Wcdma paging problem analysis by Emerson Rodrigues Setim

W Paging Problem W-Paging Optimization Guide www.huawei.com

Foreword z

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.

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Learning Guide z

Before learn this course, you should have:

Learned WCDMA signaling flow

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References z

“WCDMA Signaling Flow”

“3GPP R7 25_series”

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Objectives z

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

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Contents 1. Paging Overview 2. Paging Problem Analysis Process

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Paging Initiation z

CN initiated paging z

Establish a signaling connection

UTRAN initiated paging z

Trigger the cell update procedure

Trigger gg reading g of updated p system y information

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Paging Type 1 z

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

PAGING RANAP

RANAP

PAGING

RANAP

PCCH: PAGING TYPE 1

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Paging Type 2 z

If UE is in CELL_DCH or CELL_FACH state，the paging message will be transmitted on DCCH with paging type 2 CN

SRNC

PAGING RANAP

RANAP

DCCH: PAGING TYPE 2 RRC

RRC

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Paging Overview CN Initiated Paging UTRAN Initiated Paging

Paging Type 1 Applicable

Applicable

Paging Type 2

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 WCDMA Signaling Procedure” Procedure

Paging type 1 is the emphasis of this course

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Contents 1. Paging Overview 2. Paging Problem Analysis Process

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Contents 2. Paging Problem Analysis Process 2.1 Problem Analysis Flow 2.2 Network Information Collection 2.3 Optimization Target Confirmation 2 4 Paging Problem Locating 2.4 2.5 Typical Paging Problem Analysis 2.6 Optimization Verification

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Flow for Analyzing Paging Problems Collect network information Identify optimization goal Locate paging problem Optimize paging problem Optimization verification NO

Optimization goal achieved? YES

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Contents 2. Paging Problem Analysis Process 2.1 Problem Analysis Flow 2.2 Network Information Collection 2.3 Optimization target Confirmation 2 4 Paging Problem Locating 2.4 2.5 Typical Paging Problem Analysis 2.6 Optimization Verification

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Network Information Collection Overview z

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

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Network Information Collection z

Traffic statistics

The paging-related traffic statistics can be observed respectively on the traffic statistics console of RNC, UMSC and SGSN according to different paging areas

CN_PAGE_IDLE_UE_SUCC_RATE,, which is paging p g g success 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

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Network Information Collection z

RNC 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]

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Network Information Collection z

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 byy CN when UE is in idle status

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 times off UE success receive i response received

UE paging response message received at UTRAN side id .

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Network Information Collection z

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

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Network Information Collection z

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

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Network Information Collection z

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

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Network Information Collection z

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

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Network Information Collection z

UMSC Paging Traffic Statistics

LA paging success rate =

First paging transmission timesďź?number of delivered no - response messages First paging transmission times

First paging success rate =

First paging response times First paging transmission times

Non - first paging success rate =

Interface paging repitetion response times Interface paging repetition times

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Network Information Collection UMSC Paging Traffic Statistics 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 Paging message by MSC

Carry out statistics when MSC receives PAGING RESPONSE after the first sending 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

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

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 g g timer stay-over y statistics

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Network Information Collection z

SGSN Paging Traffic Statistics

RAPagingSuccessRate＝

RAGroupPaging Re quesTimes－RAGroupPagingFailureTimes RAGroupPaging Re questTimes

Name

Description

Standard measure point

Group paging request times of each RA

It provides delivery group paging i requestt times ti in i th the specific RA, not including retransmission messages

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

pp paging g g Group failure times of each RA

It provides group paging failure times in the specific RA

Paging retransmission message times reach maximum.

