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8/10/2019 WCDMA Access Problems Analysi
1/22
HUAWEI Mexico Training Center 1
HUAWEI TECHNOLOGIES CO., LTD. All rights reserved
www.huawei.com
Internal
OWJ200203 WCDMAAccess Problems Analysis
ISSUE 1.0
HUAWEI TECHNOLOGIES CO., LTD. Page 1All rights reserved
Access is associated with the call setup
success rate of the network. This KPI
can be optimized by means of Call
setup test and the consequent trouble-
shooting based on access failure
analysis.
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HUAWEI TECHNOLOGIES CO., LTD. Page 2All rights reserved
Upon completion of this course, you
will be able to:
Be familiar with the access
procedure in UMTS
Do analysis on access problems
HUAWEI TECHNOLOGIES CO., LTD. Page 3All rights reserved
Chapter 1 Analysis Flow of Access FailureChapter 1 Analysis Flow of Access Failure
Chapter 2 The Adjust Methods for Access FailureChapter 2 The Adjust Methods for Access Failure
Chapter 3 Typical access failure casesChapter 3 Typical access failure cases
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HUAWEI TECHNOLOGIES CO., LTD. Page 4All rights reserved
Chapter 1 Analysis Flow of Access FailureChapter 1 Analysis Flow of Access Failure
Section 1 The definitions about Access FailureSection 1 The definitions about Access Failure
Section 2 The drive test data analysis flowSection 2 The drive test data analysis flow
Section 3 The call statistic data analysis flowSection 3 The call statistic data analysis flow
HUAWEI TECHNOLOGIES CO., LTD. Page 5All rights reserved
The definitions of access failure
It will be considered as access failure if any following conditions
satisfied after RRC connection request initialed by UE
Receive RRC Connection Reject message
UE transmits or receives RRC Connection Release
message after receiving RRC Connection setup
UE receives any BCCH message in the call setup process
Timer expired, which means UE does not receive RRC
Connection setup in 3 seconds after RRC connection
request is transmitted.
Access failure definitionsAccess failure definitions
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The definitions of access failure
Random access procedure failure UE does not
transmit RRC Connection Request message after dialing
RRC Connection Setup message is not received by UE
UE does not receive RRC connection setup message
after RRC connection request message is transmitted.
RRC Connection Setup Complete message is not transmitted
by UE
UE receives RRC Connection Reject message
UE does not receive measurement control message after
transmitting RRC Connection Setup Complete message
UE does not transmit CM service request message after
measurement control message is received.
Access failure definitionsAccess failure definitions
HUAWEI TECHNOLOGIES CO., LTD. Page 7All rights reserved
The definitions of access failure
UE receives Service Request Reject message
UE does not receive Call Proceeding message after
transmitting CM service request message
UE does not receive RB Setup message after receiving Call
proceeding message
UE does not transmit RB setup complete message after
receiving RB setup message
UE does not receive Alert or Connect after transmitting RBsetup message
UE does not transmit Connect Acknowledge message after
receiving Alert or connect message
Access failure definitionsAccess failure definitions
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Chapter 1 Analysis Flow of Access FailureChapter 1 Analysis Flow of Access Failure
Section 1 The definitions about Access FailureSection 1 The definitions about Access Failure
Section 2 The drive test data analysis flowSection 2 The drive test data analysis flow
Section 3 The call statistic data analysis flowSection 3 The call statistic data analysis flow
HUAWEI TECHNOLOGIES CO., LTD. Page 9All rights reserved
The drive test data analysis flow
SubSub--flows about DT data analysisflows about DT data analysis
Data analysis flow
Paging problems analysis flow
RRC connection request problems analysis flow
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The drive test data analysis flow
N
Y
Received
pagingN
Y
Y
N
N
RRC
connection
setup failure?
Call Fail?
Paging
problems
RRC setup problems
Analysis drive test data
Calling failure? N
Y
Data analysis flowData analysis flow
HUAWEI TECHNOLOGIES CO., LTD. Page 11All rights reserved
N
N
N
Y
Y
Y
N
Is ciphering or
authentication
failure?
RAB setup
failure?
