og 205 traffic statistics analysis issue2.0

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Traffic Statistics Analysis

Issue 2.0


Reference

31160978-BSC Traffic Statistic

Manual Volume I

31033203-BSS Troubleshooting

Manual


Upon completion of this course, you will be

able to:

Know the traffic statistics system

structure

Understand some often-used traffic

measurement items

Locate some problems through the

traffic statistics system


Chapter 1 Chapter 1 Brief introduction to BSC traffic statiBrief introduction to BSC traffic statisticsstics

Chapter 2 Chapter 2 Often-used traffic statistics items anaOften-used traffic statistics items analysislysis

Chapter 3 Chapter 3 Locate problem through traffic analyLocate problem through traffic analysissis

Chapter 4 Chapter 4 Case study for traffic statisticsCase study for traffic statistics


BM1

Call process data

BM data

Hardware data

Signaling data

BM

AM/CM

BAM

¡ ¡ WS1 WSn

M2000 ServerHUB

Main Structure of Traffic Statistics System


Menu Introduction to BSC Traffic Statistics

Task list management

BSC traffic statistics platform provides the function of

registering a new task, deleting a registered task and

refreshing the task list.

Task management

BSC traffic statistics platform provides 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.



Template management

Template management provides the function of defining

item template, object template, time template, user-defined

statistic items and refreshing all templates.



Limitations

The traffic measurement task is registered using the BSC

traffic statistics console, the maximum number of tasks of

each BM module is 200.

The maximum number of subtasks in each BM module is

3000.

One task can only include 60 original items.

Items regarding to maximum/minimum value can not be

repeatedly registered in all tasks.


Brief Introduction to BSC Traffic Statistics Item

TCH Congestion Rate

TCH Congestion 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%



TCH Congestion Rate

TCH congestion rate (including handover)= (TCH seizure fa

ilures for call + TCH seizure failures for very early assignme

nt + TCH seizure failures for intra BSC incoming cell hando

ver (no radio resource) + TCH seizure failures for inter BSC

incoming cell handover (no radio resource) ) / (attempted T

CH seizures (all) + attempted TCH seizures for very early a

ssignment + attempted TCH seizures for intraBSC incoming

cell handover + attempted TCH seizures for interBSC incom

ing cell handover) * 100%



TCH Congestion Rate

TCH congestion rate (TCH overflow) = Attempted TCH seizures

meeting a TCH blocked state / Attempted TCH seizures (all) *

100%



SDCCH congestion rate (SDCCH overflow)

SDCCH congestion rate (SDCCH overflow)= times of attempted

seizures meeting an SDCCH blocked state / attempted SDCCH

seizures (all) * 100%



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%



Handover Success Rate

Inter cell handover success rate= (Successful incoming internal i

nter cell handovers + Successful incoming interBSC inter cell ha

ndovers + Successful outgoing internal inter cell handovers + Su

ccessful outgoing interBSC inter cell handovers) / (Attempted in

coming internal inter cell handovers+ Attempted incoming interB

SC inter cell handovers + Attempted outgoing internal inter cell h

andovers + Attempted outgoing interBSC inter cell handovers) *

100%




Inter cell radio handover success rate= (Successful incomin

g internal inter cell handovers + Successful incoming interB

SC inter cell handovers + Successful outgoing internal inter

cell handovers + Successful outgoing interBSC inter cell ha

ndovers) / (Incoming internal inter cell handovers + Inter BS

C incoming cell handovers + Outgoing internal inter cell han

dovers + Inter BSC outgoing cell handovers) * 100%


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.



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



Defined Adjacent Cell


Receiving Quality

Measurement

Receiving Level Measurement

Function

Up-Down Link Balance


LAPD Link Measurement

Function

Cell Frequency Scan

BTS Initial Measurement

Cell Broadcast Statistic

Outgoing Inter cell handover


Incoming Inter cell handover


Undefined Adjacent Cell


GPRS Related Measurement

Function


Often-used Traffic Statistics Items Analysis

Systematical logic

From whole system to specific cell

Integrality

Observe the change trend of the items for more than one

week and the changing trend of each day.

Relativity

Relationship between various kinds of traffic statistics items



Analysis process

First we shall analyze and compare the item of BSC

measurement function to have a rough idea for the whole

network.

During analyzing, if any important items (such as call drop

rate or handover success rate) are abnormal, we shall do

further detailed analysis for the corresponding items.



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 some

further analysis should be considered or

not.



Circuit paging (A-interface) successful rate

Immediate assignment successful rate

TCH call drop rate

TCH and SDCCH congestion rate

Handover success rate

Interference band



Circuit paging (A-interface) success rate

Relate to “ATT ”, coverage area and random access

performance.

