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7/31/2019 78502629 Traffic Statistics Analysis ISSUE1 5
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Wireless Curriculum Development Section
ISSUE
OMF000503
Traffic Statistics Analysis1.5
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Brief introduction to BSC traffic statistics
Often-used traffic statistics items analysis
Locate problem through traffic analysis
Case study for traffic statistics
Course Contents
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3
Main Structure of Traffic Statistics System
BM1
Call process data
BM data
Hardware data
Signaling data
BM
AM/CM
BAM
WS1 WSn
OMC SERVERHUB
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Advanced global Pre-set counters design
Once the host starts, the global counters begin to work at
measurement point constantly and automatically without manual
intervening.
Abundant and powerful statistics functions
Brief Introduction to BSC Traffic Statistics
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Menu Introduction to BSC Traffic Statistics
Task list management
BSC traffic statistics platform provide the function of registering
new task, deleting registered task and refreshing task list.
Task management BSC traffic statistics platform provide the function of modifying
task name, modifying statistic period of permanent task,
hanging up task, activating task, querying task information,
querying task result and querying task running state.
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Menu Introduction to BSC Traffic Statistics
Template management
Template management provides the function of Defining item
template, object template, time template, user-defined statistic
items and refreshing all templates.
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Exercises
The traffic measurement task is registered using the BSC traffic
statistics console, the maximum number of task of each module
is 200. What is the maximum number of subtasks each module.
Answer:
The correct answer is 1000. Because of the system resource
limit, The maximum number of task and subtask for each
module are 200 and 1000 respectively. And one task can only
include 60 original items.
Menu Introduction to BSC Traffic Statistics
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Brief Introduction to BSC Traffic Statistics Item
TCH Blocking Rate
TCH Blocking Rate (excluding handover) = (TCH seizure
failures for call + TCH seizure failures for very early assignment)
/ (attempted TCH seizures + attempted TCH seizures for very
early assignment) * 100%
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Brief Introduction to BSC Traffic Statistics Item
TCH Blocking Rate
TCH Blocking Rate (including handover) = (TCH seizure failures
for call + TCH seizure failures for very early assignment + TCH
seizure failures for intra BSC incoming cell handover (no radio
resource) + TCH seizure failures for inter BSC incoming cell
handover (no radio resource) ) / (attempted TCH seizures (all) +
attempted TCH seizures for very early assignment + attempted
TCH seizures for intraBSC incoming cell handover + attempted
TCH seizures for interBSC incoming cell handover) * 100%
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Brief Introduction to BSC Traffic Statistics Item
SDCCH Blocking Rate
SDCCH Blocking Rate = times of attempted seizures meeting
an SDCCH blocked state / attempted SDCCH seizures (all) *
100%
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Brief Introduction to BSC Traffic Statistics Item
TCH Call Drop Rate
TCH Call Drop Rate = TCH Call Drops / Successful TCH
Seizures (all) *100%
SDCCH Call Drop Rate SDCCH Call Drop Rate = SDCCH call drops / successful
SDCCH seizures (all) *100%
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Brief Introduction to BSC Traffic Statistics Item
Radio Link Call Setup Successful Rate
Radio Link Call Setup Successful Rate =(1-TCH Blocking Rate)
* (1-SDCCH Blocking Rate)
Note: A key index that show the performance of radio service.
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Brief Introduction to BSC Traffic Statistics Item
Handover Successful Rate
inter Cell Handover Success Rate = (Successful incoming
internal inter cell handovers + Successful incoming interBSC
inter cell handovers + Successful outgoing internal inter cell
handovers + Successful outgoing interBSC inter cell handovers)
/ (Attempted incoming internal inter cell handovers+ Attempted
incoming interBSC inter cell handovers + Attempted outgoing
internal inter cell handovers + Attempted outgoing interBSC inter
cell handovers) *100%
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Brief Introduction to BSC Traffic Statistics Item
Handover Successful Rate
Inter Cell Radio Handover Success Rate =(Successful Incoming
Internal Inter Cell Handovers + Successful Incoming InterBSC
Inter cell Handovers + Successful Outgoing Internal Inter Cell
Handovers + Successful Outgoing InterBSC Inter Cell
Handovers) / (Incoming Internal Inter Cell Handovers + Inter
BSC Incoming Cell Handovers + Outgoing Internal Inter Cell
Handovers + Inter BSC Outgoing Cell Handovers) * 100%
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Exercise
Write down the key items of the network
Answer: The most important items for the network are: call drop
rate, TCH congestion rate, SDCCH congestion rate, outgoing
and incoming handover success rate, traffic volume etc.
