Huawei WCDMA Paging Procedure and Problem Analysis

Internal

OWJ200104 WCDMA Paging Procedure and Problem Analysis ISSUE 1.0

HUAW HUAWEI EI TECH TECHNO NOLO LOGI GIES ES CO., CO., LTD. LTD.

HUAWEI Mexico Training Center

www.huawei.com

All All righ rights ts rese reserv rved ed

0

Paging is one of the most important processes in WCDMA, which is also an important KPI. This course includes basic paging process. The paging parameters, signaling, performance indicators and analysis methods are also mentioned, which is very helpful for WCDMA optimization engineers.

HUAWEI TECHNOLOGIES CO., LTD.

All rights reserved

Page 1

Different from fixed communication system, the location of the terminal in mobile communication system is not fixed. To establish a call, the CN sends a paging paging message message to to the UTRAN via the Iu interface, interface, and the the UTRAN forwards the message to the UE through the paging procedure on the Uu interface, interface, so that that the UE being being paged paged initiates initiates the the signaling signaling connection setup procedure with the CN.


1

Paging is one of the most important processes in WCDMA, which is also an important KPI. This course includes basic paging process. The paging parameters, signaling, performance indicators and analysis methods are also mentioned, which is very helpful for WCDMA optimization engineers.


All rights reserved

Page 1

Different from fixed communication system, the location of the terminal in mobile communication system is not fixed. To establish a call, the CN sends a paging paging message message to to the UTRAN via the Iu interface, interface, and the the UTRAN forwards the message to the UE through the paging procedure on the Uu interface, interface, so that that the UE being being paged paged initiates initiates the the signaling signaling connection setup procedure with the CN.


1



Upon completion of this course, you will be able to:  Paging

procedure in UMTS

 Paging

message

 Paging

procedure performance analysis



All rights reserved

2

Page 2

Chapter 1 Paging Procedure in UMTS Chapter 2 Paging Messages Chapter 3 Paging Procedure Performance Analysis Chapter 4 Paging Problem Analysis Analysis Process



All rights reserved

3

Page 3

Chapter 1 Paging Procedure in UMTS Section 1 Paging Type Section 2 DRX Process of UE



All rights reserved

4

Page 4

Paging Type



CN initiated paging



UTRAN initiated paging


All rights reserved

Page 5

Core network (CN) can initiate paging. For example, establishing a signaling connection for a call. UTRAN can also initiate a paging request to trigger the state transition procedure for UE which is in CELL_PCH or URA_PCH state. In addition, UTRAN may initiate paging to ask UE which is in idle mode, CELL_PCH and URA_PCH state to read the updated system information. In the existing network, most of pagings are initiated by CN.


5

Paging Type 1


All rights reserved

Page 6

Paging 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 The above figure shows the paging message from CN is transmitted by two RNCs. The message is transmitted in one LA or RA according to LAI or RAI. After calculating the paging time, the paging message will be transmitted at that time


6

Paging Type 2


All rights reserved

Page 7

Paging type 2: 



If UE is in Cell_DCH or Cell_FACH state ，the paging message will be transmitted on DCCH with paging type 2 The message will be only transmitted in a cell


7

Typical Call Flow of UE N SS

UE AS

UE NAS

paging

RR_PAING_IND

M SC paging

RANAP

RANAP

RR_EST_REQ (PAGING RESPONSE)

R R C s e t u p p ro c e s s INITIAL_DIRECT_TRANSFER AUTHENTICATION

REQUEST

AUTHENTICATION

RESPONSE

(PAGING RESPONSE)

RR_SECURITY_CONTROL_REQ (IK CK)

Security mode control SETUP CALL CONFIRM

RAB setup process ALERT CONNECT CONNECT ACKNOWLEDGE


All rights reserved

Page 8

Paging will be initiated on network side in the following cases: 

UE is called



Cell system information is updated



UE state transition

Many problems will cause the target UE cannot receive the paging message properly 



Power setting of paging channel is unreasonable. Unreasonable paging strategies will result in paging channel congestion, which can cause paging message loss.



