Enhanced Packet Cell Reselection Ed5

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All rights reserved 2005, Alcatel

Enhanced Packet Cell Reselection

August2005


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All rights reserved 2005, AlcatelEnhanced Packet Cell Reselection / July2005

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Enhanced Packet Cell ReselectionIntroduction

The Enhanced Packet Cell Reselection feature includes sub-featuresallowing to reduce cell reselection duration and to avoid (NC2 mode)to direct MS towards high loaded cells.

Reduction of the service outage during packet cell reselection (NC0 and

NC2 modes) : Network Assisted Cell Change Procedures (NACC) : MS acquires target cell (P)SI

in the serving cell. Only for R4 MS.

Packet (P)SI Status procedure : access to a new cell without having previouslyacquired the full set of P(SI). Mainly for R4 MS.

In NC2 mode, prevention from directing MSs towards high loaded cells,where the MS can be served with non-optimum resources, or even worse,rejected due to congestion

NC2 improvement : Cell ranking with load criteria


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Enhanced Packet Cell ReselectionContent

NC2 improvement

Network Assisted Cell ChangeNACC NC2NACC NC0

Packet (P)SI StatusPacket PSI StatusPacket SI Status


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Enhanced Packet Cell ReselectionNetwork Assisted Cell Change (NACC)

The NACC takes place in serving cell and consists of 2 independentprocedures:

CCN mode procedure (Cell Change Notification)

Procedure in MS to notifies the network when the cell reselection is decided inPacket Transfer Mode and delays the cell reselection to let the network act on need,eventually through the Cell System Information distribution procedure.

Cell System Information distribution

Procedure to assist an MS in Packet Transfer Mode with target cell systeminformation required for initial packet access after a cell change. This information issent to the MS in the serving cell and before the cell change is performed.

Cell A Cell BPartialSys Info.of Cell B


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Enhanced Packet Cell ReselectionNetwork Assisted Cell Change - NC0 (1/2)

When EN_NACC =enable, the CCN mode is ordered through System Information to allR4 MSs supporting GERAN feature package 1 in the cell.

Scenario describes the NACC procedure in NC0 modeCell BMS Cell A

Ongoing data transfer

Target cell choice (1)T3206

RLC data block polling

Packet Cell Change Notification (2)

Packet Neighbor Cell Data (PSI14)

Packet Neighbor Cell Data (PSI1)

Packet Neighbor Cell Data

(PSI2-first instances)

Packet Neighbor Cell Data(PSI2-intermediate instances)

Packet Neighbor Cell Data

(PSI2-last instances)

Packet Cell Change continue (4)

T3210

T3208

T3208n

Retrieval PSI instances

of the chosen cell (3)

Note: The figure above covers the case where there is a PBCCH in the target cell. When thereis no PBCCH channel in the target cell, the same scenario takes place with BSS sendsthe SI13, SI1 and SI3 messages instead of the PSI14, PSI1 and PSI2 messages.

(1) T3206 monitors the sending of

the Packet Cell Change

Notification.

(2) At receipt of the PACKET CELLCHANGE NOTIFICATION

message, the MFS checks

whether the proposed cell

belongs to the same BSS as

the serving cell. If the proposed

cell does not belong to the

same BSS (BSC_ID(n) (target

cell) BSC_ID (serving cell)),

a PACKET CELL CHANGE

CONTINUE (PCCC) message

is sent to the mobile station

without sending any neighbor

cell system information.


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(3) In the case, the neighbor cell belongs to the same BSS, RRM starts the timer T3208n (T3208 RTD)that monitors the sending of the PCCC and retrieves the SI13 / SI1 / SI3 or PSI14 / PSI1 / PSI2

instances currently broadcast in the neighbor cell and requests MAC to send the relevant (P)SI to the MS

if the target cell supports a PBCCH channel, RRM encodes the PSI14, PSI1 and PSI2 instances

of that cell in one or multiple instances of the PACKET NEIGHBOR CELL DATA message which

are sent to the MS, followed by a PACKET CELL CHANGE CONTINUE message .

if the target cell does not support a PBCCH channel, RRM encodes the SI13, SI1 and SI3

instances of that cell in one or multiple instances of the PACKET NEIGHBOR CELL DATA

message. When the MS sends the Packet Cell Change Notification message, the MS activates the timer

T3210 to wait for a response from the BSS, if timer expiry, the Packet Cell Change Notification is

retransmitted. The MS also activates the timer T3208 to wait for PACKET CELL CHANGE

CONTINUE from the BSS (at timer expiry, the MS will continue the cell reselection in NC0

mode).