Exercise
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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 andmanagement statistic
A-interface Equipment
Maintenance statistic
A-interface Trunk Board
message statistic
CPU Measurement Function
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Brief Introduction to BSC Traffic Statistics Item
BTS Initial Measurement
Cell Broadcast Statistic
Outgoing Inter cell handover
Measurement Function
Incoming Inter cell handover
Measurement Function
Undefined Adjacent Cell
Measurement Function
GPRS Related
Measurement Function
Defined Adjacent Cell
Measurement Function
Receiving Quality Measurement
Receiving Level MeasurementFunction
Up-Down Link Balance
Measurement Function
LAPD Link Measurement
Function
Cell Frequency Scan
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Course Contents
Brief introduction to BSC traffic statistics
Regular traffic statistics items analysis
Locate problem through traffic analysis
Case study for traffic statistics
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Often-used Traffic Statistics Items analysis
Systematical architecture
From upper to bottom
From whole to local
Integrality Observe the change trend of the item for more than one week
and the changed trend of each day.
Relativity
Relationship between all kinds of traffic statistics items
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Analysis process
First we shall analyze and compare the 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 further
detailed analysis for the corresponding items.
Often-used Traffic Statistics Items analysis
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Often-used Traffic Statistics Items analysis
Analysis process
Check the cell that has abnormal items (call drop, congestion,
handover failure and so on).
Base on whole percentage and absolute times (call drop,
congestion, handover failure and so on), decide whether do
some further analysis or not.
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Often-used Traffic Statistics Items analysis
Circuit paging (A-interface) successful rate
Immediate assignment successful rate
TCH call drop rate
TCH and SDCCH blocking rate
Handover successful rate
Interference band
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Often-used Traffic Statistics Items analysis
Circuit paging (A-interface) successful rate
Relate to ATT , coverage area and random access
performance.
Relate to the paging re-send mechanism implemented by BSC
or MSC.
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Often-used Traffic Statistics Items analysis
Circuit paging (A-interface) successful rate
Immediate assignment successful rate
TCH call drop rate
TCH and SDCCH blocking rate
Handover successful rate
Interference band
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Often-used Traffic Statistics Items analysis
Immediate assignment successful rate
When BTS receives Random Access message from MS, BTS
will apply channel from BSC. If there is no channel available,
BSC will send immediate assignment rejected message which
indicates the failure of immediate assignment. At the same time,
MSs access will be bared for some time.
The interference and collision of random access will affect
immediate assignment successful rate.
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Often-used Traffic Statistics Items analysis
Circuit paging (A-interface) successful rate
Immediate assignment successful rate
TCH call drop rate
TCH and SDCCH blocking rate
Handover successful rate
Interference band
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Often-used Traffic Statistics Items analysis
Causes of TCH call drop
TCH lost radio connections (Connection failure).
TCH lost radio connections (Error indication).