Paging parameter is unreasonable



Equipment fault


8

Chapter 1 Paging Procedure in UMTS Section 1 Paging Type Section 2 DRX Process of UE



All rights reserved

9

Page 9

DRX Procedure



UE receives the paging indicator on PICH periodically, that is the Discontinuous Reception (DRX), which can reduce the power consumption.



The value for the DRX paging cycle length is determined as follows: : DRX Cycle Length


(2^K)×PBP frames

All rights reserved

Page 10

In idle mode, the UE can monitor the paging in two modes: one is to decode SCCPCH directly every 10ms, the other is to decode the PICH periodically. The second one is the DRX, which is Discontinuous Reception Mechanism. The paging period formula: DRX Cycle Length 

＝

(2^K)*PBP frames

K is the “CN domain specific DRX cycle length coefficient”, which is in SIB1. The typical value is 8 or 6.



PBP is paging block period, which is 1 for FDD mode



The paging period cloud be 2.56s or 640ms


10

DRX Procedure



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 mod M) mod (DRX cycle length div PBP)} * PBP + n * DRX cycle length + Frame Offset


All rights reserved

Page 11

Paging SFN formula: Paging Occasion (CELL SFN) = {(IMSI mod M) mod (DRX cycle length div PBP)} *PBP + n *DRX cycle length + Frame Offset 







n =0, 1, 2……and the requirement is the calculated CELL SFN must be below its maximum value 4096 Frame Offset is 0 for FDD mode M is the number of SCCPCH which carries PCH, and the typical value is 1 The formula cloud be simplified as: SFN = IMSI mod (2^K) + n * (2^K)


11

DRX Procedure One DRX cycle

¡ £ ¡ £ ¡ £

4095

0

PI PI

¡ ¡£ ¡£ £ P I q

0 1


DRX Cycle Length

＝

¡ ¡£ ¡£ £

PI N P -1

All rights reserved

Page 12

(2^k)*10ms

UE needs to monitor the PI on these PICH frames. As shown in this figure , the UE needs to monitor the frames (paging occasions) indicated by the red dots, and then decode the qth PI of this frame.


12

PICH Structure

288 bits for paging indication b0 b1

12 bits (transmission off) b 287 b 288

b 299

One radio frame (10 ms)


All rights reserved

Page 13

The Page Indication Channel (PICH) is a fixed rate (SF=256) physical channel used to carry the paging indicators which are used to alert UE of a incoming page sent on S-CCPCH. Each radio frame for PICH is 10ms, and consists of 300 bits. The first 288 bits are used to carry the Paging Indicators (PIs), and the rest 12bits are undefined. The number of PI in one frame is Np. In WCDMA system, Np value is 18, 36, 72 and 144. That is to say, each PI has 288/Np bits. UE can get Np value from system information.


13

Paging Formula

q

=



UE must calculate q to know which PI to monitor in one frame of PICH.



The q value is achieved by the following formula :

 Np     PI +  ((18 × (SFN + SFN / 8 + SFN / 64  + SFN / 512  )) mod 144 )× 144   mod Np    


All rights reserved

PI = (IMSI div 8192) mod NP Here, SFN is the paging time of the UE


14

Page 14

Time Offset between PICH and S-CCPCH

PICH frame containing paging indicator

Associated S-CCPCH frame τPICH


All rights reserved

Page 15

The timing relationship between PICH and S-CCPCH is defined by the above figure, and the interval is 3 slots duration (2ms, 7680 chips).


