wcdma paging problem analysis

W-Paging ProblemW Paging Problem Optimization Guide

www.huawei.com

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.

ForewordForewordPaging is associated with the paging success rate of the

network. It’s closely related to the whole network

performance. This KPI can be optimized by means of

“paging test” and the consequent trouble-shooting based on

paging failure analysis.

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Page2

Learning GuideLearning Guide Before learn this course, you should have:

Learned WCDMA signaling flow


ReferencesReferences“WCDMA Signaling Flow”

“3GPP R7 25_series”


ObjectivesObjectivesUpon completion of this course, you will be able to:

Collect data regarding paging problem

Locate paging problem

Solve the located paging problem

Analyze the typical paging cases


ContentsContents1. Paging Overview

2. Paging Problem Analysis Process


Paging InitiationPaging Initiation CN initiated paging

Establish a signaling connection

UTRAN initiated paging

Trigger the cell update procedure

Trigger reading of updated system informationgg g p y


Paging Type 1Paging Type 1If UE is in CELL_PCH,URA_PCH or IDLE state，the paging

message will be transmitted on PCCH with paging type 1CN RNC1 RNC2 NODEB1.1 NODEB2.1 UE

PAGING

RANAPRANAP

RANAP RANAP

PAGING

PAGING

PCCH: PAGING TYPE 1

PCCH: PAGING TYPE 1


Paging Type 2Paging Type 2If UE is in CELL_DCH or CELL_FACH state，the paging

message will be transmitted on DCCH with paging type 2CN SRNC UE

RANAPRANAP

PAGING

DCCH: PAGING TYPE 2RRCRRC


Paging OverviewPaging OverviewCN Initiated Paging UTRAN Initiated Paging

Paging Type 1 Applicable ApplicablePaging Type 1 Applicable ApplicablePaging Type 2 Applicable Applicable

Paging type 2 could be considered as normal RRC signaling, no

more discussion about this part, for more detailed information,

please refer to the “WCDMA Signaling Procedure”please refer to the WCDMA Signaling Procedure

Paging type 1 is the emphasis of this course


ContentsContents1. Paging Overview

2. Paging Problem Analysis Process


ContentsContents2. Paging Problem Analysis Process

2.1 Problem Analysis Flow

2.2 Network Information Collection

2.3 Optimization Target Confirmation

2 4 Paging Problem Locating2.4 Paging Problem Locating

2.5 Typical Paging Problem Analysis

2.6 Optimization Verification


Flow for Analyzing Paging ProblemsFlow for Analyzing Paging ProblemsCollect network information

Identify optimization goal

Locate paging problemLocate paging problem

Optimize paging problem

Optimization verification

Optimization goal achieved?

ENDYES

NO


END




2.3 Optimization target Confirmation





Network Information Collection Overview

Data of network to be optimized could be collected by the

following ways:

Statistics

Alarm

Customers’ complaint

Network planning info & optimization record

Radio parameter configuration


Network Information CollectionNetwork Information Collection

Traffic statisticsTraffic statistics

The paging-related traffic statistics can be observed

respectively on the traffic statistics console of RNC, UMSC andrespectively on the traffic statistics console of RNC, UMSC and

SGSN according to different paging areas

CN PAGE IDLE UE SUCC RATE, which is paging success _ _ _ _ _ , p g g

rate of UE in idle state initiated by CN

UTRAN_PAGE1_SUCC_RATE, which is the success rate of

Paging Type 1 initiated by UTRAN



RNC Paging KPIRNC Paging KPI

CN_PAGE_IDLE_UE_SUCC_RATE =

[CN PAGE IDLE UE SUCC]/[CN_PAGE_IDLE_UE_SUCC]/

[CN_PAGE_IDLE_UE_REQ]

[UTRAN PAGE1 SUCC RATE = [ _ _ _

UTRAN_PAGE1_SUCC]/[UTRAN_PAGE1_REQ]



RNC Paging KPI

Name Description Standard measuring point

CN_PAGE_IDLE_UE_REQ Count paging times at IU interface of idle subscribers

Receive the PAGING messages initiated by CN when UE is in idle status

RNC Paging KPI

y

CN_PAGE_IDLE_UE_SUCC Count paging success times of idle subscribers

Receive RRC connection request message of UE and the reason belongs to the called type, such as “Terminating Conversational Call”

UTRAN_PAGE1_REQ Count times of initiating PAGING TYPE 1 initiated from UTRAN side

PAGING TYPE 1 message initiated from UTRAN side

UTRAN PAGE1 SUCC

Count PAGING TYPE 1 message initiated from UTRAN side and the ti f UE i

UE paging response message received at UTRAN id_ _ times of UE success receive

response receivedUTRAN side .


