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1. wcdma rno paging problem analysis guidance 20041101-a-1.0

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1. wcdma rno paging problem analysis guidance 20041101-a-1.0

  1. 1. Product name Confidentiality level WCDMA RNP For internal use only Product version Total 29 pages V100R001 WCDMA RNO Paging Problem Analysis Guidance (For internal use only) Prepared by: URNP -SANA Date: 2003-12-27 Reviewed by: Date: Reviewed by: Date: Approved by: Date: Huawei Technologies Co., Ltd. All rights reserved
  2. 2. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 2 of 29 Revision Record Date Revision version Description Author 2003-12-27 1.00 Initial transmittal Jiao Anqiang
  3. 3. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 3 of 29 Table of Contents 1Overview.................................................................................................................................................... 7 2Paging Problem Analysis Process.............................................................................................................. 9 2.1Problem Analysis Flow......................................................................................................................... 9 2.2Network Information Collection ......................................................................................................... 10 2.2.1Traffic Statistics............................................................................................................................ 10 2.2.2Alarm............................................................................................................................................ 13 2.2.3Subscriber Complaints.................................................................................................................. 13 2.2.4History Record of Network Planning Optimization ..................................................................... 14 2.2.5Radio Parameter Configuration .................................................................................................... 14 2.3Determining Optimization Goal.......................................................................................................... 15 2.4Locating Paging Problems .................................................................................................................. 15 2.4.1Determining Basic Location Direction......................................................................................... 15 2.4.2Direct Causes of Paging Loss ....................................................................................................... 16 2.4.3Further Analysis on Paging Loss Cause ....................................................................................... 17 2.4.4Other Cause Analysis.................................................................................................................... 17 2.5Paging Problems Optimization............................................................................................................ 17 2.6Optimization Verification ................................................................................................................... 17 3Typical Paging Problem Analysis............................................................................................................ 18 3.1Too Large Paging Area Planned ......................................................................................................... 18 3.1.1Problem Analysis.......................................................................................................................... 18 3.1.2Optimization Measures................................................................................................................. 19 3.2Improper Setting of CN Paging retransmission Times and Interval ................................................... 19 3.2.1Problem Analysis.......................................................................................................................... 19 3.2.2Optimization Measures................................................................................................................. 20 3.3Improper Setting of UTRAN Paging Retransmission Times and Interval.......................................... 21 3.3.1Problem Analysis.......................................................................................................................... 21 3.3.2Optimization Measures................................................................................................................. 21 3.4CN Adopts Whole-Network Paging.................................................................................................... 21 3.4.1Problem Analysis.......................................................................................................................... 21 3.4.2Optimization Measures................................................................................................................. 21 3.5Improper Setting of DRX Paging Cycle Coefficient........................................................................... 22 3.5.1Problem Analysis.......................................................................................................................... 22 3.5.2Optimization Measures................................................................................................................. 23 3.6Improper setting of Np value ............................................................................................................... 23 3.6.1Problem Analysis.......................................................................................................................... 23 3.6.2Optimization Measures................................................................................................................. 24 3.7UE Identifier Utilized by CN Paging .................................................................................................. 24 3.7.1Problem Analysis.......................................................................................................................... 24 3.7.2Optimization Measures................................................................................................................. 25 3.8UTRAN Should Activate IMSI ATTACH and DETACH Functions ................................................. 25 3.8.1Problem Analysis.......................................................................................................................... 25 3.8.2Optimization Measures................................................................................................................. 26 3.9Too Low Power allocation of Paging Channels.................................................................................. 26 3.9.1Problem Analysis.......................................................................................................................... 