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WCDMA Call Drop
Problem Analysis
Foreword: Causes of Call Drop in GSM & UMTS
Neighbor cell problem No response after T3103 expiry Interference problem Interference problem Coverage problem Coverage problem Handoff problem Improper parameter settingGSM
UMTS
Objectives
Definition of the call drop
Process for handling the call drop problem
Various methods to analyze call drop data
Solutions to call drop problems
Contents
1.
Definition and classification
2. Causes and handling process
3. Solutions
4. Case analysis
1 Definition and Classification
1.1 Normal release procedure
1.1 Normal release procedure
1.2 Call drop over the Um interface
1.2 Call drop over the Um interface
1.3 Call drop measurement
1.3 Call drop measurement
-
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CS
CS
Normal Release Procedure
Procedure of CS service normal release
Normal Release Procedure
CS Normal Release Procedure
1. The UE sends the RRC_UL_DIR_TRANSF message to the RNC. If the nas message carried in this message is 0325, it indicates that the message is the disconnect message of the call control sublayer. 2. The RNC sends the RANAP_DIRECT_TRANSFER message to the CN. If the nas pdu carried in this message is 0325, it indicates that the message is the disconnect message of the call control sublayer. 3. The CN sends the RANAP_DIRECT_TRANSFER message to the RNC. If the nas pdu carried in this message is 832d, it indicates that the message is the release message of the call control sublayer. 4. The RNC sends the RRC_DL_DIRECT_TRANSF message to the UE. If the nas message carried in this message is 832d, it indicates that the message is the release message of the call control sublayer. 5. The UE sends the RRC_UL_DIR_TRANSF message to the RNC. If the nas message carried in this message is 032a, it indicates that the message is the release complete message of the call control sublayer.
6. The RNC sends the RANAP_DIRECT_TRANSFER message to the RNC. If the nas pdu carried in this message is 032a, it indicates that the message is the release complete message of the call control sublayer.
Normal Release Procedure
7. The CN sends the RANAP_IU_RELEASE_COMMAND message to the RNC to release resources of the Iu interface, including resources of the RANAP layer and the ALCAP layer. 8. The RNC sends the RANAP_IU_RELEASE_COMPLETE message to the CN.
9. The RNC sends the RRC_RRC_CONN_REL message to the UE to release the RRC connection.
10. The UE sends the RRC_RRC_CONN_REL_CMP message to the RNC.
11. The RNC sends the NBAP_RL_DEL_REQ message to the NodeB to release resources of the Iu interface, including resources of the NBAP layer and the ALCAP layer.
12. The NodeB sends the NBAP_RL_DEL_RSP message to the RNC. Then, the release procedure is complete.
Normal Release Procedure
Procedure of PS service normal release
Normal Release Procedure
Procedure of PS service normal release
1. The UE sends the RRC_UL_DIR_TRANSF message to the RNC. The nas message carried in the message is 0a46, indicating that the message is the deactivate PDP context request message of the session management sublayer.
2. The RNC sends the RANAP_DIRECT_TRANSFER message to the CN. The nas pdu carried in the message is 0a46, indicating that the message is the deactivate PDP context request message of the session management sublayer.
3. The CN sends the RANAP_DIRECT_TRANSFER message to the RNC. The nas pdu carried in the message is 8a47, indicating that the message is the deactivate PDP context accept message of the session management sublayer.
4. The CN sends the RNC the RANAP_RAB_ASSIGNMENT_REQ message carrying the RAB list (to be released) with RAB IDs to be released.
5. The RNC sends the RRC_DL_DIRECT_TRANSF message to the UE. The nas message carried in the message is 8a47, indicating that the message is the deactivate PDP context accept message of the session management sublayer.
Normal Release Procedure
7. The
NodeBsends the NBAP_RL_RECFG_READY message to the RNC.
8. The RNC sends the RRC_RB_REL message to the UE to release the radio
bearer of the service.
9. The
NodeBsends the NBAP_RL_RECFG_COMMIT message to the RNC.
10. The UE sends the RRC_RB_REL_CMP message to notify the RNC that the
radio bearer of the service is released.
11. The RNC sends the RANAP_RAB_ASSIGNMENT_RESP message to notify
the CN that the radio access bearer is released.
1 Definition and Classification
1.1 Normal release procedure
1.1 Normal release procedure
1.2 Call drop over the Um interface
1.2 Call drop over the Um interface
1.3 Call drop measurement
1.3 Call drop measurement
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-
CS
CS
Call Drop over the Um Interface
Call drop defined by field tests
According to the Um interface signaling recorded on the UE side, if messages of the
Um interface meet one of the following conditions during the conversation (in the connection state), you can infer that a call is dropped.
(1) The RRC Release message is not received. The UE changes from the CELL_DCH state to the IDLE state.
(2) The RRC Release message is received in which the release cause value is not Normal.
(3) The CC Disconnect message, CC Release Complete message, or CC Release message is received in which the release cause value is not Normal Clearing, Normal Unspecified, user busy, user alerting no answer, call rejected or destination out of order.
