4 UMTS CS Call Drop Analysis
November 25, 2022 | Author: Anonymous | Category: N/A
Short Description
Download 4 UMTS CS Call Drop Analysis...
Description
UMTS Voice Drop Analysis
ZTE University
Content
Defi finit nitio ion n of o f Call Call Drop
Reasons of Call Drop
Analysis of Call Drop Optimization of Call Drop Case of Call Drop
UE Voluntarily Initiated Signaling Release
Definition of Drive Test Indicators The definition of drive test :
Call drop rate= Number of call drop times/Number of call setup success times
Number of call drop times+1 :
After the Alerting message is received, call drop drop is acknowledged if the Connect ACK message is not received but the System Information message is received. After the Connect ACK message is received, received, if the System Information message is received but the.
“radioBearerReconfigurationComplete”
“physicalChannelReconfigurationComplete”
“transportChannelReconfigurationComplete” “rrcConnectionRelease” “rrcConnectionRelease_CCCH” “rrcConnectionRelease _CCCH” messages are not received in the the subsequent subsequent five seconds, call drop is acknowledge acknowledged. d.
After the ved Connect ACK message is Release” received, received, if the Disconnect message is not received recei but the “rrcConn “rrcConnection ectionRelea se” and “rrcConnectionRelease_CCCH “messages “messages are received, call drop is acknowledged.
Definition of Drive Test Indicators
number of call setup success times+1
Definitions of Network Management Indicators
Call drop defined by the network management statistics is as follows: RNC/Cell
Radio call drop d rop rate= rate=
( SUM(RNC/Cell data. Number of CS RABs that are requested to be released by the RAB release request. All call-drop cause-corresponding submeasurement items) items) + SUM(RNC/Cell data. Number of CS RABs that Iu connection requests to be released. All call-drop call-drop cause-corresponding cause-corresponding sub-measurement items items)) + SUM(RNC/Cell data. Number of PS RABs that are requested to be released by the RAB release request. All call-drop cause-corresponding submeasurement items) items) + SUM(RNC/Cell data. Number of PS RABs that Iu connection requests to be released. All call-drop cause-corresponding sub-measurement items) items) ) / ( SUM(RNC/Cell data. Total number of released CS RABs. All submeasurement items) items) + SUM(RNC/Cell data. Total number of released PS RABs. All sub-measurement items) items) )
Counters of Call Drop Reasons Release Type
Co u n t er
C301230315 C301230316 C301230317 C301230318 Iu Release
C301230319 C301230320 C301230321 C301230322 C301230323
Reas o n
Iu connection release request by UTRAN for CS domain in cell, Repeated Integrity Checking Failure Iu connection release request by UTRAN for CS domain in cell, Release due to UE generated signal signalling ling connection release Iu connection release request by UTRAN for CS domain in cell, Radio Connection With UE Lost Iu connection release request by UTRAN for CS domain in cell, timer TRELOCoverall expiry Iu connection release request by UTRAN for CS domain in cell, Failure in the Radio Interface Procedure Iu connection release request by UTRAN for CS domain in cell, O&M Intervention Iu connection release request by UTRAN for CS domain in cell, Release due to Overload Control Iu connection release request by UTRAN for CS domain in cell, Unspecified Failure Iu connection release request by UTRAN for CS domain in cell, UTRAN Generated Reason
Counters of Call Drop Reasons Release Type
RAB release
Counter
Reason
C301230361
RAB release number request by UTRAN in cell for CS domain,RAB pre-empted
C301230362
RAB release number request by UTRAN in cell for CS domain,Release due to UTRAN in cell Generated Reason
C301230363
RAB release number request by UTRAN in cell for CS domain,Iu UP Failure
C301230364
RAB release number request by UTRAN in cell for CS domain,Release due to Overload Control
C301230365
RAB release number request by UTRAN in cell for CS domain,Unspecified Failure
Content
Definition of Call Drop
Reaso sons ns of Call Dro rop p
Analysis of Call Drop Optimization of Call Drop Case of Call Drop
Call Drop Reasons
Poor Network Coverage
Unconfigured Neighboring Cell Handover
Interference
SC Confliction Exceptions
Poor Network Coverage
Service rvice Type
Require quirement ment of RSCP (dBm) dBm) Require quirement ment of Ec/I c/Io (dB)
AMR12.2K
-105
-13
CS64K PS384K
-100 -95
-11 -10
HSDPA
-90
-8
Poor Network Coverage
The decision whether it is problem of uplink or downlink poor coverage based on the power of Dedicated Channel beforeiscall drop.