26 3.9.2Optimization Measures................................................................................................................. 26 3.10 Existence of Coverage Dead Zones.............................................................................................. 27 3.10.1 Problem Analysis ................................................................................................................... 27 3.10.2 Optimization Measures........................................................................................................... 27 3.11 UE Performance Problems............................................................................................................ 27 3.11.1 Problem Analysis ................................................................................................................... 27 3.11.2 Optimization Measures........................................................................................................... 27 4Outstanding Problems.............................................................................................................................. 27
  4. 4. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 4 of 29 List of Figures Figure 1 Typical called flow of UE ...................................................................................................... 8 Figure 2 Paging Problem Analysis Flow.......................................................................................... 10 Figure 3 System Message 1 Resolution.......................................................................................... 26
  5. 5. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 5 of 29 List of Tables Table 1 UMSC Paging Traffic Statistics Indexes................................................................................ 12 Table 2 SGSN Paging Traffic Statistics .............................................................................................. 12 Table 3 Subscriber complaint information.......................................................................................... 14 Table 4 Calculaiton Result of Paging Area When Cn Id Adopting IMSI ........................................... 19 Table 5 IMSI ATTACH and DETACH Identifier............................................................................... 25
  6. 6. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 6 of 29 WCDMA RNO Paging Problem Analysis Guidance Key words: Paging, paging area, paging retransmission Abstract: This document describes the general flow of solving paging problems, analyzes typical problems during paging in details and provides optimization measures. List of abbreviations: Abbreviations Full spelling DRX Discontinuous Reception LA Location Area PCH Paging Channel PI Paging Indication PICH Page Indication Channel RA Route Area RAN Radio Access Network RNC Radio Network Controller RNO Radio Network Optimization WCDMA Wideband Code Division Multiple Access
  7. 7. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 7 of 29 1 Overview If it is necessary for network side to contact with UE which is in idle mode or in CELL_PCH or URA_PCH state, a paging flow will be initiated. Paging is an important way for network to contact with UE. Compared with other flows, the paging flow has the characteristics of high frequency, heavy traffic and strong outburst in radio network. Paging performance is closely related to the performances of the whole radio network. Therefore, the study of paging problems is of practical significance for radio network performances. From the aspect that UE receives paging messages, paging messages consist of PAGING TYPE1 and PAGING TYPE2. Which type of paging messages will be sent to UE is decided by UTRAN. PAGING TYPE1 is used to page UEs in IDLE, CELL_PCH and URA_PCH states through PCCH logical channel. PAGING TYPE2 is used to page UEs in CELL_FACH or CELL_DCH states through DCCH. This document mainly discusses PAGING TYPE1, while PAGING TYPE2 can be regarded as the common RRC signaling to process and will not be discussed in this document. Paging will be initiated on network side in the following cases:  When UE is called: In order to set up a call, the core network (CN) sends paging message to UTRAN through Iu interface, and UTRAN sends the paging message from CN to UE through the paging process at Uu interface, which will have UE initiate a signaling connection setup process with CN.  Cell system message update: When system messages change, UTRAN will trigger paging process in order to inform UE in idle, CELL_PCH and URA_PCH state to carry out the system message update. Therefore, UE can read the updated system message. For UE in CELL_FACH state, in order to inform it to carry out corresponding system update, it is necessary to send SYSTEM INFORMATION CHANGE INDICATION message to it through BCCH (V1.2 version does not support the message, so UE in CELL_FACH state will not be processed).  UE state migration: In order to trigger UE in CELL_PCH and URA_PCH state to carry out state migration (for example, migration to CELL_FACH state), UTRAN will perform a paging process. Meanwhile, UE will initiate a cell update or URA update, as a reply to the paging. A typical called flow caused by paging is shown in Figure 1 : CN sends a paging message to UTRAN, UTRAN calculates the paging time and obtains the target cell
  8. 8. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 8 of 29 after receiving the paging message, and delivers the paging message at the air interface upon the paging time. If CN receives the paging response message from UE, the UE paging is successful. The whole process includes paging delivery and UE access. For UE access, refer to Access Process Guidance. There are probably various problems in the paging process, which will cause that the target UE cannot receive the paging message properly. For instance, during short messages multi-casting and full-text paging in network, unreasonable paging strategies will result in paging channel congestion, so large amount of messages will be lost, in more serious case, the system will be caused over-loaded for long time and the paging channel power allocation is too low, which will lead to low paging success rate. This document will make a further discussion on these problems leading to paging abnormality and present corresponding solutions. UE NAS UE AS NSS MSC paging AUTHENTICATION REQUEST AUTHENTICATION RESPONSE RR_SECURITY_CONTROL_REQ (IK CK) Security mode control SETUP CALL CONFIRM ALERT CONNECT CONNECT ACKNOWLEDGE RAB setup process paging RR_EST_REQ (PAGING RESPONSE) RR_PAING_IND INITIAL_DIRECT_TRANSFER (PAGING RESPONSE) RANAPRANAP RRC setup process Figure 1 Typical called flow of UE The general structure of this document is as follows: 1. Overview: It briefly introduces the paging time, paging flow and general paging problems; 2. Paging problem analysis process: It describes the problem analysis flow of paging, how to analyze paging problems step by step and what to do in each step.