Relate to the paging re-send mechanism implemented by

BSS or MSC.



Immediate assignment success rate

When BTS receives a Random Access message from MS,

BTS will apply a 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, MS’s access will be bared

for some time.

The interference and collision of random access will affect

immediate assignment successful rate.



TCH call drop rate

Possible causes can be

− TCH lost radio connections (Connection failure).

− TCH lost radio connections (Error indication).

− Ground link disconnection when TCH seized (Abis).

− Call drop during handover



TCH call drop formula and measurement point

TCH Call Drop Rate = TCH Call Drop / Successful TCH

Seizures (all) *100%



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%



TCH congestion rate (TCH overflow)

It is a key item used to estimate the cell load.

When the load of the cell overruns the system limitation, try

to distribute some traffic to adjacent cells.



Causes of TCH congestion ( 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



TCH Congestion Rate

TCH congestion rate (including handover)= (TCH seizure fa

ilures for call + TCH seizure failures for very early assignme

nt + TCH seizure failures for intra BSC incoming cell hando

ver (no radio resource) + TCH seizure failures for inter BSC

incoming cell handover (no radio resource) ) / (attempted T

CH seizures (all) + attempted TCH seizures for very early a

ssignment + attempted TCH seizures for intraBSC incoming

cell handover + attempted TCH seizures for interBSC incom

ing cell handover) * 100%



SDCCH congestion rate (SDCCH overflow)

SDCCH congestion rate (SDCCH overflow)= times of

attempted seizures meeting an SDCCH blocked state /

attempted SDCCH seizures (all) * 100%



SDCCH congestion measurement point

Attempted SDCCH seizure meeting a SDCCH blocked stat

e is counted when there is a SDCCH seizure but no SDCC

H available.

Attempted SDCCH seizures (all)

Receive CH_REQ and the channel type is SDCCH.

Incoming interBSC inter cell handover and the handover typ

e is SDCCH handover.

Incoming intraBSC inter cell and intra-cell handover and the

handover type is SDCCH handover.



Handover measurement point

For different objects such as BSC, band (900/1800),

incoming/outgoing, inter-cell/intra-cell handover and so on,

there are different items.

By analyzing different items, the problems can be located

more rapidly.




Inter cell handover success rate= (Successful incoming inte

rnal inter cell handovers + Successful incoming interBSC int

er cell handovers + Successful outgoing internal inter cell h

andovers + Successful outgoing interBSC inter cell handov

ers) / (Attempted incoming internal inter cell handovers+ Att

empted incoming interBSC inter cell handovers + Attempted

outgoing internal inter cell handovers + Attempted outgoing

interBSC inter cell handovers) *100%



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 with all adjacent cells are

listed in outgoing and incoming inter cell handover

measurement function.



Handover failure reasons

No available channel

Illegal frequency

Timer timeout

Illegal channel

Illegal TA

Other reasons



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.



Cell frequency scan

Shows the signal strength received by main antenna and

diversity antenna.

Reflects the interference level for specific frequency.

The difference between the measurement results of main

and diversity antenna reflects the difference between the

two antennas such as direction, gain, path loss and so on. It

is an important way to know the diversity receiving

performance.



Receiving level measurement

Receiving level measurement is based on TRX.

The receiving level is divided 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


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.


BSC Measurement Function

High call drop rate High congestion rate Low handover success rate

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Call d

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SD

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Alarm

data

Alarm

data

TC

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and

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Alarm

data


General method for traffic analysis



Combine traffic statistics analysis with other optimization

method

Drive test: simulate common subscriber’s behavior.

Analyze objects

Coverage

Quality

Handover

Signaling

Others


Traffic Statistics Analysis-TCH Call Drop

TCH call drop analysis

Cell with high call drop rate

Cell performance statistics

Call drop times

Interference band

Causes of call drop

Call drop measurement

Average uplink level at TCH call drops

Average down link level atTCH call drop

Average downlink quality at TCH call drop

Handovermeasurement

Outgoing inter cell handover success rate

Incoming inter cell handover success rate

Handover failure and re-establish

failure

Alarm and hardware fault

Average TA value atTCH call drop

Average uplink quality atTCH 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.

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.



Edge call drop

Causes

− MS is out of cell’s 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..



Short distance call drop

Causes

− Poor coverage caused by complicated terrain or high de

nse building.

Solutions

− Increase EIRP.

− Adjust antenna direction and downtilt, make the main lo

be point to high traffic area.

− Adjust parameters related to 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 source.

− Optimize frequency planning.

− Adjust antenna system, avoid “island”.

