RLC data blocks received correctly in the

reporting period, and onstransmissineededN _ is the number of transmissions needed for

correct receptions (initial transmission + retransmissions). This definition is valid for both GPRS and EGPRS.

3.2.6.2 BLER Degradation Duration Counter

QC shall maintain the BLER degradation duration counter for each TBF according to the following rules:

- The BLER degradation duration counter shall be incremented by 10, if

(%)_(%)_ BLERMeasuredBLERMAX < ;


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- the counter shall not be modified, if

(%)_(%)_(%)_ BLERMAXBLERMeasuredBLERMAX ≤≤ ;

- The counter shall be cleared (set to zero), if (%)_(%)_ BLERMAXBLERMeasured < .

The QC thread shall monitor the BLER degradation duration counter, and if the counter is larger than predefined triggering levels (BLA, BLU parameters), the corresponding corrective action is tried.

3.2.6.3 BLER Limits are Needed for the Quality Control Function in PCU2

The maximum block error rate (BLER) limit is set with different parameters in PCU1 and PCU2.

For PCU1:

• MAXIMUM BLER IN ACKNOWLEDGED MODE (BLA)

• MAXIMUM BLER IN UNACKNOWLEDGED MODE (BLU)

For PCU2:

• PFC ACK BLER LIMIT FOR TRANSFER DELAY 1 (ABL1)

• PFC UNACK BLER LIMIT FOR SDU ERROR RATIO 1 (UBL1)

The EQoS specific packet flow context (PFC) feature is not applicable with BSC SW release S13 and PCU2 Only the ABL1 and UBL1 parameters are used, although all ABL1-5 and UBL 1-6 parameters are visible. All BLER limit parameters are visible regardless of the EQoS feature’s state.

In Quality Control function the above corresponding parameters are used similarly in both PCU1 and PCU2.The BLER parameter values are not directly comparable though, so they are not converted in the upgrade.

3.2.6.4 Bitrate (BER)

QC will monitor bitrate per radio block for each TBF in RLC ACK mode, for UL and DL separately. The statistic is gathered by RLC, and reported to QC. RLC will be calculated and report values in the following way:

• In downlink, RLC shall maintain counters for transmitted bits (only the payload bits in each RLC data block are taken into account) and transmitted radio blocks.

o The counter for transmitted bits shall contain only new RLC data block transmissions; for the retransmissions, the number of bits transmitted is zero. Pending ACK retransmissions as well as the RLC data blocks


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containing only an LLC dummy block, but no real data, shall be ignored in this calculation.

• In uplink, RLC shall maintain counters for received RLC data block payload bits and received radio blocks.

o When a radio block is received, the counter of received radio block is increased by one. If the RLC data block(s) is/are received correctly, RLC will update the counter of the received RLC data block payload bits accordingly.

o If RLC data block(s) is/are received incorrectly, the number of received payload bits is zero. Radio blocks containing only pending ACK retransmission(s) shall be ignored in this calculation.

QC calculates the bitrate per radio block value once in 200 ms (execution cycle) and it is checked against the corresponding threshold value. Since the unit of the threshold values is kbit/s, QC will convert RLC reported bitrate per radio block by dividing the values with 20 ms (1 block period corresponds 20 ms). Thus the value range of QC calculated bitrate per radio block is from 0 kbit/s to 59,2 kbit/s.

The threshold values are operator parameters and there is a separate value for UL and DL, as well as for GPRS and EGPRS, respectively (look at operator parameters QC GPRS DL/UL RLC Ack Throughput Threshold (QGDRT, QGURT) and QC EGPRS DL/UL RLC Ack Throughput Threshold (QEDRT, QEURT)).

Note. Bitrate per radio block monitoring algorithm does not measure the actual throughput. The algorithm does not take into account the time between samples received from RLC, and thus cannot calculate the real throughput: the output of the algorithm merely describes the quality of the measured TBF in terms of bits it can theoretically transfer per second.

3.2.6.5 Bitrate per Radio Block Degradation Duration Counter

The bitrate per radio block degradation duration counter shall be maintained for each RAT according to the following rules:

- The bitrate per radio block degradation duration counter shall be incremented by 10, when the bitrate per radio block is below the threshold value.

- The counter shall be cleared (set to zero), when the bitrate per radio block is above or equal to the threshold value.

The QC thread shall monitor the bitrate per radio block degradation duration counter. If the counter is larger than predefined triggering levels (QGDRT, QGURT and QEDRT, QEURT parameters), the corresponding corrective action is tried.