Due to
handover
Ciphering or
authentication
problems
RAB or RB
setup problems
Refer to call drop
due to handover
Abnormal problems
Data analysis flowData analysis flow
The drive test data analysis flow
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The drive test data analysis flow
SubSub--flows about DT data analysisflows about DT data analysis
Data analysis flow
Paging problems analysis flow
RRC connection request problems analysis flow
HUAWEI TECHNOLOGIES CO., LTD. Page 13All rights reserved
The drive test data analysis flow
Paging problems
After finishing RAB assignment and call setup process (NAS), UE
received Disconnect message from CN instead of Alerting
message
The causes of paging problem have following types:
RNC does not transmit paging message
Too lower power allocated for PRACH or PICH
Cell reselection problems
Paging problems analysis flowPaging problems analysis flow
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The drive test data analysis flow
Paging problems analysis flowPaging problems analysis flow
Y
N
N
N
Y
Paging problem
RNC
transmit
page?
Power too
low ?
Cell
reselection
problem ?
Y
Y
N
Equipment abnormal
problem
Adjust power
according to
coverage
Optimize cell
reselect parameters
Abnormal
problem
UE
receive
page
HUAWEI TECHNOLOGIES CO., LTD. Page 15All rights reserved
The drive test data analysis flow
RNC does not transmit paging message
RNC has received the paging message but does not transmit paging
message through Uu interface. The reasons could be:
Capacity of paging channel is not enough
Abnormal problem could happen in equipment.
Power allocation PRACH or PICH are too low
UE does not receive paging message if RNC has transmitted.
The interference is too high comparatively, which result in the poorreceiving signal quality of PRACH or PICH if Ec/Io of PCPICH. In
this case, higher power can be allocated to these two channels
It could also be the bad coverage if Ec/Io of PCPICH is too poor
Paging problems analysis flowPaging problems analysis flow
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The drive test data analysis flow
Cell reselection
UE can not reselect to better cell in time
The cell reselection from 3G to 2G can also be the reason
by the reselection between two LAs.
Paging problems analysis flowPaging problems analysis flow
HUAWEI TECHNOLOGIES CO., LTD. Page 17All rights reserved
The drive test data analysis flow
SubSub--flows about DT data analysisflows about DT data analysis
Data analysis flow
Paging problems analysis flow
RRC connection request problems analysis flow
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The drive test data analysis flow
RRC connection setup process includes following steps:
UE transmits RRC Connection Request by RACH
RNC transmits RRC Connection Setup by FACH
UE transmits RRC Connection Setup CMP by DCH
The reasons for RRC setup failure could be :
Uplink RACH problem
Power allocation for Downlink FACH
Cell reselection parameters
Low initial power of downlink DPCH
Uplink power control
Congestion problem
Equipment abnormal problem
RRC connection problems analysis flowRRC connection problems analysis flow
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The drive test data analysis flow
RRC connection problems analysis flowRRC connection problems analysis flow
RRC setup problem
Does UE transmit RRC
connection request?
Does RNC receive
RRC connection
request?
Does RNC transmit
RRC connection
setup?
UE abnormal
problem
adjust PRACH parameters
Other problem
N
Y
N
Y
N
Y
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The drive test data analysis flow
Does UE transmit
RRC connection
setup complete
RRC connection problems analysis flowRRC connection problems analysis flow
Does UE receive
RRC connection
setup
Does RNC receive
RRC connection
setup complete
Adjust FACH power
Adjust downlink initial
transmit power parameter
Adjust uplink DPCCH open
loop power control parameter
Does cell
reselection
happen?
