wcdma-paging-problem-analysis

W-Paging ProblemW Paging Problem
Optimization Guide
www.huawei.com
Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.

ForewordForeword
Paging 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”

ObjectivesObjectives
Upon 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

ContentsContents
1. 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 1
If UE is in CELL_PCH,URA_PCH or IDLE state，the paging
message will be transmitted on PCCH with paging type 1
CN 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 2
If UE is in CELL_DCH or CELL_FACH state，the paging
message will be transmitted on DCCH with paging type 2
CN SRNC UE
RANAPRANAP
PAGING
DCCH: PAGING TYPE 2
RRCRRC

Paging OverviewPaging Overview
CN Initiated Paging UTRAN Initiated Paging
Paging Type 1 Applicable ApplicablePaging Type 1 Applicable Applicable
Paging 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

ContentsContents
1. Paging Overview

ContentsContents
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 Problems
Collect network information
Identify optimization goal
Locate paging problemLocate paging problem
Optimize paging problem
Optimization verification
Optimization goal achieved?
END
YES
NO
END

ContentsContents
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 received
UTRAN side .

RNC 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

RNC 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

RNC 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

RNC 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 timestransmisspagingFirst
messagesresponse-nodeliveredofnumberion timestransmisspagingFirst
ratesuccesspagingLA
－
=
ion timestransmisspagingFirst
timesresponsepagingFirst
ratesuccesspagingFirst =
timesrepetitionpagingInterface
timesresponserepitetionpagingInterface
ratesuccesspagingfirst-Non =

Index
Name 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
PAGING message to RNC/BSC
Successfully receiving response Carry out statistics when MSC receives
Interface 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 Iu
interface
The first sending Paging times of Iu
interface
PAGING message to RNC
Lu interface paging repeat
times
The non-first sending Paging times
of Iu interface
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

SGSN Paging Traffic Statistics
questTimesingRAGroupPag
TimesingFailureRAGroupPagquesTimesingRAGroupPag
ccessRateRAPagingSu
Re
Re －
＝
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 message
p p g g
failure times of
each RA
It provides group paging
failure times in the specific RA
Paging retransmission message
times reach maximum.

Alarm
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

Data 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

For 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

Parameters 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 Procedure
UE 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
Data
N bitsData
Pilot
N bitsPilotN bits
TFCI
TFCI
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 DRX
DRXCYCLELENCOEF
Parameter name: DRX cycle length coefficient
Recommended value: 6
PICHMODE
Parameter name: PICH mode
Recommended value: V36.

Parameters of DRXParameters of DRX
MACCPAGEREPEAT
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

ContentsContents

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%

ContentsContents

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

ContentsContents

Paging Problem Optimization OverviewPaging Problem Optimization Overview
Further 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

ContentsContents
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

ContentsContents

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
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
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

ContentsContents

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

ContentsContents

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

DRX paging cycle coefficient
CN 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

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 value
Problem 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
⎣ ⎦ ⎣ ⎦ ⎣ ⎦( )( )( ) Np
Np
SFNSFNSFNSFNPIq mod
144
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 value
Influences 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

ContentsContents
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 Paging
Problem 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

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

ContentsContents

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

ContentsContents

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

ContentsContents

UE Performance ProblemUE Performance Problem
Problem 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 Problem
Optimization 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

ContentsContents

Optimization VerificationOptimization Verification
After 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

SummarySummary
We 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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