  9. 9. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 9 of 29 3. Typical problem analysis of paging: It analyzes typical problems of paging, including the phenomenon, principles and optimization methods of the problems. 4. Outstanding problems: They refer to problems which cannot be solved in this document. 2 Paging Problem Analysis Process 2.1Problem Analysis Flow The paging problem analysis flow is as shown in Figure 2 . Similar to the general analysis methods of network problems, there are four steps of paging problem analysis, which are detailed as follows: Network information collection: Collect traffic statistics information 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 optimizing and adjusting measures according to location results; Optimization verification: Verify whether the KPI meets the requirements and whether other information about paging is normal after optimization.
  10. 10. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 10 of 29 Collect network infomration Identify optimization goal Locate paging problem Optimize paging problem Optimization verification Optimization goal achieved? END YES NO Figure 2 Paging Problem Analysis Flow 2.2Network Information Collection Network information collection is the first step of paging problem analysis. The optimization personnel should obtain the paging-related information to-be-optimized, such as traffic statistics, subscriber complaints, alarms, optimization history record of network planning and radio parameters configuration, so as to prepare for the subsequent analysis. 2.2.1 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. RNC traffic statistics corresponds to a RNC area, UMSC traffic statistics corresponds to a location area and SGSN traffic statistics corresponds to a RA. In the actual traffic statistics analysis process, the traffic statistics of CN is mainly analyzed, with combination of the traffic statistics data of RNC and CN. If there is no paging-related traffic statistics on the traffic statistics console, it is necessary for equipment users to establish the paging traffic statistics tasks. The paging-related traffic statistics of RNC, UMSC and SGSN are discussed below based on the paging traffic statistics of our company.
  11. 11. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 11 of 29 The traffic statistics of RNC is shown in Table 1 . Attention should be paid to CN_PAGE_IDLE_UE_SUCC_RATE (paging success rate of UE in idle state initiated by CN) and UTRAN_PAGE1_SUCC_RATE (The success rate of Paging Type 1 initiated by UTRAN). These two indexes indicate the page success rate of the corresponding paging area of RNC. CN_PAGE_IDLE_UE_SUCC_RATE indicates the page success rate from the aspect of CN, while UTRAN_PAGE1_SUCC_RATE includes not only CN paging, but also UTRAN system information update and UE state migration (the paging information of UE is cell updating). The two indexes can be used to analyze the paging performance of an RNC area which includes one or more location areas. Table 1 RNC Paging Traffic Statistics Index Name Description Standard measuring point CN_PAGE_REQ Count paging times at IU interface Receive the PAGING messages initiated by CN 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 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 times of UE success receive response received UE paging response message received at UTRAN side . CN_PAGE_IDLE_UE_SUCC_ RATE Count paging success rate of idle UE initiated by CN The calculation index, obtained by the formula of [CN_PAGE_IDLE_UE_SUCC]/ [CN_PAGE_IDLE_UE_REQ] UTRAN_PAGE1_SUCC_RAT E Count the paging success rate of Page Type 1 initiated by UTRAN The calculation index, obtained by the formula of [UTRAN_PAGE1_SUCC]/[UTRAN_P AGE1_REQ] The relevant traffic statistics of UMSC paging are all based on a location area, as shown in Table 1. Generally, the location area will not be configured cross RNC and BSC, so we can carry out statistics on the paging success rate, the first paging success rate and non-first paging success rate of a location area. The location area paging success rate focuses on the paging status of a location area, not on paging
  12. 12. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 12 of 29 repeat times, while first paging success rate and non-first paging success rate focus on the influence of paging repeat times on paging success rate. ion timestransmisspagingFirst messagesresponse-nodeliveredofnumberion timestransmisspagingFirst ratesuccesspagingLA -  ion timestransmisspagingFirst timesresponsepagingFirst ratesuccesspagingFirst  timesresponserepitetionpagingInterface timesrepitetionpagingInterface ratesuccesspagingfirst-Non  Table 1 UMSC Paging Traffic Statistics Indexes 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 timer stay-over statistics The relevant traffic statistics indexes of SGSN paging are all based on a RA, as shown in Table 2, the paging success rate of a certain RA can be obtained. questTimesingRAGroupPag TimesingFailureRAGroupPagquesTimesingRAGroupPag ccessRateRAPagingSu Re Re - = Table 2 SGSN Paging Traffic Statistics Name Description Standard measure point Group paging request times of each RA It provides delivery group paging request times in the SGSN sends Iu interface paging request message (PAGING), and its
  13. 13. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 13 of 29 specific RA, not including retransmission messages CN Domain is PS. Group paging failure times of each RA It provides group paging failure times in the specific RA Paging retransmission message times reach maximum. During traffic statistics analysis, attention should be paid to “location area paging success rate” and “ RA paging success rate”, which are KPI measuring paging performance. The RNC paging traffic statistics CN_PAGE_IDLE_UE_SUCC_RATE and UTRAN_PAGE1_SUCC_RATE can be taken as reference analysis. 2.2.2 Alarm Based on the current realization in our company, CN is only “RNC overload” alarm related to paging, alarm occurs when CN receives the overload message of RNC. In order to guarantee the system operation stability and avoid the strike on system by outburst messages, RNC flow-controls the paging-included message with high processing frequency. When RNC receives paging messages from CN, the judging system will discard the paging message and record the quantity of paging message loss if it is in paging flow control state. If the loss proportion has reached a certain threshold, RNC will send Overload message to CN, then CN will reduce the message flow by certain step. If CN has not received Overload message within a certain period, the message flow of IU will increase gradually till it get normal. The paging-related alarm of RNC is “the flow control alarm”. When RNC is in paging flow control state, the paging message will be lost unconditionally. When the CPU occupation or the message packet occupation of a board sub-system exceeds the threshold, the system will be switched into 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 lost 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. 2.2.3 Subscriber Complaints If paging messages are lost, UE will not be called. The calling party will hear the system prompt tone “the subscriber you dialed is out of service”. We can learn about the subscriber complaints from 1860 Customer Service Center of pilot office or learn about the cases of “out of service” by contacting with the complainer directly.