Ground link disconnection when TCH seized (Abis). Call drop during handover
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Often-used Traffic Statistics Items analysis
TCH call drop formula and measurement point
TCH Call Drop Rate = TCH Call Drop / Successful TCH
Seizures (all) *100%
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Often-used Traffic Statistics Items analysis
RF lost rate
TCH RF Lost Rate = (times of radio link disconnection when
TCH seized (connection failure) + times of radio link
disconnection when TCH seized (error indication)) / successful
TCH seizures (all) * 100%
SDCCH RF Lost Rate = (times of radio link disconnection when
SDCCH seized (connection failure) + times of radio link
disconnection when SDCCH seized (error indication)) /
successful SDCCH seizures (all) * 100%
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Often-used Traffic Statistics Items analysis
Circuit paging (A-interface) successful rate
Immediate assignment successful rate
TCH call drop rate
TCH and SDCCH blocking rate
Handover successful rate
Interference band
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Often-used Traffic Statistics Items analysis
TCH blocking rate
It is a key item used to assess cell load.
When the load of the cell overruns the system limitation,
try to distribute some traffic to adjacent cells.
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Often-used Traffic Statistics Items analysis
Causes of TCH blocking ( TCH seizure failure )
Assignment failure
Equipment fault
Invalid ground resource
Ground resource already allocated
Illegal message contents
Radio interface failure and return to original channel
No channel available
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Often-used Traffic Statistics Items analysis
TCH blocking rate
TCH Blocking Rate (including handover) = (TCH seizure failures
for call + TCH seizure failures for very early assignment + TCH
seizure failures for intra BSC incoming cell handover (no radio
resource) + TCH seizure failures for inter BSC incoming cell
handover (no radio resource) ) / (attempted TCH seizures for
call + attempted TCH seizures for very early assignment +
attempted TCH seizures for intraBSC incoming cell handover +
attempted TCH seizures for interBSC incoming cell handover)
*100%
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Often-used Traffic Statistics Items analysis
SDCCH blocking rate
SDCCH Blocking Rate = times of attempted seizures meeting
an SDCCH blocked state / attempted SDCCH seizures (all)
*100%
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Often-used Traffic Statistics Items analysis
SDCCH Blocking measurement point
Attempted SDCCH seizure meeting a SDCCH blocked state is
counted when there is a SDCCH seizure but no SDCCH
available.
Attempted SDCCH seizures (all)
Receive CH_REQ and the channel type is SDCCH.
Incoming interBSC inter cell handover and the handover type is
SDCCH handover. Incoming intraBSC inter cell and intra-cell handover and the
handover type is SDCCH handover.
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Often-used Traffic Statistics Items analysis
Circuit paging (A-interface) successful rate
Immediate assignment successful rate
TCH call drop rate
TCH and SDCCH blocking rate
Handover successful rate
Interference band
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Often-used Traffic Statistics Items analysis
Handover measurement point
For different objects such as BSC, band (900/1800),
incoming/outgoing, intra-cell handover and so on, there are
different items.
By analyzing different items, the problems can be located more
rapidly.
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Often-used Traffic Statistics Items analysis
Handover Successful Rate
inter Cell Handover Success Rate = (Successful incoming
internal inter cell handovers + Successful incoming interBSC
inter cell handovers + Successful outgoing internal inter cell
handovers + Successful outgoing interBSC inter cell handovers)
/ (Attempted incoming internal inter cell handovers+ Attempted
incoming interBSC inter cell handovers + Attempted outgoing
internal inter cell handovers + Attempted outgoing interBSC inter
cell handovers) *100%
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Often-used Traffic Statistics Items analysis
Causes of handover
Power budget
Poor uplink signal quality
Poor downlink signal quality
Low uplink signal strength
Low downlink signal strength
Too large TA value
Other reasons
Note: Handover types and times for all adjacent cells are
listed in outgoing and incoming inter cell handover
measurement function.
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Often-used Traffic Statistics Items analysis
Handover failure reasons
No available channel
Illegal frequency
Timer timeout
Illegal channel
Illegal TA
Other reasons
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Often-used Traffic Statistics Items analysis
Circuit paging (A-interface) successful rate
Immediate assignment successful rate
TCH call drop rate
TCH and SDCCH blocking rate
Handover successful rate
Interference band
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Often-used Traffic Statistics Items analysis
TCH Interference Band measurement
The result in each TCH interference band shows the average
number of idle TCH within this interference band in the statistic
period, which reflects the average interference level.
