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Product name Confidentiality level
WCDMA RNP Internal open
Product versionTotal 45 pages
2.0
WCDMA RNO Special Guide to
Access Problems Analysis(For internal use only)
Drafted by: URNP-SANA Date: 2004-12-22
Reviewed by: Date:
Reviewed by: Date:
Approved by: Date:
Huawei Technologies Co., Ltd.
All Rights Reserved
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Revision Records
Date Revisedversion
Description Author
2004-08-23 1.00 Outline Guan Shiguo
2004-11-03 1.00 Initial transmittal Guan Shiguo
2004-12-20 1.10 Guan Shiguo
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Table of Contents
Chapter 1 Introduction to Access Problems ................................................................................. 7 Chapter 2 Definition of Classified Access Failure ........................................................................ 7
2.1 Definition from Analyzer ........................................................................................................ 7 2.2 Definition from TEMS ............................................................................................................ 7 2.3 Access-related indexes ......................................................................................................... 8
Chapter 3 Process and Methods for Analyzing Access Failure .................................................. 9 3.1 Processing for Analyzing Classified Data ............................................................................. 9
3.1.1 Processing for Analyzing DT Data ............................................................................. 9 3.1.2 Process for Analyzing Traffic Measurement Data .................................................... 16 3.1.3 Process for Tracing Data .......................................................................................... 18 3.1.4 Process for Analyzing Alarm Data ........................................................................... 18 3.1.5 Process for Analyzing Subscribers' Complaints ....................................................... 18
3.2 Adjustment .......................................................................................................................... 18 3.2.1 Engineering Parameters ........................................................................................... 18 3.2.2 Cell Parameters ........................................................................................................ 19
Chapter 4 Analysis of Typical Access Failure Problems ........................................................... 21 4.1 Paging Problems ................................................................................................................. 21
4.1.1 Improper Configuration of Paging-related Channel Power ...................................... 21 4.1.2 UE Location Update during Paging .......................................................................... 21 4.1.3 Paging Failure Due to UE Implicit Split UE .............................................................. 21
4.2 Cell Reselection Problems .................................................................................................. 22 4.2.1 Phenomenon and Analysis....................................................................................... 22 4.2.2 Solution..................................................................................................................... 25
4.3 RRC Connection Problems ................................................................................................. 25 4.3.1 Improper Configuration of Uplink Access Channel Parameters............................... 25 4.3.2 Improper Configuration of AICH Power .................................................................... 29 4.3.3 Improper Configuration of FACH Power .................................................................. 29 4.3.4 Improper Configuration of Downlink DCH Initial Power ........................................... 33
4.4 RAB and RB Connection Problem ...................................................................................... 33 4.4.1 Rejection of RAB Setup Request by RNC ............................................................... 33 4.4.2 Rejection of IUB Interface Admission ....................................................................... 34 4.4.3 RAB Setup Failure due to Failure in Replying RB by UE ......................................... 34 4.4.4 RAB Setup Failure due to Failure of Air Interface RB Setup ................................... 35
4.5 Incomplete Signaling Flow .................................................................................................. 36 4.5.1 Phenomenon and Analysis....................................................................................... 36 4.5.2 Solution..................................................................................................................... 38
4.6 Authentication Failure ......................................................................................................... 38
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4.6.1 MAC Failure ............................................................................................................. 38 4.6.2 Synchronization Failure ............................................................................................ 38
4.7 Encryption Failure ............................................................................................................... 39 4.7.1 Phenomenon and Analysis....................................................................................... 39
4.8 Equipment Abnormality ....................................................................................................... 39 4.8.1 NodeB Abnormality .................................................................................................. 39 4.8.2 UE Abnormality ........................................................................................................ 41
Chapter 5 Important Items Cared in RNO Stages ........................................................................ 43 5.1 Single NodeB Test Stage .................................................................................................... 43 5.2 Evaluation Stage before Optimization ................................................................................ 43 5.3 RF Optimization Stage ........................................................................................................ 43 5.4 Parameter Optimization Stage ............................................................................................ 43 5.5 RNO Subject Acceptance Stage ......................................................................................... 44
Chapter 6 Appendix: Access Process Introduction.................................................................... 44
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List of Figures
Figure 3-1 Process for analyzing DT and tracing data ....................................................... 10 Figure 3-2 Calling UE signaling process ............................................................................ 12 Figure 3-3 Process for analyzing paging problems ............................................................ 13 Figure 3-4 Process for analyzing RRC connection problems ............................................ 15 Figure 3-5 Process for analyzing traffic measurement data .............................................. 17 Figure 4-1 UE signaling ...................................................................................................... 22 Figure 4-2 Signal quality of first sending connection request by UE ................................. 23 Figure 4-3 Signal quality of first sending connection request by UE ................................. 24 Figure 4-4 UE signaling of Improper configuration of uplink access channel parameters . 25 Figure 4-5 Single subscriber signaling traced by RNC ...................................................... 26 Figure 4-6 Downlink signal quality ..................................................................................... 26 Figure 4-7 Regular interference in the cell 248 .................................................................. 27 Figure 4-8 Amplified diagram of interference ..................................................................... 28 Figure 4-9 Figure 4-10 shows the UE signaling of Improper Configuration of FACH Power.