Call Drop over the Um Interface
Call Drop over the Um Interface
Call drop defined by traffic statistics
1 Definition and Classification
1.1 Normal release procedure
1.1 Normal release procedure
1.2 Call drop over the Um interface
1.2 Call drop over the Um interface
1.3 Call drop measurement
1.3 Call drop measurement
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CS
CS
Summary of measurement classification
Call drop defined by the measurement
CS call drop
Object-oriented statistics: RNC, cell
Service-oriented statistics: AMR, VP service
PS call drop
Object-oriented statistics: RNC, cell
Service-oriented statistics: PS service, HSDPA, HSUPA
Definition of Measurement
Definition of Measurement
Call Drop Measurement - CS
CS Service Drop Ratio
% 100 Re Re _ = × lease CSRAB lease mal CSRABAbnor CDR CS
The RNC level KPIs can be calculated by aggregating all the cell counters and Iur counters.
Notes Formula
Cell
Measurement Scope
CS Service Drop Ratio
KPI Name
VS.RAB.Loss.CS.Norm: Numbers of Released RABs Triggered by RNC due to CS Normal Cause in a cell
VS.RAB.Loss.CS.RF + VS.RAB.Loss.CS.Abnorm + VS.RAB.Loss.CS.Norm CSRABRelease (cell)
VS.RAB.Loss.CS.RF: Number of Released RABs Triggered by RNC due to RF Reason
VS.RAB.Loss.CS.Abnorm: Numbers of abnormally released RABs except RF causes in a cell
VS.RAB.Loss.CS.Abnorm+ VS.RAB.Loss.CS.RF CSRABAbnormalRelease (cell)
This measurement helps evaluate the call drop rate of CS services in a RNC or cluster. This counter is measured when the RNC initiates the abnormal release procedure through the RAB RELEASE
Call Drop Measurement - CS
AMR Call Drop Ratio
% 100 Re Re _ = × lease AMRRAB lease rmal AMRRABAbno CDR AMR
The RNC level KPIs can be calculated by aggregating all the cell counters and Iur counters. Notes Formula Cell Measurement Scope
AMR Call Drop Ratio
KPI Name
VS.RAB.Loss.CS.Norm.AMR: Numbers of Released RABs Triggered by RNC due to CS Normal Cause in a cell(AMR)
VS.RAB.Loss.CS.AMR + VS.RAB.Loss.CS.Norm.AMR AMRRABRelease
Number of released CS AMR service RABs triggered by RNC in a cell
VS.RAB.Loss.CS.AMR AMRRABAbnromalRelease (cell)
Call Drop Measurement - CS
VP Call Drop Ratio
% 100 Re Re _ = × lease VPRAB lease mal VPRABAbnor CDR VP
The RNC level KPIs can be calculated by aggregating all the cell counters and Iur counters. Notes Formula Cell Measurement Scope
VP Call Drop Ratio
KPI Name
Numbers of VP Service RABs released
VS.Norm.Rel.CS.Conv.RB.64 + VS.RAB.Loss.CS.Conv64K VPRABRelease (cell)
Number of released CS 64 k service RABs triggered by RNC in a cell VS.RAB.Loss.CS.Conv64K
VPRABAbnormalRelease (cell)
This measurement helps evaluate the call drop rate of VP services in a RNC or cluster. This counter is measured when the RNC initiates the abnormal release procedure through the RAB RELEASE
1 Definition and Classification
1.1 Normal release procedure
1.1 Normal release procedure
1.2 Call drop over the Um interface
1.2 Call drop over the Um interface
1.3 Call drop measurement
1.3 Call drop measurement
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-
CS
CS
Call Drop Measurement - PS
PS Service Drop Ratio
% 100 Re Re _ = × lease PSRAB lease mal PSRABAbnor CDR PS
The RNC level KPIs can be calculated by aggregating all the cell counters and Iur counters. Notes Formula Cell Measurement Scope
PS Service Drop Ratio
KPI Name
VS.RAB.Loss.PS.Norm: Numbers of released RABs triggered by RNC due to PS normal causes in a cell
VS.RAB.Loss.PS.RF + VS.RAB.Loss.PS.Abnorm + VS.RAB.Loss.PS.Norm
PSRABRelease (cell)
VS.RAB.Loss.PS.Abnorm: Number of released RABs triggered by RNC due to RF reason
VS.RAB.Loss.PS.RF:
Numbers of abnormally released RABs except RF causes in a cell VS.RAB.Loss.PS.RF +
VS.RAB.Loss.PS.Abnorm PSRABAbnormalRelease
(cell)
This measurement helps evaluate the call drop rate of PS services in a RNC or cluster. This counter is measured when the RNC initiates the abnormal release procedure through the RAB RELEASE
REQUEST and IU RELEASE REQUEST messages.
Note: The cell level counter calculates only the RAB releases on the SRNC, whereas the result of the above formula includes the R99 call drop and HSPA call drop.
Call Drop Measurement - PS
HSDPA Service Drop Ratio
% 100 Re _ Re _ _ = × lease RB HSDPA lease RBAbnormal HSDPA CDR HSDPA
1. The RNC level KPIs can be calculated by aggregating all the cell counters.
2. The normal transition from HS-DSCH to FACH/DCH is considered as normal HS-DSCH release
( including transitions due to mobility).