  14. 14. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 14 of 29 Attention should be paid to the cases of UE called failure, and information to be collected is shown in Table 3, but not limited to it 【5】: Table 3 Subscriber complaint information Time Name (complainer) UE No. (complainer) UE No. (the called) UE type (the called) Place Whether it is often Description Sort out complaint information, seek for rules and observe whether the information belongs to the following cases:  Whether complaints occurs when paging is busy in the daytime and idle at night; if paging failure occurs at the peak traffic, paging congestion analysis should be emphasized on; if not at the peak traffic, other factors should be analyzed.  Whether types of the called UE are the same. Problems probably exist in UE itself.  Whether the complaint place is centralized; it is possibly because of signal coverage; Find the rules and solve problems more quickly. 2.2.4 History Record of Network Planning Optimization Obtain the network planning report, and pay attention to the division of the paging area (location area and RA). Obtain network planning report: If it is the optimization before network is put into service, the planning report can be obtained from the planning manager responsible for the project; if it is the optimization after network is put into service, the planning report can be obtained from the client. The planning report mentioned above should include planning reports after each network capacity expansion. For the network that has been put into service, it may have experienced several optimization processes before this optimization. Then we should obtain the history optimization records and learn about the network adjusting process and outstanding problems. Emphasis should be put on optimization records about coverage absence, system overload, paging loss and low paging channel powerallocation. 2.2.5 Radio Parameter Configuration Parameters related to paging are as follows, which should be collected before optimization:
  15. 15. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 15 of 29  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 paging;  UE ID used by CN paging (IMSI,TMSI or PTMSI) 2.3Determining Optimization Goal Two KPI of “location area paging success rate” and “RA paging success rate” should meet the optimization requirements. The paging success rate is recommended to be over 86% 【3】. 2.4Locating Paging Problems 2.4.1 Determining Basic Location Direction Paging problem optimization is intended to guarantee the paging KPI. Whether UE can respond successfully is directly related to the paging KPI. From this aspect, paging problems can be generally divided into three parts:  Paging message is not delivered at the air interface at all. If paging message is not delivered at the air interface at all, it is most likely that paging is lost. Paging loss is a frequently-seen problem during paging process and it is the emphasis of analysis in this document. For detailed paging loss analysis, please refer to Section 2.4.2 and Section 2.4.3. However, the reason why paging has not been sent out is probably the transmission faults of IUB interface or faults of other equipments, which can be seen through viewing the alarm information.  Paging message has been delivered, but UE does not receive the message or receives the wrong message. According to the specific subscriber complaints, if problems exist on called UE only (prompt tone “the subscriber you dialed is out of service”), because the reason is probably that the power allocation of PICH and PCH is too low or there are problems with UE performance; if problems exist in calling and called UE, the reason is probably that signal coverage dead zones exist in the area.