.................................................................................................................................. 29 Figure 4-10 UE signaling of improper configuration of FACH power ................................. 30 Figure 4-11 Signal strength of first RRC connection request ............................................. 30 Figure 4-12 Single subscriber signaling traced by RNC ..................................................... 31 Figure 4-13 Signaling and signal strength of send RRC Connection Request message ... 32 Figure 4-14 UE signaling of incomplete signaling flow ....................................................... 36 Figure 4-15 Single subscriber signaling traced by RNC ..................................................... 37 Figure 4-16 Signal strength before the disconnection ........................................................ 37 Figure 4-17 UE signaling .................................................................................................... 40 Figure 4-18 Single subscriber signaling traced by RNC ..................................................... 40 Figure 4-19 Downlink signal strength ................................................................................. 41 Figure 4-20 UE signaling .................................................................................................... 42 Figure 4-21 Downlink signal quality .................................................................................... 42
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WCDMA RNO Special Guide to Access Problems
Analysis
Key words: Access, connected ratio, FACH, power distribution, RAB, authentication,
encryption, and traffic measurement
Abstract: The connected ratio is a key performance index (KPI) in the network. It differs
with different optimization methods and key items in stages of network
optimization. The document describes the methods for optimizing connected
ratio from aspects of traffic measurement, drive test (DT), and tracing data. It
also describes the methods for locating and analyzing problems of different
types by abundant cases.
Acronyms and abbreviations
Acronyms and abbreviations Full Spelling
FACH Forward access channel
RACH Random access channel
AICH Acquisition indication channel
RB Radio bearer
RRC Radio resource control
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Chapter 1 Introduction to Access Problems
This document details the process and methods for locating access problems
from DT and traffic measurement data, and then analyzes for the causes to
connection failure. For knowledge related to access, not key in the document, see
Reference (1). Chapter 4 classifies typical access problems, and details the
analysis for causes and locating process. Chapter 5 lists the important items
concerning stages of network optimization.
Chapter 2 Definition of Classified AccessFailure
2.1 Definition from Analyzer
The data analyzing tool Analyzer defines access failure as follow:
If the calling UE sends an RRC Connection Request message, the access to the
network fails upon any of the following conditions:
The calling UE receives an RRC Connection Reject message.
After it receives an RRC Connection setup message, it receives or sends an
RRC Connection Release message.
It receives any messages on BCCH during Call setup process.
The timer expires. Namely, the calling UE fails in receiving the RRC
Connection setup message within 3s after sending RRC Connection
Request.
2.2 Definition from TEMS
The data analyzing tool TEMS defines access failure (for calling voice service) as
follows:
Random access failure.
After dialing, the calling UE does not sends an RRC Connection Request
message.
The calling UE fails in receiving the RRC Connection Setup message.
After it sends an RRC Connection Request message, it fails to receive an
RRC Connection Setup message.
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The calling UE fails in sending the RRC Connection Complete message.
After it receives an RRC Connection Setup message, it fails in sending the
RRC Connection Setup Complete message.
The calling UE receives an RRC Connection Reject message.
The calling UE receives an RRC Connection Reject message, and does not
resends the RRC Connection Request message.
The calling UE fails in receiving the measurement control message.
After it sends the RRC Connection Complete message, it fails in receiving
the measurement control message.
The calling UE fails in sending the CM Service Request message.
After it receives a measurement control message, it fails in sending the CM
Service Request message.
The UE receives the Service Request Reject message.
The UE receives the Service Request Reject message.
The UE fails in receiving the Call Proceeding message.
After it sends CC SETUP message, it fails in receiving the Call Proceeding
message.
The UE fails in receiving the RB setup message.
After it receives a Calling proceeding message, it fails in receiving the RB
setup message.
The UE fails in sending the RB Setup Complete message.
After it sends an RB setup message, it fails in sending the RB Setup
Complete message.
The UE fails in receiving the Alert or Connect message.
After it sends an RB Setup Complete message, it fails in receiving the Alert
or Connect message.
The UE fails in sending the Connect Acknowledge message.
After it receives an Alert or Connect message, it fails in sending the Connect
Acknowledge message.
2.3 Access-related indexes
The back system of RNC does not define access failure. However, you can judge
whether the access fails according to the Call Setup follow.
Traffic measurement statistics includes success rate of multiple processes of
access, including:
CN_PAGE_IDLE_UE_SUCC_RATE
Success rate of paging UE in IDLE mode by CN
UTRAN_PAGE1_SUCC_RATE
Success rate of receiving response to the Universal Terrestrial Radio Access
Network (UTRAN) original Page1
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RRC_SETUP_SUCC_RATE/RRC_REJ_RATE
Success rate and rejection rate of RRC establishment
RRC_ABNORM_REL_RATE
Ratio of abnormal release of RRC
RB_SETUP_SUCC_RATE
Success rate of RB establishment
RAB_SETUP_SUCC_RATE
Success rate of RAB assignment
Based on previous indexes, you can obtain the success rate at each stage.
Chapter 3 Process and Methods for Analyzing
Access Failure
3.1 Processing for Analyzing Classified Data
3.1.1 Processing for Analyzing DT Data
I. Major Process for Analyzing DT Data
Analyze the DT data and data of tracing single subscriber as shown in Figure 3-1.
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Figure 3-1 Process for analyzing DT and tracing data
1) Obtaining DT data.
The DT data are obtained by E6474 of Agilent or Huawei Probe, connected
to test UE.
Tracing data of single subscriber of RNC is performed on the RNC operation
& maintenance (O&M) console.
The RNC records call detailed log (CDL) data.
2) Determining whether Call Fail occurs and corresponding time.
Determine the Call Fail time, pilot information collected by Scanner before
and after Call Fail, information about active set and monitoring set collected
by UE, and signaling process by DT data analytical software, such as
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Analyzer and DA. Adjust the signaling collected by UE and time for tracing
single subscriber signaling by RNC, and locate the point when the problem
occur in the process of single subscriber signaling traced by RNC.