(4) When RLC has sent all the instances of the PACKET NEIGHBOUR CELL DATA message, the PACKET

CELL CHANGE CONTINUE (PCCC) message is sent on the PACCH of the MS and the timer T3208n isstopped. It is to be noted that no PCA is requested to acknowledge the PCCC (No T_Ack_Wait timer is

launched by the BSS when sending the PCCC because at the timer expiry, the mobile station has

already left the CCN mode either because it has received the PCCC or because T3208 has already

expired and it is not necessary to send the PCCC again).

When the mobile station receives the PACKET CELL CHANGE CONTINUE message, it shall leave CCN

mode and continue cell reselection in NC0 mode.


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NC2 cell reselection execution with Cell System Information Distribution(1) An UL or DL TBF is assumed on-going.

(2) The MS sends a Packet Measurement Report message on one of the allocated UL block onPACCH

(3) Upon receipt of the Packet Measurement Report message, the BSS detects that a cell reselectionmust be triggered. It finds out that the target cell, belongs to the same BSS, and the MS supportsthe acquisition of neighbor cell (P)SI.

MS BSS Serving cell BSS Target cell

Ongoing UL or DL TBF (1)

Packet Measurement Report / PACCH (2)

Packet Neighbor Cell Data / PDCHs (4)

Packet Neighbor Cell Data / PDCHs

Packet Cell Change Order / PACCH (5)

Packet Control Acknowledgement / PACCH (7)

T_ACK_WAIT

(3)

(6)

(4) The BSS sends the PNCDs to the MS,on all the PDCHs of the TBF, totransmit the (Packet) SystemInformation for the target cell:

SI13, SI1 and SI3 for a target cellwithout PBCCH

or PSI14 (containing the same

information as SI13), PSI1 and aconsistent set of PSI2 for a targetcell with a PBCCH.

In case both a UL and a DL TBF exist,PNCDs are sent on the DL TBF.


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(5) When all the PNCDs have been sent, the BSS orders the MS to reselect a new cellby sending a Packet Cell Change Order message on the PACCH of the DL or ULTBF. If both an UL and a DL TBFs are on-going, the message is preferentiallyaddressed by a DL TFI.

The Packet Cell Change Order message is sent in acknowledged mode andcontains the ARFCN and the BSIC of the target cell.

When sending the Packet Cell Change Order message, the BSS starts the timerT_ACK_WAIT to monitor the receipt of the Packet Control Acknowledgementmessage.

(6)-(7) Upon receipt of the Packet Cell Change Order message, the MS aborts its on-goingTBF in the serving cell and sends the Packet Control Acknowledgement message,then switches to the new cell.


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NC2 improvement

Network Assisted Cell Change NACC NC0

NACC NC2

Packet (P)SI StatusPacket PSI StatusPacket SI Status


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Enhanced Packet Cell ReselectionPacket (P)SI Status

Packet (P)SI status feature allows MS to make an access to a new cell withouthaving previously acquired the full set of SYSTEM INFORMATION (resp.PACKET SYSTEM INFORMATION if PBCCH is present in the target cell)messages sent on the BCCH channel (resp. PBCCH) of the target cell.

The Packet (P)SI Status procedure takes place in the target cell if in this cell,

EN_PSI_STATUS = Enable.

Packet PSI Status procedure is a feature standardized from Release 97 onwards,optional for Release 97, Release 98 and Release 99 MS, and mandatory for Release4 onwards MS supporting GERAN Feature Package 1.

Packet SI Statusprocedure is a new feature standardized in Release 4, mandatoryfor Release 4 onwards mobile stations supporting GERAN Feature Package 1.

Cell A Cell BPartial

Sys Info.

Remaining

Sys Info.


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Enhanced Packet Cell ReselectionPacket SI Status (1/2)

(1) When reselecting a new cell withouta PBCCH channel and supportingthe PACKET SI STATUS procedure(EN_PSI_STATUS = enable), theMS can immediately request the

establishment of an uplink TBFprovided it has acquired the SI13,SI3 and SI1 message (if present) ofthis new cell. It can then send a cellupdate or restarts its on-going datatransfer.

(2) The MS asks BSS to provide themissing system information bysending a PACKET SI STATUSmessage on PACCH.