Notes Formula
Cell
Measurement Scope
HSDPA Service Drop Ratio
KPI Name
This measurement helps evaluate the call drop rate of PS services carried by the HSDPA in a RNC or cluster. This counter is measured when the RNC initiates the abnormal release procedure through the RAB RELEASE REQUEST and IU RELEASE REQUEST messages.
VS.HSDPA.HHO.H2D.SuccOutInterFreq:
Number of successful inter-frequency hard handovers from the HS-DSCH to the DCH between two cells
VS.HSDPA.HHO.H2D.SuccOutIntraFreq:
Number of successful intra-frequency hard handovers from the HS-DSCH to the DCH between two cells
VS.HSDPA.ChR.HSDSCHtoFACH: Number of successful channel handovers from the HS-DSCH to the FACH in the same cell
VS.HSDPA.ChR.HSDSCHtoDCH: Number of successful channel handovers from the HS-DSCH to the DCH in the same cell
VS.HSDPA.RAB.Loss.InActivity: Number of released PS service RABs carried by HSDPA triggered. The cause is User Inactivity.
VS.HSDPA.RAB.Loss.Norm: Number of released PS service RABs carried by HSDPA triggered. The cause is normal. VS.HSDPA.RAB.Loss.Norm + VS.HSDPA.RAB.Loss.InActivity + VS.HSDPA.ChR.HSDSCHtoDCH + VS.HSDPA.ChR.HSDSCHtoFAC H + VS.HSDPA.HHO.H2D.SuccOutInt raFreq + VS.HSDPA.HHO.H2D.SuccOutInt erFreq HSDPA_RBNormalRelease VS.HSDPA.RAB.Loss.RF:
Number of released PS service RABs carried by HSDPA triggered by RNC in a cell. The cause is RF.
VS.HSDPA.RAB.Loss.Abnorm.NonRF: Number of released PS service RABs carried by HSDPA triggered by RNC in a cell. The cause is not RF.
VS.HSDPA.RAB.Loss.Abnorm.No nRF + VS.HSDPA.RAB.Loss.RF HSDPA_RBAbnormalRele
ase
Call Drop Measurement - PS
HSDPA Service Drop Ratio
Call Drop Measurement - PS
HSUPA Service Drop Ratio
% 100 Re _ Re _ _ = × lease RB HSUPA lease RBAbnormal HSUPA CDR HSUPA
1. The RNC level KPIs can be calculated by aggregating all the cell counters.
2. The normal transition from E-DCH to FACH/DCH is considered as normal E-DCH release
( including transitions due to mobility).
Notes Formula
Cell
Measurement Scope
HSUPA Service Drop Ratio
KPI Name
This measurement helps evaluate the call drop rate of PS services carried by the HSUPA in a RNC or cluster. This counter is measured when the RNC initiates the abnormal release procedure through the RAB RELEASE REQUEST and IU RELEASE REQUEST messages.
Call Drop Measurement - PS
HSUPA Service Drop Ratio
VS.HSUPA.ChR.EDCHtoFACH.Succ: Number of successful attempts to switch the channel type from EDCH to FACH in the same cell of the RNC
VS.HSUPA.ChR.InterFreq.EDCHtoDCH.Succ: Number of successful attempts to switch the channel type from EDCH to DCH due to inter-frequency hard handover between two cells. VS.HSUPA.ChR.IntraFreq.EDCHtoDCH.Succ: Number of successful attempts to switch the channel type from EDCH to DCH due to intra-frequency hard handover between two cells. VS.HSUPA.ChR.IntraCell.EDCHtoDCH.Succ: Number of successful attempts to switch the channel type from EDCH to DCH in the same cell of the RNC
VS.HSUPA.RAB.Loss.Norm: Number of released PS service RABs carried by HSUPA triggered. The cause is normal. VS.HSUPA.RAB.Loss.Norm + VS.HSUPA.ChR.IntraCell.EDCHtoDCH.Succ + VS.HSUPA.ChR.IntraFreq.EDCHtoDCH.Succ + VS.HSUPA.ChR.InterFreq.EDCHtoDCH.Succ + VS.HSUPA.ChR.EDCHtoFACH.Succ HSUPA_RBNormalRelease VS.HSUPA.RAB.Loss.Abnorm: Number of abnormal released PS service RABs carried by HSUPA triggered by RNC in a cell
VS.HSUPA.RAB.Loss.Abnorm HSUPA_RBAbnormalReleasego back
Contents
1. Definition and classification
2. Causes and handling process
3. Solutions
4. Case analysis
2 Causes and Handling Process
2.1 Common reasons for call drop2.1 Common reasons for call drop
2.2 Drive test data analysis procedure 2.3 Measurement data analysis procedure 2.4 Signaling tracing data analysis procedure 2.5 User complaint data analysis procedure
Common Reasons for Call Drop
Neighbor Cell Missing
Generally, the call drop is caused by neighbor cell missing during the early phase of
optimization. For the intra-frequency neighbor cells, you can use the following methods to determine whether the call drop is caused by intra-frequency neighbor cell missing.
