WCDMA Call Drop Problem Analysis
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Transcript of WCDMA Call Drop Problem Analysis
HUAWEI Mexico Training Center 1
HUAWEI TECHNOLOGIES CO., LTD. All rights reserved
www.huawei.com
Internal
Call Drop Problem Analysis
ISSUE 1.0
HUAWEI TECHNOLOGIES CO., LTD. Page 1All rights reserved
Call drop analysis is a useful way for
optimization and trouble-shooting.
Following discussion will give general
ideas on this special topic.
HUAWEI Mexico Training Center 2
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Upon completion of this course, you will be able to:
Describe the categories for call drop causes
Describe the flow of general call drop analysis
Analyze common call drop cases
HUAWEI TECHNOLOGIES CO., LTD. Page 3All rights reserved
Chapter 1 Principle of call dropChapter 1 Principle of call drop
Chapter 2 Analysis of call dropChapter 2 Analysis of call drop
Chapter 3 Call drop casesChapter 3 Call drop cases
HUAWEI Mexico Training Center 3
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Principle of Call Drop
� Content:
�Calculation formula of call drop rate on
signaling plane and measurement points.
�Calculation formula of call drop rate on
user plane and measurement points.
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Principle of Call Drop
� There are two types of call drop: signaling plane call
drop and user plane call drop:
�Signaling plane call drop means RNC will send the
message “IU RELEASE REQUEST” to CN after CN
receives the “IU connection setup complete”
�User plane call drop means RNC will send the
message”RAB release request “to CN after CN
receives the “RAB setup complete”
HUAWEI Mexico Training Center 4
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Formula of Signaling Plane Call Drop Rate
� The formula of Call Drop Rate of CS Signaling Plane:
�Call Drop Rate of CS Signaling Plane = RNC-originated CS
Domain Iu Connection Release / RNC-originated CS Domain Iu
Connection Setup Success× 100%
� The formula of Call Drop Rate of PS Signaling Plane:
�Call Drop Rate of PS Signaling Plane = RNC-originated PS
Domain Iu Connection Release / RNC-originated PS Domain Iu
Connection Setup Success× 100%
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Measurement points of Signaling plane call drop
� Measurement points of Signaling plane call drop
�Call Drop Rate of Signaling Plane is calculated by counting RNC-
originated Iu connection release
A
IU RELEASE COMMAND
IU RELEASE COMPLETE
RNC CN
IU RELEASE REQUEST
HUAWEI Mexico Training Center 5
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Cause of Signaling Plane call drop
� Usually, the typical causes for sending the IU_release
message are as follows:
�OM intervention
�Repeated integrity checking failure
�RNC generated signaling connection release
�RL out-of-synchronization
HUAWEI TECHNOLOGIES CO., LTD. Page 9All rights reserved
Formula of User Plane Call Drop Rate
� The formula of Call Drop Rate of CS User Plane:
� Call Drop Rate of CS User Plane = RNC-originated
CS Domain RAB Release / RNC-originated CS
Domain RAB Setup Success × 100%
� The formula of Call Drop Rate of PS User Plane:
� Call Drop Rate of PS User Plane = RNC-originated
PS Domain RAB Release / RNC-originated PS
Domain RAB Setup Success × 100%
HUAWEI Mexico Training Center 6
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Measurement points of User plane call drop
� Measurement points of User plane call drop
�Call Drop Rate of User Plane is calculated by
counting RNC-originated RAB connection
release
A
RNC CN
RAB RELEASE REQUEST
HUAWEI TECHNOLOGIES CO., LTD. Page 11All rights reserved
Chapter 1 Principle of call dropChapter 1 Principle of call drop
Chapter 2 Analysis of call dropChapter 2 Analysis of call drop
Chapter 3 Call drop casesChapter 3 Call drop cases
HUAWEI Mexico Training Center 7
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Analysis of Call Drop
� content
�main causes of high call drop rate
� troubleshooting of high call drop rate
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Analysis of Call Drop
� According to the definition of call drop
measurement point, call drop is usually caused by
the following:
�Equipment problem. That is, call drop due to
the equipment defects, such as UE , NodeB,
RNC,CN;
�RF problem. that is, call drop due to coverage
problem or unsuitable radio layer parameters.
