2.WCDMA RNO Special Guide Access Problems Analysis-20050316-A-2.0

7/29/2019 2.WCDMA RNO Special Guide Access Problems Analysis-20050316-A-2.0

http://slidepdf.com/reader/full/2wcdma-rno-special-guide-access-problems-analysis-20050316-a-20 1/45

WCDMA RNO Special Guide to Access Problems Analysis-20050316-A-2.0 Security Level

2006-01-23 Confidential Information of Huawei.No Spreading without Permission

of 45

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





of 45

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





of 45

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





of 45

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





of 45

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





of 45

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





of 45

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.





of 45

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





of 45

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.





of 45

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





of 45

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.





of 45

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.





of 45

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.





of 45

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





of 45

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





of 45

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.





of 45

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.





of 45

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,





of 45

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.


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.


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.





of 45

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





of 45

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





of 45

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.





of 45

Figure 4-2 Signal quality of first sending connection request by UE





of 45

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.





of 45

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





of 45

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.





of 45

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





of 45

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.





of 45

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


Figure 4-9 Figure 4-10 shows the UE signaling of Improper Configuration of FACH

Power.





of 45

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.





of 45

The signals of two cells keep fluctuating.


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.





of 45

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.





of 45

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:





of 45

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,





of 45

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.





of 45

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


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.





of 45


Figure 4-16 shows the signal strength of the cell before the disconnection.

Figure 4-16 Signal strength before the disconnection





of 45

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


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.





of 45

HLR helps solve the problem in the V62.

4.7 Encryption Failure


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.





of 45



Figure 4-19 shows that the downlink signal strength.





of 45

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.





of 45


Figure 4-21 shows the downlink signal quality.

Figure 4-21 Downlink signal quality





of 45

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





of 45

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.




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.

2.WCDMA RNO Special Guide Access Problems Analysis-20050316-A-2.0

Documents

Transcript of 2.WCDMA RNO Special Guide Access Problems Analysis-20050316-A-2.0