3.2.6.6 Corrective Actions

When any of the degradation duration counters monitored by QC gets larger than a predefined action trigger threshold, QC will try to take the corresponding corrective action. Each action will be triggered only once for a TBF in QC (once for a call


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(UL+DL TBFs of the same phone) during one degradation period (degradation timer = 1 second). If the degradation period ends and a new starts, new actions can be tried). For example, if reallocation is already done, next action to be performed is NCCR, triggered when a degradation duration counter exceeds the NCCR trigger threshold. The flags of already performed actions will be cleared when the degradation ends, i.e. when all the degradation duration counters are cleared.

The action trigger thresholds are expressed in block periods and the values can be set by operator, see operator parameters QC Action Trigger Threshold:

• QC reallocation action trigger threshold (QCATR)

• QC NCCR action trigger threshold (QCATN)

• QC QoS renegotiation action trigger threshold (QCATQ) (not implemented in S13)

• QC drop action trigger threshold (QCATD) (not implemented in S13)

It is possible to change the order of different actions by modifying the action trigger threshold values (If the value is set to 0, then no action of that kind is tried).

3.2.7 ISNCCR

Inter-System Network-Controlled Cell Re-selection uses two criteria: coverage and service priority.

The coverage criterion enables the operator to set whether IS-NCCR is started as soon as WCDMA FDD cell coverage is available or whether IS-NCCR is done only when GSM coverage is ending.

In service priority criterion, the actual configuration of the GSM/EDGE vs. WCDMA FDD prioritization for different services is done in the core network. The PCU follows the core network prioritization information received in the Service UTRAN CCO information element.

In target WCDMA FDD cell prioritization, the PCU ranks the target cell candidates based on the reported Ec/No value.


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If the BSC parameter WCDMA FDD NCCR Preferred (WFNP) is set on (Y),

• Y = ISNCCR is triggered as soon as an appropriate WCDMA cell is available. • N = ISNCCR is triggered only in case there is not an appropriate GSM/EDGE cell

available and an appropriate WCDMA cell is available.

the Service UTRAN CCO IE value is ignored and IS-NCCR to WCDMA FDD cell is triggered when any of the WCDMA FDD neighbor cells fulfils the following equation:

AV_3G_MES_QUAN(n) > CellReselQual3GRATThr(n)

– AV_3G_MES_QUAN(n) is the average of 3G measurement quantity – CellReselQual3GRATThr(n) is the value that the AV_3G_MES_QUAN(n)

parameter has to exceed before a cell change to cell 'n' can be ordered. CellReselQual3GRAThr is determined by new adjacent WCDMA RAN cell parameter ISNCCR FDD quality threshold (FQT) CPICH Ec/Io level measured by mobiles (default: -15 dB).

If the parameter WCDMA FDD NCCR Preferred is set off (No), IS-NCCR to WCDMA FDD cell is triggered if

• SGSN has not denied IS-NCCR by Service UTRAN CCO IE • serving and neighbor GSM cells do not fulfill the minimum RXLEV requirements

– AV_RXLEV_SERV > RxLevMinCell + Max(0, Pa), or – AV_RXLEV_NCELL(n) > RxLevMinCell(n) + Max(0, Pa)

• any of the WCDMA FDD neighbor cells fulfill the equation AV_3G_MES_QUAN(n) > CellReselQual3GRATThr(n)


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If there are several WCDMA FDD neighbor cells that fulfill the equation, the cell that has the highest AV_3G_MES_QUAN(n) is selected as the IS-NCCR target cell.


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4. NCCR planning and optimization

4.1 Power budget The averaged serving and neighbor cell RX LEV values are main input to Power budget algorithm.

• Minimum path loss must be provided • C31 and C32 related parameters are used for HCS in S11.5 even if PBCCH is

not configured to a segment • Can be used to force EGPRS MSs to reselect EGPRS cells and keep the GPRS

MSs in non EGPRS capable cells • Can be used to select cells based on their CS3/4 capabilities

Due to separate thresholds for EGPRS capable and non-capable MSs, this criterion cannot be used before the MS EGPRS capability is known.

4.1.1 Example

Negative power budget margin value:

• Network will order the EGPRS MS to select neighbouring cell around the location A.

=> EGPRS MS would be pushed to EDGE capable cell.

• This is done although the average received signal level from the EDGE capable cell is lower than on from the regular cell.