In urban and suburb area, because of different density of base
station and the frequency reuse pattern, the acceptable
interference level is different.
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Often-used Traffic Statistics Items analysis
Cell frequency scan
Show the signal strength received by main antenna and diversity
antenna.
Reflect the interference level for this frequency.
The difference between the measurement results got by main
and diversity antenna reflects the difference between the two
antennas such as direction, gain, path loss and so on.
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Often-used Traffic Statistics Items analysis
Receiving level measurement
Receiving level measurement function is base on per TCH
channel.
The receiving level is divide into 6 bands
Band 0 : -110~-100dBm
Band1 : -100~-95dBm
Band 2 : -95~-90dBm
Band 3 : -90~-80dBm
Band 4 : -80~-70dBm
Band 5 : > -70dBm
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Exercise
List the often-used traffic statistics tasks that we use to locate
and analyze the problem.
Answer: The often-used traffic statistics tasks are: BSC
measurement function, TCH and SDCCH measurement function,
inter-cell and intra-cell handover measurement function,
outgoing and incoming inter cell handover measurement
function, up-down link balance measurement function, call drop
measurement function, cell frequency scan etc.
.
Exercise
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Course Contents
Brief introduction to BSC traffic statistics
Often-used traffic statistics items analysis
Locate problem through traffic analysis
Case study for traffic statistics
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BSC Measurement Function
High call drop rate High congestion rate Low handover successful rate
TCH
performance
Cal
ldrops
SDCCHperformance
Link
balance
Outgoinghandover
Alarmdata
Alarmdata
TCHpe
rformance
TCHpe
rformance
Incomin
ghandover
Link
balance
Link
Balance
Alarmdata
General method for traffic analysis
Traffic Statistics Analysis
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Traffic Statistics Analysis
Combine Traffic statistics analysis with other optimization
method
Drive Test: simulate common subscribers behavior.
Analyze objects
Coverage
Quality
Handover
Signaling
Others
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TCH call drop analysis ( Analysis diagram )
Cell with high call drop rate
Cell performancestatistics
Call drop measurementHandovermeasurement
Call drop times
Interferenceband
Causes ofcall drop
Average uplink level atTCH call drops
Average down link level atTCH call drop
Average uplink quality atTCH call drop
Average downlink qualityat TCH call drop
Average TA value atTCH call drop
Outgoing inter cellhandover success rate
Incoming inter cellhandover success rate
Handoverfailure and re-establish
failure
Alarm andhardware fault
Traffic Statistics Analysis-TCH Call Drop
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Call drop types
Edge call drop: low receiving signaling strength, large TA.
Short distance call drop: low receiving signal strength and small
TA.
BQ call drop: high receiving signal strength and poor quality.
Sudden call drop: before call drop, the call is normal then call
drop happened suddenly.
Traffic Statistics Analysis-TCH Call Drop
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Edge call drop
Causes
MS is out ofcells effective coverage area.
Island phenomenon caused by over shooting or missing neighbor.
isolated 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..
Traffic Statistics Analysis-TCH Call Drop
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Short distance call drop
Causes
Poor coverage caused by complicated terrain or high dense
building.
Solutions
Increase EIRP.
Adjust antenna direction and downtilt, make the main lobe point to
high traffic area.
Adjusting parameters related to call drop.
Traffic Statistics Analysis-TCH Call Drop
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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 source.
Optimize frequency planning.
Adjust antenna system, avoid island.
Solve the problem of transmission bit ERROR
Traffic Statistics Analysis-TCH Call Drop
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Traffic Statistics Analysis-TCH 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.
NoteFirst, we shall know the type of the call drop.
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Traffic Statistics Analysis-TCH Call Drop
The main causes for call drop
Interference (internal and external).
Poor coverage (coverage hole and island).
Improper handover (neighbor planning and handover parameter
setting).
Unbalanced up-down link (TMA, power amplifier, antenna
direction).