15

Example for DRX 

In system information, the parameters about paging: 

K=8, the CN domain specific DRX c ycle length coefficient



Np=36, the number of PI per frame



After UE received the information, the paging time, PI and q can be calculated



Assume the IMSI of a UE is 448835805669362, then



DRX cycle length=2^8=256, the paging interval is 2.56s



Cell SFN



PI= (448835805669362 div 8192) mod 36 = 14



“448835805669362” mod 256+ n ×256 = 242 + n ×256 (n = 0,1,2,...)

q={14+[(18×(242+[242/8]+[242/64]+[242/512])) mod 144)×0.25]} mod 36 = 27


All rights reserved

Page 16

Conclusion: Each PICH radio frame contains 36 PIs, and each PI has 8bits (288/36). UE has to monitor bit 216 (27*8) ～bit 223 of each frame, if all of these 8 bits become “1111 1111”, UE will know there is a paging for it, and receive the paging information in SCCPCH.


16

Chapter 1 Paging Procedure in UMTS Chapter 2 Paging Messages Chapter 3 Paging Procedure Performance Analysis Chapter 4 Paging Problem Analysis Process



All rights reserved

17

Page 17

System Information


All rights reserved

The value of “K” is transmitted in SIB1


18

Page 18

System Information


All rights reserved

Page 19

The detailed parameters about PCH and PICH are transmitted in SIB5


19

Paging From CN


All rights reserved

Page 20

Paging from CN contains the following information: CN Domain Indicator 

The domain where the paging comes from

Permanent NAS UE Identity 

The UE IMSI

DRX Cycle Length Coefficient 

K value

Temporary UE Identity 

Which is optional, TMSI or P-TMSI

Paging Area 

LAI if the paging is from CS domain



RAI if the paging is from PS domain

Paging Cause


20

Paging Type1


All rights reserved

Page 21

Paging type1 contains the following information element: Paging record list 

If paging is from CN, the CN identification, UE NAS identification, paging cause should be included.



If paging is from UTRAN, the AS identification URNTI should be included.



The protocol defines at most 8 UE can be paged in one paging time

BCCH modification info 

It is optional, and value tag is used to show the change of system information. If this IE exist, UE will neglect paging record list, and read system information directly


21

Paging Type2



For the UE in CELL_DCH or CELL_FACH state, the UTRAN sends the PAGING TYPE 2 message with AM RLC on DCCH channel to initiate the paging procedure


All rights reserved

Page 22

UTRAN should set the information element (IE) "Paging cause" to the cause for paging received from upper layers. If no cause for paging is received from upper layers, UTRAN should set the value "Terminating cause unknown".


22

Paging Channel Setup



PICH and PCH channels are established in cell setup procedure


All rights reserved

Page 23

RNC will send information about PCH and PICH to NodeB through the Iub message “Common Transport Channel Setup Request” From the above figure, we can get the following information: 2 transport block format (0 ×240,1 ×240) of PCH Power offset (2dB) of PCH Np value (36) of PICH Power offset ( −3dB) of PICH


23




All rights reserved

24

Page 24

Paging Scheduling 

The paging scheduling is performed in the MAC-C



After the MAC-C receives the paging message from the upper layer, it will calculate the paging time, and then stores the paging record at the corresponding location. For the MAC-C, a maximum of 8 paging records can be stored at one paging time, and the excessive ones will be discarded.



When each paging time comes, the MAC-C codes the paging records corresponding to this paging time, and delivers them to the NodeB, and then clears them. NodeB delivers the paging records through the cell paging channel


All rights reserved

Page 25

If the paging is caused by system message update, the MAC-C will immediately code them and deliver them, and clears all the paging records. At present, the transport block of the PCH supported by the MAC-C is 240 bits. The coded paging message supported by each frame cannot exceed 240 bits. According to the signaling structure of PAGING TYPE 1 and ASN.1 PER coding rule, if the UE ID of the paging message is IMSI, a maximum of 3 UEs can be paged at each paging time. If the UE ID is TMSI or PTMSI, a maximum of 5 UEs is supported. Therefore, with the current coding mode of PCH, the number of UEs paged at one paging frame can’t reach the protocol value 8. If the number of UEs paged at the same paging time exceed the system capacity, it will lead to paging loss, and consequently call loss.