Optimize cell
reselection parameters
Y
N
Y
Y
N
N
Y
N
Y
HUAWEI TECHNOLOGIES CO., LTD. Page 21All rights reserved
The drive test data analysis flow
The possible reasons for RRC connection establishment failure:
RACH
Usually, it could be the problem on RACH if the RNC does not receive
RRC Connection Request message. Meanwhile, the Ec/Io of CPICH is
normal
The cell reselection parameters
The improper parameters setting could result in that UE can not stay in
the best cell to initiate the access procedure
Lower power allocation for initial transmission power of downlink DPCH
The insufficient power of DPCH can cause the out of synchronization. Uplink initial transmission power
The initial transmission power of PRACH
The initial transmission power of uplink DPCH
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The drive test data analysis flowThe drive test data analysis flow
RRC connectionRRC connection
1. CCCH: RRC Connection Request
5. Downlink Synchronisation
UENode B
Serving RNS
Serving
RNC
DCH - FP
Allocate RNTISelect L1 and L2parameters
RRCRRC
NBAPNBAP
3. Radio Link Setup Response
NBAPNBAP2. Radio Link Setup Request
RRCRRC7. CCCH: RRC Connection Set up
Start RXdescription
Start TX
description
4. ALCAP Iub Data Transport Bearer Setup
RRCRRC9. DCCH: RRC Connection Setup Complete
6. Uplink Synchronisation
NBAPNBAP8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
HUAWEI TECHNOLOGIES CO., LTD. Page 23All rights reserved
Chapter 1 Analysis Flow of Access FailureChapter 1 Analysis Flow of Access Failure
Section 1 The definitions about Access FailureSection 1 The definitions about Access Failure
Section 2 The drive test data analysis flowSection 2 The drive test data analysis flow
Section 3 The call statistic data analysis flowSection 3 The call statistic data analysis flow
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The call statistic data analysis flow
Check RAB setup success rate and RRC setup success rate intraffic statistics data
Get familiar with the network operating situation, and then position thespecific area for the problems
The RRC/RAB setup success rate are calculated by the followingformulas:
%100=ervicesfour QoS sts in allRRC requesNumber of
ervicesfour QoS sup in allRRCs setNumber ofccRateRRCSetupSu
%100=ervicesfour QoS sts in allRAB requesNumber of
ervicesfour QoS sup in allRABs setNumber ofccRateRABSetupSu
%100=
ccRateRABSetupSuccRateRRCSetupSuuccRateCallSetupS
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The call statistic data analysis flow
Analysis accessindex about cell
Check systemalarm
Solve problem ofequipment abnormal
RRC setupsuccess rate istoo low
Solve problem of
RRC setup failure
Y
Y
N
Analysis access indices inRNC call statistic data
N
Call Statistic Data Analysis Flow chartCall Statistic Data Analysis Flow chart
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The call statistic data analysis flow
RAB setup
success rate istoo low
RB setupsuccess rate istoo low
pagingsuccess rateis too low
Solve problem of
RAB setupfailure
Solve problem ofRB setup failure
Solve problem ofpaging failure
over
Y
Y
Y
N
N
N
Y
Call Statistic Data Analysis Flow chartCall Statistic Data Analysis Flow chart
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Chapter 1 Analysis Flow of Access FailureChapter 1 Analysis Flow of Access Failure
Chapter 2 The Adjust Methods for Access FailureChapter 2 The Adjust Methods for Access Failure
Chapter 3 Typical access failure casesChapter 3 Typical access failure cases
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Chapter 2 The Adjust Methods for Access FailureChapter 2 The Adjust Methods for Access Failure
Section 1 project parametersSection 1 project parameters
Section 2 cell parametersSection 2 cell parameters
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Project parameters
Project parameters main include antenna azimuth, antenna
tilt, antenna gain, antenna direction,etc.
In general, project parameters can be adjusted only in poor
coverage condition.
The influence on the original coverage quality has to be
considered when adjusting the project parameters.
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Chapter 2 The Adjust Methods for Access FailureChapter 2 The Adjust Methods for Access Failure
Section 1 project parametersSection 1 project parameters
Section 2 cell parametersSection 2 cell parameters
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Cell parameters
Transmission power of FACH, PCH and PICH
In the edge of cell, UE can not receive the signaling or
service correctly if the transmission power is too low. But on
the contrary, higher transmission power can increase theinterference, which can result in the decline of adjacent
cells capacity
Transmission power of AICH
In the edge of cell, UE can not receive the AI if the power is
too low
PRACHThe maximum times of retransmission for preamble
The power ramping step
The power offset between preamble and message
Physical channels parametersPhysical channels parameters
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Cell parameters
Qhyst:
This parameter is use to avoid ping-pang cell reselection in
the cell edge. Ping-pang cell reselection will cause signaling
load increase and waste power of UE because of frequent
cell reselection, LA update or URA update.
The parameter value is related to local slowing fade
characteristics.
Treselections
The duration time that target cell signal quality is better than
current camp cell is longer than Treselections. The cell will
be selected to the camping cell.