HUAWEI Mexico Training Center 8
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Equipment Problem
� Call drop arising from equipment problem
�Hardware problem
�Transmission problem
�Antenna and feeder fault
�Other causes
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Radio Link Failure
Signaling process chart of radio link failureSignaling process chart of radio link failure
UE NodeB RNC CN
Measurement Report
Measurement Result
RL Failure INDICATION
IU RELEASE REQUEST (RL Failure)
HUAWEI Mexico Training Center 9
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Analysis of Causes of Radio Link Failure
� Analyze the causes of the failure of radio links. The causes can be:
� Interference
− Internal interference, external interference and the equipment interference
�Poor coverage
− Coverage hole, dead zone, isolated island, uplink/downlink unbalance
�parameter setting not proper
− radio link timeout counter, handover, power control etc.
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Radio Link Fault - Coverage
� Coverage:
�Coverage over shooting
�Coverage hole
�Signal fading
� Incomplete definition of adjacent cells
�unbalance of uplink/downlink
HUAWEI Mexico Training Center 10
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Radio Link Fault - Interference
� Interference:
�Strong downlink interference (CPICH RSCP is
not low, but Ec/Io is low)
�Strong uplink interference. On the basis of the
RSSI scanning result or analysis of the SIB7,
there is uplink interference
HUAWEI TECHNOLOGIES CO., LTD. Page 19All rights reserved
Handover Problem
� 1 、Handover is too late
� 1)The soft handover threshold is too high or the time-to-trigger
setting is too big.
� 2) The soft handover area is too small.
� 2 、Ping Pong Handover
� In the handover area, because of the signal fluctuation, the UE
will continually handover between source cell and target cell. For
intra-frequency hard handover, since there are intra-frequency
interferences, call drops are likely to occur; for inter-frequency
handover, since the compressed mode measurement is required,
ping pong handover will bring serious influence on the
communication quality.
HUAWEI Mexico Training Center 11
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Chapter 1 Principle of call dropChapter 1 Principle of call drop
Chapter 2 Analysis of call dropChapter 2 Analysis of call drop
Chapter 3 Call drop casesChapter 3 Call drop cases
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General call drop analysis flow:
HUAWEI Mexico Training Center 12
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Call drop location analysis
� Call drop location analysis: based on the location of
the call drop event in the map window in the post
processing tool, following information can be got:
�a. The place of the drop call
�b. At the edge of the 3G coverage or not
�c. Related cells
�d. Distance between related 3G cells and the drop
call point
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Neighbor list analysis
� Neighbor list analysis: to find out any cell not defined in the
neighbor list, following information need to be got:
�a.Best serving cell before the call dropped
�b.Best serving cell after the call dropped
�c. Existing neighbor list of the best serving 3G cell
HUAWEI Mexico Training Center 13
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Coverage analysis
� Coverage analysis Analyze the pilot coverage to get information about:
� i) CPICH transmission power
� ii) Whether following coverage events take place or not:
− a. Coverage limited
− b. System interference
− c. Poor uplink coverage
− d. Poor downlink coverage
− e. Pilot pollution
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Coverage analysis
� Coverage analysis Analyze the service coverage to get information about:
�a. Service related Maximum downlink transmission
power
�b. SIR before the call dropped
�c. Max uplink transmission power allowed for UE
�d. Actual uplink transmission power before the call
dropped
HUAWEI Mexico Training Center 14
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Handover analysis
� Handover analysis to get information about:
� i) Signal strength change of the target call and the serving cell
− a. insufficient handover area
− b. too late to start CM
− c. too late to add target cell
− d. interaction problem among 3 type of handover
� ii) Following cause exist or not:
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Signaling analysis
� Signaling analysis:
�a. Signaling of different interface including: Iu, Iub, Iur, Uu
�b. Signaling of different layer including : NAS, RRC
�c. In addition, analyze signaling in UE side in conjunction
with signaling in network side.