  16. 16. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 16 of 29  UE fails in responding after receiving paging messages. As shown in Figure 1,The problem is related to access failure, for solutions, please refer to WCDMA RNP Access Process Problem Analysis Guidance. During paging problem location, problems can be located by analyzing paging traffic statistics, alarms and subscriber complaints. Paging loss generally occurs in the period when traffic is heavy. Check “location area paging success rate” and “RA paging success rate” of CN traffic statistics, if these two indexes are low (lower than 86%) when traffic is heavy, and subscriber complaints are centralized in this period, paging loss is serious and attention should be paid to analyzing it. Meanwhile, check whether RNC overload alarm or RNC flow control alarm occurs in CN. If these alarms exist, the probability of paging loss is big. If events that two indexes are low are evenly distributed on the time, and subscriber complaints are regional, check other reasons except “paging loss”: paging channel power allocation, signal coverage and UE performance. It is necessary to make dialing test analysis on the site for further analysis on paging problems. Select the period when traffic is heavy and the area where subscriber complaints are centralized, trace paging message delivery and UE paging response process on the CN and RNC maintenance consoles during the dialing test process. 2.4.2 Direct Causes of Paging Loss Paging will be lost in the following cases: 1. RNC system is in paging flow control state. Because paging message is sent frequently and RNC flow-controls paging. 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 lost unconditionally. 2. PCH capacity restriction; Based on the current PCH coding mode, one TTI can only transmit 240bits. If IMSI paging is utilized, only three UEs can be paged at the same paging period; and if TMSI and PTMSI paging are utilized, only five UEs can be paged at the same paging period【2】. If the quantity of UEs paged at the same paging period is beyond the system processing capability, paging loss will occur.
  17. 17. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 17 of 29 3. Other causes: Transmission faults of IUB interface and equipments faults. Probability of those faults is small and can be viewed from the alarm console. 2.4.3 Further Analysis on Paging Loss Cause The direct causes of paging loss are system overload and paging channel overload, after further analysis of its causes, it is found that CN and RNC have adopted inappropriate paging strategies, for detailed analysis, please refer to hyperlinks as follows:  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 2.4.4 Other Cause Analysis  Too low power allocation of paging channels  Existence of coverage dead zones  UE performance problems 2.5Paging Problems Optimization The paging problem optimization methods are described in detail in Section 3. 2.6Optimization Verification After network is optimized and adjusted, the optimization results should be verified. The frequently-used verifying methods are available as follows: have it run and check relevant paging traffic statistics, check whether there are paging alarms, collect subscriber complaint information, and carry out UE called dialing test on site.  Traffic statistics: Check mainly whether “location area paging success rate” and “RA paging success rate” achieve the optimization goal 86% specified in advance;
  18. 18. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 18 of 29  Alarm: Check whether there is any “RNC overload” alarm in CN or whether there is any flow control alarm in RNC;  Subscriber complaint: Whether there is any subscriber complaint in a certain period;  Dialing test: Test UE called success rate when traffic is at the peak and in the place where subscriber complaint occurs. During dialing test, it is unnecessary to through-connect UE, just listen to ring back tone and prompt tone. 3 Typical Paging Problem Analysis 3.1Too Large Paging Area Planned 3.1.1 Problem Analysis In general, CN pages target UE in one paging area (location area or RA), which is called intra-office paging. For CS domain service, CN identifies and pages UE with location area. In protocols, location area is defined as the area where mobile terminals can move freely without updating VLR. A location area may contain one or more cells. For PS domain service, CN identifies and pages UE with routing area. RA is defined as the area where mobile terminals can move freely without updating SGSN in a specified operation mode. A RA may contain one or more cells. The relationship between location area and RA is specified in GSM, namely, RA can be equal to location area in size, or only the subset of a certain location area. If 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. If the paging channel of a cell is overloaded in a certain period, the paging message sent to UE in the cell will be caused lost and the power-on subscriber within the service area can not be paged (The subscriber is out of service). On the contrary, if paging area is planned too small, subscribers will update locations frequently while moving, which will increase signaling flow of the system. When network is just put into service, PS paging traffic is not heavy, RA may be planned larger, it can be planned as per n=1. With the development of network, the demands for PS paging traffic are increasing, in this case RA can be planned smaller consequently. However, too small RA may cause more paging area update events of subscribers while moving, and that signaling overhead on network side becomes larger. Moreover, frequent location update will influence the standby time of UEs.