25

In the configuration of IMSI, the detailed planning should be made according to the calculation formula for paging time, IMSI mod 2^k+n*2^k, so as to ensure the paging occasion of every UE are evenly distributed on the frames of a paging cycle. On the other hand, the network can improve the paging success rate by means of re-transmission. After the paging timer is expired, the CN will retransmit the paging message at the Iu interface, and the UTRAN can also re-transmit paging through the scheduling of the MAC-C, but in different paging cycles.


26

Paging Parameters Analysis



DRX Paging Cycle Coefficient



Np Value



Paging Retransmission Times and Interval


All rights reserved

Page 27

(1) The higher K value, the longer the DRX cycle, and the lower the UE power consumption. This value can be modified by the command MOD CNDOMAIIN. The modified value will be transmitted to UE by paging type 1. (2) Np is the number of PIs per frame, which is in the value range of (18, 36, 72, 144). After UE gets PI, it will demodulate the subsequent S-CCPCH frame. All the UEs will be divided into Np groups, and all the UEs in the same group share the same PI. If Np is small, more UE will share one PI, then UE will be waken more times; If Np is big, less UE will share one PI, then UE will be waken less times. More Np means the higher PICH demodulation requirement for UE because each PI has less bits. HUAWEI Mexico Training Center

27

(3) To increase the paging success rate, the CN and RNC will re-transmit the paging message. Paging re-transmission leads to some negative effect, such as paging traffic increase. The CN re-transmission times and interval should be considered together with the re-transmission of the UTRAN The default configuration is the Paging type 1 information is transmitted twice by RNC. And the interval is one paging period. CN can support four retransmissions.


28

Traffic Statistics for Paging

Traffic statistics item name

Meaning

CN_PAGE_REQ

Measures the times of paging at the Iu interface

When the PAGING message initiated by the CN is terminated

CN_PAGE_IDLE_UE_REQ

Measures the times of paging idle UEs at the Iu interface

When the PAGING message initiated by the CN is terminated by an idle UE.

Measures the times of paging idle UEs successfully

When the RRC connection request message of UE is received, with the request cause being a called type cause, for example, Terminating Conversational Call.

CN_PAGE_IDLE_UE_SUCC


Statistics point of time

All rights reserved

Page 29

This table shows the traffic statistics item for paging in the RNC. Among them, the two main items CN_PAGE_IDLE_UE_SUCC_RATE and UTRAN_PAGE1_SUCC_RATE greatly indicate the actual paging performance. The paging success rate, the first paging success rate and second paging success rate at the CN side can also be measured.


29

Traffic Statistics for Paging

UTRAN_PAGE1_REQ

Measures the number of PAGING TYPE 1 messages initiated by the UTRAN

When the UTRAN initiates a PAGING TYPE 1 message

UTRAN_PAGE1_SUCC

Measures the times of successful response from the UE after the UTRAN initiates the PAGING TYPE 1 message

When the UTRAN receives the paging response message from the UE

CN_PAGE_IDLE_UE_SUCC_RATE

Measures the success rate of paging to idle UEs initiated by the CN

UTRAN_PAGE1_SUCC_RATE

Measures the success rate of PAGING TYPE 1


All rights reserved

A calculation index, calculated with the formula of [CN_PAGE_IDLE_UE_SUCC]/ [CN_PAGE_IDLE_UE_REQ] A calculation index, calculated with the formula of [UTRAN_PAGE1_SUCC]/[UTRAN_PAGE1_R EQ]

Page 30

Success of paging is indicated by “paging response” in the initial DT sent by the called user after his RRC connection is setup.


30

Paging Abnormity Handling System Abnormity Abnormity



To ensure the stability of the system and avoid impact of burst message storm, the RNC performs flow control on the messages (including paging messages) with high processing frequency.