Method 1: Check the EcIo information about cells in the active set recorded by the UE and the Best Server EcIo information recorded by the Scanner. If the EcIo recorded by the UE is poor and the Best Server EcIo recorded by the Scanner is good, check whether the Best Server scrambling code recorded by the Scanner is included in the intra-frequency
measurement control. If the scrambling code is not included, you can infer that the call drop is caused by the neighbor cell missing.
Method 2: If the UE reconnects to the network immediately after the call drop and the cell scrambling code used during the reconnection of the UE is inconsistent with that used during the call drop, the call drop may be caused by the neighbor cell missing. You can confirm the cause through the measurement control. The neighbor cell missing, including the inter-frequency neighbor cell missing and the inter-RAT neighbor cell missing can result in call drop.
Method 3: Adopt the Nastar neighbor cell analysis function to check whether the neighbor cell missing problem exists.
Common Reasons for Call Drop
Coverage Problem
Generally, poor coverage implies that both the RSCP and EcIo are poor. You
can confirm the coverage problem by checking the transmit power of
uplink/downlink special channels through the following methods:
If the uplink transmit power reaches the maximum value before the call drop
and the uplink BLER is poor or the single user tracing recorded by the RNC
suggests that Node B reports RL failure, you may infer that the call drop is
caused by poor uplink coverage. If the downlink transmit power reaches the
maximum value before the call drop and the downlink BLER is poor, you may
infer that the call drop is caused by poor downlink coverage.
You can also confirm the coverage problem through the following simple and
direct method:
Check the data collected by the Scanner. If both the RSCP and EcNo of the
best cell are poor, you can determine that the poor coverage results in the call
drop.
Common Reasons for Call Drop
Handoff Problem
There are two reasons for the call drop caused by the soft handoff/inter-frequency, that is, it is too late to perform the handoff or ping-pong handoff. In terms of the signaling process, for the CS service, the UE does not receive the active set update command; for the PS service, the TRB is reset before the handoff of the UE.
In terms of signal, there are two scenarios in which it is too late for the handoff:
(1) Corner: The EcIo of the source cell has a sudden sharp drop, and the EcNo of the target cell has an unexpected dramatic increase.
(2) Pinpoint: The EcIo of the source cell increases after a period of time in rapid fall. The EcIo of the target cell has a sudden increase in a short time period.
The ping-pong handoff involves the following cases:
(1) The primary cell changes rapidly: Two or more cells take turns to be the primary cell. The primary cell has better RSCP and EcIo and exists in a short period of time.
(2) There are multiple secondary cells: The RSCP is normal, and there is slight difference between RSCPs of cells. The EcIo in each cell is poor.
Common Reasons for Call Drop
Interference Problem
For the downlink, if the CPICH RSCP is greater than 85 dB and the EcIo is smaller than -13 dB, the call drop tends to occur. This may be caused by downlink interference.
For the uplink, if the RTWP is 10 dB greater than the normal value (-104 to -105), there may be a call drop. This is caused by pilot pollution.
Common Reasons for Call Drop
Other Abnormal Problems
If the preceding causes are excluded, the call drop may be caused by equipment problems. You need to perform further cause analysis by checking logs and alarms of the equipment. For example:
The synchronization failure causes repeated addition or deletion of links.
The UE does not report the la measurement report, which results in the call drop.
Interaction Process Problem
Processes, such as AMR control, enabling or disabling the DCCC, compression mode, and UE state transition may fail due to reasons relating to the signal, UE capability, or the
interaction between the equipment in the RAN and UE, which finally results in call drop. There is no common method to solve these problems. The method varies depending on the specific process or UE.
2 Causes and Handling Process
2.1 Common reasons for call drop
2.2 Drive test data analysis procedure2.2 Drive test data analysis procedure
2.3 Measurement data analysis procedure 2.4 Signaling tracing data analysis procedure 2.5 User complaint data analysis procedure
Drive Test Data Analysis Procedure
Drive Test Data Analysis Procedure 1. Prepare data.
Compare the best cell of the UE and that of the Scanner stable
Consistent
N
2. Obtain call drop location and time
3. Analyze signal changes of the primary cell of the
Scanner
4.1 Both the RSCP and the EcIo are
poor.
4.2 The RSCP is normal, and the EcIo
is poor. 4.3 Both the RSCP
and the EcIo are normal. Neighbor cell missing Uplink interference Untimely handoff Check whether
the call drop is caused by the neighbor cell missing. Coverage problem Abnormal call drop Pilot frequency interference Inconsistent Uplink interference or not Y
Are signals of the primary cell stable?
4 RSCP and EcIO of the best cell of the Scanner
Ping-pong handoff problem Frequently changed
Y
Drive Test Data Analysis Procedure
Drive Test Data Analysis Procedure
1.
Prepare the following data:
Data files collected by the drive test software
Single user tracing data recorded by the RNC
CDL recorded by the RNC
2. Obtain the call drop location.
Adopt the drive test software, such as the Analyzer to obtain the call drop time
and location, pilot frequency data collected by the Scanner before and after
the call drop, information about the active set and monitored set collected by
the UE, and signaling process.