UL Poor Coverage:
DL Poor Coverage:
TX Power reaches the maximum; UL BLER is poor or NodeB report “RL failure”
TX Power reaches the maximum; DL BLER is poor
Scanner:
If thecan RSCP of the th e celliswith the best coverage are poor, you inferand thatEc/Io the coverage poor.
Unconfigured Neighboring Cell
During the driv During drive e test, the UE obt obtains ains the nei neighbor ghbor lilist st from the base station, Scanner will make a record all the value of Ec/Io,If a certain main SC is not in the neighbor list and its strength exceeds the specified threshold for several seconds.
If call drop occurs, the SC of the UE residing cell is inconsistent with the SC “Measu before call drop. It may be caused Check “Measurement rement Contr Control” ol” messag message. e. by unconfigured cells.
Some UE may report the Detected Set message. If the detected set information before call drop includes relevant SC information, you can infer that unconfigured cells exist.
Handover
The handover process is incomplete UE Radio Environment becoming bad, UE can not receive the “Active Set Update”
RNC Measurement Report (1A event)
Active Set Update
Active Set Update Complete
Handover
Ping-pong Handover UE
In a short time, UE send different Report for delete or add cell A
RNC Measurement Report (1B event, Delete cell A) Active Set Update (Delete cellA)
Measurement Report (1A event, Add cell A) Active Set Update (Add cell A)
Downlink Interference
Reasons for Pilot Pollution:
Cross-cell coverage of high Node-B Node-B in ring layout
Signal distortion caused by street effect or strong reflection
Uplink Interference
The average RTWP of an idle cell and is around -105 dBm
and for 50% uplink load is -102 dBm. If the Average RTWP in the idle state exceeds -100 dBm and the Max RTWP is around -90 dBm, you can infer that uplink interference exists.
Case-Interference
UL interference = -93(dBm)
Case-Interference
SC Confliction
When analyzing such call drop, check Cell ID in the call drop signaling besides SCs because the neighbor relation is identified by CellID.
Content
Definition of Call Drop
Reasons of Call Drop
An A n al aly y s i s o f Cal Calll Dr Dro op
Optimization of Call Drop Case of Call Drop
Common Analysis Methods for Call Drop
multi-dimension analysis
trend analysis accident analysis
comparison analysis
ranking analysis cause-and-effect analysis
Multi-Dimension Analysis
Multi-dimension analysis is carried out from different
perspectives. For the call drop problem, not only the call drop itself, but also related factors such as
access handover
traffic statistics
time
RTWP
Next page is a table which contains some important parameter from the statistic of OMCR.
Cell ID Cell Name CS Call Drop Rate [%] Number of Successful CS RAB establishment Total Abnormal Release Repeated Integrity Checking Failure Radio Connection With UE Lost TRELOCoverall expiry Abnormal Iu Released Number,by Number,by Cause Failure in the Radio Interface Procedure Unspecified Failure UTRAN Generated Reason Release due to UTRAN in cell Generated Reason Abnormal RAB Released Number,by Cause
Iu UP Failure Unspecified Failure
CS Traffic [Erl] PS Traffic [Kbyte] HSDPA RLC Throughput [Mbps] Max Cell Freq RTWP [dBm] Average Cell Freq RTWP [dBm] [dBm] Max Cell Freq Tcp [dBm] Average Cell Freq Tcp [dBm] [dBm] Max HSDPA users in cell Average HSDPA users in cell Max HSUPA users in cell Average HSUPA users in cell
Trend Analysis
Accident Analysis
Check the equipment alarm and system log of this period to find out hardware problems;
Check the transmission of this
period; Check whether the upgrade or cell blocking is performed
during this period; Check whether there is an occasion with abrupt high traffic requirements such as a concert, game, or exhibition.
Comparison Analysis and Ranking Analysis
Comparison analysis
Comparison analysis is carried out through comparing various data sets from the same perspective and finds out the differences.
Ranking analysis
Ranking analysis carried out through and bottom N dataisfrom a large amount classifying of data. data into top N
Ranking Analysis Ind nde ex Reaso son n of fail failur ure e for for Handov ndove er
Failur ilure e time ti mes s
Perc rce ent nt((%)
1
Failure when getting the decision of handover from database
0
0
2
Timeout for setup of service channel in handover
0
0
3 4
Failure for decision of NodeB hard handover Failure when build the service channel
0 0
0 0
5
Timeout for waiting for the handover of UE complete
0
0
10
Other errors
3104
9.24
12
Basic channel switch, cannot find appointed frequency
0
0
13
Basic channel switch, ffa ailed to allocate the resource
0
0
14
Basic channel switch, failed to setup channel board
0
0
21
Not enough resource for channel
0
0
22
OVSF code is not engough
0
0
24 25
Timeout for handover of UE The frequency is configured in the neighbouring cell list
29966 0
89.16 0
26
Overload for power allocation of the frequency for the service cell
0
0
27
There is no idle channel in service cell
0
0
29
There is not suitable frequency in service cell
0
0
30
Different reason of failure for several service cells
0
0
32
Can not find UE
416
1.24
34
Abnormal release in CN
9
0.09
Cause-and-Effect ct Analysis Cause-and-Effe
For a certain effect, the cause-and-effect analysis is performed to locate the causes that may result in the effect and to determine the influence of the causes.