− Solve the problem of transmission quality.



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.

Analyze the call drop measurement function.

Check the interference band.

First of all, we shall know the type of the 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).



Interference analysis process

Analyze the appearance period of the interference.

Block TRX in turn and monitor the interference

measurement results.

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 of call drops.

Through drive test, check the interference and signal

quality.

Use spectrum analyzer to find the interference source.

Dispose equipment fault (such as: TRX self-oscillation,

antenna inter-modulation).



Coverage problem analysis

Traffic items

− In power control measurement function, the average uplink or

downlink signal strength is too low.

− In receiving level measurement function, a lot of low signal

strength records can be found.

− In inter-cell handover measurement function, the average

receiving signal strength is too low when handover is triggered.

− In call drop measurement, the signal strength is too low when call

drop happens, or the TA value is abnormal.

− In undefined adjacent cell measurement function, the potential

neighbor cells with high average signal strength can be find.


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.

▪ Check whether the maximum distance between MS and

BTS is abnormal in several continuous periods.

− In outgoing inter-cell handover measurement function

▪ check whether the handover successful rate to some cells

is low.

▪ check the number of unsuccessful handover with

unsuccessful reversion (call drop caused by handover).



Coverage problem analysis

Disposing method

− Drive test in the suspected poor coverage area.

− Adjust the following parameters based on the drive test r

esults

▪ BTS transmitting power

▪ Antenna downtilt and height

▪ RXLEVEL_ACCESS_MIN

− Add site to ensure the continuous coverage.



Improper handover (neighbor planning and handover paramet

ers） Disposing method

− Check the handover parameters to see whether there ar

e improper parameter settings.

− In inter-cell handover measurement function, check whe

ther there are many unsuccessful outgoing cell handove

rs with unsuccessful reversions.

− In undefined adjacent cell measurement function, check

whether the signal strength and the number of measure

ment reports for the undefined neighbor cell are high.



Imbalanced 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 balanced.

− 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.



Balance between uplink and downlink

Let D= (downlink receiving level − uplink receiving level) − (MS sensitivity − BTS sensitivity).

Usually the MS sensitivity is -102 dBm and the BTS sensitivity is -108dBm. The formula can be simplified as

− D= downlink receiving level − uplink receiving level – 6dB

If D=0, it means uplink and downlink are balanced

If D>0, it means downlink is better than uplink

If D<0, it means uplink is better than downlink

Link balance rank Range of D

1 ≤ -15

2 -14 ~ -10

3 -9 ~ -6

4 -5 ~ -3

5 -2 ~ 0

6 0

7 1 ~ 2

8 3 ~ 5

9 6 ~ 9

10 10 ~ 14

11 ≥15



Improper radio parameter setting (Radio Link timeout, SACCH

multi-frames)

Judgment method

− In system information data, check the radio link timeout

− In cell property data, check SACCH multi-frames, and

the timer for radio link connection (T3105).



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, there are many call drops due to ground links.

− In TCH measurement function, there are many TCH seizure failures due to equipment failure.

Disposing method

− Monitor transmission and board alarms (FTC board failure, A interface PCM synchronization alarm, LAPD link disconnected, TRX alarm); analyze whether transmission is disconnected or some boards are faulty.


Traffic Statistics Analysis-SDCCH Call Drop

SDCCH call dropSDCCH call drop

Refer to TCH call drop analysis.

The cause and mechanism of SDCCH call drop are almost the same as TCH.


Low Handover Success Rate

Handover Measurement Function

Alarm (Clock),Hardware Fault TCH Measurement Function

Outgoing Inter Cell Failure Incoming 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



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 method

− Find out the cells with low handover success 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 part of the neighbor cells).



Improper parameter settings

Disposing method

− Check whether the handover threshold such as TA, BQ and hand

over function switch are suitable or not.

− Check whether the successful TCH seizures for handover are mu

ch more than successful TCH seizures for call. If handover times

divided by call times is larger than 3, then it indicates that there m

ay be ping-pong handover. Check the parameter settings and adj

ust them (layer setting, layer handover hysteresis, inter cell hando

ver hysteresis, PBGT threshold, etc.).

− Check whether the average signal strength is low when the hando

ver happens. If so, it indicates the edge handover threshold is too

low.



Hardware fault

Problem description

− The target cell has idle channels but when applying for the

channels CH_ACT_NACK or TIMEOUT message appears.

− TCH availability is abnormal.

− If the call drop rate and congestion rate are both high, the

equipment may have some fault.



Hardware fault

Disposing process

− Monitor transmission and board alarms (FTC board failure, A

interface PCM sync alarm, LAPD link disconnected, TRX

alarm).