Different data analyzers define access failure differently. The TEMS defines
access failure as that the UE resends an RRC Connection Request
message. However Analyzer thinks it normal. If you analyze data by
Analyzer, you must obtain the point when the UE resends the RRC
Connection Request message, by taking statistics of traced signaling of
single subscriber and UE signaling (or using a word search tool).
3) Analyzing problems.
According to process for tracing signaling of single subscriber by RNC and
UE signaling, determine the access failure point based on process shown in
Figure 3-1. Follow the process to solve the problems, including:
Paging problems
RRC connection problems
RAB and RB connection problems
Authentication and encryption problems
Equipment problems
II. Processing for Analyzing Paging Problems
The paging problems feature that after the calling UE completes RAB assignment,
it receives Disconnect message sent by CN while waiting for the Alerting
message, as shown in Figure 3-2.
You cannot see abnormalities from called UE signaling. Sometime, the UE
receives a Page message, but does not send the RRC Connection Request
message. According to the signaling of single subscriber traced by RNC, the CN
sends a Page message without sequent messages.
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Figure 3-2 Calling UE signaling process
The CC CALL PROCEDING is supposed to be after CC SETUP.
Figure 3-3 shows the process for analyzing paging problems.
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Figure 3-3 Process for analyzing paging problems
According to Figure 3-3, the paging problems include:
The RNC fails to send the Page message.
The power of paging channel and paging indicator channel is low.
The UE reselects a cell.
If the Uu interface does not send the Page message which is send by CN to RNC,
probably the capacity of the paging channel is inadequate (now the network load
is light, so the problem occurs in a small probability. When the network load is
higher, the Page message might be blocked at Uu interface), or the equipment is
abnormal.
To solve the problem, proceed as follows:
If the RNC sends the Page message, and the UE fails in receiving it, check
the Ec/Io of camped cell and monitored cell.
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If the common pilot channel (CPICH) Ec/Io of camped cell and monitored cell
is smaller than –12 dB, the power of paging channel (PCH) or paging
indicator channel (PICH) must be low, or the coverage at this point is low.
If the signals of the cell where the UE camps are weak, but that in the
monitored cell are strong, probably it is a cell reselection problem. In addition,
the UE reselects a 2G cell form 3G networks while being paged, or the UE
performs a cross-LAC reselection.
III. Process for Analyzing RRC Connection Problems
Obtain the RRC connection failure problems by UE signaling process and
signaling of single subscriber traced by the RNC.
The RRC connection process includes the following steps:
1) The UE sends an RRC Connection Request message over forward access
channel (FACH).
2) The RNC sends an RRC Connection Setup message over FACH.
3) The UE creates a downlink dedicated channel, and synchronize it. It sends
an RRC Connection Setup CMP message.
The RRC connection fails due to the following causes:
Uplink RACH problems
Downlink FACH power distribution
Cell reselection parameters problems
Downlink dedicated initial transmit power problems (low)
Uplink initial power control problems
Congestion problems
Abnormal equipment problems.
Among the previous problems, the uplink RACH problems, downlink FACH power
distribution, cell reselection parameters problems, and abnormal equipment
problems are most probable.
After the UE sends an RRC Connection Request message, the RNC fails in
receiving it. If the downlink CPICH Ec/Io is not over low (such as greater than –14
dB), the problem must be about RACH. The causes might be:
Inaccurate estimation of uplink open loop power control
Inadequate increment of Preamble power
UE transmit power being lower than required
After the RNC receives the RRC Connection Request message sent by UE, it
sends the RRC Connection Setup message which later the UE fails in receiving it.
If the CPICH Ec/Io is smaller than –12 dB (baseline is –12 dB), and no cell of
better quality is listed in the monitoring set, you can raise FACH power if it is
about coverage. If cells of better quality are listed in the monitoring set, the
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problem might be cell reselection. To sole this problem, you can adjust cell
reselection parameters to quicken cell reselection.
If the UE receives an RRC Connection Setup message but fails in sending RRC
Connection Setup Complete message, and the downlink signaling are strong, theproblem is abnormal UE. Otherwise, probably low downlink DCH initial power
causes asynchronization.
The UE sends an RRC Setup Complete message, but the RNC fails in receiving it.
The uplink initial power control enables UE transmit power to increase, so it is
less probably. To solve the problem, increase the DCH Constant Value.
Figure 3-4 Process for analyzing RRC connection problems
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3.1.2 Process for Analyzing Traffic Measurement Data
Analyzing traffic measurement indexes is based on RNC RAB connection
success rate and RRC connection success rate. After obtaining the whole
situation of the network, you can take statistics to cell performance.
The filtering method is used in analyzing. Do as follows:
1) Analyze the cells that are apparently abnormal.
Problems might be version, hardware, transmission, antenna-feeder or data
configuration.
2) Check the version, hardware, transmission, antenna-feeder or data
configuration based on alarm information of NodeB and RNC.
The traffic measurement indexes according to cells include some cause
value. For example, RRC_REJ_CONG_CELL means that RRC connection
is rejected due to congestion.
3) Take statistics of carriers in each sector according to indexes if normal.
You can output a list of cells with worse KPIs, and analyze the traffic
measurement indexes of these cells further, such as whether RRC
connection failure is due to calling UE or called UE.
4) Perform drive test (DT) in problematic cells to solve problems.
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Figure 3-5 Process for analyzing traffic measurement data
II. Analyzing Indexes Related to RNC Traffic Measurement and Access
Indexes related to RNC traffic measurement and access include:
RRC connection success rate
RAB connection success rate
RB connection success rate
Paging success rate
For the calculation of these indexes, see traffic measurement analysis
guidebooks.