All rights reserved

Page 31

When the RNC receives the paging message of the CN, it will judge whether the system is overloaded. If so, it will discard the paging message, and record the number of discarded paging message. If the loss proportion reaches a specific threshold, the RNC will send the message “Overload” to the CN, then the CN will control the message transmission flow by decreasing the flow based on a certain step . Thereafter, if the CN does not receive “Overload” within a certain period of time, the traffic of the Iu interface will increase to the normal status step by step. In addition, if some failure occurs in the system, for example, the Iub interface transmission layer failure or cell in abnormal state, it may cause paging loss. NodeB also will not process the paging message packet when it is overloaded. To minimize the call failure caused by paging loss, the network adopts the method of paging message re-transmission.


31

Paging Abnormity Handling Paging Channel Capacity Restriction



Due to the restriction of the PCH capacity, the number of UEs that can be paged at the same paging time is limited. If the number of UEs exceeds this limit, paging message will be discarded. This will occur in two c ases:  The

number of UEs paged at the same paging time exceeds eight (the protocol value) Decided Decided by by the the buffer of MAC-C buffer of MAC-C

 The

transport block of each frame after coding is 240 bits at the maximum Decided Decided by by the the IMSI or TMSI IMSI or TMSI


All rights reserved

Page 32

(1) If the number of UEs paged at the same time is more than eight (the protocol value), it will exceed the processing capability of the MAC-C (The MAC-C applies a memory for eight paging records at each paging time.). (2) As the transport block of each frame after coding is 240 bits at the maximum, even if the number of UEs of each paging time is smaller than 8, paging loss cannot be avoided. If the UE ID of the paging record is IMSI, the paging message of each frame can contain the paging records of only 3 UEs. If the UE ID of the paging record is TMSI or PTMSI, the paging message of each frame can contain the paging records of only 5 UEs. If this limit is exceeded, the excessive paging records will be discarded.


32




All rights reserved

33

Page 33

Chapter 4 Paging Problem Analysis Process Section 1 Problem Analysis Process Section 2 Network Information Collection Section 3 Troubleshooting Paging Problems Section 4 Optimization Optimization Verification Verification



All rights reserved

34

Page 34

Problem Analysis Flow Collect network information

Identify optimization goal

Locate paging problem

Optimize paging problem

Optimization verification NO

Optimization goal achieved? YES END


All rights reserved

Page 35

Network information collection: 

Traffic statistics related to network and paging,



Alarm information, complaints of subscribers,



Network planning information, optimization records and configuration of network parameters

Determination of optimization goal: 

Determine KPI of paging problem optimization

Paging problems location: 

Locate causes of paging problems

Paging problems optimization: 

Take corresponding problems

optimization methods according to the specific

Optimization verification: 

Verify whether the KPI meets the requirements and whether other information about paging is normal after optimization


35




All rights reserved

36

Page 36

Network Information Collection 

Network information collection is the first step of paging problem analysis  Traffic statistics  Subscriber complaints  Alarms  Optimization  Radio

parameters configuration



history record of network planning

All rights reserved

37

Page 37

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


All rights reserved

Page 38

CN_PAGE_IDLE_UE_SUCC_RATE is paging success rate of UE in idle state initiated by CN UTRAN_PAGE1_SUCC_RATE

is the success rate of Paging Type 1

initiated by UTRAN These two items indicate the paging success rate of the corresponding paging area of RNC. CN_PAGE_IDLE_UE_SUCC_RATE indicates the paging success rate from CN, while UTRAN_PAGE1_SUCC_RATE includes not only CN paging, but also UTRAN system information update and UE state transition, which will request UE for cell update.


38

Alarm





Paging alarm  Paging

flow control alarm in RNC

 Paging

overload in CN

Boards alarm


All rights reserved

Page 39

Based on the current realization of Huawei, there is only “RNC overload” alarm related to paging, alarm occurs when CN receives the overload message of RNC. The paging-related alarm of RNC is “flow control alarm”. When RNC is in paging flow control state, the paging message will be discarded . When the CPU occupation or the message packet occupation of a board sub-system exceeds the threshold, the system will switch to the flow control state, and the flow control alarm will occur. When the system returns to normal operation state from the flow control state, the “flow control recovery” alarm will occur. However, it is not absolute that paging will be discarded when “flow control alarm” occurs, because RNC owns different flow control thresholds for different flow control objects (paging, serial port printing and message tracing), as long as there is flow control, alarm will occur; but paging loss will occur only when paging loss occurs.


