06 g-lii 304 traffic statistics analysis-20071205-a-2.0

8/12/2019 06 G-LII 304 Traffic Statistics Analysis-20071205-A-2.0

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HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

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Traffic Statistics Analysis

Issue 2.0


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HUAWEI TECHNOLOGIES CO., LTD. Page 2All rights reserved

Reference

31160978-BSC Traffic Statistic

Manual Volume I

31033203-BSS Troubleshooting

Manual


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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 thetraffic statistics system


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Chapter 1Chapter 1 Brief introduction to BSC trafficBrief introduction to BSC traffic

statisticsstatistics

Chapter 2Chapter 2 Locate problem through trafficLocate problem through traffic

analysisanalysis

Chapter 3Chapter 3 Case study for traffic statisticsCase study for traffic statistics


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Brief Introduction to BSC Traffic Statistics Item

TCH Congestion Rate

TCH congestion rate (TCH overflow) = Attempted TCHseizures meeting a TCH blocked state / Attempted TCH

seizures (all) * 100%


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SDCCH congestion rate (SDCCH overflow)

SDCCH congestion rate (SDCCH overflow)= times of attemptedseizures meeting an SDCCH blocked state / attempted SDCCH

seizures (all) * 100%


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TCH Call Drop Rate

TCH Call Drop Rate = TCH Call Drops / Successful TCHSeizures (all) *100%

SDCCH Call Drop Rate

SDCCH Call Drop Rate = SDCCH call drops / successful

SDCCH seizures (all) *100%


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Handover Success Rate

Inter cell handover success rate= (Successful incoming internalinter 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 incominginterBSC inter cell handovers + Attempted outgoing internal

inter cell handovers + Attempted outgoing interBSC inter cell

handovers) *100%


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Handover Success Rate

Inter cell radio handover success rate= (Successfulincoming 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 cellhandovers + Inter BSC incoming cell handovers + Outgoing

internal inter cell handovers + Inter BSC outgoing cell

handovers) * 100%


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TCH interference band measurement

The result in each TCH interference band shows theaverage 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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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


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Chapter 1Chapter 1 Brief introduction to BSC trafficBrief introduction to BSC trafficstatisticsstatistics

Chapter 2Chapter 2 Locate problem through trafficLocate problem through traffic

analysisanalysis



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BSC Measurement Function

High call drop rate High congestion rate Low handover success rate

TCH

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Alarm

data

Alarm

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TCH

perform

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TCH

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Incomin

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Link

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Alarm

data


General method for traffic analysis


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Combine traffic statistics analysis with other optimization

methodDrive test: simulate common subscribers behavior.

Analyze objects

Coverage

Quality

Handover

Signaling

Others


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Traffic Statistics Analysis-TCH Call Drop

TCH call drop analysis

Cell with high call drop rate

Cell performancestatistics

Call drop times

Interferenceband

Causes of

call drop

Call drop measurement

Average uplink level at

TCH call drops

Average down link level atTCH call drop

Average downlink qualityat TCH call drop

Handovermeasurement

Outgoing inter cellhandover success rate

Incoming inter cell

handover success rate

Handoverfailure and re-establish

failure

Alarm and

hardware fault

Average TA value at

TCH call drop

Average uplink quality at

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.


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Edge call drop

Causes

MS is out of cells effective coverage area.

Island phenomenon caused by over shooting or missingneighbor.

Isolated site.

Solutions

Add new site to guarantee the effective continuous coverage.

Add the necessary neighbor.

Adjust antenna height and antenna downtilt, use high gainantenna

Modify some parameters: SACCH multi-frames, Radio linktimeout counter, handover threshold, handover statistic time,etc..


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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.

Adjust parameters related to 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 quality.


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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.


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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).


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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.


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Coverage problem analysis

Disposing method

Drive test in the suspected 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 ensure the continuous coverage.


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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

handovers with unsuccessful reversions.

In undefined adjacent cell measurement function, check

whether the signal strength and the number of

measurement reports for the undefined neighbor cell are

high.


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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.


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Balance between uplink and downlink

Let D= (downlink receiving level

uplink receiving level) (MSsensitivity 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 anddownlink are balanced

If D>0, it means downlink is betterthan uplink

If D


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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).


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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, Ainterface PCM synchronization alarm, LAPD link disconnected,

TRX alarm); analyze whether transmission is disconnected or some

boards are faulty.


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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.


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Low Handover Success Rate

Handover Measurement

FunctionAlarm (Clock),Hardware Fault TCH Measurement Function

Outgoing Inter Cell FailureIncoming Inter Cell

Failure

Outgoing Inter cellHandoverMeasurement Function

Incoming Inter cellHandover

Measurement Function

Cause of Failure in BSC

1.Illegal Channels2.Illegal Carrier

3.Illegal TA4.Timer out5.No available channel

6.Others

Traffic Statistics Analysis-Handover

Handover analysis


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Handover failure analysis

Causes of handover failure

Improper handover parameters.