Network Information CollectionNetwork Information CollectionRNC counters for paging messages to idle UE

Number of PAGING TYPE 1 messages from the RNC to the

UEs in idle mode after it receives the PAGING messages from

the CN

VS.RANAP.Paging.Att.IdleUE


Network Information CollectionNetwork Information CollectionRNC counters for successful paging messages to idle UE

number of RRC CONNECTION REQUEST messages from the

UEs to the RNC that has sent a PAGING TYPE 1 messages to

page the UEs in idle mode

VS.RANAP.Paging.Succ.IdleUE


Network Information CollectionNetwork Information CollectionRNC counters for PAGING TYPE 1 message initiated from

UTRAN side

number of PAGING TYPE 1 messages originated by the RNC

for triggering the state transition of an UE in CELL_PCH or

URA_PCH state

VS.UTRAN.Paging1.Att


Network Information CollectionNetwork Information CollectionRNC counters for successful PAGING TYPE 1 message

initiated from UTRAN side

number of CELL UPDATE messages from the UEs to the RNC

These messages are taken as successful responses to the

PAGING TYPE 1 messages sent by the RNC to the UEs in

CELL_PCH or URA_PCH state

VS.UTRAN.SuccPage1



UMSC Paging Traffic Statistics

ion times transmisspagingFirst messages response-no delivered ofnumber ion times transmisspagingFirst rate success pagingLA －

=

UMSC Paging Traffic Statistics

ion times transmisspagingFirst timesresponse pagingFirst rate success pagingFirst =

timesrepetition paging InterfacetimesresponserepitetionpagingInterfacerate success pagingfirst -Non =


Network Information CollectionNetwork Information CollectionUMSC Paging Traffic Statistics

IndexName Description Standard measure point

The first paging times The first sending times of Paging Req by MSC

Carry out statistics when MSC sends PAGING message to RNC/BSC

The first paging response times

Successfully receiving response times after the first sending of

Carry out statistics when MSC receives PAGING RESPONSE after the first sending times Paging message by MSC of Paging message

Interface paging repeat times The non-first paging times of MSC Carry out statistics when MSC sends PAGING message to RNC/BSC

Successfully receiving response Carry out statistics when MSC receivesInterface paging repeat response times

Successfully receiving response times after the non-first sending of Paging message by MSC

Carry out statistics when MSC receives PAGING RESPONSE after the non-first sending Paging message

The first paging times of Iuinterface

The first sending Paging times of Iu interface

Carry out statistics when MSC sends PAGING message to RNC

Lu interface paging repeat times

The non-first sending Paging times of Iu interface

Carry out statistics when MSC sends PAGING message to RNC not at the first time

Delivery paging no-response times

Times of having no paging response messages received Paging timer stay-over statistics


times response messages received g g y

Network Information CollectionNetwork Information CollectionSGSN Paging Traffic Statistics

questTimesingRAGroupPagTimesingFailureRAGroupPagquesTimesingRAGroupPagccessRateRAPagingSu

ReRe －

＝

Name Description Standard measure point

Group paging It provides delivery group i t ti i th SGSN sends Iu interface pagingGroup paging

request times of each RA

paging request times in the specific RA, not including retransmission messages

SGSN sends Iu interface paging request message (PAGING), and its CN Domain is PS.

Group paging It provides group paging Paging retransmission messagep p g gfailure times of each RA

It provides group paging failure times in the specific RA

Paging retransmission message times reach maximum.