The RRC connection success rate and RAB connection success rate indicate the
network connection rate. Obtain the network connection rate situations by the
previous indexes. In addition, you need know how to optimize the indexes.
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III. Analyzing Indexes Based on Cell and Access
Based on step one in Figure 3-5, analyze related indexes according to cell
statistics, you can obtain the cell distribution of worse indexes in the cell. Analyze
the cell with much worse indexes carefully. The indexes according to cell statistics
include causes as follows:
Causes to RB connection failure
Configuration Unsupported
physicalChannelFailur
IV. Chechking for Abnormal Alarms
Check alarm information about cells and RNC with apparently worse traffic
measurement indexes for abnormal equipment.
V. Analyzing and Solving Problems of Worse Indexes
Accumulate more experiences in solving connection rate problems by traffic
measurement.
(This part is to be supplemented.)
3.1.3 Process for Tracing Data
Tracing data includes tracing signaling of single subscriber of RNC and signaling
at each interface. For methods, see the processing for analyzing DT data.
3.1.4 Process for Analyzing Alarm Data
None.
3.1.5 Process for Analyzing Subscribers' Complaints
None.
3.2 Adjustment
3.2.1 Engineering Parameters
You can adjust the following engineering parameters:
Antenna directional angle
Tilt angle
Antenna beamwidth
Antenna gain
When you solve access problems due to coverage, you must consider adjusting
the previous parameters. You can construct sites in coverage dead zone,
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increase the antenna gain of neighbor serving cells, or reduce the antenna tilt
angle of neighbor cells. While you adjust these parameters, you must ensure not
to impact signal quality of the coverage area.
3.2.2 Cell Parameters
The following paragraphs include parameters closely related to access problems.
On locating causes to access failure, you can adjust these parameters according
to the actual situation.
I. FACH Transmit Power
FACH transmit power defines the transmit power of FACH.
If it is over small, the UE at the bordering areas between cells cannot receive
services and signaling carried by FACH, the downlink CCH coverage is impacted,and cell coverage is impacted.
If it is over great, the FACH may interfere other channels, and it may occupy
downlink transmit power, so cell capacity is affected. In the baseline, the FACH
transmit power is –1 dB because the bordering CPICH Ec/Io is –1 dB. If the onsite
coverage is worse, you must increase FACH transmit power according to
bordering CPICH Ec/Io.
II. PCH Transmit Power
PCH transmit power defines the transmit power of PCH.
If it is over small, the UE at the bordering areas between cells cannot receive
paging information, the paging is delayed, the paging success rate is lowered,
and access success rate is impacted.
If it is over great, it wastes power and increase downlink interference.
III. PICH Transmit Power
PICH transmit power defines the transmit power of PICH.
If it is over small, the UE at the bordering areas between cells cannot receive
paging indicator information, the call is delayed, operation error might occurs inobtaining PCH information, UE batteries might be wasted, uplink CCH coverage
is impacted, and cell coverage is impacted.
The power of PICH is transmitted continuously. If it is over great, PICH might
interfere other channels, occupy downlink transmit power, and impact cell
capacity. So no increasing PICH power is recommended. To increase PICH
coverage, you can reduce NP to 18. If you reduce NP, you will reduce the paging
capacity at Uu interface. At the early stage of network construction, NP = 18 is
enough for paging capacity, which is also an industry typical configured value.
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IV. Cell Reselection Parameters-Meausrement Hysteresis 2 (Qhyst2s)
According to the R rule, after the measured value of the serving cell is added with
hysteresis, it is sorted. Parameter values are related to slow fading features. This
parameter avoid ping-pong handover in cell reselection due to slow fading,
otherwise, the frequent location update (in idle state), URA update (URA_PCH),
or cell update (CELL_FACH, CELL_PCH) might occur, network signaling load,
and UE consumes battery power more quickly.
V. Cell Reselection Parameteres-Reselection Hysteresis Time
Treselections
If other cell CPICH Ec/No measured by UE is better than that of the camped cell
in the time specified by the parameter, the UE reselects to camp on the cell. This
parameter prevents UE from ping-pong reselection.
VI. Cell Reselection Parameter-Sintrasearch
It is the starting threshold of intra-frequency cell measurement
Start intra-frequency cell measurement when the serving cell Ec/Io is smaller than
QRelxmin + 2 * Sintrasearch.
It affects the speed of cell reselection, single access success rate of UE, single
paging success rate at Iu interface. If the UE consumes little power, configure this
parameter greater.
VII. Cell Reselection Parameter-Qoffset2
Signal quality of neighbor cells minus an offset Qoffset2 is evaluated by R criteria.
For a common single-storey cell, the value can be set to 0, by Qhyst to reach the
same aim. It is recommended that it is not configured.
VIII. AICH Transmit Power
If acquisition indication channel (AICH) transmit power is over small, the UE at
the bordering areas between cells cannot receive paging indicator information,
and the downlink CCH coverage is affected. In the baseline, AICH transmit power
is configured to –6 dB. According to the optimization result, the AICH power is
suitable for downlink coverage. The AICH transmits power continuously, so it
occupies more downlink capacity if transmit power increases.
IX. PRACH-related Parameters
For uplink pack random access channel (PRACH) problems, adjust
PRACH-related parameters, including:
Preamble retransmission times
Preamble power increment step
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Preamble and Message power deviation
The previous parameters restrict each other. For PRACH problems, adjust
preamble retransmission times. The baseline value is 8, so you can configure it to
20 to avoid PRACH problems.