Improper parameter settings ( RLT and SACCH multi-frames).
Equipment problem (TRX, power amplifier, and TMA).
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Traffic Statistics Analysis-TCH Call Drop
Interference analysis process
Analyze the appearance period of the interference.
Block TRX one by one to monitor the interference.
Calculate the handover caused by poor quality and check the
average receiving quality level for each TRX.
In call drop measurement function: check the average signal
strength and quality for each call drop.
Through drive test, check the interference and signal quality.
Use spectrum analyzer.
Dispose equipment fault (Such as: TRX self-oscillation, antenna
inter-modulation).
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Traffic Statistics Analysis-TCH Call Drop
Coverage problem analysis
Traffic items
In power control measurement function: the average uplink and
downlink signal strengths are too low.
In receiving level measurement function: a lot of low signal strength
records are found.
In inter cell handover measurement function: the average receiving
signal strength are too low when handover is triggered.
In call drop measurement: the signal strength is too low when calldrop happens, or the TA volume is abnormal.
In undefined adjacent cell measurement function: the neighbor cells
with high average signal strength can be find.
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Traffic Statistics Analysis-TCH Call Drop
Coverage problem analysis
Judgment method
In Power Control measurement: check whether the average
distance between MS and BTS comply with design.
In power control measurement function: check whether the
maximum distance between MS and BTS have abnormal value in
several continuous periods.
In outgoing inter cell handover measurement function: check
whether the handover successful rate to some cells is low.
In outgoing inter cell handover measurement function: check the
number of unsuccessful handover with unsuccessful reversion (call
drop caused by handover).
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Traffic Statistics Analysis-TCH Call Drop
Coverage problem analysis
Disposing method
Drive test in the expected poor coverage area.
Adjust the following parameters based on the drive test results: BTS
transmitting power, antenna downtilt and height,
RXLEVEL_ACCESS_MIN.
Add site to guarantee the continuous coverage.
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Traffic Statistics Analysis-TCH Call Drop
Improper handover (neighbor planning and handover
parameters
Disposing method
Check the handover parameters to see whether there are improper
parameter settings.
In Inter cell handover measurement function: check whether there
are many unsuccessful outgoing cell handover with unsuccessful
reversion.
In undefined adjacent cell measurement function: check whetherthe signal strength and the number of measurement reports for the
undefined neighbor cell is high.
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Traffic Statistics Analysis-TCH Call Drop
Unbalanced up-down link (tower amplifier, power amplifier,
and antenna directions)
Disposing method
Analyze up-down link balance measurement function statistics
result and confirm whether the uplink and downlink are unbalanced.
In call drop measurement function: analyze the average receiving
signal strength and quality for both the uplink and downlink.
In power control measurement function: analyze the average
receiving signal strength for both the uplink and downlink.
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Balance between uplink and downlink
All the measurement reports for certain TRX are sorted into
different level, it reflects the traffic volume of the TRX.
When sort the result, modifications are made according to power
control, receiving sensitivity of MS and BTS.
Traffic Statistics Analysis-TCH Call Drop
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Balance between uplink and downlink
All the measurement reports for certain TRX are sorted into
different level, it reflects the traffic volume of the TRX.
When sort the result, modifications are made according to power
control, receiving sensitivity of MS and BTS.
Traffic Statistics Analysis-TCH Call Drop
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Traffic Statistics Analysis-TCH Call Drop
Improper radio parameter setting (Radio Link timeout, SACCH
multi-frames)
Judgment method
In system information table: check the radio link timeout counter
In cell attribute table: check SACCH multi-frames, and the timer for
radio link connection.
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Traffic Statistics Analysis-TCH Call Drop
Equipment problem (TRX, power amplifier, tower amplifier, etc.)
Judgment method
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 method
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 doesnt work).
ffi S i i A i S CC C
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Traffic Statistics Analysis-SDCCH 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.