3. Analyze changes of the primary cell of the Scanner.
If the primary cell is relatively stable, perform further analysis on the RSCP
and EcIo.
If the primary cell changes frequently, analyze causes. If there is no primary
cell, perform the cause analysis on the call drop occurring during the ping-pong
Drive Test Data Analysis Procedure
Drive Test Data Analysis Procedure
4. Analyze the RSCP and EcIo of the primary cell of the Scanner.
Check the RSCP and EcNo of the best cell of the Scanner and take appropriate measures accordingly.
4.1 If both the RSCP and EcNo are poor, the coverage problem leads to the call drop. 4.2 If the RSCP is normal, and the EcNo is poor, the call drop is caused by the pilot
frequency interference problem rather than untimely handoff and inter-frequency neighbor cell.
4.3 If both the RSCP and the EcNo are normal and the cell of the active set of the UE are inconsistent with the best cell of the Scanner, the call drop may be caused by the neighbor cell missing or untimely handoff. If the cell of the active set of the UE is consistent with the best cell of the Scanner, the uplink interference may result in call drop or an abnormal call drop occurs.
5. Carry out the drive test repeatedly.
A drive test may not collect all the information required by call drop location. Therefore, you need to carry out the drive test for several times to collect data and check whether the call drop location is random or fixed. Generally, take related measures to eliminate call drops occurring on the fixed location and check whether to eliminate call drops occurring on random locations based on the occurrence probability.
2 Causes and Handling Process
2.1 Common reasons for call Drop 2.2 Drive test data analysis procedure
2.3 Measurement data analysis procedure2.3 Measurement data analysis procedure
2.4 Signaling tracing data analysis procedure 2.5 User complaint data analysis procedure
Measurement Data Analysis Procedure
Measurement Data Analysis Procedure2. Analyze the call drop rate index of the cell.
1. Analyze the call drop rate of the RNC.
Y N N Y N Y
3. Check whether the equipment in the cell is
normal.
3.1 Solve the equipment problem.
4. Analyze call drop reasons.
4.1The signaling RB reset or service RB reset causes the
call drop.
4.2 Check whether the call drop is caused by the
handoff?
4.3 Check whether the call
Solve the coverage problem.
Solve the call drop problem arising from the handoff.
Measurement Data Analysis Procedure
Measurement Data Analysis Procedure
1. Analyze call drop rate indexes of the RNC.
Check whether the call drop rate index is normal based on the overall call drop rate index of the RNC.
2. Analyze call drop rate indexes of the cells such as AMR call drop rate, VP call drop rate, PS call drop rate, hard handoff call drop rate, inter-RAT handoff call drop rate and sort all of these cells according to the indexes. Analyze causes of call drops
occurring in the cells with worse or worst indexes. 3. Check whether the cell is normal.
Measurement Data Analysis Procedure
Measurement Data Analysis Procedure
4. Analyze call drop causes.
If the call drop is not caused by aa12 abnormality of the Iu interface or the GTPU abnormality, check whether the reset of signaling RLC or service RLC is the call drop cause. Analyze related handoff indexes (incoming handoff success rate and outgoing handoff success rate) related to the cell to check whether the call drop is caused by the handoff failure. Analyze the measurement relating to the overall bandwidth receiving power to check whether related uplink interference indexes are high during the period of the high call drop rate. Then, you can determine whether the call drop is caused by uplink interference.
5. Carry out the drive test to make call drop problems reoccur.
If the call drop problem persists after the analysis of measurement data, carry out drive tests in the cell to trace the signaling process on the UE side and the RNC. For detailed analysis method, see the drive test analysis procedure.
2 Causes and Handling Process
2.1 Common reasons for call drop 2.2 Drive test data analysis procedure 2.3 Measurement data analysis procedure
2.4 Signaling tracing data analysis procedure2.4 Signaling tracing data analysis procedure
Signaling Tracing Data Analysis Procedure
Signaling tracing data analysis procedure
2. Obtain information about the call drop location.
1. Obtain the single user tracing message
3. Check whether the call drop occurs on the
signaling plane.
Y
N 4 . Check whether the call
drop occurs on the user plane.
5. Check whether abnormal call drop occurs.
3.1 Solve call drop problems arising on the signaling plane.
4.1 Solve call drop problems arising on the user plane.
5.1 Solve abnormal call drop problems.
Check whether call drop problems are solved.
Signaling Tracing Data Analysis Procedure
Signaling Tracing Data Analysis Procedure
1. Obtain single user tracing messages.
Trace the single user on the RNC or M2000 before recording related single user tracing messages. Generally, the messages recorded during the IMSI-based tracing is sufficient for the analysis of the call drop problems.
2. Obtain information about the call drop location.
Single user tracing messages suggest that the cause of a call drop on the user plane is that the RNC actively sends the RANAP_RAB_RELEASE_REQ message to
release the RAB and the cause of a call drop on the signaling plane is that the RNC actively sends the RANAP_IU_RELEASE_REQ message to release the Iu interface. By checking the two messages, you can obtain the call drop time and signaling
Signaling Tracing Data Analysis Procedure
Signaling Tracing Data Analysis Procedure
3.