Chapter 4 Analysis of Typical Access Failure
Problems
4.1 Paging Problems
4.1.1 Improper Configuration of Paging-related Channel Power
The PICH and PCH are related to paging. When the power of the two channels is
configured to low to meet UE modulation requirements, the UE cannot receive
correct paging messages. The baseline PCH transmit power is configured to
–2 dB, that of PICH is –7 dB. According to parameter optimization result, the
configuration meets the paging requirements of cell signal quality as –12 dB.
If the cell signal quality is worse than –12 dB, you can increase PCH transmit
power and reduce NP. Without UE DT data and single subscriber data traced by
RNC, if the paging-related indexes are worse, you can analyze the distribution
diagram of coverage, to judge whether to increase the power distribution
assignment of these two channels.
4.1.2 UE Location Update during Paging
UE location update during paging occurs when the UE reselect a 2G cell from 3G
networks. When the UE reselect a 2G cell, and before location is updated, the UE
cannot receive paging messages sent by UMTS networks. The reselection from
3G to 2G networks takes 5s, within which the UE fails in receiving paging
messages.
When UE LAC changes, the UE might fail in receiving paging messages. The
time between reselection of the target cell and location update is short, so
according to Iu interface, the paging does not fail.
4.1.3 Paging Failure Due to UE Implicit Split UE
The UE location is updated periodically, usually every two hours. The corn
network (CN) has a timer with longer period that for periodical location update.
During the period configured by CN timer, if the network fails in receiving the
locating update message of the UE, the network originates implicit split and
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remove the calling allowed standard of the UE, so paging the UE fails. The
causes to the previous phenomenon are as follow:
The UE camps on the coverage voids area permanently. Due to GSM seamless
coverage over the areas and no UMTS network coverage, the UE reselects aGSM cell. This is less probably. In addition, paging failure occurs when you
perform incorrect operations, such as taking battery or USIM from UE directly.
4.2 Cell Reselection Problems
4.2.1 Phenomenon and Analysis
Figure 4-1 shows a typical case of resending the RRC Connection Request
message due to cell reselection.
Figure 4-1 UE signaling
The interval between two times of resending RRC Connection Request message
is 1.2s.
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Figure 4-2 Signal quality of first sending connection request by UE
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Figure 4-3 Signal quality of first sending connection request by UE
According to baseline parameter configuration, Treselection is 1, Qhyst2 is 2 dB,
Qoffset2 is 0 dB, and Sintraserach is 5. When the signals of target cell are
stronger than that of the serving cell, the UE takes at least 1s to complete
reselection. Therefore the signals of the target cell and serving cell fluctuate like
the previous phenomena, and the optimizing reselection parameters has little
effect. The Treselection is configured to equal to or more than 1. If it is configured
to 0, the DRX can only be configured to equal to or more than 0.64s.
Consequently, the reselection time takes 8 * DRX, much greater than 1s. If the
Treselection is configured to 0, protocols define that Ec/Io of target cell must be 3
dB greater than that of original cell. An average of multiple statistics of cell
reselection time is 1.2s to 1.4s.
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4.2.2 Solution
To reduce cell reselection time, the Qhyst2 was changed to 0, SintraSearch to 7,
and ping-pong reselection occurred, but the reselection time remained the same.
Therefore, keep Qhyst2 fixed at 2 dB. For SintraSearch configuration, Enable UE
to start intra-frequency measurement earlier. Based on little impact on power
consumption by UE, configure SintraSearch as 7 as recommended.
4.3 RRC Connection Problems
4.3.1 Improper Configuration of Uplink Access Channel Parameters
I. Phenomenon and Analysis
Figure 4-4 shows a UE signaling of improper configuration of uplink accesschannel parameters.
Figure 4-4 UE signaling of Improper configuration of uplink access channel
parameters
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Figure 4-5 Single subscriber signaling traced by RNC
After adjusting time and signaling, the RNC responses to the second RRC
Connection Request message sent by UE. For quality of downlink signals, see
Figure 4-6.
Figure 4-6 Downlink signal quality
According to the figure, the downlink signal quality is strong, so the uplink signals
must not be over weak? Why does the first access fail?
The problem absolutely repeats in Warsick office static test every half an hour.
Sometimes, 4 failures in retransmitting RRC Connection Request messages
cause Call Fail. According to analysis of RNC and signaling traced by TMSI, the
RNC fails in receiving the RRC Connection Request message. The RSCP of the
cell is –60 dB to –70 dB, and Ec/No is –2 dB to –4 dB.
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According to the previous interference analysis, Figure 4-7 shows the regular
interference in the cell.
Figure 4-7 Regular interference in the cell 248
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Figure 4-8 Amplified diagram of interference
Note:
Each interference lasts for about 40s. Figure 4-7. The last peak is not a periodical
interference as before. It lasts for only a short time (a sample point). Interference
occurs between 8:00 and 21:00.
Probably the problems occur due to interference. According to sampled data,
RNC messages, UE messages, and recorded RTWP, no interference exists
within 1 minute before and 1 minute after it (the UE sends four RRC Connection
Request messages). Therefore the problems are unrelated to interference.
To locate causes to the problems, proceed as follows:
1) Test with Qualcomm 6200 handset. During the one-hour call, no
phenomenon like previous phenomenon occurs. During the period, the
interference still exists. Therefore the Qualcomm 6200 handset is normal.
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2) To exclude AICH problems, increase the AICH transmit power to 0 dB. After
this, the Moto test handset is still problematic. Therefore the problem is
unrelated to AICH power.
3) Recover the AICH power to –7 dB, and change Preamble retransmission
times from 8 to 20. During one-hour test, no problem occurs.
