78502629 traffic statistics analysis issue1 5

7/31/2019 78502629 Traffic Statistics Analysis ISSUE1 5

1/104

Wireless Curriculum Development Section

ISSUE

OMF000503

Traffic Statistics Analysis1.5


2/104

Brief introduction to BSC traffic statistics

Often-used traffic statistics items analysis

Locate problem through traffic analysis

Case study for traffic statistics

Course Contents


3/104

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


4/104

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


5/104

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.


6/104


Template management

Template management provides the function of Defining item

template, object template, time template, user-defined statistic

items and refreshing all templates.


7/104

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.



8/104

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%


9/104


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%


10/104


SDCCH Blocking Rate

SDCCH Blocking Rate = times of attempted seizures meeting

an SDCCH blocked state / attempted SDCCH seizures (all) *

100%


11/104


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%


12/104


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.


13/104


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%


14/104



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%


15/104

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


16/104


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


17/104


BTS Initial Measurement

Cell Broadcast Statistic

Outgoing Inter cell handover


Incoming Inter cell handover


Undefined Adjacent Cell


GPRS Related


Defined Adjacent Cell


Receiving Quality Measurement

Receiving Level MeasurementFunction

Up-Down Link Balance


LAPD Link Measurement

Function

Cell Frequency Scan


18/104

Course Contents


Regular traffic statistics items analysis




19/104

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


20/104

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.



21/104


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.


22/104


Circuit paging (A-interface) successful rate

Immediate assignment successful rate

TCH call drop rate

TCH and SDCCH blocking rate

Handover successful rate

Interference band


23/104



Relate to ATT , coverage area and random access

performance.

Relate to the paging re-send mechanism implemented by BSC

or MSC.


24/104




TCH call drop rate



Interference band


25/104



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.


26/104




TCH call drop rate



Interference band


27/104


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


28/104


TCH call drop formula and measurement point

TCH Call Drop Rate = TCH Call Drop / Successful TCH

Seizures (all) *100%


29/104


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%


30/104




TCH call drop rate



Interference band


31/104


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.


32/104


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


33/104


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%


34/104


SDCCH blocking rate

SDCCH Blocking Rate = times of attempted seizures meeting

an SDCCH blocked state / attempted SDCCH seizures (all)

*100%


35/104


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.


36/104




TCH call drop rate



Interference band


37/104


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.


38/104



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%


39/104


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.


40/104


Handover failure reasons

No available channel

Illegal frequency

Timer timeout

Illegal channel

Illegal TA

Other reasons


41/104




TCH call drop rate



Interference band


42/104


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.


43/104


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.


44/104


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


45/104

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


46/104

Course Contents






47/104

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


48/104

Traffic Statistics Analysis

Combine Traffic statistics analysis with other optimization

method

Drive Test: simulate common subscribers behavior.

Analyze objects

Coverage

Quality

Handover

Signaling

Others


49/104

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


50/104

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.



51/104

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..



52/104

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.



53/104

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



54/104


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.


55/104


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).


56/104


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).


57/104


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.


58/104



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).


59/104



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.


60/104


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.


61/104


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.


62/104

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.



63/104

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.



64/104


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.


65/104


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


66/104

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


67/104

Low Handover Success Rate

Handover MeasurementFunction Alarm (Clock),Hardware FaultTCH Measurement Function

Outgoing Inter Cell FailureIncoming Inter Cell

Failure

Outgoing Inter cell

Handover


Incoming Inter cell

Handover


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


68/104


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


69/104

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).




70/104


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.


71/104



72/104


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.


73/104



74/104


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


75/104

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


76/104

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


77/104

Traffic Statistics Analysis-TCH Congestion

TCH congestion

Main causes

Insufficient system capacity

Interference

Coverage

Antenna and feeder problems

Improper parameter setting (system information parameters)



78/104


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).



79/104


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.



80/104


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.



81/104



Check the relevant parameters such as RXLEV_ACCESS_MIN,

CRO, BTS transmitting Power, handover threshold etc..



82/104


Coverage

-- Refer to coverage analysis for TCH call drop rate.

Traffic Statistics Analysis-SDCCH Congestion


83/104


SDCCH congestion

Main causes

Improper parameter settings (system information)


Improper LAC planning

Interference



84/104



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).



85/104



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



86/104


Improper LAC planning

The border of different location area is the street.

The border of different location area is at the high

traffic area.


87/104

Course Contents


88/104





Case Study-One (Handover)


89/104

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.



90/104

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



91/104

Traffic statistics for 13th.Dec

y

handover radio handover Intra BSC Intra BSC TCH




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%



92/104

y

Site location



93/104

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.



94/104

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.



95/104

Traffic statistics for 17th.Dec

handover radio handover Intra-BSC Intra-BSC TCH




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


96/104

Case Study-Two (Call drop)


97/104

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.



98/104

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.



99/104

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.


100/104

Case Study-three (SDCCH blocking)


101/104

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.



102/104

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.



103/104

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.


104/104

78502629 traffic statistics analysis issue1 5

Documents