TROUBLE SHOOTING
Series 4
TROUBLE SHOOTING
Series 4
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
Monitor Network Performance
Monitor Network Performance
ProposeAction Plan
ProposeAction Plan
Trouble TicketTrouble TicketDrive TestDrive TestNetwork StatisticNetwork Statistic
Is Performance OK?Is Performance OK?
YesYes
NoNo
Parameter, Configuration and Hardware Changes
Parameter, Configuration and Hardware Changes
Implement Action PlanImplement Action Plan
Optimization Work FlowOptimization Work Flow
STEP 1: Identify Problem
Customer Complaints Drive Test
Traffic Statistics
Alarm
What Problem ?
Optimization Work FlowOptimization Work Flow
STEP 2: Analyze Problem
How to solve?Any activity? Alarm / Hardware
Call Statistics
Drive Test
Optimization Work FlowOptimization Work Flow
STEP 3: Implement Solutions
Change what?Re-configurationHardware Change/Antenna tilting
Parameter Change
Software Upgrades
Optimization Work FlowOptimization Work Flow
STEP 4: Monitor Performance
Change Success? Alarm
Call Statistics
Drive test
CustomerFeedback
Optimization Work FlowOptimization Work Flow
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
Standard for Drive Test
Define Route drive test
Specific drive test measurement tools
Time period for Drive Test
Summary drive test results
Drive Test
Standard for Drive Test
Used external ANT outdoor mounted on rooftop of drive test
car.
Trace mode drive test
Drive test same direction in each route
Drive Test
Define Route drive test
Main road level 1
Normal road level 2
Route in city
Drive Test
Specific drive test measurement tools
TEMS investigation version 2.0.4 or higher version.
External ANT 0 dB(i) Gain with cable and connector to Ericsson
R520
Log files from TEMS investigation will be process by GIMS (post pr
ocessing software) to Mapinfo table .
Drive Test
Time period for Drive Test
For optimization perform drive test after launched in each batch
For trouble shooting drive test
Drive Test
Drive Test after launched in each batch
Print out RXlevel and RXQUAL in whole region.
Graph or table of %RXleve >= -84 dBm compare with base line in
each route.
Graph or table of %RXqual <= 4 compare with base line in each
route.
Summary drive test results.
Trouble shooting drive test
The report in each route will show detail as the following :
Print out RXlevel, RXQUAL and mark problem point.
Summary sheet
-how many problem that found in that route.
-which type of problem ( Missing neigbouring ,Drop call, HO fail,
interference, bad quality).
-give suggestion how to solve and due date.
Example summary sheet added in Appendix. (Demo)
Remark: If changed parameter to solve problem must be re-drive test for
verify results.
Summary drive test results.
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
BM1
Call process data
BM data
Hardware data
Signaling data
BM
AM/CM
BAM
¡ ¡ WS1 WSn
OMC SERVERHUB
Brief Introduction to BSC Traffic Statistics Item
Brief Introduction to BSC Traffic Statistics Item
MTP Measurement Function
Cell Measurement Function
Power-control Measurement
Call Drop Measurement
Site Initialization Measurement
Function
BSC Cell Broadcast
Measurement Function
BSC Measurement Function
SCCP Measurement Function
A-interface Operation and
management statistic
A-interface Equipment
Maintenance statistic
A-interface Trunk Board
message statistic
CPU Measurement Function
Demo
BTS Initialization
Measurement
Cell Broadcast Statistic
Outgoing Inter-cell handover
Measurement Function
Incoming Inter-cell handover
Measurement Function
Undefined Adjacent Cell
Measurement Function
GPRS Measurement Function
Defined Adjacent Cell
Measurement Function
Receiving Quality Measurement
Function
Receiving Level Measurement
Function
Link Balance Measurement
Function
LAPD Link Measurement Function
Cell Frequency Scan
Brief Introduction to BSC Traffic Statistics Item
Demo
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
Limitation of statisticsLimitation of statistics
1. Traffic statistics task occupies some of the system resources. If too many
tasks are implemented simultaneously or a task is implemented too
frequently, too much resource of BSC system will be used. Therefore, there
are restrictions to the number and period of traffic statistics task in BSC
system:
At most 200 tasks can be created in each BM (Basic Module).
At most 3000 subtasks can be created in each BM.