T ffi S i i A l i H d
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Low Handover Success Rate
Handover MeasurementFunction Alarm (Clock),Hardware FaultTCH Measurement Function
Outgoing Inter Cell FailureIncoming Inter 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)
T ffi S i i A l i H d
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Traffic Statistics Analysis-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)
T ffi St ti ti A l i H d
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Handover failure analysis
Disposing method
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 orparts of the neighbor cells).
Traffic Statistics Analysis-Handover
T ffi St ti ti A l i H d
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Traffic Statistics Analysis-Handover
Improper parameter settings
Disposing method
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 times
divide by call times 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.
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T ffi St ti ti A l i H d
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Traffic Statistics Analysis-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.
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T ffi St ti ti A l i H d
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Traffic Statistics Analysis-Handover
Congestion
Disposing process
Adjust the cells 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.
E ercise
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Exercise
The index radio handover success rate is the ratio of
successful handovers to handovers. The handovers is the
measured when sending or receiving HO_CMD or
HO_REQ_RSP in the handover process of handover. Please
write down the possible reason why the radio handover success
rate between BSC is low.
Exercise
Exercise
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Answer:
There are two kind of outgoing handovers. One is intraBSC
handover, the other is interBSC handover.
The possible reasons are list as following. For interBSC
handover:
1.If the uplink signal strength of the target cell is low, so MS
cant access the target cell. Thus the handover fails
2.If the target cell is a wrong cell that has same BCCH and BSIC
as the real target cell, MS will send access request to a wrong
cell. Then MS cant access. Thus the handover fails.
3.If the CGI is wrong, MSC will send the handover request with
wrong CGI. Then MS will send access request to a wrong cell. It
has the same effect as the above one.
Exercise
Traffic Statistics Analysis TCH Congestion
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Traffic Statistics Analysis-TCH Congestion
TCH congestion
Main causes
Insufficient system capacity
Interference
Coverage
Antenna and feeder problems
Improper parameter setting (system information parameters)
Traffic Statistics Analysis TCH Congestion
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Traffic Statistics Analysis-TCH Congestion
Insufficient system capacity or traffic unbalanced
Judgment method
The traffic is high and is unbalanced between cells.
There are many channel requests rejection due to channel busy.
Incoming Handover Measurement shows that there are too many
unsuccessful incoming cell handovers (congestion).
Disposing process
Expand or adjust the configurations between high and low traffic cell.
Adjust coverage (adjust BTS transmitting power, antenna direction,
downtilt, height, etc.).
Adjust parameters (CRO, minimum MS access signal level, enable load
handover, cell priorities, handover parameters).
Traffic Statistics Analysis TCH Congestion
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Traffic Statistics Analysis-TCH Congestion
Interference (external and internal interference)
Problem description
Interference brings unacceptable BER which will affects the
assignment process.
Downlink Interference makes MSs DSC decrease to 0, then MS
reselect to another cell with low signal strength, this is the other
potential reason for TCH seizure failure.
If TCH seizures (including handover) minus TCH seizures meet a
blocking state is large, then there maybe have some interference.
Disposing process
--Refer to TCH call drop caused by interference.
Traffic Statistics Analysis TCH Congestion
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Traffic Statistics Analysis-TCH Congestion
Antenna and feeder problem
Disposing process
Cell frequency scan: check the measurement results got from main
receiving antenna and diversity receiving antenna.
In Up-down link balance measurement function: check the
measurement report numbers in each rank.
Check antenna direction, downtilt and connection.
Traffic Statistics Analysis TCH Congestion
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Traffic Statistics Analysis-TCH Congestion
Improper parameter settings
Check the relevant parameters such as RXLEV_ACCESS_MIN,
CRO, BTS transmitting Power, handover threshold etc..
Traffic Statistics Analysis TCH Congestion
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Traffic Statistics Analysis-TCH Congestion
Coverage
-- Refer to coverage analysis for TCH call drop rate.