For example, the call congestion of a cell may be caused by insufficient capacity of the hardware, of the downlink, or of the uplink.
Content
Definition of Call Drop
Reasons of Call Drop
Analysis of Call Drop Opt ptim imiza izati tion on of Call Dro rop p Case of Call Drop
Optimization Methods for Call Drop
Engineer optimization:
Directional angle, downtilt, position of Antenna, type of Antenna, Transmit power of BS, position of BS, new BS.
Radio parameter optimization:
Time Trigger, CIO, threshold Mode,toMaximum transmit powerofofenabling/disabling DL RL, ThresholdCompression of Interfrequency and Inter-system.
Soft Handover Event Detection and Reporting Time To Trigger
Time To Trigger (TTT) refers to the interval between the detection and reporting of events (1A, 1B, 1C, and 1D). The setting of TTT has an impact on the promptness of handovers.
Neighboring Cell Offset CIO
A higher value of this parameter results in easier soft handovers, more UEs in the soft handover state, and more used resources.
A lower value results in more difficult handovers. The CIO has an impact on the non-best cell. In detail, the CIO is effective for 1a events in neighboring cells and effective for 1b events in cells to be deleted.
Enabling/Disabling bling Threshold of Enabling/Disa Compression Mode
The compression mode is used in inter-frequency and
inter-system handovers. The compression mode is enabled before the handover.
Currently, the compression mode is enabled by the 2D
event and disabled by the 2F event. The measurement can be RSCP or Ec/Io. By default, the RSCP is currently used.
Maximum Downlink Transmit Power of Radio Link
If call drop occurs frequently in a cell due to coverage problem, increase the maximum downlink transmit power of services.
However, a user in the edge area may consume great transmit power, which affects other users and reduces the downlink capacity of the system.
If users fail to access a cell due to heavy traffic, consider changing the value of this parameter to a smaller value.
Threshold of Inter-frequency and Inter-system handover
When the measured value of inter-frequency and intersystem neighboring cell signal exceeds the specified threshold, handover is triggered.
If you set this parameter to a small value, handover is triggered ahead of time. If you set this parameter to a great value, handover is delayed.
Timer and Counter Related to Call Drop Val u e Ran g e
Default Value
Nam e
Des c r i p t i o n
T312 Connected
T312 of connection mode, that is, the t he time when the UE waits for L1 synchronization indicator when the special physical channel is set up
(1..15)s
1s
N312 Connected
N312 of connection mode, that is, the number of synchronization indicators that the UE should receive continuously from L1 before the special channel is set up successfully
(1, 2, 4, 10, 20, 50, 100, 200, 400, 600, 800, 1000)
1
T313
Waiting time after the DPCCH channel set up in CELL_DCH mode loses synchronization
(0..15)s
3s
N313
Maximum number of lost synchronization indicators that the UE receives continuously from the L1
(1, 2, 4, 10, 20, 50, 100, 200)
20
T314
Time cell update, in T314-related radio bearerofwhen wirelessexisting connection fails
(0, 4, 6, 8, 12, 16, 2, 20)s
4s
T315
Time of cell update, existing in T315-related radio bearer when wireless connection fails
(0,10, 30, 60, 180, 600, 1200, 1800)s
30s
Maximum number of synchronization indicators
(1, 2, 4, 10, 20, 50,
N315
that the UE receives continuously from L1 in T313 activated state
100, 600, 200, 800, 400, 1000)
1
T309
Waiting time after initiating requests to access other RATs, such as GSM
(1..8)s
3s
Content
Definition of Call Drop
Reasons of Call Drop
Analysis of Call Drop Optimization of Call Drop Cas e o f Cal Cal l Dro rop p
Neighboring Relation Adjustment
Reason
High call drop rate caused by b y improper neighbor list configuration
Description
The call drop rate of the TRI135W-1 cell corresponding to RNC1 in Libyacell is always around 3%, on andthe nosea. hardware alarm is generated. The coverage is mainly
Neighboring Relation Adjustment
Neighboring Relation Adjustment
After the neighbor relation is adjusted, the CS call drop rate of TRI135W-1 decreases from 3％ to 1.3%.