HUAWEI Mexico Training Center 15
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Case 1
� Fault description: The position of the drop call was not in the
edge of the 3G coverage. The call dropped on cell SC209.
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Case1
� Analysis:
�1.Poor coverage :from the page shown ,we can find that
− 1) prior to the drop, the best server for the UE is not the
same as that of the scanner.
− 2) the CPICH Ec/Io (and CPICH RSCP) degrades for
UE ONLY while scanner shows no degradation.
HUAWEI Mexico Training Center 16
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Case 1
� Analysis:
�2:Compared UE data with scanner data, it can be
concluded that the best serving cell is not the signal
strongest cell. The best serving cell should be picked out by
the latest measurement control message and corresponding
event measurement report.
�3: Check the latest measurement control message .
Corresponding measurement control shows there’s no
neighbor relation between SC209 and SC128.
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Case 1
� Trouble-shooting
add the neighbor relation between
SC209 and SC128
HUAWEI Mexico Training Center 17
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Case 2
� Fault description : The position of the drop call was in the edge of the
3G coverage, the call dropped on cell SC314, the distance between
cell SC314 was very far away from the drop call point.
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Case 2� Analysis
�1. analyze the active set and monitor set information
before call drop from UE measurement results
only sc314 in the active set,
no cell in the monitor set.
HUAWEI Mexico Training Center 18
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Case2
� Analysis
2 Analyze the scanner data in conjunction with the UE data
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case2
� Troubleshooting
the coverage should be enhanced here
to avoid the call drop in this place
HUAWEI Mexico Training Center 19
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case2
� Conclusion To analyze the coverage, need to:
�1)Analyze the pilot coverage in conjunction with the
service coverage
�2)Analyze the uplink coverage in conjunction with the
downlink coverage
�3)Analyze the scanner data in conjunction with the UE
data
�4)Analyze the CPICH RSCP in conjunction with CPICH
Ec/Io, SC
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case3
� Fault description: The call drop happened in the area of frequent
change of best server shown by the scanner
HUAWEI Mexico Training Center 20
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case3� Analysis
�1.Compare Ec/Io from both scanner and UE at the time of
the drop: the UE Ec/Io drop to < -18 dB while the scanner
remained above -6 dB :
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case3
� Analysis
� 2.Comparing the best servers from the UE and the scanner at the time of drop:
for the scanner and UE SC506 is the best server prior to the drop. However,
before the drop, the scanner selected SC505 as the best server while the UE
continued to have only SC506 in its active set resulting in the drop call.
Immediately after the drop, the UE camps on SC505:
HUAWEI Mexico Training Center 21
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Case 3
� Analysis
3. according the latest measurement control
message, we can find SC506 is in the list. The
drop call is not the case of missing neighbor.
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Case 3� Analysis
�4. It seems that the best cell changes from SC506 to SC505
too fast for the UE to perform soft handover on time.
HUAWEI Mexico Training Center 22
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Case 3
� Analysis
�As the handover Reporting range of 1A event is 4.5dB,
the hysteresis is 0dB, the delay trigger time is 320ms,
the filter coefficient is 3 (1 second is required), so the
requirement for the handover area is: the lasting time
when (Ec/Io of 506 cell – Ec/Io of 505 cell) < 4.5dB is
about 2 seconds . The value in the circle as shown in
the diagram cannot meet the requirement.
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Case3
� Analysis
Uu Interface messages that 1A event of SC505 was triggered at 54:04:
HUAWEI Mexico Training Center 23
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Case3
� Analysis
But SC506 went bad too severe for the procedure of “Active
Set Update” to be finished:
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Case3
� Troubleshooting
� Increase the value of range-to-report
�decrease the value of trigger-to-time
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Case3
� Conclusion
handover analysis to get information about:
�1)the signal strength change of the target call and the
serving cell
�2)whether following cause exist or not: insufficient
handover area, too late to start CM, too late to add
target cell, too early to delete serving cell, interaction
problem among 3 type of handover
�3)whether ping-pang handover exist or not
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