4) The test is performed indoor, so signals are stable and strong. The Ec/Io is
about –3 dB, and RSCP is about –50 dBm. Probably Moto handset is
problematic in power where signals are strong. When you lowers downlink
Ec/Io to –7 dB by starting downlink load, the problem still occurs.
5) To ensure that the problem is not due to interference, perform the test after
22:00. RTWP indicates that no interference exists. After testing for more
than one hour, there are four times of resending Request with other two
Calls' Failure. According to the UE system information and NodeB
interference record, the interference is updated in time. During time for
resending Request messages, the interference level of front and back
system keep fixed ( –105 dB). This indicates that the Request retransmission
of Moto handset is unrelated to external interference.
From previous test, the following conclusion is met:
The problem is unrelated to uplink interference and AICH power configuration.
The Qualcomm 6200 handset is normal, so the problem is due to uplink RACH of
Moto handset.
II. Solution
Change the Preamble retransmission times and test it in pilot network, and no
problem alike occurs.
4.3.2 Improper Configuration of AICH Power
The power configuration of AICH directly affects the demodulation of AICH by UE.
If the power is low, the UE will demodulate AICH code error and cannot access to
the network. The AICH power used to be configured as –12 dB, so the problems
occur frequently. Now the baseline configuration is –6 dB, able to meet the
demodulation of AICH by Moto, Qualcomm, and NEC handset when Ec/Io is –12
dB. The UE by different vendors varies in demodulating signaling on AICH. For
the untested UE, you must pay attention to power distribution of AICH when
PRACH-related problems occur.
4.3.3 Improper Configuration of FACH Power
I. Phenomenon and Analysis
Figure 4-9 Figure 4-10 shows the UE signaling of Improper Configuration of FACH
Power.
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Figure 4-10 UE signaling of improper configuration of FACH power
Figure 4-11 shows the signal strength of first RRC connection request
Figure 4-11 Signal strength of first RRC connection request
In Figure 4-11,
Column 2 lists the strength of signals in the camped area.
Column 3 lists the scrambles of the camped area
Column 4 and 5 list the strength and scramble number of signals in the
monitored optimal cell.
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The signals of two cells keep fluctuating.
Figure 4-12 Single subscriber signaling traced by RNC
The downlink coverage is poor, so the UE sends a RRC Connection Request
message which later is received by RNC. However, the downlink signals are
weak, so the UE fails in receiving them.
Figure 4-13 shows the signaling and signal strength of send RRC Connection
Request message.
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Figure 4-13 Signaling and signal strength of send RRC Connection Request
message
When the UE sends the second RRC Connection Request message, the
downlink signal strength is about –13 dB, so the connection succeeds. Obviously,
when the downlink signal Ec/Io is smaller than –12 dB, the UE cannot receive
signals on downlink FACH correctly.
Now the FACH power distribution is –1 dB. It is provided after the relation curve of
Ec/No and power distribution when cell bordering Ec/Io is assumed to be –12 dB.
To increase the receiving success rate when FACH transmit power is –14 dB.
Increase the FACH power by 2 dB based on starting threshold of inter-system
measurement.
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II. Solution
Change the FACH power to +1 dB, and then test. In the KPI test route, the
problem does not occur that the UE cannot receive the RRC Setup so access
fails.
4.3.4 Improper Configuration of Downlink DCH Initial Power
The RNC obtains the downlink initial transmit power according to the current
Ec/Io. Before inner loop power control is performed in uplink and downlink, the
initial transmit power keeps fixed. If the power low, the UE cannot be synchronous,
so the RRC connection fails.
When the UE receives the RRC Connection Setup message, but does not send
the RRC Connection Setup Complete message, you can confirm whether it is a
downlink initial transmit power problem by checking Ec/Io and downlink code
domain transmit power when the UE sends the RRC Connection Request
message.
Now in most cases, the initial transmit power calculated by RNC is over high, so
the problem is less probable.
4.4 RAB and RB Connection Problem
4.4.1 Rejection of RAB Setup Request by RNC
The probability is small in commercial networks that illegal configuration of
parameters causes that the RNC replies RAB Setup failure, but special
subscriber causes it due to special operations. The main scene is that the RNC
directly rejects the request because the uplink creating of an account in PS
services and activation application information exceeds the capability of UE.
For example, the uplink and downlink capacity of creating account by a special
subscriber is 384K but the actual capacity is 64K and the uplink and downlink
maximum rate of QoS information is 384K when the subscriber sets and activates
PDP (the Sony-Ericsson handset software can set and activate QoS in
application freely), so when the RNC receives RAB assignment request, the
uplink maximum rate exceeds UE capability and replies an RAB setup failure
message, instead of sending RB setup message.
After RAB setup failure due to improper configuration which exceeds the UE
capability, the SGSN resends the RAB assignment message until the UE can
support it. Finally, the RAB assignment is complete. For subscribers, the PDP
activation can still succeed, and the obtained maximum rate is the maximum rate
supported by UE.
The UE sends a PDP activation request message when:
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The minimum guaranteed rate required in QoS configuration in the PDP
activation request by UE exceeds UE capability
The network compromise by lower rate to accept PDP activation request by
UE
Finally, the UE cannot complete PDP activation.
4.4.2 Rejection of IUB Interface Admission
The problem occurs in Hong Kong networks frequently. In the pilot network, the
AAL2 band of IUB in multiple cells supports only one 384k service. If a 12.2k
voice service exists, and you active a PS384k service, the IUB interface will reject
the service request due to restricted band. The reason for RAB assignment
Response is that the rate in application is unobtainable, so the SNCN sends RAB
assignment message. An RAB setup failure message is in the trafficmeasurement.