− Analyze whether the transmission is disconnected or the

boards have some fault (for example: the TRX is damaged).

− Check whether there is clock alarm.



Congestion

Objects needed to be analyzed

− Cells with low incoming handover success rate.

− Neighbor of the cell with low incoming handover success rate.

Locating the problem

− In incoming inter cell handover measurement function, check

whether many handover failures are caused by congestion.

− For low incoming handover success rate, check the cell’s traffic .

− For low outgoing handover success rate, check the neighbor

cell’s traffic.



Congestion

Disposing process

− Adjust the cell’s coverage (adjust BTS transmitting powe

r, RXLEVEL_ACCESS_MIN, RACH access threshold, a

nd the antenna downtilt and height).

− Adjust parameters (CRO, load handover parameters, cel

l priority and handover parameters).

− Expand or adjust TRX configuration between high and lo

w traffic cells.


Question

The item “radio handover success rate” is the ratio of successful han

dovers to handovers. The handovers are counted when sending or r

eceiving HO_CMD or HO_REQ_RSP in the handover process. Plea

se write down the possible reasons that can cause the low radio han

dover success rate between BSCs.


Answer

There are two kinds of outgoing handovers. One is intra-BSC

handover, and the other is inter-BSC handover.

The possible reasons are list as following. For inter-BSC handover:

If the uplink signal strength of the target cell is low, the MS cannot

access the target cell. Thus the handover fails

If the target cell is a wrong cell which has the same BCCH and

BSIC as the expected target cell, MS will send access request to a

wrong cell. Then MS cannot access. Thus the handover fails.

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.


Traffic Statistics Analysis-TCH Congestion

TCH congestion

Main causes

− Insufficient system capacity

− Interference

− Coverage

− Antenna and feeder problems

− Improper parameter setting (system information paramet

ers)



Insufficient system capacity or traffic imbalanced

Judgment method

− The traffic is high and is imbalanced between cells.

− There are many channel request rejections due to channel busy.

− Incoming handover measurement shows that there are too many unsucces

sful incoming cell handovers (congestion).

Disposing process

− Expand or adjust the configuration between high and low traffic cells

− Adjust coverage (adjust BTS transmitting power, antenna direction, downt

ilt, height, etc.).

− Adjust parameters (CRO, Rx_Lev_Access_Min, load handover parameters,

cell priorities, handover parameters).



Interference (external and internal interference)

Problem description

− Interference brings unacceptable BER which affects the

assignment process.

− Downlink Interference makes MS’s DSC decrease to 0, then

MS reselects to another cell with low signal strength, and this is

a potential reason for TCH seizure failure.

− If TCH seizure failures (including handover) minus attempted

TCH seizures meeting TCH overflow is large, then there may

be some interference.

Disposing process

− Refer to TCH call drop caused by interference.



Antenna and feeder problem

Disposing process

− In cell frequency scan measurement function, check the

measurement results got from main receiving antenna a

nd diversity receiving antenna.

− In Up-down link balance measurement function, check t

he measurement report numbers in each rank.

− Check antenna direction, downtilt and connection.




Check the relevant parameters such as

RXLEV_ACCESS_MIN, CRO, BTS transmitting power,

handover threshold etc..



Coverage

Refer to coverage analysis for TCH call drop rate.


Traffic Statistics Analysis-SDCCH Congestion

SDCCH congestion

Main causes

− Improper parameter settings (system information)

− Insufficient system capacity

− Improper LAC planning

− Interference




Judgment method

− Successful immediate assignments / immediate assignment transmissio

ns >85%.

− The above formula shows the ratio between number of EST_IND mess

ages that MS sends to BSC and the immediate assignment commands

that BSC sends to BTS. It indicate whether there are some improper par

ameters in the system information.

Disposing process

− Adjust the access parameters (Random access error threshold, RACH

minimum access level, MS Max Retrans, Tx-integer).

− Adjust the location update related parameters (dual-band network param

eters such as CRO, cell reselection hysteresis, T3212).



Insufficient system capacity

Problem description

− Many location updates happen at the border of different locati

on areas.

− Massive location updates happen simultaneously.

Disposing method

− Properly plan the location area

− Configure more SDCCHs

− Use SDCCH dynamic allocation

− Add more TRX



Improper LAC planning

The border of different location area is the street.

The border of different location area is at the high traffic

area.



Interference

Problem description

− RACH minimum access level is low.

− Interference in the system, which will bring a lot of illusory

SDCCH channel requests.