Analyze the call drop on the signaling plane.
If a call drop occurs on the signaling plane, the UE or the RNC cannot receive the confirmation message, which leads to the SRB reset and connection release. The SRN reset can be caused by uplink messages such as the measurement control message, active set update message, physical channel reconfiguration message, transmission channel reconfiguration message, RB reconfiguration message, and command for the handoff from 3G networks to 2G networks. You need to check messages traced on the UE side to determine whether the UE receives these
commands. The SRN reset can also be caused by downlink messages such as the measure report, active set update completion message, physical channel
reconfiguration completion message, transmission channel reconfiguration
completion message, and RB reconfiguration completion message. You need to check messages traced on the RNC side to determine whether these tracing messages are received.
Signaling Tracing Data Analysis Procedure
Signaling Tracing Data Analysis Procedure
4. Analyze the call drop on the user plane.
If the call drop occurs on the user plane, the TRB resets. The TRB resetting occurs during a PS call rather than a Voice or VP call.
If there is only one link in the active set, the RL failure may cause the RNC to initiate the Iu release procedure. The lost synchronization of the uplink causes the RL
failure. The lost synchronization of the downlink causes the UE to shut down the transmitter, which results in lost synchronization of the uplink. To check whether the lost synchronization of the uplink or lost synchronization of the downlink causes the release process, you need to analyze the transmit power of the UE and the
monitored code transmit power of the downlink before the call drop. Poor downlink coverage, strong downlink interference, or uplink interference may lead to TRB reset. If the number of retransmission times of data services is set improperly, the TRB reset occurs before the SRB reset when it is too late for handoff. You must take this case into account.
Signaling Tracing Data Analysis Procedure
Signaling Tracing Data Analysis Procedure
5. Analyze abnormal call drops.
The abnormal call drop is caused by abnormalities occurs on the equipment or the UE (for example, the transmission is interrupted, the base station equipment is abnormal, and the UE crashes abruptly) rather than the coverage problem, interference problem, or causes of the call drop occurs on the user plane or the signaling plane. If the call drop is caused by the abrupt transmission interruption, you can analyze the CDL or alarms to locate the cause of the call drop; if the call drop is caused by the abnormalities of the base station equipment, you can check the status of the base station; if the call drop is caused by abnormalities of the UE, you can analyze the data recorded by the UE.
6. Carry out drive tests to make the call drop problem reoccur.
If the existing data is not sufficient to locate the call drop problem, trace more detailed data. The best way is to carry out drive tests on the call drop location and perform further analysis.
2 Causes and Handling Process
2.1 Common reasons for call drop 2.2 Drive test data analysis procedure 2.3 Measurement data analysis procedure 2.4 Signaling tracing data analysis procedure
User Complaint Data Analysis Procedure
User Complaint Data Analysis Procedure
1. Understand user complaint.
When a user complaint is received, record when and where the problem occurs and describe the problem in detail.
2. Check the measurement.
Analyze the related measurement to determine whether the complaint is a specific problem of the user or a general network problem. For a general network problem, perform further analysis on the complaint by referring to the analysis on the
measurement.
3. Check alarms.
According to the complaint time, check the CN, RNC or check whether the alarm of the base station on the location where the problem occurs can result in call drop. If such alarm exists, clear the alarm.
4. Check the CDL.
The CDL records the signaling used by the user or the user status when the
abnormality occurs. By analyzing the CDL, you can learn about the details about the complaints.
User Complaint Data Analysis Procedure
User Complaint Data Analysis Procedure
5. Perform the dialing test on the complained location to make the problem
reoccur.
If the problem persists after you analyze the related measurement, alarm,
and CDL, perform the dialing test to solve the problem. Record the data
generated during the dialing test by using the same method for recording
the data generated in the drive test. If it is inconvenient to record the
information on the UE side in certain scenarios, use the RNC to record
various information, in particular, record and collect the reported
information about the EcIo and RSCP to solve the call drop problem
caused by the poor coverage. In the case of special locations where it is
impossible to perform the dialing test, obtain the IMSI according to the
mobile phone number and trace the call on the RNC to locate causes of
the call drop.
Contents
1. Definition and classification
2. Causes and handling process
3. Solutions
4. Case analysis
3 Solutions
3.1 Engineering parameter
3.1 Engineering parameter
adjustment
adjustment
Engineering Parameter Adjustment
The engineering parameter adjustments are limited. Basically, you can adjust the height, down tilt, lobe width, gain, and deflection angle of the antenna.
1. For the call drop caused by the uplink or downlink coverage problem
Adjust the height and the down tilt of the antenna or replace with the antenna providing more gain or increase the TMA.2. For the pinpoint or corner effect
An effective way is to adjust the antenna. The pinpoint or corner effect occurs on the corner of the street or the junction of the two streets. In this case, you can make a certain angel between the antenna and the street by adjusting the deflection angle. Note that this action should not greatly affect the signal coverage of nearby shops on the street.