A traffic statistics task is divided into subtasks according to the traffic statistics
objects in the task. The number of traffic statistics objects of a traffic statistics task
equals to the number of the subtasks contained in this task. The number of subtasks
of a BM is the total number of the subtasks of all tasks created in this BM. For
example, if a BM is fully configured to supports 128 cells, there will be 128 subtasks
after creating a measurement task of cell performance for "all cells in the module".
A task can have at most 60 different initial indices.
For example, BSC Measurement Function has more than 120 primitive indices. Cell
Measurement Function has more than 220 primitive indices. At least three tasks are
to be created to measure all indices of BSC Measurement Function. At least four
tasks are to be created to measure all indices of Cell Measurement Function.
Minimum traffic statistics cycle: 15 minutes
If the statistic cycle is too short and the task results are too many, the system load will
increase. Therefore, the statistic cycle should not be shorter than 15 minutes. The
default setting is 30 minutes. The maximum statistic cycle is 1440 minutes.
Limitation of statisticsLimitation of statistics
Limitation of statisticsLimitation of statistics
At most 16 cells can be selected in each Outgoing/Incoming inter cell
handover measurement function task
There is a limitation about the communication between Host and BAM; So,
Outgoing inter cell handover measurement function and Incoming inter cell
handover measurement function only support 16 cells in one task.
2. Statistic items that cannot be registered more than once
Do not register the statistic items concerning maximum/minimum values (e.g.
Maximum num. of busy TCHs) in multiple tasks. Otherwise, the data of these
indices may be incorrect.
The BSC traffic statistics indices concerning maximum/minimum values and their
traffic statistics function types are listed in the following
Limitation of statisticsLimitation of statistics
Limitation of statisticsLimitation of statistics
BSC indices concerning maximum/minimum values
Traffic statistics function type Index concerning maximum/minimum value
CPU Measurement Function Peak percentage of CPU occupation
Cell Measurement Function Maximum num. of busy SDCCHs
Cell Measurement Function Maximum TCH queue length
Cell Measurement Function Maximum num. of busy TCHs
Power-Control Measurement Function Maximum distance between MS and BTS
Power-Control Measurement Function Maximum downlink power duration
percentage
Power-Control Measurement Function Maximum uplink power duration percentage
GPRS Related Measurement Function Max num. of available PDCH
GPRS Related Measurement Function Min num. of available PDCH
Limitation of statisticsLimitation of statistics
3. Do not modify the time of BAM and OMC Server.
Since the management and time of traffic statistics are closely related, if the time
is modified, the result of this cycle that outputted may be incorrect.
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
Analysis process
First we shall analyze and compare the sub-item of BSC measurement
function to have a roughly acknowledgement for the whole network.
During analyzing, if any important items (such as call drop rate or handover
successful rate) are abnormal, we shall do some further and detailed analysis
for the corresponding contents.
Analyze the cell with abnormal items (call drop, congestion, handover failure
and so on).
Use percentage and absolute times (call drop, congestion, handover failure
and so on) together to decide whether doing some further analysis or not.
Traffic Statistics Analysis
BSC Measurement Function
High call drop rate High congestion rate Low handover successful rate
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General method for traffic analysis
Traffic Statistics Analysis
TCH call drop analysis ( Analysis diagram )
Cell with high call drop rate
Cell performance statistics
Call drop measurementHandovermeasurement
Call drop times
Interference band
Causes of call drop
Average uplink level at TCH call drops
Average down link level atTCH call drop
Average uplink quality atTCH call drop
Average downlink quality at TCH call drop
Average TA value atTCH call drop
Outgoing-cell handover success rate
Incoming inter cell handover successful rate
Handover failure and re-establish
failure
Alarm and hardware fault
Traffic Statistics Analysis-TCH Call Drop
Low Handover Success Rate
Handover Measurement Function
Alarm (Clock),Hardware FaultTCH Measurement Function
Outgoing-Cell Failure Incoming-cell Failure
Outgoing Inter-cell Handover
Measurement Function
Incoming Inter cell Handover
Measurement Function
Cause of Failure in BSC
1.Illegal Channels 2.Illegal Carrier 3.Illegal TA 4.Timer out 5.no available channel 6.others
Traffic Statistics Analysis-Handover
Handover analysis (Analysis diagram)
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
Call drop is usually caused by the following:
Radio link fault. During the communication, messages can not
be received correctly.