  19. 19. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 19 of 29 The paging area maximum value is determined by the paging channel capacity. For estimation methods of paging area capacity, please refer to【2】, for paging mixture capacity in typical environments in【2】, please refer to Table 4: Table 4 Calculaiton Result of Paging Area When Cn Id Adopting IMSI n Mmix RA LA 1 3 1.738624042 0.002592996 133 133 2 3 1.741614489 0.003616996 95 190 3 3 1.74665366 0.004640996 74 222 4 3 1.744911078 0.005664996 61 244 5 3 1.745096566 0.006688996 51 255 6 3 1.745372494 0.007712996 44 264 7 3 1.745680526 0.008736996 39 273 8 3 1.745680526 0.009760996 35 280 9 3 1.746014764 0.010784996 32 288 10 3 1.746024614 0.011808996 29 290 Meaning of each field in the table: n is the proportion of location area size to RA size, LA=nRA; Mmix is the UEs paged quantity by each TTI of PCH; H  is traffic supported by a specified paging module in a DRX cycle length period; is the identification of the supported by a specified paging module in an RA during a DRX cycle length period. For instance, n=2, LA=190 means 190 cells in a location area. If the actual location area of network is larger than 190, it is necessary to divide the location area. It is recommended by GSM network optimization experiences that the location area capacity of each local network is larger than 300 carrier frequencies and the location area with paging traffic exceeding 50,000 in busy hour is divided. 3.1.2 Optimization Measures Divide location areas where network capacity or paging traffic is bigger than a specified threshold, which can reduce paging message flow efficiently. 3.2Improper Setting of CN Paging retransmission Times and Interval 3.2.1 Problem Analysis 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 H  RAPerDRXCycleLengthInNErlang RAPerDRXCycleLengthInNErlang
  20. 20. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 20 of 29 configured. Because paging is initiated specific to location area, paging retransmission will increase paging traffic. Especially in case of public downlink channel congestion at the air interface, paging traffic will double due to paging repeat, which will waste downlink channel resources seriously. CN paging retransmission configuration should be in accordance with UTRAN. CN paging retransmission is the retransmission paging in case that UE has not responded at the first time, which can increase paging success rate and connection rate. But from data in GSM network, paging retransmission success rate is low, especially at the second time or even more, which contributes a little to paging success rate and connection rate. Experience data indicates that: Generally, the success rate of the first paging is approaching to 86%, and the retransmission paging rate is 1.8%. Herein, retransmission paging success is mainly the second paging success, while success rate of the third paging is estimated less than 0.2% calculated by the decreasing pattern, and the third paging (the second repeat) has little influence on paging success rate【6】. The paging mode of WCDMA is similar with that of GSM, from online statistics, frequent CN paging contributes little to the paging success rate; contrarily, it increases the system load. It is no good for CN paging interval to be too short. CN sends paging messages to RNC through the IU interface, and RNC calculates the paging time according to IMSI attached by the paging message and arranges a delivery at the corresponding paging time of the nearest paging cycle. Currently, RNC of our company also adopts the paging retransmission mode, the default is repeating once and the retransmission interval is a paging cycle. From analysis above, the maximum interval between the time that RNC receives CN paging and the time that message is delivered to the air interface is a paging cycle. If RNC retransmits once, CN paging interval should be longer than two paging cycles. The paging cycle realized by our company is 2.56s. If CN paging interval is bigger than 2.56s and less than 5.12, when CN retransmitted paging reaches, and RNC has not finished repeat paging, RNC will arrange paging in the following paging cycle, Thus only three paging messages are sent in fact, not four expected, which causes paging message loss 3.2.2 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 (totally twice) at the interval longer than two paging cycles. If the paging cycle is 2.56s, it is suggested that CN paging retransmission interval be 5s and configuration be 5s with the consideration of paging loss during Iu/Iub flow control【4】. Reduce paging repeat times and increase paging interval, keep the time
  21. 21. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 21 of 29 of no paging responses unchanged, interval of reporting prompt tones when there is no paging response will not be influenced. CN paging interval and repeat times can be configured through software parameters. 3.3Improper Setting of UTRAN Paging Retransmission Times and Interval 3.3.1 Problem Analysis In order to reduce paging message flow at the Iu interface and increase the probability that UE receives paging message, UTRAN can retransmit paging messages. UTRAN paging retransmission configuration should be in accordance with CN paging retransmission. 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 general. Therefore, we can adjust the UTRAN paging repeat interval by adjusting DRC paging cycle coefficient k. UTRAN paging repeat times should not be too many; otherwise, adding paging repeats at Iu interface, the paging channel load at UU interface will increase rapidly. In addition, UTRAN is realized on MACC layer, and MACC does not identify the specific PRC message, MACC will go on repeating paging even if UE replies paging response message. Too many UTRAN paging repeat times will cause the unnecessary system overhead and message flow at UU interface. 3.3.2 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 WFMRCFGDATA. 3.4CN Adopts Whole-Network Paging 3.4.1 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 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. 3.4.2 Optimization Measures