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Network Information Collection z

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

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Network Information Collection z

Data collection from customers’ complaint

Time

Place

Terminated UE type

Others

Subscriber name

Originated phone number

Terminated phone number

Happened frequently or not

Process description

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Network Information Collection z

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 this optimization. Emphasis should be put on optimization records about:

Coverage absence

System overload

Paging lost

Low power allocation of paging channel

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Network Information Collection z

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 p g global p paging g g

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

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DRX Procedure z

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

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Paging Indicator Channel (PICH) z

Carrying Paging Indicators (PI)

Fixed rate (30kbps), SF = 256

N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72 72, or 144 12 bits (undefined)

288 bits for paging indication b0 b1

b 287 b 288

One radio frame ((10 ms))

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b 299

Secondary Common Control Physical Channel (SCCPCH) z

Carrying FACH and PCH, SF = 256 - 4

Pilot: used for demodulation

TFCI: Transport Format Control Indication, used for describe data fformatt Data

TFCI N TFCI bits

T slot = 2560 chips,

Slot #0

Pilot N Pilot bits

N Data bits

Slot #1

20*2 k bits (k=0..6)

Slot #i

Slot #14

1 radio frame: T f = 10 ms

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DRX Procedure (Cont.) z

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

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DRX Procedure (Cont.) z

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

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Parameters of DRX z

DRXCYCLELENCOEF

Parameter name: DRX cycle length coefficient

Recommended value: 6

PICHMODE

Parameter name: PICH mode

Recommended value: V36.

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Parameters of DRX z

MACCPAGEREPEAT

Parameter name: Number of page re-TX

Recommended value: 1

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Common Physical y Channel Power Parameters z

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 330 330, namely 33dBm

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Common Physical y Channel Power Parameters z

MAXFACHPOWER

Parameter name: Max transmit power of FACH

The recommended value is 10, namely 1dB

PCHPOWER

Parameter name: PCH transmit power

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

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Common Physical y Channel Power Parameters z

PICHPOWEROFFSET

Parameter name: PICH power offset

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

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Optimization Target z

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%

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Paging Problem Allocating Overview z

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

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Paging Problem Optimization Overview z

Further analysis on paging loss cause

Too 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 zones

UE performance problems

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Contents 2.5 Typical Paging Problem Analysis 2 5 1 Paging Area 2.5.1 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 value 2.5.4 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

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Paging Area Problem Analysis z

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 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

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Paging Area Problem Analysis z

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

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Paging Area Problem Analysis (Cont.) z

Calculaiton Result of Paging Area When Cn Id Adopting IMSI :

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Paging Area Problem Analysis (Cont.) z

Optimization Measures Â&#x2021;

Split location areas where network capacity or paging traffic is bigger than a specified threshold, which can reduce paging message flow efficiently

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Improper Setting of CN Paging retransmission Times and Interval z

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

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Improper Setting of CN Paging retransmission Times and Interval z

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 short

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Improper Setting of CN Paging retransmission Times and Interval z

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 short

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Improper Setting of CN Paging retransmission Times and Interval z

Optimization Measures

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

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

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Improper Setting of UTRAN Paging Retransmission Times and Interval z

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 y in general g

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

Optimization Measures

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

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

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CN Whole Network Paging g g Problem Analysis y z

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 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 time

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CN Whole Network Paging g g Problem Analysis y z

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 paging i d does nott work k

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Improper p p Setting g of DRX Paging g g Cycle y Coefficient z

DRX paging cycle coefficient of UE has CN-specific DRX and UTRAN-specific DRX

CN CN-specific ifi DRX

UTRAN UTRAN-specific ifi DRX

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Improper p p Setting g of DRX Paging g g Cycle y Coefficient z

DRX paging cycle coefficient

CN CN-specific ifi DRX cycle l llength th coefficient ffi i t iis used d ffor idl idle mode d 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 ADD CNDOMAIN” CNDOMAIN for BSC6810 or “ADD ADD UCNDOMAIN” UCNDOMAIN for BSC6900 UTRAN-specific DRX cycle length coefficient is configured by command “SET SET FRC FRC” for BSC6810 or “SET SET UFRC UFRC” for BSC6900

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Improper p p Setting g of DRX Paging g g Cycle y Coefficient z

Questions: Â&#x2021;

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?

