013 wcdma access problems analysis
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HUAWEI Mexico Training Center 1
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Internal
OWJ200203 WCDMA Access Problems Analysis
ISSUE 1.0
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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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� Upon completion of this course, you
will be able to:
�Be familiar with the access
procedure in UMTS
�Do analysis on access problems
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Chapter 1 Analysis Flow of Access Failure Chapter 1 Analysis Flow of Access Failure
Chapter 2 The Adjust Methods for Access Failure Chapter 2 The Adjust Methods for Access Failure
Chapter 3 Typical access failure casesChapter 3 Typical access failure cases
HUAWEI Mexico Training Center 3
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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
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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
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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 “RB
setup ” message
� UE does not transmit “Connect Acknowledge” message after
receiving “Alert or connect” message
Access failure definitionsAccess failure definitions
HUAWEI Mexico Training Center 5
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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
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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
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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
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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
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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
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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 poor
receiving 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
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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 Mexico Training Center 10
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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
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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 BServing 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 RX description
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
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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 Mexico Training Center 13
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The call statistic data analysis flow
� Check “RAB setup success rate” and “RRC setup success rate” in traffic statistics data
� Get familiar with the network operating situation, and then position the
specific area for the problems
� The RRC/RAB setup success rate are calculated by the following formulas:
%100
×=
ervicesfour QoS sts in all RRC requesNumber of
ervicesfour QoS sup in all RRCs setNumber of ccRateRRCSetupSu
%100
×=
ervicesfour QoS sts in all RAB requesNumber of
ervicesfour QoS sup in all RABs setNumber of ccRateRABSetupSu
%100××= ccRateRABSetupSuccRateRRCSetupSuuccRateCallSetupS
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The call statistic data analysis flow
Analysis access
index about cell
Check system
alarmSolve problem of
equipment abnormal
”RRC setup
success rate” is too low
Solve problem of
RRC setup failure
Y
Y
N
Analysis access indices in
RNC 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” is
too low
RB setup
success rate” is
too low
paging
success rate”is too low
Solve problem of
RAB setup
failure
Solve problem of RB setup failure
Solve problem of
paging 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 Failure Chapter 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 Failure Chapter 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 Failure Chapter 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 the
interference, 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
� PRACH
�The 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+2×Sintrasearch, 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 Failure Chapter 1 Analysis Flow of Access Failure
Chapter 2 The Adjust Methods for Access Failure Chapter 2 The Adjust Methods for Access Failure
Chapter 3 Typical access failure casesChapter 3 Typical access failure cases
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Typical Access Failure Cases
� Inappropriate Setting for the power of PCH and PICH
� UE can’t 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
happened
�Do 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 abnormal
UE 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 the open 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.
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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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