• In opposite direction: EDGE MS moves away from EDGE capable cell and approach to non EDGE capable cell the cell-reselection would be triggered in location B.


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� EGPRS MS is held longer on EDGE capable cell.

The following graph shows the negative power budget functionality:

Average RXLEV from GSM

cell A

verage RXLEV

from ED

GE cell

Distance between cells

EDGE capable cellGSM capable cell

Power budget margin

AB

Positive power budget margin value:

• GPRS MSs are kept in regular cells as long as possible to reserve EDGE resources for EGPRS MSs.

• Network will order the GPRS MS to select neighbouring cell around the location A.

=> GPRS MS is kept in the GSM cell longer.

• When GPRS MS move away from EDGE capable cells and approach to non-EDGE-capable cells the cell-reselection is triggered in location B.


cell A

verage RXLEV

from ED

GE cell



Power budget margin

AB


cell A

verage RXLEV

from ED

GE cell



Power budget margin

AB


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4.1.2 Parameters

NCCR EGPRS PBGT margin (EPM)

• With this parameter you define the threshold which is used for EGPRS MSs as a power budget margin in the NCCR power budget process.

• Range: -63 to 63 (dB) • Default: 6 (dB)

NCCR GPRS PBGT margin (GPM)

• With this parameter you define the threshold which is used for GPRS MSs as a power budget margin in the NCCR power budget process.

• Range: -63 to 63 (dB) • Default: 6 (dB)

HCS signal level threshold (HCS)

• With this parameter you define the signal strength threshold for applying HCS in GPRS reselection.

• Range: -110 to –48 (dBm) and N • Default: N (= HCS not in use)

Priority class (PRC)

• With this parameter you define the HCS (hierarchical cell structures) priority for the cells. 0 is the lowest and 7 is the highest priority.

• Range. 0 to 7 • Default: 0

GPRS temporary offset (GTEO)

• With this parameter you define the negative offset of the HCS criterion for the duration of the GPRS penalty time (GPET) after the MS has placed the cell on the list of the strongest carriers.

• Range: 0 to 70 (dB) with a step size of 10 dB • Default: 0 (dB)

GPRS penalty time (GPET)

• With this parameter you define the duration for which the GPRS temporary offset (GTEO) applies.

• Range: 10 to 320 (s) with a step size of 10 s • Default: 10s

4.1.3 OSS counter flow chart The following flow chart shows the functionality of counters for power budget NCCR.


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Measurement

received

Order cell changePCCO message

NCCR

successful?

Cell change successful

Run NCCR algorithm

yes

no

95012, 95016, 72187

95002, 9500395005

Trigger NCCRConditions

Met?

yes72188 & 72189

PBGTISNCCR

Con

tinue

in o

ld c

ell

9501

4

95009CS connection

Ass. reject

No response MS

Other

95008

95013

95007

95011

PCU time expire

MS in standby95010

Con

tinue

in o

ld c

ell

9501

4

95009CS connection

Ass. reject

No response MS

Other

95008

95013

95007

95011

PCU time expire

MS in standby95010

noContinue

In old cell

No counterEnough

Resources?

yes

No started

due to AC95015

4.1.4 Drive test measurement results

Serving cell RxLev

Packet Transfer Mode

Default values

Offset 6 dB when going from EDGE to GPRS cell

Offset 6 dB when going from GPRS to EDGE cell


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Result: Cell reselection locations same as in Idle Mode.

EDGE

EDGE

GPRS

BTS

EDGE

EDGE

GPRS

BTSBTS



Offset -6 dB when going from GPRS to EDGE cell

Result: EDGE MS stay longer on EDGE cell and re-enters EDGE cell earlier.


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EDGE

EDGE

GPRS

BTS

Cell border with default values


EDGE

EDGE

GPRS

BTSBTS






Result: EDGE MS does not enter GPRS cell.


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EDGE

EDGE

BTS



EDGE

EDGE

BTSBTS



Packet Idle Mode

Offset 24dB when going from EDGE to GPRS cell


Result: NCCR functions also properly in Packet Idle Mode. EDGE MS does not enter GPRS cell.

Measurement reporting period:

• Packet Idle Mode = 3,84s • Packet Transfer Mode = 0,48s

As long as MM Ready Timer has not expired (44s default) MS will stay in Packet Idle Mode.

When timer expires MS will move to Idle Mode

=> MS is not longer controllable by NCCR


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EDGE

EDGE

BTSBTS




• GPRS cell: HCS threshold = -60dBm • EDGE cell: HCS threshold = -110dBm

Result:

Use of the HCS threshold can significantly increase the Ping-pong-effect and decrease the network performance.