The parameter is use to avoid ping-pang cell reselection
Cell reselection parametersCell reselection parameters
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Cell parameters
Sintrasearch
Sintrasearch is the threshold for intra-frequency cells
measurement. When the RSCP of current cell is less than
Qrxlevmin+2Sintrasearch, the measurement will be initiated.
It will influence on the rapidity of cell reselection, and then the
access success rate.
This value could be set as great as possible if the UE battery is not
a problem
Cell reselection parametersCell reselection parameters
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Chapter 1 Analysis Flow of Access FailureChapter 1 Analysis Flow of Access Failure
Chapter 2 The Adjust Methods for Access FailureChapter 2 The Adjust Methods for Access Failure
Chapter 3 Typical access failure casesChapter 3 Typical access failure cases
HUAWEI TECHNOLOGIES CO., LTD. Page 35All rights reserved
Typical Access Failure Cases
Inappropriate Setting for the power of PCH and PICH
UE cant receive paging message correctly when PICH and PCH
power are too low. The power could be increased with the poor
network coverage
The paging message is being transmitted while UE is doing LA update
It mainly happens the procedure of inter-system cell reselection.
UE leaves the network without detach procedure
CN does not receive the LA update from UE periodically
UE is out of service area for a long time
Inappropriate operation, such as unplug battery of UE directly, or
SIM card directly
Paging problemsPaging problems
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Typical Access Failure Cases
UE transmitted RRC Connection Request message twice in different cells
And the interval between them is 1.2s
Cell reselection problemCell reselection problem
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Typical Access Failure Cases
Reasons
UE did not initiate the reselection in time
Solution methods
The Tselections could be minimized, but the default value is
already the minimum.
Minimize the Qhyst2 value, but the reselection is still not in
time. On the contrary, the ping-pong cell reselection
happenedDo not modify Qhyst2, but increase the Sintrasearch value.
Since the measurement is initiated earlier, the reselection
can happed earlier too.
Cell reselection problemCell reselection problem
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Typical Access Failure Cases
The calling success rate and called success rate are greater than 97% from KPI,
but RRC establishment success rate is about 94% from traffic statistic
After analysis, the RRC Connection Request retransmission is the result of
following reasons:
Cell phone abnormalUE dose not transmit RRC Connection Request after
receiving paging
Other reasons
After cell reselection, UE retransmits the RRC
Connection Request in new cell
After UE transmits RRC Connection Request
message, the cell quality decreased sharply, and UE
has to do cell reselection immediately
UE can not receive RRC Connection Setup from RNC in
downlinkThe area with poor downlink coverage
RNC can not receive the RRC Connection Request
message from UE in uplinkThe area with good downlink coverage
RRC connection problemsRRC connection problems
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RRC connection problemsRRC connection problems
Typical Access Failure Cases
Solution
Adjust the maximum preamble retransmission times from 8 to 20
Increase the transmission power of PRACH and FACH
Experimental conclusion
The error of initial preamble transmission power, which is calculated by theopen loop power control, could be +/-9dB, or even +/-12dB
The preamble power climbing step is 2dB, and the error could be +/-1.5dB
If the outside interference is higher 10dB, enough margin should be given
for the preamble transmission power
Increase the FACH power from the default value -1dB to +1dB
Increase the access success rate in the condition that Ec/Io is -14dB
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Typical Access Failure Cases
RAB or RB establishment problemsRAB or RB establishment problems
Establishment request is refused
The register information in HLR is not identical with the service
request
The request is beyond the ability of UE
If the service request is beyond the ability of UE, SGSN will
renegotiate QoS to initiate a new RAB assignment again till the
ability of UE can satisfy the QoS. Usually, the maximum data rate is
same as the maximum ability of UE
If the maximum ability of UE still can not support the QoS, the RAB
establishment is failed.
HUAWEI TECHNOLOGIES CO., LTD. Page 41All rights reserved
Typical Access Failure Cases
Handover can also happen
in the process from RRC
Connection complete to
RAB assignment complete
or RB establishment
complete
The following figure is the
RNC signaling trace for
single UE
Handover problemsHandover problems
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Typical Access Failure Cases
Cell signaling strength record
From the record, the strength of cell 121 decreased sharply.
Meanwhile, RNC transmitted ActiveSet Update. But UE can not
receive it To solve this problem, the handover parameters should be adjusted to
make it happen earlier
Handover problemsHandover problems
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