Trainning to Maintenance 4 (Trouble Shooting)

7/30/2019 Trainning to Maintenance 4 (Trouble Shooting)

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TROUBLE SHOOTING

Series 4

Internal Training to Maintenance Staff


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Optimization Work Flow

Drive Test

Traffic statistics

Brief Introduction

Limitation of statistics

Traffic statistics analysis

Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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Monitor

Network Performance

Propose

Action Plan

Trouble TicketDrive TestNetwork Statistic

Is Performance OK?

Yes

No

Parameter, Configuration

and Hardware ChangesImplement

Action Plan



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STEP 1: Identify Problem

CustomerComplaints

Drive Test

Traffic Statistics

Alarm

What Problem ?



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STEP 2: Analyze Problem

How to solve?Any activity? Alarm / Hardware

Call Statistics

Drive Test



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STEP 3: Implement Solutions

Change what?Re-configurationHardware Change/Antenna tilting

Parameter Change

Software Upgrades



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STEP 4: Monitor Performance

Change Success? Alarm

Call Statistics

Drive test

CustomerFeedback



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Drive Test

Traffic statistics

Brief Introduction



Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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Standard for Drive Test

Define Route drive test

Specific drive test measurement tools

Time period for Drive Test

Summary drive test results

Drive Test


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Standard for Drive TestUsed external ANT outdoor mounted on rooftop of drive test

car.

Trace mode drive test

Drive test same direction in each route

Drive Test


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Define Route drive testMain road level 1

Normal road level 2

Route in city

Drive Test


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Specific drive test measurement toolsTEMS investigation version 2.0.4 or higher version.

External ANT 0 dB(i) Gain with cable and connector to Ericsson

R520

Log files from TEMS investigation will be process by GIMS (post

processing software) to Mapinfo table .

Drive Test


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Time period for Drive TestFor optimization perform drive test after launched in each batch

For trouble shooting drive test

Drive Test


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Drive Test after launched in each batch

Print out RXlevel and RXQUAL in whole region.

Graph or table of %RXleve >= -84 dBm compare with base line in

each route.

Graph or table of %RXqual


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Trouble shooting drive testThe report in each route will show detail as the following :

Print out RXlevel, RXQUAL and mark problem point.

Summary sheet

-how many problem that found in that route.

-which type of problem ( Missing neigbouring ,Drop call, HO fail,

interference, bad quality).

-give suggestion how to solve and due date.

Example summary sheet added in Appendix. (Demo)

Remark: If changed parameter to solve problem must be re-drive test for

verify results.

Summary drive test results.


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Drive Test

Traffic statistics

Brief Introduction



Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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Brief Introduction to BSC Traffic Statistics Item

MTP Measurement FunctionCell Measurement Function

Power-control Measurement

Call Drop Measurement

Site Initialization Measurement

Function

BSC Cell Broadcast

Measurement Function

BSC Measurement FunctionSCCP Measurement Function

A-interface Operation and

management statistic

A-interface Equipment

Maintenance statistic

A-interface Trunk Board

message statisticCPU Measurement Function

Demo


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BTS InitializationMeasurement

Cell Broadcast Statistic

Outgoing Inter-cell handover


Incoming Inter-cell handover


Undefined Adjacent CellMeasurement Function

GPRS Measurement Function

Defined Adjacent CellMeasurement Function

Receiving Quality Measurement

Function

Receiving Level Measurement

Function

Link Balance Measurement

FunctionLAPD Link Measurement Function

Cell Frequency Scan

Brief Introduction to BSC Traffic Statistics Item

Demo


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Drive Test

Traffic statistics

Brief Introduction



Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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1. Traffic statistics task occupies some of the system resources. If too manytasks are implemented simultaneously or a task is implemented too

frequently, too much resource of BSC system will be used. Therefore, there

are restrictions to the number and period of traffic statistics task in BSC

system: At most 200 tasks can be created in each BM (Basic Module).