Ping-ponging occurs when the RXLEVEL fluctuates around the HCS threshold => cell is included in the NCCR calculations on and off.

HCS threshold should not be used together with the PRC parameter.

Best is to avoid the use of the HCS threshold.


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EDGE

EDGE

GPRS

BTS

EDGE

EDGE

GPRS

BTSBTS

Ping pong

Ping pong

Ping pong


• GPRS cell: PRC = 1 • EDGE cells: PRC = 7

With Priority Class (PRC) parameter one can prioritize one cell over another. The parameter is used in cells which fulfil the HCS statement ≥≥≥≥ 0.

• Can e.g. be used to prioritize Pico- and Micro cells. (indoor sites)

Result: GPRS cell is not selected since its priority is lower than the EDGE cells.

Prioritization should be used very carefully and only in cells with sharp borders (in practice indoor sites).

Prioritizing can increase ping-ponging and decrease the network performance if wrongly used.

Best is to avoid the use of the Priority Class Parameter.


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EDGE

EDGE

BTS

EDGE

EDGE

BTS


GPRS temporary offset (GTEO)

• Pico cell = 70 dB

GPRS penalty time (GPET)

• Pico cell = 120 s

Result: Pico cell is not selected during the Penalty timer.

GPET and GTEO should mainly be used for indoor sites to avoid unnecessary cell reselections from moving MSs to these sites.


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No Penalty Penalty

Pico cell Pico cell

Pico cell is not selected during the Penalty timer.

=> Unnecessary cell reselection to Pico cell is avoided.

No Penalty Penalty

Pico cell Pico cell

Pico cell is not selected during the Penalty timer.

=> Unnecessary cell reselection to Pico cell is avoided.


EPM = 12 dB when going from EDGE to GPRS cell

EPM = 0 dB when going from GPRS to EDGE cell

Result: EDGE MS stay slightly longer on EDGE cells and re-enters EDGE slightly earlier.


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GPRS

EDGE

EDGE

BTS

GPRS

EDGE

EDGE

BTSBTS



4.1.5 Summary With NCCR Power Budget parameters it is possible to:

• push EGPRS capable MSs to EGPRS cells • push non-EGPRS capable MSs to non-EGPRS capable cells • delay MSs entrance into a cell • avoid moving MSs unnecessary entrance into cells they only briefly pass

NCCR EGPRS PBGT margin (EPM) and NCCR GPRS PBGT margin (GPM) can be used to effectively allocate EDGE and GPRS capable MSs on different cells.

GPRS temporary offset (GTEO) and GPRS Penalty Time (GPET) can be used to avoid unnecessary cell reselection from moving MS to cells they briefly pass. E.g. Pico cells.

Priority Class (PRC) and HCS signal level threshold (HCS) These two parameters should be used carefully! Preferably not used at all! Wrongly used they can increase ping-ponging and decrease network performance.

4.2 Quality Control The detailed analysis of quality controlled NCCR will be explained later on, because the unreliability of the QC counters. The corrections are promised from S12 CD8.0 onwards.


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4.2.1 OSS counter flow chart

The following flow chart shows the functionality of quality control counters.

TR BL BR

Trigger

NCCR

find

Neighbor

Conditions

Met?

95006

97027

>QCATR

< QCATN?Trigger (TBF)

Re-allocation

>QCATN

< QCATQ?

QC indicator under

Target?

- BLU / BLA

- DRT/URT (QE/QG)

- UBL1-3

Eva

luat

e nr

of b

elow

targ

et b

lock

s

noNo good ncell

Found due to QC

Order cell changePCCO message

72185

Continue in

old cell

97028 97029

TR BL BR97030 97031 97032

yes

No started

due to AC95015

yes

no

reallocation72027, 72028

106024

Enough

Resources?NCCR

successful?

successful?