Network Information CollectionNetwork Information CollectionAlarm

From CN

RNC overload

From RNC

the flow control alarm

– When RNC is in paging flow control state, the paging message will be

lost unconditionally


Network Information CollectionNetwork Information CollectionData collection from customers’ complaint

Time

Place

Terminated UE typeTerminated UE type

Others

Subscriber name

Originated phone number

Terminated phone number

Happened frequently or not

Process description


Network Information CollectionNetwork Information CollectionFor the network that has not been put into service

Pay more attention to the division of location area & route area

For the network that has been put into service, it may have experienced several optimization processes before thisexperienced several optimization processes before this optimization. Emphasis should be put on optimization records about:

Coverage absence

System overload

Paging lost

Low power allocation of paging channel


Network Information CollectionNetwork Information CollectionParameters to be checked before optimization:

CN paging retransmission times and paging interval

UTRAN paging retransmission times and paging interval

DRX paging cycle coefficient k (DRX paging cycle = 2k)

Paging indication quantity NP included in a PICH frame

Channel power allocation of PICH and PCH

Whether CN adopts global pagingp g p g g

UE ID used by CN paging (IMSI,TMSI or PTMSI)


DRX ProcedureDRX ProcedureUE receives the paging indicator on PICH periodically, that

is the Discontinuous Reception (DRX)

The value for the DRX paging cycle length is determined as

follows: :

DRX Cycle Length ＝ MAX (2k, PBP) frames


Paging Indicator Channel (PICH)Paging Indicator Channel (PICH)Carrying Paging Indicators (PI)

Fixed rate (30kbps), SF = 256

N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72 14472, or 144

288 bits for paging indication 12 bits (undefined)

b1b0 b287 b288 b299

One radio frame (10 ms)


( )

Secondary Common Control Physical Channel (SCCPCH)(SCCPCH)

Carrying FACH and PCH, SF = 256 - 4

Pilot: used for demodulation

TFCI: Transport Format Control Indication, used for describe data

f tformat

DataN bitsData

PilotN bitsPilotN bits

TFCITFCI

T slot = 2560 chips, 20*2 k bits (k=0..6)

Slot #0 Slot #1 Slot #i Slot #14

1 radio frame: T f = 10 ms


DRX Procedure (Cont.)DRX Procedure (Cont.)Through DRX, UE only listens to PICH at certain predefined

time. And UE will read the paging information on SCCPCH if

the paging indicator is 1.

The value of the Paging Occasion is determined as follows:

Paging Occasion (CELL SFN) =

{(IMSI div K) mod (DRX cycle length div PBP)} * PBP

+ n * DRX cycle length + Frame Offset+ n DRX cycle length + Frame Offset


DRX Procedure (Cont.)DRX Procedure (Cont.)In FDD the UE shall monitor its paging indicator in the PICH

frame with SFN given by the Paging Occasion

The Page Indicator to use is calculated by using the

following formula:

PI = (IMSI div 8192) mod NP


Parameters of DRXParameters of DRXDRXCYCLELENCOEF

Parameter name: DRX cycle length coefficient

Recommended value: 6

PICHMODE

Parameter name: PICH mode

Recommended value: V36.


Parameters of DRXParameters of DRXMACCPAGEREPEAT

Parameter name: Number of page re-TX

Recommended value: 1


Common Physical Channel Power Parametersy

MAXTXPOWER

Parameter name: Max transmit power of cell

The recommended value is 430, namely 43dBm

PCPICHPOWER

Parameter name: PCPICH transmit power

The recommended value is 330 namely 33dBmThe recommended value is 330, namely 33dBm



MAXFACHPOWER

Parameter name: Max transmit power of FACH

The recommended value is 10, namely 1dB

PCHPOWERPCHPOWER

Parameter name: PCH transmit power

The recommended value is 20 namely 2dBThe recommended value is -20, namely -2dB



PICHPOWEROFFSET

Parameter name: PICH power offset

The default value of this parameter is -7, namely -7dB


Optimization TargetOptimization Target Determining optimization KPI goal

Two KPI, “location area paging success rate” and “RA paging

success rate” , should meet the optimization requirements. The

paging success rate is recommended to be higher than 86%


Paging Problem Allocating OverviewPaging Problem Allocating Overview

Paging problems can be divided into three categories:

Paging message is not delivered at the air interface at all

Paging message has been delivered, but UE does not receive

the message or receives the wrong message

UE fails in responding after receiving paging messages


Paging Problem Optimization OverviewPaging Problem Optimization OverviewFurther analysis on paging loss cause

Too large paging area plannedToo large paging area planned

Improper setting of CN paging retransmission times and interval

Improper setting of UTRAN paging retransmission times and interval

CN adopts whole-network paging

Improper setting of DRX paging cycle coefficient

Improper setting of Np value

CN adopts improper UE identifier

Too low power allocation of paging channels

Existence of coverage dead zonesExistence of coverage dead zones

UE performance problems


ContentsContents2.5 Typical Paging Problem Analysis

2 5 1 Paging Area2.5.1 Paging Area

2.5.2 CN and UTRAN Paging retransmission Times and Interval

2.5.3 Whole-Network Paging strategy

2 5 4 DRX Paging Cycle Coefficient and Np value2.5.4 DRX Paging Cycle Coefficient and Np value

2.5.5 UE Identifier Utilized by CN Paging

2.5.6 Power allocation of Paging Channels

2.5.7 Coverage Dead Zones

2.5.8 UE Performance Problems and DETACH Functions


Paging Area Problem AnalysisPaging Area Problem Analysis

In general, CN pages target UE in one paging area (LA or RA)

LA is defined for CS service paging

Mobile terminals can move freely without updating VLR

Contain one or more cellsContain one or more cells

RA is defined for PS service paging

Mobile terminals can move freely without updating SGSN in a specified operation mode

A RA may contain one or more cells

LA ≥ RA


Paging Area Problem AnalysisPaging Area Problem Analysis

Paging area is planned too large

the same paging message of a network paging mobile station

may be sent in multi cells, which will overload the paging

channel as well as increasing signaling flow at the Iub interface

Paging area is planned too small

subscribers will update locations frequently while moving,

which will increase signaling flow of the system. Moreover,

frequent location update will influence the standby time of UEs


Paging Area Problem Analysis (Cont.)Paging Area Problem Analysis (Cont.)

Calculaiton Result of Paging Area When Cn Id Adopting

IMSI :


Paging Area Problem Analysis (Cont.)Paging Area Problem Analysis (Cont.)

Optimization Measures

Split location areas where network capacity or paging traffic is

bigger than a specified threshold, which can reduce paging

message flow efficiently


Improper Setting of CN Paging retransmission Times and IntervalTimes and Interval

In order to guarantee the paging success rate, CN will

retransmission paging message at the IU interface

CN paging retransmission times and interval can be configured

Paging is initiated specific to location area, paging

retransmission will increase paging traffic

CN paging retransmission configuration should be in

accordance with UTRAN



Problem Analysis

In order to guarantee the paging success rate, CN will retransmission paging message at the IU interface

CN paging retransmission is the retransmission paging in case that UE has not responded at the first time

It is no good for CN paging interval to be too shortIt is no good for CN paging interval to be too short




CN paging retransmission configuration should be in accordance with UTRAN. When UTRAN retransmits paging once it is suggested for CN configuration to retransmit onceonce, it is suggested for CN configuration to retransmit once (totally twice) at the interval longer than two paging cycles

Reduce paging repeat times and increase paging interval keepReduce paging repeat times and increase paging interval, keep the time of no paging responses unchanged, interval of reporting prompt tones when there is no paging response will not be influenced


Improper Setting of UTRAN Paging Retransmission Times and IntervalTimes and Interval

Problem Analysis

Paging is delivered at the fixed time (a paging cycle), and UTRAN paging interval is the integer multiple of a paging cycle, one paging cycle in generaly g

we can adjust UTRAN paging repeat interval by adjusting DRX paging cycle coefficient k


It is reasonable for paging retransmission times to keep the current default configurationdefault configuration

It is also reasonable to adjust paging retransmission times on RNC maintenance console using MML command SET UDPUCFGDATA