The cell-based traffic measurement includes a statistics of RAB setup failure due
to various causes. You can obtain the causes to RAB setup failure by these
indexes.
4.4.3 RAB Setup Failure due to Failure in Replying RB by UE
The incorrect operation by UE causes the RB setup failure, including the
following situation.
I. Situation 1
The UE uses downlink 128K data services, and then receives RB setup request
of calling or called VP service. Most terminals cannot support downlink VP and
high rate PS service (≥ 64K), so the UE replies the RB set failure message due to
unsupported configuration.
II. Situation 2
An 3G UE originates VP service to another UE that camps in GSM networks (not
supporting VP service), so the CN sends a Disconnect message (reason is
Bearer capability not authorized) after the RNC receives RAB assignment request.
Yet the UE just receives a RB_SETUP message, unable to complete RB setup,
so it receives the Disconnect message and immediately originates RB setup
failure due to failure in radio interface procedure.
After tested, the Sony-Ericsson Z1010 UE stably supports multiple-RAB setup of
VP and PS128K, while the Moto UE does not support, but replies RB setup failure.
You must verify the terminal ability of more UEs and versions. For the RAB setup
failure due to subscribers' behavior, in RNC B03D205 version KPI statistics,
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reflecting them by PS (/CS) _RAB_SETUP_FAIL_PARAM_CELL, not direct. In
the subsequent KPI version statistics, the following items are needed:
Clearer traffic measurement points
Traffic measurement points of subscribers' requirements QoS higher thansubscription
Traffic measurement points of insufficient capability of self-judgment by UE
Traffic measurement points of insufficient called capability
With the previous traffic measurement points, you can analyze the network quality
more impersonally.
4.4.4 RAB Setup Failure due to Failure of Air Interface RB Setup
If RB setup message is not replied to, the RNC judges that RB setup fails. It
appears most frequently in commercial networks that RB setup fails due to poor
quality of signals at air interface. The process shows that no ACK message to RB
setup message is received or no RB setup complete message is received. This
problem occurs in areas with weak signals due to the following causes:
The UE does not access the network in the optimal cell.
The coverage is poor.
The UE does not access the network in the optimal cell. If the active set is
updated during RB setup process by adding the optimal cell (quick fluctuation of
signals lead to signals at camped cell attenuates sharply), but the process cannot
be nested (both the network and UE do not support), the active set is updated
only after RB setup is complete, so the RB setup proceeds in a cell with weak
signals, and then fails. For this problem, you must increase the starting threshold
and rate of intra-frequency cell reselection to enable UE to camp on the optimal
cell as possible and to access the network. For early-stage networks with light
load, configure the starting threshold of intra-frequency cell reselection to –4 dB,
Treselection to 1. For cells of different LAC borders, the parameters can be
configured lower to reduce signaling traffic of location update and cell update.
Poor coverage causes RB setup failure, unqualified downlink coverage and
unqualified uplink coverage.
Unqualified downlink coverage is that the UE cannot receive RB setup messages,
because the UE cannot demodulate correctly and partially due to insufficient RF
optimization.
Unqualified uplink coverage is that the UE receives the RB setup message, but
the RAN cannot receive the ACK message to RB setup. This is due to insufficient
performance of outer loop power control in uplink signaling stage. You can avoid
this by increasing initial uplink SIRtarget.
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Now in the commercial networks, configure the uplink initial SIRtarget to as high
as 5 dB, which can enhance capability to process uplink signaling and have little
impact on uplink capacity.
4.5 Incomplete Signaling Flow
4.5.1 Phenomenon and Analysis
The UE may perform the handover from RRCConnectionSetupComplete to RAB
Assignment or after the RBConnectionSsetupComplete.
The handover failure results in the subjective access failure of the subscriber.
The following example shows an access failure in the Analyzer software.
Figure 4-14 UE signaling of incomplete signaling flow
Figure 4-15 shows the single subscriber tracing signaling of RNC.
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Figure 4-15 Single subscriber signaling traced by RNC
Figure 4-16 shows the signal strength of the cell before the disconnection.
Figure 4-16 Signal strength before the disconnection
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The RNC signaling shows that the signal of No. 121 cell becomes bad fast. At that
time, No.56 cell will be added to the active set, but the UE cannot receive the
ActiveSet Update message sent by the RNC.
4.5.2 Solution
The problem can be solved through adjusting the soft handover parameters. For
details, see Call Drop Analysis Guide.
4.6 Authentication Failure
4.6.1 MAC Failure
I. Phenomenon and Analyis
The problem is present when the new USIM card is used. The authentication fails
because the Ki and OP (OPc) are different in the USIM card and HLR. The cause
value is Mac Failure.
Check whether the Ki and OP (OPc) of the IMSI are the same according to the
subscriber definition information.
II. Solution
The Ki and OP (OPc) are defaulted in the USIM card, but the reader cannot read
the values. Therefore, before the subscriber definition, you must know the Ki and
OP (OPc) of the USIM card in advance or reset the Ki and OP (OPc) in the USMI
card to the same values in the HLR.
4.6.2 Synchronization Failure
I. Phenomenon and Analysis
USIM card thinks that the SQN received from the VLR/SGSN cannot meet the
needs and returns the synchronization failure.
The authentication process cannot discriminate CS authentication request or PS
authentication request because of the HLR internal processing mechanism.
Therefore, the Index values of SQN of CS and PS cannot be allocated, and the
USIM card overlaps the Index value of SQN of CS or PS when the CS
authentication request and PS authentication request are performed
synchronously. The synchronization failure is present occasionally.