72032

72033

no

yes

no

Cel

l cha

nge

succ

essf

ul

yes

NCCR

unsuccessful 95014

9501

2, 9

5016

, 721

87

95007-95011, 95013

4.2.2 Parameters The following parameters can be used to adjust QC functionality:

• Maximum BLER in acknowledged mode (BLA)

• Maximum BLER in unacknowledged mode (BLU)

• QC GPRS DLRLC Ack Throughput Threshold (QGDRT)

• QC GPRS DL RLC Ack Throughput Threshold (QGURT)

• QC EGPRS DL RLC Ack Throughput Threshold (QEDRT)

• QC EGPRS UL RLC Ack Throughput Threshold (QEURT)

• NCCR_NON_DRX_PERIOD

• NCCR_STOP_UL_SCHEDULING

• NCCR_STOP_DL_SCHEDULING

• NCCR_MEAS_REPORT_TYPE

• BSSGP_T5


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• BSSGP_RAC_UPDATE_RETRIES


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5. Cell (re)-selection measurements

5.1 OSS measurements

5.1.1 Cell re-selection Measurements (NC_0)

The following KPIs tell how often a TBF is interrupted due to a cell re-selection.

• tbf_63

• tbf_64

This is calculated on the source cell, there is no information of where the target is, so it is not possible to distinguish between e.g. C2 and C31/C32 effects.

The duration and thereby the impact on the applications are not known.

The following parameter shows the number of NACC usage to assist MS in network control mode 0.

• c95017 (NACC_WITH_NC0)

Drive tests are needed to measure cell re-selection behavior properly.

5.1.2 Cell re-selection Measurements (NC_2)

The following KPIs show the NCCR functionality.

• Nccr_12: Number of network controlled cell reselections compared to data amount

• Nccr_13: Successful NCCR ratio

• Nccr_14: Average duration of successful NCCRs

The following parameter shows the number of NACC usage to assist MS in network control mode 2.

• c95018 (NACC_WITH_NC2)

QC triggers actions (reallocations/NCCR) due to RB bitrate if measured radio block bitrate stays under configured thresholds (QC EGPRS DL RLC ack throughput threshold (QEDRT), QC EGPRS UL RLC ack throughput threshold (QEURT), QC GPRS DL RLC ack throughput (QGDRT), QC GPRS UL RLC ack throughput (QGURT)). Default values for the parameters are 10, 10, 6 and 6 kbit/s, correspondingly. It seems that the QC action is triggered too sensitively with the default parameter setup, so the mentioned parameter values could be lowered.

Because the NCCR_QC_TRIG_NO_GOOD_NEIG counter used in nccr_13 seems to be triggered heavily, the nccr_13 will shows bad figures. NCCR_QC_TRIG_NO_GOOD_NEIG counter upgrade can be reduced, if the QC parameter setup has lower values.

5.2 Drive tests


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Between the first system info message and the Packet Uplink Assignment the connection is established between the MS and PCU.

Between the first system info message and the Packet Downlink Assignment the connection is established between the MS and SGSN.

The following table shows the layer3 messages during cell selection with NC0.

Event name Time Channel MessageRLC/MAC Uplink 20:42.0 PACCH "EGPRS_PACKET_DOWNLINK_ACK/NACK"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_1"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_2"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_3"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_4"… … … …

Layer 3 Downlink 20:42.6 BCCH "SYSTEM_INFORMATION_TYPE_4"Cell Reselection 20:42.8 from CI 5032 to CI 5033Layer 3 Downlink 20:42.8 BCCH "SYSTEM_INFORMATION_TYPE_2"… … … …

Layer 3 Downlink 20:43.1 BCCH "SYSTEM_INFORMATION_TYPE_13"Layer 3 Uplink 20:43.1 RACH "CHANNEL_REQUEST"Layer 3 Downlink 20:43.2 CCCH "IMMEDIATE_ASSIGNMENT"Layer 3 Downlink 20:43.2 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.2 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.3 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.3 BCCH "SYSTEM_INFORMATION_TYPE_2"… … … …

Layer 3 Downlink 20:43.8 BCCH "SYSTEM_INFORMATION_TYPE_13"RLC/MAC Uplink 20:43.8 PACCH "PACKET_RESOURCE_REQUEST"RLC/MAC Downlink 20:44.0 PACCH "PACKET_UPLINK_ASSIGNMENT"RLC/MAC Downlink 20:44.0 PACCH "PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK"RLC/MAC Downlink 20:44.0 PACCH "PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK"… … … …

RLC/MAC Downlink 20:44.2 PACCH "PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK"RLC/MAC Downlink 20:44.2 PACCH "PACKET_DOWNLINK_ASSIGNMENT"RLC/MAC Uplink 20:44.3 PACCH "EGPRS_PACKET_DOWNLINK_ACK/NACK"

The following table shows the layer3 message flow in cell selection with NCCR (Packet Cell Change Order).


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nccr

Documents

prior written

predefined

system info

power budget

nokia siemens

user data

rxlev access

correct blocks