Adjustment of Engineering Parameters
3. For the coverage problem caused by the pilot frequency
You can adjust engineering parameters of a certain antenna to make the
interfered location a primary cell. You can also adjust engineering
parameters of other antennas to weaken signals of these cells to
decrease the number of pilot frequencies. If permitted, use two base
stations to cover the area. If the interference is from two sectors of a base
station, incorporate the two sectors.
You must consider the adjustment effect of the entire cell when adjusting
engineering parameters. Ensure that the measures taken to solve the
problem does not bring about new problems in other areas.
3 Solutions
3.1 Engineering parameter
adjustment
Cell Parameter Adjustment
1. Cell individual offset (CIO)
The sum of the CIO and the actual measured value is used to determine whether the intra-frequency handoff is to be performed in the event evaluation process of the UE. In addition, the sum can serve as the mobile cell boundary. If the value is larger, the soft handoff is easier and more UEs are in the soft handoff state. In this case, the forward resources are occupied. If the value is smaller, the soft handoff is more difficult and the quality of received signals may be affected. For the pinpoint or corner effect, the better method is to configure the CIO as about 5 dB.
2. Time to trigger the delay related to the soft handoff
The delay triggering time refers to the time to trigger 1A, 1B, 1C, or 1D event. The triggering time may affect the promptness of the handoff. Generally, the default triggering time can meet requirements of most scenarios. Set handoff-related parameters according to the environment and adjust the configuration of related parameter for each cell. You can limit the impact of the parameter modifications to certain cells, which reduces the impact on the system.
Cell Parameter Adjustment
3. FilterCoef
The layer 3 filter tries to filter out the random impingement samples to enable the filtered measured values to reflect the main change trend of actual measured values. The measured values input in the layer 3 filter are filtered by the layer 1 filter.
Therefore, the impacts of fast fading are removed, and the layer 3 filter performs the smooth filtering on shadow fading and few fast fading burrs to provide higher quality measurement data.
The filter with greater filtering coefficient has stronger ability to smooth burrs but weaker ability to trace signals.
Typical values are set as follows:
a. If signals in the handoff area change slowly, the intra-frequency filtering coefficient is set to 7.
b. If signals in the handoff area change at a moderate speed, the intra-frequency filtering coefficient is set to 6.
c. If signals in the handoff area change rapidly, the intra-frequency filtering coefficient is set to 3.
Cell Parameter Adjustment
4. Threshold for enabling or disabling the compression mode
The compression mode is enabled before the inter-frequency or inter-RBT handoff. You can use the compression mode to check the quality of frequency or inter-RBT cells. The compression mode is enabled only when the RSCP or EcIo of the CPICH meet requirements. In actual applications, the common triggering condition is that the RSCP must meet requirements.
Generally, the compression mode requires to measure the quality of the target cell (inter-frequency or inter-RAT cell) to obtain related information. Movements of the UE deteriorate the quality of the current cell. Therefore, the requirement for setting the threshold for enabling the compression mode is to measure that the target cell completes the handoff before the quality deterioration of the current cell leads to the call drop; the requirement for setting the threshold for disabling the compression mode is to avoid the compression mode being enabled or disabled frequently.
Cell Parameter Adjustment
5. RLMaxDLPwr (Maximum Downlink Transmit Power of Radio Links)
The high transmit power of special links is favorable for solving call drop problems caused by the poor coverage but causing the interference problem. In this case, the single user consumes high power at the edge of the cell, which impacts on other users and reduces the downlink capacity of the system. Generally, the downlink transmit power is determined by the link budget with a variation of 1-2dB. If the drive test is carried out for once, it is difficult to measure the impact of the high power on the call drop. The measurement, however, reveals the impacts. If the poor coverage causes a higher call drop rate in certain cells, you can raise the maximum transmit power of special links. If the overload results in a higher access failure rate, you can consider to reduce the maximum transmit power.
Cell Parameter Adjustment
6. Number of signaling/service retransmission times
If the number of retransmission times of the signaling over links with higher block error rate reaches the maximum value, the signaling is reset, which causes the call drop. If the number of retransmission times of the service transmitted in AM mode reaches the maximum value, the signaling is reset. If the number of the reset times reaches the configured maximum value, the system releases the service, which causes the call drop. The default configuration only ensures that the unexpected error blocks do not cause a call drop. In certain scenarios with poorer coverage, however, the signaling reset results in the call drop and causes the resources occupied by the service to be released. In certain scenarios with more burst
interference or remarkable pinpoint effect, the block error rate may reach 100%. If the call drop rate is required to be not too high in such scenarios, you can
appropriately increase the number of retransmission times to weaken the impact of the burst interference. This parameter is configured on the RNC.
Cell Parameter Adjustment
7. RSCP (Inter-RAT Hard Handoff Threshold)
After the frequency measurement is started, the UE starts measuring the inter-frequency cells. If the signal quality of the inter-inter-frequency cells is higher than the threshold, the RNC initiates the inter-frequency handoff. You can configure the
parameter based on the threshold for enabling or disabling the compression mode. If the parameter value is smaller, the handoff is triggered earlier. If the parameter value is greater, the triggering of the hard handoff is delayed. In this way, you can control the handoff area or reduce the call drop rate.