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Improper setting of Np value z

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 ⎥ ⎞ ⎢ q = ⎜⎜ PI + ⎢((18 × (SFN + ⎣SFN / 8⎦ + ⎣SFN / 64⎦ + ⎣SFN / 512⎦)) mod 144 ) × ⎥ ⎟⎟ mod Np 144 ⎣ ⎦⎠ ⎝

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

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Improper setting of Np value z

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 increases, 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 However, larger, the bit number of each PI will decrease and PICH demodulation performance of UE will be required higher

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Contents 2.5 Typical Paging Problem Analysis 251 P 2.5.1 Paging i A 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 value 2.5.5 UE Identifier Utilized by CN Paging 2 5 6 Att 2.5.6 Attach h&D Detach t hS Switch it h S Swtich ti h 2.5.7 Power allocation of Paging Channels 2.5.8 Coverage Dead Zones 2.5.9 UE Performance Problems

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UE Identifier Utilized by CN Paging z

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

Optimization Measures

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

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Contents 2.5 Typical Paging Problem Analysis 251 P 2.5.1 Paging i A 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 value 2.5.5 UE Identifier Utilized by CN Paging 2 5 6 Att 2.5.6 Attach h&D Detach t hS Switch it h 2.5.7 Power allocation of Paging Channels 2.5.8 Coverage Dead Zones 2.5.9 UE Performance Problems

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IMSI ATTACH & DETACH F Function ti z

Problem Analysis

Aft UE iis powered After d on and d registered i t d successfully, f ll MSC/VLR will ill sett th 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 detach. Generally Generally, HLR will not be informed by this flow

UE determines whether IMSI ATTACH and DETACH processes can be adopted d t d th through h receiving i i th the system t message 1 1. G Gsm MAP IE consists i t off 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 processes, “1” refers f tto th the admission d i i

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

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IMSI ATTACH & DETACH Function (Cont.) ( ) z

SIB1

Optimization Measures

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

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Contents 2.5 Typical Paging Problem Analysis 251 P 2.5.1 Paging i A 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 value 2.5.5 UE Identifier Utilized by CN Paging 2 5 6 Att 2.5.6 Attach h&D Detach t hS Switch it h 2.5.7 Power allocation of Paging Channels 2.5.8 Coverage Dead Zones 2.5.9 UE Performance Problems

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Too Low Power allocation of P i Ch Paging Channels l z

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

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Too Low Power allocation of P i Ch Paging Channels l z

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

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Contents 2.5 Typical Paging Problem Analysis 251 P 2.5.1 Paging i A 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 value 2.5.5 UE Identifier Utilized by CN Paging 2 5 6 Att 2.5.6 Attach h&D Detach t hS Switch it h 2.5.7 Power allocation of Paging Channels 2.5.8 Coverage Dead Zones 2.5.9 UE Performance Problems

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Existence of Coverage Dead Zones z

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 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

Optimization Measures

Carry out coverage optimization, for specific optimization measures, please refer to relevant Guidance

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Contents 2.5 Typical Paging Problem Analysis 251 P 2.5.1 Paging i A 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 value 2.5.5 UE Identifier Utilized by CN Paging 2 5 6 Att 2.5.6 Attach h&D Detach t hS Switch it h 2.5.7 Power allocation of Paging Channels 2.5.8 Coverage Dead Zones 2.5.9 UE Performance Problems

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UE Performance Problem z

Problem Analysis

The receiving performance and demodulation performance of different UEs are also different Sort out and analyze subscriber complaint materials. materials If the called UE is of the same type, problem may exist in UEs

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UE Performance Problem z

Optimization Solution

Take a called verification test on UEs from different manufacturers compare 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

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Optimization Verification z

After network is optimized and adjusted, the optimization results lt should h ld b be verified. ifi d Th The ffrequently-used tl d verifying if i methods are available as follows:

Traffic statistics

Alarm

Subscriber complaint p

Dialing test

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Summary z

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 function, i low l power allocation ll i off paging i channels, h l and d specified UE performance.

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