T3103 counter gives no response after timeout
Other system faults (for example, the matching between BSC
timer and MSC timer)
Timers that may cause call drops (BSC timer):
T3103: Time counting from sending up HANDOVER CMD start
to receive HANDOVER CMP end, If it is timeout.(20s)
T3109: Time counting from sending up CHAN REL to receive
REL IND end. If it is timeout.(5s)
Trouble shooting--Call DropTrouble shooting--Call Drop
Analyze the causes of the fault of radio links. The causes can be: Interference
• Internal interference, external interference and the equipment
interference
Poor coverage • Coverage insufficient, isolated island, uplink/downlink unbalance
Improper parameter setting• radio link timeout counter, SACCH multi-frame number, handover,
power control etc.
Equipment problem (Antenna---Feeder---CDU---TRX)
Clock problem
Transmission problem
Trouble shooting--Call DropTrouble shooting--Call Drop
Call drop types
Edge call drop: low receiving signaling strength, large TA.
Short distance call drop: low receiving signal strength and
small TA.
Bad Qual call drop: high receiving signal strength and poor
quality.
Sudden call drop: before call drop, the call is normal then
call drop happened suddenly.
Trouble shooting--Call DropTrouble shooting--Call Drop
Edge call drop
Causes
• MS is out of cell’s effective coverage area.
• “Island” phenomenon caused by over shooting or missing neighbor.
• Stand along site.
Solutions
• Add new site to guarantee the effective continuous coverage.
• Add the necessary neighbor.
• Adjust antenna height and antenna downtilt, use high gain antenna
• Modify some parameters : “SACCH multi-frames ” , “Radio link
timeout counter”, “handover threshold”, “handover statistic time”, etc..
Trouble shooting--Call DropTrouble shooting--Call Drop
Short distance call drop
Causes
• Poor coverage caused by complicated terrain structure or high
dense building.
Solutions
• Increase EIRP.
• Adjust antenna direction and downtilt, make the main lobe point to
high traffic area.
• Adjusting call drop related parameters.
Trouble shooting--Call DropTrouble shooting--Call Drop
BQ call drop( high signal strength)
Causes
• High transmission bit error rate (BER).
• Uplink or downlink interference.Interference caused by Repeater.
Interference caused by Radar or other similar equipment.
Interference caused by improper frequency planning.
Self-interference caused by BTS.
Solutions
• Try to find the external interference.
• Optimize frequency planning.
• Adjust antenna system, avoid “island”.
• Avoid transmission BER.
Trouble shooting--Call DropTrouble shooting--Call Drop
Equipment problem (TRX, power amplifier, tower amplifier, etc.)
Problem description
• In TCH measure function: many TCH seizure failures due to A interface
problem.
• In call drop measurement function: many call drops due to ground links.
• In TCH measurement function: many TCH seizure failures due to
equipment failure.
Disposing process
• Monitor transmission and board alarms (TC board failure, A interface
PCM synchronization alarm, LAPD link disconnected, TRX alarm);
analyze whether transmission is disconnected or some boards have
fault (for example, the TRX can’t work).
Trouble shooting--Call DropTrouble shooting--Call Drop
Overall process for call drop analysis
Find out cells with high call drop rate.
Classify the call drop according to the character.
Analyze the cells’ traffic load and total call drop times.
In the call drop measurement function :analyze the call drop
performance.
Check the interference band.
Note : First, we shall know the type of the call drop.
Trouble shooting--Call DropTrouble shooting--Call Drop
TCH Call Drop items
N:TCH call drop
A: TCH lost radio connections (connection failure)
B: TCH lost radio connections (error indication)
C: TCH seizure failures due to terrestrial link failure (A-bis)
D: TCH drop during Handover and preemption (No item in
OMC)
N=A+B+C+D
Trouble shooting--Call DropTrouble shooting--Call Drop
SDCCH call drop Refer to TCH call drop analysis.
Note: The cause and mechanism of SDCCH call drop are almost the
same as TCH.
Trouble shooting--Call DropTrouble shooting--Call Drop
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
Trouble Shooting--Handover
Handover failure analysis
Causes of handover failure
• Improper handover parameters.
• Hardware fault (TRX board fault).
• Congestion
• Interference
• Coverage
• Clock fault (Internal clock, external clock)
Handover failure analysis
Disposing process
• Find out the cells with low handover successful rate.