Traffic Statistics Analysis-SDCCH Congestion
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Traffic Statistics Analysis-SDCCH Congestion
SDCCH congestion
Main causes
Improper parameter settings (system information)
Insufficient system capacity
Improper LAC planning
Interference
Traffic Statistics Analysis-SDCCH Congestion
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Traffic Statistics Analysis-SDCCH Congestion
Improper parameter settings
Judgment method
Successful immediate assignments / immediate assignment
transmissions >85%.
The above formula shows the ratio between number of EST_IND
messages that MS sends to BSC and the immediate assignment
commands that BSC sends to BTS. It indicate whether theres
some improper parameters in the system information.
Disposing process
Adjust the access parameters (Random access error threshold,
RACH access threshold, Max. retrans, Tx-integer).
Adjust the Location Update related parameters (dual-band network
parameters such as CRO, cell reselection hysteresis, T3212).
Traffic Statistics Analysis-SDCCH Congestion
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Traffic Statistics Analysis-SDCCH Congestion
Insufficient system capacity
Problem description
Many location updates happen at the border of different
location areas.
Massive location updates happen suddenly.
Disposing method
Properly plan the location area
Configure more SDCCH
Use SDCCH dynamic allocation
Add more TRX
Traffic Statistics Analysis-SDCCH Congestion
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Traffic Statistics Analysis-SDCCH Congestion
Improper LAC planning
The border of different location area is the street.
The border of different location area is at the high
traffic area.
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Course Contents
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Brief introduction to BSC traffic statistics
Often-used traffic statistics items analysis
Locate problem through traffic analysis
Case study for traffic statistics
Case Study-One (Handover)
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y ( )
Fault description
Handover successful rate is always very low because of the
congestion (about 70%)
--Refer to busy hour traffic statistics on next page.
In the evening of 3th. Dec, site D located at urban is expanded
from S2/2/2 to S3/3/3. Busy hour handover successful rate
doesnt got improved after expansion. Sometimes handover
successful rate is lower than before, at the same time lots of
users complain the networks quality.
--Refer to busy hour traffic statistics of 3th. Dec.
Case Study-One (Handover)
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Traffic statistics for 24th.Nov
y ( )
handover radio handover Intra BSC Intra BSC TCH
success success incoming incoming congestion
rate rate handover failures handover failures
(no channel available ) (others)
D 1 53.41% 90.02% 397 18 47.53%
D 2 49.82% 93.98% 389 2 67.23%
D 3 57.67% 90.06% 314 51 48.31%
C 61.25% 91.67% 502 25 40.61%
A 2 78.40% 89.07% 0 33 0
A 3 77.14% 93.80% 0 20 0
F 2 76.36% 76.36% 0 12 0
E 1 66.22% 88.10% 26 63 5.33%
E 2 92.73% 94.44% 0 2 0
E 3 83.25% 91.91% 0 6 0
B 3 83.48% 95.53% 0 5 0.75%
Cell
Case Study-One (Handover)
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Traffic statistics for 13th.Dec
y
handover radio handover Intra BSC Intra BSC TCH
success success incoming incoming congestion
rate rate handover failures handover failures
(no channel available ) (others)
D 1 49.75% 52.95% 17 246 5.27%
D 2 56.48% 58.56% 1 161 0.58%
D 3 65.92% 66.08% 0 86 22.37%
C 3 60.58% 113 166 0.00%
A 2 70.55% 71.71% 0 0 1.06%
A 3 68.02% 68.95% 0 0 0.00%
F 2 60.61% 60.61% 0 13 0.56%
E 1 64.08% 1 55 0.00%
E 2 61.77% 62.69% 0 20 0.00%
E 3 0 0 0.00%
B 3 78.60% 82.45% 0 11 0.34%
Cell
66.3%
63%
50.3% 50.3%
Case Study-One (Handover)
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y
Site location
Case Study-One (Handover)
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Analyze
Analyze traffic statistics before expansion and after expansion,
we find handover failure caused by congestion. Radio handover
success rate is normal before expansion. In Urban area many
cells radio handover success rate decreased after expansion,
therefore we conclude that the cause of handover failure after
expansion has been changed.