Cell BMS Cell A

RLC data block (1)

Packet SI status (SI2, SI2bis, SI2ter message type missing) (2)

Scheduling of the serving cell SI message to MS

Packet serving cell data (SI2 message) (4)

Packet serving cell data (SI2bis message)

Packet serving cell data (SI2ter message)

Completion of UL LLC PDU transfer

RLC data block

Packet Uplink ACK/NACK

T_PSCD_SCHE

DULE_ACK

(3)

Scenario of the Packet SI Status procedure


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Enhanced Packet Cell ReselectionPacket SI Status (2/2)

(3) When receiving the MS request, if a downlink TBF is already established, or ifa downlink TBF is being established, or if a downlink TBF will soon beestablished (DL LLC PDU are being rerouted to the new cell), then the BSSshall wait until full establishment of the DL TBF to send requested SIs on allthe downlink PDCHs allocated to the MS. Otherwise, SIs are sent on all thePDCHs of the uplink TBF.

A supervision timer (T_PSCD_SCHEDULE_ACK) is started to monitor thesending of the SI messages to the mobile.

(4) The SI instances are encapsulated in one or multiple instances of a PACKETSERVING CELL DATA message and sent individually to the mobile station.

When the last SI is sent to the mobile, T_PSCD_SCHEDULE_ACK is stopped

(RLC indicates to RRM that all the SIs have been sent).


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Enhanced Packet Cell ReselectionPacket PSI Status (1/2)

(1) When reselecting a new cell with aPBCCH channel and supporting thePACKET PSI STATUS procedure(EN_PSI_STATUS = enable), theMS can immediately request the

establishment of an UL TBF,provided it has acquired the PSI14,PSI1 and PSI2 messages of thisnew cell. It can then send a cellupdate or restarts its on-going datatransfer.

(2) The MS asks the BSS to provide themissing system information bysending a PACKET PSI STATUSmessage on a PACCH block.

Scenario of the Packet PSI Status procedure

Cell BMS Cell A

RLC data block (1)

Packet PSI status (PSI3, PSI3bis missing) (2)

Scheduling of the serving cell PSI messages to MS

Packet serving cell data (PSI3bis message) - first instance

Packet serving cell data (PSI3bis message) - intermediate instance

Packet serving cell data (PSI3bis message) - last instance

Completion of UL LLC PDU transfer

RLC data block

Packet Uplink ACK/NACK

T

_PSCD_SCHEDULE_

ACK

(3)

Packet serving cell data (PSI3 message)


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Enhanced Packet Cell ReselectionPacket PSI Status (2/2)

(3) When receiving the MS request, if a DL TBF is already established, or isbeing established, or will soon be established (DL LLC PDU are beingrerouted to the new cell), then the BSS shall wait until full establishment ofthe DL TBF to send requested PSIs on all the downlink PDCHs allocated tothe MS. Otherwise, PSIs are sent on all the PDCHs of the uplink TBF. Asupervision timer (T_PSCD_SCHEDULE_ACK) is started to monitor thesending of the PSI messages to the mobile.

(4) When the last PSI is sent to the mobile, T_PSCD_SCHEDULE_ACK isstopped.


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NC2 improvement

Network Assisted Cell Change NACC NC0

NACC NC2

Packet (P)SI Status Packet SI Status Packet PSI Status


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Enhanced Packet Cell ReselectionNC2 improvement (1/4)

Cell load evaluation

NC2 load sampling

The NC2 load is sampled every T_NC2_LOAD_RANKING seconds bydividing the used bandwidth by the total bandwidth available in the cell

with:

UL_PS_used_Bandwidth => bandwidth used by PS traffic in the UL direction

DL_PS_Used_Bandwidth => bandwidth used by PS traffic in the DL direction,

CS_Used_Bandwidth => bandwidth used by CS trafficTotal_PS_Bandwidth => total bandwidth available in the cell.


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UL_PS_Used_Bandwidth

nULTBF,i defines the number of UL TBFs on the allocated PDCH i.

NULTBF is the maximum number of UL TBFs that can be pilled up on the PDCHs (defined by the parameterMAX_UL_TBF_SPDCH).

The UL PS used bandwidth is then defined as the sum of the bandwidth used by the UL TBFs over all the PDCHsallocated to the MFS.

DL_PS_Used_Bandwidth

In the DL direction, the DL used bandwidth is computed in a similar way as the UL direction.

CS_Used_Bandwidth

The bandwidth used by the CS traffic is defined by the difference between:

The maximum number of slave PDCHs that can be allocated in the cell (number of slave PDCHs = MAX_PDCH -NB_TS_MPDCH) ,

The number of slave PDCHs currently allocated to the MFS in the cell

N

nB

TBFUL

i,TBFUL

i,UL

OCATEDN_PDCH_ALL

1i

i,ULUL BB


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Example: It is assumed:

The following repartition of the DL TBFs is used,

The UL_PS_Used_Bandwidth is lower than the DL_PS_Used_Bandwidth. Thus, it is not computed.