CN Whole Network Paging Problem Analysisg g y

Problem Analysis

Considering improving call connection rate, CN side can be

configured with whole-network paging, which bears the characteristics

that paging has overridden the concept of location area and isthat paging has overridden the concept of location area, and is

initiated specific to all UTRANs suspended under whole CN

In this case, paging traffic becomes larger, especially when multiple

location areas are suspended under CN, the location areas with

smaller capacity will be overloaded, and can not recover for a long

timetime


CN Whole Network Paging Problem Analysisg g y

Optimization measures

Global paging should be avoided in CN

CN global paging is useful only when UE location area is recorded

as failure by NLR, which hardly occurs

once it occurs, it means serious fault occurs; even more CN global

i d t kpaging does not work


Improper Setting of DRX Paging Cycle Coefficientp p g g g yDRX paging cycle coefficient of UE has CN-specific DRX and UTRAN-specific DRX

CN ifi DRX UTRAN ifi DRXCN-specific DRX UTRAN-specific DRX

SIB1


RRC CONNECTION SETUP

Improper Setting of DRX Paging Cycle Coefficientp p g g g y

DRX paging cycle coefficientCN ifi DRX l l th ffi i t i d f idl dCN-specific DRX cycle length coefficient is used for idle mode

Minimum K value in CN-specific DRX cycle length coefficient and UTRAN-specific DRX cycle length coefficient is used for connection state ( CELL-PCH & URA-PCH )

CN-specific DRX cycle length coefficient is configured by command “ADD CNDOMAIN” for BSC6810 or “ADD UCNDOMAIN” forADD CNDOMAIN for BSC6810 or ADD UCNDOMAIN for BSC6900

UTRAN-specific DRX cycle length coefficient is configured by command “SET FRC” for BSC6810 or “SET UFRC” for BSC6900command SET FRC for BSC6810 or SET UFRC for BSC6900


Improper Setting of DRX Paging Cycle Coefficientp p g g g y

Questions:Suppose that the CN paging repeat time is 1 (totally broadcasting 2 times), and the interval is 2s, so how should the UTRAN repeat times and the intervals be set?UTRAN repeat times and the intervals be set?


Improper setting of Np valueImproper setting of Np valueProblem Analysis

Np refers to PI paging indication number delivered in a certain frame by paging

indication channel PICH, the value of which is within the range of (18, 36, 72,

144), which is indicated by Number of PI per frame in SIB5, UE will receive

PICH frame at the specified paging time and find the corresponding PI

indicator bit (the qth PI). Only when the corresponding PI indicator bit is

effective, UE demodulates the corresponding S-CCPCH frame

⎣ ⎦ ⎣ ⎦ ⎣ ⎦( )( )( ) NpNpSFNSFNSFNSFNPIq mod144

144mod512/64/8/18 ⎟⎟⎠

⎞⎜⎜⎝

⎛⎥⎦⎥

⎢⎣⎢ ×+++×+=

Significance of Np in the actual network: IMSI is divided into Np groups by this

parameter, and all IMSIs in each group adopt the same PI


Improper setting of Np valueImproper setting of Np valueInfluences of Np value on network

If Np value is too small, the corresponding UE number in each group

will be larger. For each IMSI, if the probability that PI indication occurs

increases times that IMSI is waken up will increase which is no goodincreases, times that IMSI is waken up will increase, which is no good

in saving UE power

If Np value is too large, the corresponding IMSI number in each group

will be smaller. For each IMSI, if the probability that PI indication

occurs decreases, times that IMSI is waken up will decrease.

However if Np is larger the bit number of each PI will decrease andHowever, if Np is larger, the bit number of each PI will decrease and

PICH demodulation performance of UE will be required higher



2 5 1 P i A2.5.1 Paging Area



2.5.4 DRX Paging Cycle Coefficient and Np value


2 5 6 Att h & D t h S it h S ti h2.5.6 Attach & Detach Switch Swtich



2.5.9 UE Performance Problems


UE Identifier Utilized by CN PagingUE Identifier Utilized by CN PagingProblem Analysis

When UE is in IDLE state, CN can only page 3 UEs at the same paging time using IMSI

When UE is in IDLE state, CN can only page 5 UEs at the same paging time using TMSI or PTMSI