39

Subscriber Complaints 

In subscriber complaints, the following information should be concerned  Complaints

occur no matter the network is busy or not. If paging failure occurs at the busy time, paging congestion analysis should be emphasized. If not, other factors should be analyzed

 If

the terminated UEs are of the same type. Problems probably exist in UE itself

 If

the complaints are centralized in a certain place; it is possibly caused by poor coverage


All rights reserved

Page 40

Subscribers’ complaints are very valuable to locate specific network fault, we should find the rules and solve problems as soon as possible


40

Network Planning Optimization Record



Obtain the network planning report, and pay attention to the division of the paging areas ------LA and RA



For the network that has been put into service, it may have experienced several optimization processes before. Emphasis should be put on the former optimization records about coverage hole, system overload, paging loss and paging channel power allocation.


All rights reserved

Page 41

We should notice the difference between the LA and RA.


41

Radio Parameter Configuration



CN paging retransmission times and paging interval



UTRAN paging retransmission times and paging interval



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



Paging indication quantity Np included in a PICH frame



Channel power allocation of PICH and PCH



Whether CN adopts global paging



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


All rights reserved

Page 42

In practice, we should pay more attention to the first, second one and the fifth one.


42

Determining Optimization KPI Goal



Two KPIs, “location area paging success rate” and “RA paging success rate” , should satisfy the optimization requirements.


All rights reserved

Page 43

The paging success rate is recommended to be higher than 86%


43




All rights reserved

44

Page 44

Position the problems



Paging problems can be divided into three categories  Paging

message is not transmitted at the air interface at all

 Paging

message has been transmitted, but UE does not

receive the message or receive wrong message  UE

fails to respond after receiving paging messages.






Page 45

Paging message is not transmitted at the air interface at all 



All rights reserved

If paging message is not transmitted at the air interface at all, it is most likely that paging is discarded.

Paging message has been transmitted, but UE does not receive the message or receive the wrong message 

The power allocation for PICH or PCH is too low



Coverage problems

UE fails to respond after receiving paging messages.


45

Direct Causes of Paging Loss



RNC is in paging flow control state



PCH capacity restriction



Other causes


All rights reserved

Page 46

(1) If RNC detects that CPU occupation or message queuing occupation reaches the preset threshold, paging flow control will be triggered and paging message will be discarded. (2) Based on the structure of PCH, if IMSI is used for paging, only three UEs can be paged at one paging period; and if TMSI or PTMSI paging is used, only five UEs can be paged at one paging period . (3) Transmission faults of Iub interface and equipments faults. Probability of those faults is small and can be viewed from the alarm console.


46

Further analysis on paging loss cause



The following problems could be the main causes for paging loss  Too

large paging area

 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


All rights reserved

Page 47

Other Cause Analysis 

Too low power allocation of paging channels



Existence of coverage dead zones



UE performance problems


47




All rights reserved

48

Page 48

Optimization Verification 



After network is optimized and adjusted, the optimization results should be verified 

Traffic statistics



Alarm

Subscriber complaint 



Whether there is any subscriber complaint in a certain period

Call test 

Test call success rate when traffic is at the peak and in the place where subscriber complaint occurs


All rights reserved

Page 49

Traffic statistics





Check mainly whether “location area paging success rate” and “RA paging success rate” achieve the optimization goal 86% specified in advance

Alarm





Check whether there is any “RNC overload” alarm in CN or whether there is any flow control alarm in RNC


49

Huawei WCDMA Paging Procedure and Problem Analysis

Recommend Documents