Disposing process

− Properly set the RACH minimum access level

− Eliminate the interference


Case Study-One (Handover)

Problem description

Handover success rate is always very low because of the

congestion (about 70%)

In the evening of 3rd. Dec, site D located in urban is

expanded from “S2/2/2” to “S3/3/3”. The busy hour

handover success rate does not get improved after

expansion. Sometimes handover success rate is lower than

before. At the same time, lots of subscribers complain about

the network quality.

Refer to busy hour traffic statistics of 3rd. Dec.



CellHandover

success rateRadio handover

success rate

Intra-BSCincoming handover

failures(no channel available)

Intra-BSCincoming handover failures(others)

TCHcongestion

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_3 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%

Traffic statistics for 24th.Nov



CellHandover

success rate

Radio handover

success rate

Intra-BSC

incoming handover failures

(no channel available)

Intra-BSC

incoming handover failures

(others)

TCH

congestion

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% 66.3% 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 63% 64.08% 1 55 0.00%

E_2 61.77% 62.69% 0 20 0.00%

E_3 50.3% 50.3% 0 0 0.00%

B_3 78.60% 82.45% 0 11 0.34%

Traffic statistics for 13th.Dec



Site location



Analysis

Analyzing the traffic statistics before expansion and after

expansion, we find that before the expansion the handover

failure is caused by congestion and the radio handover

success rate is normal. 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.

Analyzing the urban site location diagram, we find lots of cells’

radio handover success rate are low and these cells have

handover relationship with site D. Therefore we can suspect

that the handover problem may be caused by site D.



Analysis

After checking the 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. For sure, the high call drop rate is caused by

handover failures.

The day after processing, the busy hour handover success

rate is higher than 90%. Thus the problem is solved.

Refer to busy hour traffic statistics of 17th. Dec.



CellHandover

success rateRadio handover

success rate

Intra-BSCincoming handover

failures(no channel available)

Intra-BSCincoming handover failures(others)

TCHcongestion

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%

Traffic statistics for 17th.Dec



Conclusion and suggestion

Pay attention to the difference between radio handover

success rate and handover success rate because it can

help us to locate handover problem efficiently.

Handover problem sometimes is accompanied with call

drops and others; it is an important clew for locating and

solving problems.


Case Study-Two (Call drop)

Fault description

When we analyze the traffic statistics, we find that a cell’s

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 imbalance between uplink and downlink.

In up-down link balance measurement function: we find one

TRX is normal, but there may be some problem with the

other one. Result of rank 1 is 0, while that of rank 11 is

5833. It means the downlink is better than uplink.



Analysis

We can exclude the problem of antenna and feeder becaus

e only one of the two TRXs is abnormal. Therefore we think

that the problem may be caused by the uplink channel of T

RX or CDU.

After we change the CDU, the problem is solved.




To find the cause of call drop, we should register the following useful traffic statistics:

− TCH measurement function

− Call drop measurement function

− Inter cell handover measurement function

− Up-down link balance measurement function

By analyzing the result of the above traffic statistics, we can locate the cause of the call drop (handover, interference, coverage etc.) and then register more detailed traffic measurement tasks.

DT also is a effective method to find call drop problem.


Case Study-three (SDCCH congestion)

Fault description

In the network, the radio link connection success rate is low.

After analyzing the traffic statistics, we find that it caused by

SDCCH congestion and the congestion only exists in a few

sites.

Analyzing traffic statistics we find that in the congested cell,

attempted SDCCH seizures are from 300 to 400 in a certai

n hour. The configuration of all the related BTSs is S1/1/1.

Each cell has one SDCCH/8 channel. Normally, it can deal

with 300-400 SDCCH seizures. But it is very strange that th

ere are dozens of SDCCH congestions in busy hour.


Case Study-three (SDCCH congestion)

Analysis

Register “SDCCH measurement function” and analyze the result. We find that most of the SDCCH seizures are used for location update. After we analyze the site distribution, we find that the congested BTSs are located at the border of two location areas along the railway. So we can conclude that SDCCH congestion shall be caused by massive location updates.

In SDCCH measurement function, we find that most of the location update happened in a specific 5 minutes. After checking the train timetable, we find that 4 or 5 trains passed by in this period. When the trains pass by, a large amount of location updates happen simultaneously.

After adding more fixed SDCCHs and switching on “Dynamic SDCCH allocation” function, the problem is solved.


Case Study-three (SDCCH blocking)


For SDCCH congestion, firstly we should register SDCCH

measurement function, and then 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.

Adding SDCCH channels or enabling 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.


Summary

Traffic statistics system basics

Key traffic measurement items

Traffic statistics analysis method

Some cases

SummarySummary

www.huawei.com

Thank You

og 205 traffic statistics analysis issue2.0

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