N_PDCH_ALLOCATED = 8;

MAX_DL_TBF_SPDCH = 3

MAX_SPDCH = 8 and 7 slave PDCHs are allocated to the MFS.

In this example, the total bandwidth is equal to 8, the DL_PS_used_bandwidth is equal to 4x1/3 + 3x2/3 = 10/3.

Therefore, the NC2_load is equal to [(10/3)+ 1]x100/8 = 13x100/24 = 54.16 %

Time Slot 0 1 2 3 4 5 6 7

3

CS2 DL TBF3

1 DL TBF1 DL TBF2

BDL , i 1/3+1/3=2/3 1/3+1/3=2/3 1/3+1/3=2/3 1/3 1/3 1/3 1/3 0


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NC2 load averaging

The NC2 load samples are further averaged using a sliding window. The size of thesliding window is defined by the parameter NC2_LOAD_EV_PERIOD.

Load evaluation of internal BSS cells

Every T_NC2_LOAD_RANKING, the BSS compares the computed NC2 load of thecell to the threshold THR_NC2_LOAD_RANKING:

If the NC2 load average is lower than or equal to the threshold, the cell is considered in a low loadsituation

If the NC2 load average is higher than the threshold, the cell is considered in a high load situation.

The MFS shares the NC2 load situation information among the different cells of theBSS (or at least between the cells having a cell reselection link to the serving cell),i.e. low/high load. That exchange of information is taking place everyMULTI_GPU_INFO_BROADCAST_PERIOD.

Load evaluation of external BSS cells

All external cells to the BSS will always be considered as in low load situation,because of the threshold THR_NC2_LOAD_RANKING of an external cell is unknownfor the BSS.


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Enhanced Packet Cell ReselectionNC cell reselection ranking

The NC2 cell ranking process consist of 2 cases.

Case 1: there is a PBCCH in the serving cell

The cell ranking list is built as follows:

Cells with C31NC2 > 0

NC2_Load situation [low => high PS load];

Cell PRIORITY_CLASS [high => low]; C32NC2 [high => low]

Cells with C31NC2 < 0

C32NC2 [high => low]

Case 2: there is no PBCCH in the serving cell

The cell ranking list is built as follows:

Cells with C31NC2 > 0

NC2_Load situation [low => high PS load];

C2NC2 [high => low]

Cells with C31NC2 < 0

C2NC2 [high => low]

C31NC2

NC2_load

C2NC2

high

low

priority

NC2_load

PRIORITY_CLASS

C32NC2

high

low

priority

C31NC2


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Enhanced Packet Cell ReselectionOMC-R parameters

HMI name Definition Sub-system

Instance

OMC-Raccess

Type Defvalue

Range Unit

EN_NACC Enables the Network Assisted Cell Change feature. MFS cell Changeable

Flag 0 [0,1] None

T3208n Timer guarding on network side the sending of PacketNeighbor Cell Data messages for NACC feature. It isstarted at reception of Packet Cell Change Notificationmessage, and stopped when all PNCDs have beensent to MS (as indicated by RLC layer to RRM layer).

MFS MFS None(DLS)

Timer 0.8 [0,1] sec

EN_PSI_STATUS Enables the Packet SI Status feature in cells w/oPBCCH or the Packet PSI Status feature in cells with aPBCCH.

MFS cell Changeable

Flag 0 [0,1] None

T_PSCD_SCHEDULE_ACK Timer guarding on network side the sending of PacketServing Cell Data or PSI messages for Packet (P)SI

Status feature. It is started at reception of Packet PSIStatus / Packet SI Status message, and stopped whenall PSCDs / PSIs have been sent to the mobile (asindicated by RLC layer to RRM layer).

MFS MFS None(DLS)

Timer 0.84 [0,2] sec

T_NC2_LOAD_RANKING Period of the cell load evaluation for the NC2 cellranking process MFS MFS None(DLS) Timer 5 [1,100] secNC2_LOAD_EV_PERIOD Number of NC2 load samples used to compute theNC2 load average MFS MFS None(DLS) Number 3 [3,30] NoneTHR_NC2_LOAD_RANKING Threshold above which the load of the serving cell isconsidered in a high load situation in the NC2 cell

ranking process

MFS cell Changeable

Threshold

0 [0,100] None

Multi_GPU_INFO_BROADCAST_PERIOD RRM reporting period to update the information (percell) necessary for the Multi-GPU feature. MFS MFS None(DLS) Timer 10 [1,255] sec


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Enhanced Packet Cell ReselectionMFS counters

Counternumber Name DefinitionP456 NB_PSI_PROC Number of times the procedure of broadcast of serving

cell PSI for Packet PSI Status or the procedure ofsending of Packet Serving Cell Data for Packet SI Statusis invoked.