At most 3000 subtasks can be created in each BM.

A traffic statistics task is divided into subtasks according to the traffic statistics

objects in the task. The number of traffic statistics objects of a traffic statistics taskequals to the number of the subtasks contained in this task. The number of subtasks

of a BM is the total number of the subtasks of all tasks created in this BM. For

example, if a BM is fully configured to supports 128 cells, there will be 128 subtasks

after creating a measurement task of cell performance for "all cells in the module".


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A task can have at most 60 different initial indices.

For example, BSC Measurement Function has more than 120 primitive indices. Cell

Measurement Function has more than 220 primitive indices. At least three tasks are

to be created to measure all indices of BSC Measurement Function. At least four

tasks are to be created to measure all indices of Cell Measurement Function.

Minimum traffic statistics cycle: 15 minutes

If the statistic cycle is too short and the task results are too many, the system load will

increase. Therefore, the statistic cycle should not be shorter than 15 minutes. The

default setting is 30 minutes. The maximum statistic cycle is 1440 minutes.



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At most 16 cells can be selected in each Outgoing/Incoming inter cell

handover measurement functiontask

There is a limitation about the communication between Host and BAM; So,

Outgoing inter cell handover measurement functionand Incoming inter cell

handover measurement functiononly support 16 cells in one task.


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2. Statistic items that cannot be registered more than once

Do not register the statistic items concerning maximum/minimum values (e.g.

Maximum num. of busy TCHs) in multiple tasks. Otherwise, the data of these

indices may be incorrect.

The BSC traffic statistics indices concerning maximum/minimum values and their

traffic statistics function types are listed in the following



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BSC indices concerning maximum/minimum values

Traffic statistics function type Index concerning maximum/minimum value

CPU Measurement Function Peak percentage of CPU occupation

Cell Measurement Function Maximum num. of busy SDCCHs

Cell Measurement Function Maximum TCH queue length

Cell Measurement Function Maximum num. of busy TCHs

Power-Control Measurement Function Maximum distance between MS and BTS

Power-Control Measurement Function Maximum downlink power duration

percentage

Power-Control Measurement Function Maximum uplink power duration percentageGPRS Related Measurement Function Max num. of available PDCH

GPRS Related Measurement Function Min num. of available PDCH


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Drive Test

Traffic statistics

Brief Introduction



Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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Analysis process First we shall analyze and compare the sub-item of BSC measurement

function to have a roughly acknowledgement for the whole network.

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

successful rate) are abnormal, we shall do some further and detailed analysis

for the corresponding contents.

Analyze the cell with abnormal items (call drop, congestion, handover failure

and so on).

Use percentage and absolute times (call drop, congestion, handover failure

and so on) together to decide whether doing some further analysis or not.

Traffic Statistics Analysis


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BSC Measurement Function

High call drop rate High congestion rate Low handover successful rate

TCH

p

erformance

Ca

lldrops

SDCCH

performance

Link

balance

Outgoin

ghandover

Ala

rmdata

Ala

rmdata

TCHperformance

TCHperformance

Incominghandover

Link

balance

Link

Balance

Ala

rmdata

General method for traffic analysis

Traffic Statistics Analysis


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TCH call drop analysis ( Analysis diagram )

Cell with high call drop rate

Cell performancestatistics

Call drop measurementHandovermeasurement

Call drop times

Interferenceband

Causes ofcall drop

Average uplink level atTCH call drops

Average down link level atTCH call drop

Average uplink quality atTCH call drop

Average downlink qualityat TCH call drop

Average TA value atTCH call drop

Outgoing-cellhandover success rate

Incoming inter cellhandover successful rate

Handoverfailure and re-establish

failure

Alarm andhardware fault

Traffic Statistics Analysis-TCH Call Drop


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Low Handover Success Rate

Handover MeasurementFunction

Alarm (Clock),Hardware FaultTCH Measurement Function

Outgoing-Cell FailureIncoming-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)


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Drive Test

Traffic statistics

Brief Introduction Limitation of statistics


Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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Call drop is usually caused by the following: Radio link fault. During the communication, messages can not

be received correctly.