8. GsmRSSICSThd and GsmRSSIPSThd
GsmRSSICSThd and GsmRSSIPSThd specify the inter-system handoff thresholds of the CS service and the PS service respectively. The method for setting the two
Contents
Training.huawei.com
1. Definition and classification
2. Causes and handling process
3. Solutions
4. Case analysis
4 Case analysis
4.1 Cases of call drop caused by
4.1 Cases of call drop caused by
poor coverage
poor coverage
4.2 Cases of call drop caused by
interference
4.3 Cases of call drop caused by
handoff
4.4 Cases of call drop caused by
Cases of Call Drop Caused by Poor Coverage
Call drop location
To analyze cases of the call drop caused by poor coverage, you must take the following issues into account:
Pilot frequency coverage and service coverage
Uplink coverage and downlink coverage
Measurement results recorded by the Scanner and UE
Cases of Call Drop Caused by Poor Coverage
The call drop occurs on the SC314 cell, the coverage edge of the 3G network. Before the call drop, the UE measurement suggests that the No.314 cell is only included in the active set rather than the
Cases of Call Drop Caused by Poor Coverage
The Ec/Io measured by the UE and that measured by the scanner shows the same
degradation trend.
The RSCP measured by the UE and that measured by the scanner shows the same
degradation trend.
4 Case analysis
4.1 Cases of call drop caused by
poor coverage
4.2 Cases of call drop caused by
4.2 Cases of call drop caused by
interference
interference
4.3 Cases of call drop caused by
handoff
4.4 Cases of call drop caused by
Cases of call drop caused by interference
Cases of Call Drop Caused by Interference
Cases of Call Drop Caused by Interference
The interference is subdivided into uplink interference and downlink
interference.
4 Case analysis
4.1 Cases of call drop caused by
poor coverage
4.2 Cases of call drop caused by
interference
4.3 Cases of call drop caused by
4.3 Cases of call drop caused by
handoff
handoff
4.4 Cases of call drop caused by
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
As shown in this figure, the call drop does not occur at the edge of the 3G
network coverage area.
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
Before the call drop, the Ec/Io measured by the UE is decreased to lower than
-21 dB, whereas the Ec/Io measured by the scanner is still above -11 dB.
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
Before the call drop, the SC018 cell is not measured in the monitored set of the UE. The neighbor relation is found to be defined in the neighbor list. Therefore, the possible call drop cause is that the best cell changes rapidly from the SC009 cell to the SC011 cell and SC018 cell, and thus the UE fails to perform the soft handoff timely.
Cases of Call Drop Caused by Handoff
Cases of Call Drop Caused by Handoff
4 Case analysis
4.1 Cases of call drop caused by
poor coverage
4.2 Cases of call drop caused by
interference
4.3 Cases of call drop caused by
handoff
4.4 Cases of call drop caused by
4.4 Cases of call drop caused by
other reasons
The material is not available.
Cases of Call Drop Caused by Other Reasons
Contents
Training.huawei.com
1. Definition and classification
2. Causes and handling process
3. Solutions
4. Case analysis
5 Concerns in Various Network Optimization Phases
5.1
5.1
Concerns in various
Concerns in various
network optimization
Concerns in Various Network Optimization Phases
The entire network optimization process consists of the following phases:
Sign the project contract
Optimize the network
Generate the network optimization report
Here, we focus on the causes of the call drop in phases from the single site test phase to the subsequent acceptance phase.
1. Single site test phase
In the single site test phase, analyze the equipment problem to locate the abnormal call drop cause. If the call drop occurs during the drive test, check whether the call drop is caused by the poor coverage.
Concerns in Various Network Optimization Phases
Concerns in Each Phase
2. RF optimization phase
Evaluation before the optimization
During the evaluation phase, check the drive test results for call drop rate indexes and learn about the call drop rate of the entire network according to the measurement analysis.
In this phase, emphasize on and differentiate call drops caused by poor coverage, interference, or untimely handoff. In addition, the call drops caused by the untimely handoff should be taken into account.
RF optimization
The emphasis of this phase is to check whether call drops are caused by the poor coverage or strong interference. Check whether such call drop problems can be solved by adjusting engineering parameters of the antenna. In addition, call drops caused by the untimely handoff should be taken into account. Check whether the corner or pinpoint effect can be avoided by adjustment of the antenna.
Concerns in Each Phase
3. Parameter optimization phase
If certain call drops cannot be avoided by RF optimization or the RF optimization
cannot be performed in some scenarios, optimize parameters to solve these problems after the RF optimization. In this phase, lay special stress on call drops caused by the handoff, inter-frequency handoff, and inter-RAT handoff. Generally, call drops due to latter causes occur in indoor area or subway. In this case, carry out the walking dialing test accordingly and trace messages of the single user on the RNC for data analysis.
4. Acceptance phase
To evaluate the optimization effect, collect drive test indexes and measurements related to the call drop rate during the optimization and acceptance phases. Not all these call drop problems are required to be solved, but you are advised to analyze the detailed causes of each call drop and put forward further suggestions on the future optimization.