When UE is in CELL_PCH or URA_PCH state, no matter what paging identifier CN uses, UTRAN transfers UE identifier to U-RNTI and pages, it can only page five UEs at the same paging time


CN ti i ti b i UE t id tifi TMSI dCN optimization pages by using UE temporary identifier TMSI and PTMSI, and it can be adjusted with software parameters








2 5 6 Att h & D t h S it h2.5.6 Attach & Detach Switch





IMSI ATTACH & DETACH F tiFunction

Problem Analysis

Aft UE i d d i t d f ll MSC/VLR ill t thAfter UE is powered on and registered successfully, MSC/VLR will set the subscriber state as ATTACH state. IMSI DETACH means that after mobile subscribers power off, MS initiates a DETACH flow and MSC/VLR sets the subscriber state as IMSI detach Generally HLR will not be informed by thissubscriber state as IMSI detach. Generally, HLR will not be informed by this flow

UE determines whether IMSI ATTACH and DETACH processes can be d t d th h i i th t 1 G MAP IE i t fadopted through receiving the system message 1. Gsm MAP IE consists of

two octets, one is T3212, and bit1 of the other octet is ATT identifier. “0” means that the network does not allow UE to adopt IMSI ATTACH and DETACH “1” f t th d i iDETACH processes, “1” refers to the admission

During actual network operation, UTRAN should activate IMSI ATTACH and DETACH functions


IMSI ATTACH & DETACH Function (Cont.)( )

SIB1

Optimization MeasuresCheck and modify IMSI attachment and detachment admission indication by using the Command “LST CNDOMAIN and MOD CNDOMAIN” on RNC maintenance console


Too Low Power allocation of P i Ch lPaging Channels

Phenomenon

Subscriber complaints are centralized in some certain areas

when UE is called, the prompt tone “the subscriber is out of

service” will occur

Problem Analysis

the print message of paging decoding failure can be seen at

the UE daemon, which is the problem of the over-low paging

channel power allocation


Too Low Power allocation of P i Ch lPaging Channels

Optimization measures

The current baseline power allocation: PICH is -3dB and PCH

is -2dB, which are both relative to pilot channels power.

Improve the power allocation between PICH and PCH properly

Check and modify PICH power by using MML Command LST

CHPWROFFSET and MOD PICHPWROFFSET on RNC

maintenance console

Check and modify PCH power by using Command LST

SCCPCH and MOD SCCPCH


Existence of Coverage Dead ZZones

Problem Analysis

Phenomenon: Subscriber complaints are centralized in a certain area,

UE fails both in calling and being called, the signal strength shown in

UE panel is low and RSCP and EC/IO of pilot signals tested with theUE panel is low, and RSCP and EC/IO of pilot signals tested with the

drive test equipment are lower than indexes required for UE normal

access, by which coverage dead zone is identified in this area


Carry out coverage optimization, for specific optimization measures,

please refer to relevant Guidance


UE Performance ProblemUE Performance ProblemProblem Analysis

The receiving performance and demodulation performance of different UEs are also different

Sort out and analyze subscriber complaint materials If theSort out and analyze subscriber complaint materials. If the called UE is of the same type, problem may exist in UEs


UE Performance ProblemUE Performance ProblemOptimization Solution

Take a called verification test on UEs from different manufacturers

compare UE receiving performance parameters andcompare UE receiving performance parameters and demodulation performance parameters

including testing RSCP and EC/IO of pilot signals received at the same place and learn about the service demodulation thresholds of UEs


Optimization VerificationOptimization VerificationAfter network is optimized and adjusted, the optimization

lt h ld b ifi d Th f tl d if iresults should be verified. The frequently-used verifying methods are available as follows:

Traffic statisticsTraffic statistics

Alarm

Subscriber complaintp

Dialing test


SummarySummaryWe have learned the some typical cases of paging problem,

the paging problem could be caused by improper paging

area division, improper paging retransmission times and

interval, improper DRX paging cycle coefficient and Np

value, weak coverage, whether switch on attach/detach

f i l ll i f i h l dfunction, low power allocation of paging channels, and

specified UE performance.


wcdma paging problem analysis

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