  22. 22. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 22 of 29 Global paging should be avoided in CN. From experiences on GSM network, the whole-network paging of CN is the important cause of overload of location area with smaller capacity; meanwhile, CN global paging contributes little to the improvement of connection rate of long-distance incoming call. CN global paging is useful only when UE location area is recorded as failure by NLR, which hardly occurs, however, once it occurs, it means serious fault occurs; even more CN global paging does not work【6】. 3.5Improper Setting of DRX Paging Cycle Coefficient 3.5.1 Problem Analysis When UE is in IDLE and PCH state, UE will utilize the discontinuous reception technology “Discontinuous Reception (DRX)” to reduce power overhead. According to Protocol TS25.304, paging cycle length (DRX cycle length) = MAX (2K ,PBP). where, K refers to DRX cycle length coefficient, PBP refers to Paging Block Periodicity which is applied only in TDD mode, for FDD, PBP=1, so, DRX cycle length = 2K . DRX paging cycle coefficient of UE has three sources: system message, CN paging message and UU interface signaling of UTRAN, while the processing way of CS and PS is different. For PS domain, DRX paging cycle coefficient is obtained by the negotiation between UE and SGSN through NAS layer message (attach process), and the negotiation data is adopted as standard whether UE is in IDLE or connection state, however, paging coefficient of CS domain is adopted if negotiation fails. For CS domain, the minimum values of system message and CN paging message are taken as DRX paging cycle coefficient if UE is in IDLE state. And the minimum values of system message, CN paging message and signaling at UU interface of UTRAN are taken as DRX paging cycle coefficient if UE is in connection state. Settings of DRX paging cycle coefficient K should be considered with the following factors: 1. DRX paging cycle coefficient K determines the DRX cycle length, the larger the value of K is, the longer the DRX cycle is. Meanwhile, UE power consumption will be lower, however, the value of K makes UE paging cycle longer. Namely, UE paging response time becomes longer. If K is set too small, paging cycle will become smaller, and UE processing paging overhead and power consumption will increase. In the protocol, the value is
  23. 23. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 23 of 29 within the range of 2 ~12, the current value of our company is 8, and the paging cycle is 2.56 seconds. 2. According to the current coding mode of PCH, a TTI can transmit only 240 bits, if IMSI paging is utilized, only 3 UEs can be paged at the same paging moment; if TMSI paging is utilized, only 5 can be paged at the same paging moment. And if the number of UE paging at the same paging moment exceeds the processing capacity of system, it will cause paging loss and call loss. If K is set too small, the paging cycle will become shorter, the probability of the same calculated UE paging moment will increase, consequently, the probability of paging loss will increase. 3. Because UTRAN paging retransmission interval is a paging cycle, when setting DRX paging cycle coefficient K, we should consider the retransmission interval of UTRAN paging, and the K value should be set in coordination with CN paging retransmission. 3.5.2 Optimization Measures The lower limit of value K should be set with the consideration of saving UE power consumption and reducing the probability of the same UE paging moment, and the upper limit of value K should be set with the consideration of the repeat interval of UTRAN paging. During the actual setting process, the value K should be a value within 2 ~12, i.e., 5, 6, 7 and 8, and the corresponding paging cycles are 320ms, 640ms, 1280ms and 2560ms. 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? Generally, the following rules should be followed: 1. If the UTRAN retransmission time is 0 (no retransmission of UTRAN), the DRX cycle of UTRAN shall be smaller than CN retransmission interval (2s) ,namely, the value K at this time should be set to 7 or 8 (1.28s,2.56s), the setting to be 8 is considered with the paging loss【4】during lu/luB paging flow control; 2. If the UTRAN retransmission time is 1, the DRX cycle of UTRAN shall be smaller than half of the CN retransmission interval (1s) , namely, the value K at this time should be set to 6 or 7 (0.64,1.28s), the setting to be 7 is considered with the paging loss【4】during lu/luB paging flow control; (Configuration recommended) 3.6Improper setting of Np value 3.6.1 Problem Analysis
  24. 24. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 24 of 29 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 System Message 5. 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            Where, PI = DRX index mod NP = (IMSI div 8192) mod NP, SFN refers to UE paging moment. 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. 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 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 and PICH demodulation performance of UE will be required higher. 3.6.2 Optimization Measures Np value is within the range of (18, 36, 72, 144), which should be determined according to the current network subscriber quantity (subscriber traffic). Generally, the value should be larger when subscribers are of large amount, and the value should be smaller when there are fewer subscribers. In the actual network, the intermediate 36 or 72 can be selected. 3.7UE Identifier Utilized by CN Paging 3.7.1 Problem Analysis Network can page multi UEs at the air interface at the same paging time using paging type 1 message. Because of PCH capacity restriction, UE quantity is closely related to UE identifiers used in paging messages, namely, UE identifier influences the paging channel capacity. Compared with CN paging, the probability that UTRAN initiate paging is much smaller. Only the case that CN initiates paging is considered: When UE is in IDLE state, CN can only page three UEs at the same paging time using IMSI;