• Find the out the cells with high handover failures.
• Compare the incoming cell handover failures and outgoing cell
handover failures.
• Register the task to measure the incoming cell handover and
outgoing cell handover.
• Find out handover failure relation (failure to all the neighbor cells or
parts of the neighbor cells).
Trouble Shooting--Handover
Improper parameter settings
Disposing process
• Check whether the handover parameter threshold such as TA, BQ
and handover function switch are suitable or not.
• Check whether the successful TCH seizures for handover are much
more than successful TCH seizures for call. If handover divide by
call is larger than 3, then it indicates that there maybe has Ping-
Pong handover. Check the parameter setting and adjust them (layer
setting, inter-lay handover hysteresis, inter-cell handover
hysteresis, PBGT threshold, etc.).
• Check whether the average signal strength is low When the
handover happens. If it is, it indicate the edge handover threshold
are too low.
Trouble Shooting--Handover
Hardware fault
Problem description
• The target cell has active channels but when applying for the
channels, get NACK or TIMEOUT message.
• TCH availability is abnormal.
• If the call drop rate and congestion rate are high, the equipment
may have some fault.
Trouble Shooting--Handover
Hardware fault
Disposing process
• Monitor transmission and board alarms (TC board failure, A
interface PCM sync alarm, LAPD link disconnected, power amplifier
board, HPA, TRX alarm board, and CUI/FPU alarm).
• Analyze whether the transmission is disconnected or the boards
have some fault (for example: the TRX is damaged).
• Check whether there is a clock alarm.
Trouble Shooting--Handover
Congestion
Objects needed to be analyzed
• Cells with low incoming handover successful rate.
• Neighbor of the cell with low incoming handover successful rate.
Analysis process
• In incoming inter-cell handover Measurement function: check
whether many handover failures caused by congestion.
• Low incoming handover successful rate: check the cell’s traffic .
• Low outgoing handover successful rate: check the neighbor cell’s
traffic.
Trouble Shooting--Handover
Congestion
Disposing process
• Adjust the cell’s coverage (adjust BTS transmitting power,
RXLEVEL_ACCESS_MIN, RACH access threshold, and the antenna
downtilt and height).
• Adjust parameters (CRO, load handover parameters, cell priority and
handover parameters).
• Expand or adjust TRX configuration between high and low traffic cell.
Trouble Shooting--Handover
Optimization Work Flow
Drive Test
Traffic statistics
• Brief Introduction
• Limitation of statistics
• Traffic statistics analysis
Trouble shooting
•Call Drop
•Handover
•SDCCH Congestion
Topics
SDCCH congestion
Main causes
• Transmission fault and Board fault
• Excessive SDCCH location updating in location area boundary
• More traffic
• Improper setting of system parameters
• Interference
Trouble Shooting—SDCCH Congestion
Transmission fault and Board fault
Problem description
Massive location updates happen suddenly.
Solution:
Check transmission
Check hardware
Trouble Shooting—SDCCH Congestion
Excessive SDCCH location updating in location area boundary
Problem description
The border of different location area is the street.
The border of different location area is at the high traffic area.
Solution:
Modify location area selection
Modify CRH (Cell Reselect Hysteresis)
Modify the parameters of periodical area updating.(T3212)
Modify the frequent handover problem of the dual-frequency
network
Add more SDCCH channel
Trouble Shooting—SDCCH Congestion
More traffic
Problem description
Many location updates happen at the border of different location
areas.
Solution:
Hardware fault in adjacent cell cause to suddenly traffic
increase
Traffic balance
Reduce CRO to reduce C2
Add more SDCCH channel
Trouble Shooting—SDCCH Congestion
Improper setting of system parameters
Solution:
Increase RACH access threshold (for coping with interference)
Decrease maximum resend times “MS MAX retrans”
Increase extended transmission timeslots appropriately
T3101 3s (Used to limit the duration of immediate assignment.)
T3122 10s Wait indication time, defines the MS waiting time before the
MS attempts another channel request after IMMEDIATE ASSIGNMENT
REJECT.
Trouble Shooting—SDCCH Congestion
Interference
Problem description
RACH threshold is low. At the same time, there is some
interference in the system, which will bring a lot of illusory
SDCCH channel requests.
Disposing process
Properly set the RACH threshold
Dispose interference
Trouble Shooting—SDCCH Congestion
Thank You for Attention