Analyze urban sites location diagram, we find lots ofcells radio
handover successful rate are low and these cells have handover
relationship with site D. Therefore we think the handover
problem should cause by site D.
Case Study-One (Handover)
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Analyze
After we check hardware of site D through maintenance console,
we find the state of TMU board is abnormal and clock is
unstable. Finally we affirm the low handover success rate is
caused by the wrong setting of switches in TMU board. Of
course, the high call drop rate is caused by handover failure.
The day after processing , busy hour handover success rate is
higher than 90%. So the problem is solved.
--Refer to busy hour traffic statistics of 17th. Dec.
Case Study-One (Handover)
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Traffic statistics for 17th.Dec
handover radio handover Intra-BSC Intra-BSC TCH
success success incoming incoming congestion
rate rate handover failures handover failures
(no channel available ) (others)
D 1 86.58% 95.90% 47 10 13.00%
D 2 93.09% 96.88% 10 15 3.40%
D 3 95.57% 96.79% 0 10 0.00%
C 3 86.84% 95.94% 80 7 18.26%
A 2 88.43% 91.51% 1 21 0.48%
A 3 92.56% 94.12% 0 6 0.00%
F 2 98.47% 89.47% 0 1 0.00%
E 1 93.69% 95.59% 1 6 1.44%
E 2 93.55% 93.55% 0 2 0.00%
E 3 97.40% 97.45% 0 1 0.00%
B 3 91.80% 96.89% 10 1 7.92%
Cell
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Case Study-Two (Call drop)
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Fault description
When we analyze the traffic statistics, we find that one cells call
drop rate is very high, call drop rate in busy hour is large than 2%.
In cell call drop measurement function: we find that the average
uplink level of call drop is 1 (-109dBm), while the downlink level is
26 (-84dbm). High call drop rate is caused by unbalance between
uplink and downlink.
In up-down link balance measurement function: we find one TRX is
normal, but theres some problem for another TRX. Times of level 1
is 0, while times of level 11 is 5833, it means downlink is better
than uplink.
Case Study-Two (Call drop)
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Analyze
We exclude the problem of antenna and feeders problem
because only one TRX is abnormal. Therefore we think that the
problem maybe caused by the uplink channel of TRX and CDU.
After we change the CDU, the problem is solved.
Case Study-Two (Call drop)
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Conclusion and suggestion
To find the cause of call drop, we should register the following
useful traffic statistics:
1. TCH measurement function
2. Call drop measurement function
3. Inter cell handover measurement function
4. Up-down link balance measurement function
By analyzing the result of the above traffic statistics to locate the
cause of the call drop (handover, interference, coverage etc.)
and then register more detailed traffic measurement task.
DT also is a effective method to solve call drop problem.
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Case Study-three (SDCCH blocking)
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Analyze
RegisterSDCCH measurement function and analyze the result,
we find that most of the SDCCH seizure are used for location
update. After we analyze the site distribution, we find that the
congested BTS are located at the cross area of two location
area along railway. So we think that SDCCH congestion shall be
caused by massive location update.
Case Study-three (SDCCH blocking)
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Analyze
In SDCCH measurement function: we find that most of the
location update happened in the specific 5 minutes. After
querying the train timetable we find that 4 or 5 trains pass by in
this period. When the trains pass by, a large amount of location
updates happen suddenly.
After adding more fixed SDCCH and switching on Dynamic
SDCCH allocation function, the problem is solved.
Case Study-three (SDCCH blocking)
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Conclusion and suggestion
For SDCCH congestion, firstly, we should register SDCCH
measurement function, and analyze the traffic statistics to find
the cause of the problem (Location update, SDCCH handover,
call setup etc.).
Then check the parameter settings, interference, location area
planning etc., to do further analysis.
Add SDCCH channel or enable dynamic SDCCH allocation
function can solve the congestion caused by insufficient capacity.
Set the parameter and plan the location area properly to
decrease the SDCCH congestion.
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