Unconfigured Neighboring Cell
9
74
Unconfigured Neighboring Cell
Main parameters:
Troubleshooting process:
The cell with SC 9 is in the detection set and cannot be added to the active set when the quality of the serving cell with SC 74 is extremely poor. This is a typical unconfigured neighboring cell.
Solution:
Cells in the system
Adjust the neighbor relation: Add the cell with SC 9 to the neighbor list of the cell with SC 74.
Result:
In the same test, the cell with SC 9 is in the active set of the th e serving cell with SC 74. When the th e signal cell with SC 9 is strong enough, the UE hands over from the serving cell to the cell with SC 9.
Unconfigured Neighboring Cell 9
74
9
74
Soft Handover Parameter Optimization
Reason:
Description:
Low handover success rate because of improper soft handover parameter configuration
The success ratetoofsector the handover from 1 (SC 436) of the Shuqian Lu site 2 (SC 434) of sector the Meihuacun hotel is low. This area is within the Shuqian Lu section.
Main parameters:
Soft handover 1a/1b event handover h andover threshold, trigger time
Soft Handover Parameter Optimization
The signal quality of the Shuqian Lu section is poor and unstable because there are overpasses in this section, s ection, Because the comparative threshold decision algorithm is used, a cell with poor signal quality may be added to the active set if the 1a threshold is excessively high. If the RNC sends the ActiveSet Update Command message to instruct the UE to enter this cell, the soft handover may fail because the radio link cannot be set up due to poor and unstable signal quality of this cell.
436 BS-2
434
BS-1
Soft Handover Parameter Optimization
Adjust the 1a/1b event handover threshold and trigger time
of cell 436. Lower the 1a event handover threshold and shorten the trigger time to ensure that the cells with good signal quality
can firstly enter the active set. Raise the 1b event handover threshold and extend the trigger time so that the cells are not deleted too early due to drastic signal deterioration.
Soft Handover Parameter Optimization
Result
After the parameter optimization, cell 434 of the BS-1 (Meihuacun hotel site) can be added to the active set quickly and is not deleted too early. According to the drive test result from more than 100 times of handover tests, the success rate of the handover between the BS-2 (Shuqian Lu site) and the BS-1 (Meihuacun hotel site) increases greatly.
Data Configuration Optimization in 2G/3G Handover
Reason
Call drop because of incorrect data configuration
Description
When the 2G/3G handover tests are performed at the boundary of the 3G network, theinhandover from the 3G network to the 2G network succeeds the west to east direction, but the handover fails in the east to west direction. d irection.
Main parameters
BSC ID, LAC, NCC, and BCCH of the 2G neighboring cell
3G fail 2G
Data Configuration Optimization in 2G/3G Handover
Troubleshooting process
Because the handover from 3G network to 2G network fails, you should firstly check whether 2G neighboring cells are configured. If all 2G neighboring cells are configured, go to the next step. Record whether the 2G Sagem UE starts the compression mode when the signal quality of a 3G UE is lower than the threshold for starting the compression mode, and record the CI of the 2G cell where the compression mode is started.
You can find that UE starts thesignaling compression after the preceding step is the performed. The is as mode follows:
Data Configuration Optimization in 2G/3G Handover
However, after the UE starts the compression mode, the repositioning fails. The signaling is as follows:
And the cause of the repositioning failure is as follows:
According to the preceding signaling analysis, you can infer that the UE does not recognize the BSC of the 2G cell during the 3G-to-2G handover. In this case, the failure may be caused by unconfigured BSC ID or LAC.
Data Configuration Optimization in 2G/3G Handover
Solution:
Result:
Check the BSC and LAC of the target 2G cell on the CN. You can find that the LAC is not configured. Then, reconfigure the LACs of all 2G neighboring cells on the CN. After the data is configured again, all 3G-to-2G handovers succeed.
Suggestion for similar problems:
In the 3G-to-2G handover, the BSC ID, LAC, NCC, and BCCH of 2G neighboring cells must be configured in the 2G neighboring cell database of the OMCR and on the CN.
Call Drop Case-Handover
Call Drop Case-Handover
Delete Cell 51 and Cell 53
Call Drop Case-Handover
Report e1A to add cell 51 and Cell 53 into Active Set after 0.4 second
Call Drop Case-Handover
Report e1a to add cell 51,64,53,52 to Active Set
Call Drop Case-Handover
Call Drop Case-Handover
Continue report e1a to add stronger cells to Active Set But UE cannot receive the AcitiveUpdate message because the poor signal of the cells in ActiveSet.
Call Drop Case-Handover
Call Drop Case-Handover
Call Drop Happened
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