II. Solution
The authentication is performed again if the synchronization fails. The
authentication set is reacquired from the SQN saved in the USIM card, so the
twice synchronization failures are not present at the same time.
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HLR helps solve the problem in the V62.
4.7 Encryption Failure
4.7.1 Phenomenon and Analysis
The UE does not support encryption algorithm and the encryption mode
configurations of RNC and core network are mismatched. For example, MSC
configures encryption algorithm UEA0 only but RNC configures UEA1 only. At
that time, an Encryption Mode Reject message may be present at the Iu interface.
Check whether UE report capability is supported through the RRC Connect Setup
CMP message.
NEC single-mode MS, NEC C606, and NEC C616 do not support encryption.
Nokia 7600, Nokia 6650, Moto A835, Qualcomm 6200, Qualcomm 6250 and
Siemens U15 MSs support encryption.
The encryption modes supported by the MSC or SGSN must be consist with that
supported by the RNC.
I. Solution
Replace the UE or the network side selects non-encryption mode.
The MSC and SGSN can select all the encryption modes and RNC selects UEA0
or UEA1 based on actual conditions.
4.8 Equipment Abnormality
The problem phenomena vary, so you must analyze the problem based on actual
conditions.
4.8.1 NodeB Abnormality
I. Phenomenon and analysis
The UE fails to access the RNC during the drive test. The UE sends continuously
an RRC Connection Request message. From the perspective of single subscriber
signaling traced by RNC, RNC receives the message and returns a RNC
Connection Setup message, but the UE fails to receive the message.
Figure 4-17 and Figure 4-18 show the signaling.
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Figure 4-17 UE signaling
Figure 4-18 Single subscriber signaling traced by RNC
Figure 4-19 shows that the downlink signal strength.
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Figure 4-19 Downlink signal strength
The message at IUB interface and internal message of NodeB are normal and
there is no alarm.
When locating the equipment room where the NodeB is located, you find that the
UE can access the RNC discontinuously, and the Ec/Io near the antenna is about
-3 dB. RSCP is about -70 dB.
The Ec/Io far away from the antenna is -5 dB, and 80% cell access fails. The UE
stills cannot receive the Setup message from the downlink.
The detection shows that the output power of NodeB is 24 dBm. In normal
conditions, the output power is 36 dBm. Therefore, the PA may be faulty.
The FACH configuration is normal when the Ec/Io is -12 dB. The maximum power
of CPICH is 24dBm. In normal conditions, the power is 33 dBm.
Supposing that the PA output power is reduced and relative power of each
channel is not changed, the connection may be established. The relative power of
each common channel is changed after the PA output power is reduced. At that
time, locating the PA is required.
II. Solution
The problem is cleared when the PA is replaced.
4.8.2 UE Abnormality
Take the UE performance for an example as follows:
I. Phenomenon and analysis
The UE fails to access the RNC for a period.
Figure 4-20 shows the UE signaling.
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Figure 4-20 UE signaling
Figure 4-21 shows the downlink signal quality.
Figure 4-21 Downlink signal quality
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Column 2 indicates downlink scramble measured by the UE, column 3 indicates
the Ec/Io on the CPICH of the cell. Column 4 four indicates the Ec/Io of optimal
cell measured by Scanner. Column 5 indicates the scrambles measured by
Scanner.
During the duration when the UE fails to access the RNC, the quality of signal
measured by the UE is largely different from that measured by the Scanner.
Before and after the time period, the difference of signal measured by the UE and
Scanner is no greater than 2 dB.
II. Solution
This problem is related to the UE performance, and no solution is available
temporarily.
Chapter 5 Important Items Cared in RNO Stages
5.1 Single NodeB Test Stage
In this stage, you must pay attention to equipment problems and engineering
installation problems at network side. The access problems are due to abnormal
equipment, so you can refer to equipment alarms to locate problems. Also you
must pay attention to the power output, and NodeB clock system.
5.2 Evaluation Stage before Optimization
In this stage, you must obtain the connection rate situations by DT and traffic
measurement. By analyzing causes to access through DT data and classified
indexes in traffic measurement, you can obtain the causes to access failure, and
you must solve the problems in RF optimization and parameters optimization.
5.3 RF Optimization Stage
In this stage, you must pay attention to coverage and special scenes problems.
By DT analysis, you can adjust engineering parameters to solve coverage
problems due to access failure or pilot pollution. For special scenes, such as
turning corner effect and needlepoint effect, you must consider adjusting direction
angle of antenna.
5.4 Parameter Optimization Stage
This stage is after the RF optimization stage. In this stage, you must pay attention
to downlink CCH power distribution, intra-frequency cell reselection and
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inter-system cell reselection, paging problems, and handover problems in
accessing the network. This stage is the major stage when access failure
problems are solved. You can use single subscriber signaling traced by RNC and
DT data for help.
5.5 RNO Subject Acceptance Stage
After optimization in the previous stages, the major access problems are solved.
In this stage, you can trace the access success rate in the network (by DT if
necessary). You need trace and analyze problems in this stage. For abnormal
indexes, check whether the cell equipment is normal.
Chapter 6 Appendix: Access ProcessIntroduction
See Reference 4.
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References
1) UAE Commercial Network Optimization and KPI Analysis Summary.doc.
Wang Wei. Internal document.2) RAN System Problems Tracking Guide to Authentication and Encryption.doc.
Yuan Guangxie. Internal document.
3) Hong Kong WCDMA Network Access Problems Analytical Report.doc. Guan
Shiguo. Internal document.
4) Key Signaling Process Analysis Access Process.doc. Chen Qi. Internal
document.