P457 NB_PSI_MES Signaling load induced in the cell by the procedure of

broadcast of (P)SI messagesP458 NB_NEIGH_PSI_PROC Number of times the procedure of broadcast of neighbor

(P)SI messages is invoked

P459 NB_NEIGH_PSI_MES Signaling load induced in the cell by the procedure ofbroadcast of neighbor (P)SI messages

P460a AV_SOURCE_NACC_CELL_RESEL_TIME Average Network Assisted cell reselection duration.

P460b MAX_SOURCE_NACC_CELL_RESEL_TIME Maximum Network Assisted cell reselection duration.

P460c MIN_SOURCE_NACC_CELL_RESEL_TIME Minimum Network Assisted cell reselection duration.

P464 NB_NC2_CELL_RESEL_FAIL_LOAD Number of NC2 cell reselection failures reported by theMS due to load (cause: "immediate assign reject" or"packet access reject on target cell")


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Enhanced Packet Cell ReselectionNPA indicators

Ref. name Name Formula Unit TableName

QRCR2FLRLN CELL_RESEL_NC2_FAILURE_LOAD_NUMBER P464 number GPQOS1

QRCR2FLRLO CELL_RESEL_NC2_FAILURE_LOAD_RATIO tdiv(P464,P437a,0,0) % NONE

QRCR2FLRLR CELL_RESEL_NC2_FAILURE_LOAD_RATE tdiv(P464,P433a + P433b + P433c +P433d,0,0)

% NONE

QRCR2FLBPN CELL_RESEL_NC2_FAILURE_BSS_PROBLEM_NUMBER

P433a + P433b + P433c + P433d -(P435a + P435b + P435c + P435d)-

P437a - P437b-P464

number GPQOS1

QRCRNSCAVT AV_SOURCE_NACC_CELL_RESEL_TIME P460a ms GPQOS1

QRCRNSCMAT MAX_SOURCE_NACC_CELL_RESEL_TIME P460b ms GPQOS1

QRCRNSCMIT MIN_SOURCE_NACC_CELL_RESEL_TIME P460c ms GPQOS1

TRCRNN NB_NEIGH_PSI_PROC P458 number GPQOS1

TRCRPN NB_PSI_PROC P456 number GPQOS1

TRPADNAN NB_NEIGH_PSI_MES P459 number GPQOS1

TRPADNAR DL_PACCH_NACC_RATE tdiv(P459,P59 + P459 + P457,0,1) number GPQOS1

TRPADPSN NB_PSI_MES P457 number GPQOS1

TRPADPSR DL_PACCH_PSI_RATE tdiv(P457,P59 + P459+P457,0,1) number GPQOS1


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Enhanced Packet Cell ReselectionRNO indicators

Ref. name Name Formula Unit

QRCR2FLRLN GPRS_NC2_reselect_fail_load P464 number

QRCR2FLRLO GPRS_NC2_reselect_fail_load_ratio tdiv(P464,P437a,0,0) %

QRCR2FLRLR GPRS_NC2_reselect_fail_load_rate tdiv(P464,P433a + P433b +P433c + P433d,0,0)

%

QRCR2FLBPN GPRS_NC2_reselect_fail_BSS P433a + P433b + P433c +P433d - (P435a + P435b +

P435c + P435d)- P437a - P437b-

P464

number

QRCRNSCAVT GPRS_NC_reselect_NACC_avg_duration P460a ms

QRCRNSCMAT GPRS_NC_reselect_NACC_max_duration P460b ms

QRCRNSCMIT GPRS_NC_reselect_NACC_min_duration P460c ms

TRCRNN GPRS_NC_reselect_neighb_SI_messages P458 number

TRCRPN GPRS_NC_reselect_packet_SI_status P456 number

TRPADNAN GPRS_NC_reselect_neighb_SI_messages_load P459 number

TRPADNAR GPRS_DL_RLC_block_neighb_SI_messages_rate tdiv(P459,P59 + P459 +P457,0,1)

number

TRPADPSN GPRS_NC_reselect_packet_SI_status_load P457 number

TRPADPSR GPRS_DL_RLC_block_PSI_Status_rate tdiv(P457,P59 + P459+P457,0,1) number

Enhanced Packet Cell Reselection Ed5

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