Hardware fault (TRX board fault).

Congestion Interference

Coverage

Clock fault (Internal clock, external clock)


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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 andoutgoing 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).


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Improper parameter settings

Disposing method

Check whether the handover 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 handovertimes divided by call times is larger than 3, then it indicates that

there may be ping-pong handover. Check the parameter settings

and adjust them (layer setting, layer handover hysteresis, inter

cell handover hysteresis, PBGT threshold, etc.).

Check whether the average signal strength is low when the

handover happens. If so, it indicates the edge handover threshold

is too low.


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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.


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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.


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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 cells traffic .

For low outgoing handover success rate, check the neighbor

cells traffic.


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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 cells.


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Question

The item radio handover success rate is the ratio of successful

handovers to handovers. The handovers are counted when sending

or receiving HO_CMD or HO_REQ_RSP in the handover process.Please write down the possible reasons that can cause the low radio

handover success rate between BSCs.


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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)


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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

unsuccessful 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,

downtilt, height, etc.).

Adjust parameters (CRO, Rx_Lev_Access_Min, load handover parameters,

cell priorities, handover parameters).


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Interference (external and internal interference)

Problem description

Interference brings unacceptable BER which affects the

assignment process.

Downlink Interference makes MSs DSC decrease to 0, then

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


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Antenna and feeder problem

Disposing process In cell frequency scan measurement function, 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.


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Check the relevant parameters such asRXLEV_ACCESS_MIN, CRO, BTS transmitting power,

handover threshold etc..


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Coverage

Refer to coverage analysis for TCH call drop rate.


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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


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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 there are some

improper parameters 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

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


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Insufficient system capacity

Problem description

Many location updates happen at the border of different

location areas.

Massive location updates happen simultaneously.

Disposing method

Properly plan the location area

Configure more SDCCHs

Use SDCCH dynamic allocation

Add more TRX


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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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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


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Chapter 1Chapter 1 Brief introduction to BSC trafficBrief introduction to BSC trafficstatisticsstatistics

Chapter2Chapter2 Locate problem through trafficLocate problem through traffic

analysisanalysis



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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 afterexpansion. 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.


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0.75%5095.53%83.48%B_3

06091.91%83.25%E_3

02094.44%92.73%E_25.33%632688.10%66.22%E_1

012076.36%76.36%F_2

020093.80%77.14%A_3

033089.07%78.40%A_240.61%2550291.67%61.25%C_3

48.31%5131490.06%57.67%D_3

67.23%238993.98%49.82%D_2

47.53%1839790.02%53.41%D_1

TCH

congestion

Intra-BSC

incominghandoverfailures

(others)

Intra-BSC

incoming handoverfailures

(no channel available)

Radio handover

success rate

Handover

success rateCell

Traffic statistics for 24th.Nov


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0.34%11082.45%78.60%B_3

0.00%0050.3%50.3%E_3

0.00%20062.69%61.77%E_20.00%55164.08%63%E_1

0.56%13060.61%60.61%F_2

0.00%0068.95%68.02%A_3

1.06%0071.71%70.55%A_20.00%16611366.3%60.58%C_3

22.37%86066.08%65.92%D_3

0.58%161158.56%56.48%D_2

5.27%2461752.95%49.75%D_1

TCH

congestion

Intra-BSC

incominghandoverfailures

(others)

Intra-BSC

incoming handoverfailures

(no channel available)

Radio handover

success rate

Handover

success rateCell

Traffic statistics for 13th.Dec


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Site location


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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.


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7.92%11096.89%91.80%B_3

0.00%1097.45%97.40%E_3

0.00%2093.55%93.55%E_2

1.44%6195.59%93.69%E_1

0.00%1089.47%98.47%F_2

0.00%6094.12%92.56%A_3

0.48%21191.51%88.43%A_2

18.26%78095.94%86.84%C_3

0.00%10096.79%95.57%D_3

3.40%151096.88%93.09%D_2

13.00%104795.90%86.58%D_1

TCHcongestion

Intra-BSCincominghandoverfailures

(others)

Intra-BSCincoming handover

failures(no channel available)

Radio handoversuccess rate

Handoversuccess rate

Cell

Traffic statistics for 17th.Dec


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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 andsolving problems.


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Case Study-Two (Call drop)

Fault description

When we analyze the traffic statistics, we find that a cells

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 causedby 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 is5833. It means the downlink is better than uplink.


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Analysis

We can exclude the problem of antenna and feeder

because only one of the two TRXs is abnormal. Therefore

we think that the problem may be caused by the uplink

channel of TRX or CDU.

After we change the CDU, the problem is solved.


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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 trafficmeasurement tasks.

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


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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

certain 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 there are dozens of SDCCH congestions in

busy hour.


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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, locationarea 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.


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Summary

Traffic statistics system basics

Key traffic measurement items

Traffic statistics analysis method

Some cases

SummarySummary


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06 g-lii 304 traffic statistics analysis-20071205-a-2.0

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