  25. 25. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 25 of 29 When UE is in IDLE state, CN can only page five 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【2】. From analysis above, CN can increase PCH capacity using UE temporary identifiers “TMSI and PTMSI”. 3.7.2 Optimization Measures CN optimization pages by using UE temporary identifier TMSI and PTMSI, and it can be adjusted with software parameters. 3.8UTRAN Should Activate IMSI ATTACH and DETACH Functions 3.8.1 Problem Analysis After 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 this flow. In DETACH state, if the MS is called, CN will directly inform the calling party that the MS is powered off, which skips of the process of sending useless paging messages to UE. As shown in Figure 3 , UE determines whether IMSI ATTACH and DETACH processes can be adopted 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 processes, “1” refers to the admission of【1】. In Figure 3 , “0a 01” means that T3212 is 60 minutes, UE is admitted to adopt IMSI ATTACH and DETACH processes. During actual network operation, UTRAN should activate IMSI ATTACH and DETACH functions. Table 5 IMSI ATTACH and DETACH Identifier 8 7 6 5 4 3 2 1 T3212 octet 1 Spare ATT octet 2
  26. 26. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 26 of 29 Figure 3 System Message 1 Resolution 3.8.2 Optimization Measures Check and modify IMSI attachment and detachment admission indication by using the Command “LST CNDOMAIN and MOD CNDOMAIN” on RNC maintenance console. 3.9Too Low Power allocation of Paging Channels 3.9.1 Problem Analysis Phenomenon: Subscriber complaints are centralized in some certain areas, when UE is called, the prompt tone “the subscriber is out of service” will occur, while UE can work normally while calling; 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. Paging channels include PICH and PCH. Too low PICH power will lead to UE resolution PI indication error. Resolution of PI value from “0” to “1” will cause false alarm and UE power waste; resolution of P1 value from “1” to “0” will cause paging miss and loss. If PCH power is too low, UE will fail in decoding the paging messages. The current baseline power allocation: PICH is -3dB and PCH is -2dB, which are both relative to pilot channels power. 3.9.2 Optimization Measures
  27. 27. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 27 of 29 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. 3.10 Existence of Coverage Dead Zones 3.10.1 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 the drive test equipment are lower than indexes required for UE normal access, by which coverage dead zone is identified in this area. 3.10.2 Optimization Measures Carry out coverage optimization, for specific optimization measures, please refer to relevant Guidance. 3.11 UE Performance Problems 3.11.1 Problem Analysis UEs of different subscribers may be made by different manufacturers, the receiving performance and demodulation performance of different UEs are also different. From GSM network experiences, some paging problems are located in UEs themselves. Sort out and analyze subscriber complaint materials. If the called UE is of the same type, problem may exist in UEs. 3.11.2 Optimization Measures Take a called verification test on UEs from different manufacturers, if conditions permit, 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. 4 Outstanding Problems Currently, there are mainly the following outstanding problems existing: 1. Relationship between paging retransmission times and interval of CN and UTRAN is complicated. In case of PCH capacity, paging success rate and paging
  28. 28. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 28 of 29 loss rate specified, it is necessary to make simulation analysis on how to work out the best paging retransmission strategy. 2. The upper limit of location area division is closely related to the service model and the traffic model of location area. Currently, the theoretical value can be worked out by using paging area planning tool. Since 3G service model and traffic model are very complicated, some problems still exist: how big is the difference between preconditions of paging area planning tool and actual cases, how is the agreement of the theoretical value and the actual value, which require further theoretical study and experiences from the network optimization practices.
  29. 29. WCDMA RNO Paging Problem Analysis Guidance For Internal Use Only 2004-07-09 Confidential Page 29 of 29 List of references: [1] 3GPP R1999 25_series, 2002/09 [2] Miao Jiashy, WCDMA RNP Paging Area Planning Guidance, 2003/03 [3] Chen Qi, Dong Yan, Zhou Xinjie, Zhi Bo, WCDMA RNP Network Optimization Method Soft Subject Research Report, 2003/08 [4] Zhang Jiayi, WCDMA Paging Strategy Study, 2003/12 [5] Li Peng, Guidance that Subscribers Are out of Service, 2001/11 [6] Huawei GSM Paging Tackling Data, 2003/06 [7] Jiao Anqiang, WCDMA RNP Special Technologies Key Signaling Process Analysis Paging Process, 2003/11

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