T3103 counter gives no response after timeout

Other system faults (for example, the matching between BSC

timer and MSC timer)

Timers that may cause call drops (BSC timer):

T3103: Time counting from sending up HANDOVER CMD start

to receive HANDOVER CMP end, If it is timeout.(20s)

T3109: Time counting from sending up CHAN REL to receive

REL IND end. If it is timeout.(5s)

Trouble shooting--Call Drop


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Analyze the causes of the fault of radio links. The causes can be:

Interference

Internal interference, external interference and the equipment

interference

Poor coverage

Coverage insufficient, isolated island, uplink/downlink unbalance Improper parameter setting

radio link timeout counter, SACCH multi-frame number, handover,

power control etc.

Equipment problem (Antenna---Feeder---CDU---TRX)

Clock problem

Transmission problem



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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 missing neighbor.

Stand along site.

Solutions

Add new site to guarantee the effective continuous coverage.

Add the necessary neighbor.

Adjust antenna height and antenna downtilt, use high gain antenna

Modify some parameters : SACCH multi-frames , Radio link

timeout counter, handover threshold, handover statistic time, etc..



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Short distance call drop Causes

Poor coverage caused by complicated terrain structure or high

dense building.

Solutions

Increase EIRP.

Adjust antenna direction and downtilt, make the main lobe point

to high traffic area.

Adjusting call drop related parameters.



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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.

Optimize frequency planning.

Adjust antenna system, avoid island.

Avoid transmission BER.



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Equipment problem (TRX, power amplifier, tower amplifier, etc.)

Problem description

In TCH measure function: many TCH seizure failures due to A interface

problem.

In call drop measurement function: many call drops due to ground links.

In TCH measurement function: many TCH seizure failures due to

equipment failure.

Disposing process

Monitor transmission and board alarms (TC board failure, A interface

PCM synchronization alarm, LAPD link disconnected, TRX alarm);

analyze whether transmission is disconnected or some boards have

fault (for example, the TRX cant work).



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TCH Call Drop items

N:TCH call drop

A: TCH lost radio connections (connection failure)

B: TCH lost radio connections (error indication)

C: TCH seizure failures due to terrestrial link failure (A-bis) D: TCH drop during Handover and preemption (No item in

OMC)

N=A+B+C+D



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SDCCH call drop Refer to TCH call drop analysis.

Note: The cause and mechanism of SDCCH call drop are almost the

same as TCH.



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Optimization Work Flow Drive Test

Traffic statistics



Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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Trouble Shooting--Handover

Handover failure analysis Causes of handover failure

Improper handover parameters.

Hardware fault (TRX board fault).

Congestion

Interference

Coverage

Clock fault (Internal clock, external clock)


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Handover failure analysis Disposing process

Find out the cells with low handover successful rate.

Find the out the cells with high handover failures.

Compare the incoming cell handover failures and outgoing cell

handover failures.

Register the task to measure the incoming cell handover and

outgoing cell handover.

Find out handover failure relation (failure to all the neighbor cells or

parts of the neighbor cells).



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Improper parameter settings Disposing process

Check whether the handover parameter threshold such as TA, BQ

and handover function switch are suitable or not.

Check whether the successful TCH seizures for handover are much

more than successful TCH seizures for call. If handover divide by

call is larger than 3, then it indicates that there maybe has Ping-

Pong handover. Check the parameter setting and adjust them (layer

setting, inter-lay handover hysteresis, inter-cell handover hysteresis,

PBGT threshold, etc.).

Check whether the average signal strength is low When the

handover happens. If it is, it indicate the edge handover threshold

are too low.



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Hardware fault Problem description

The target cell has active channels but when applying for the

channels, get NACK or TIMEOUT message.

TCH availability is abnormal.

If the call drop rate and congestion rate are high, the equipment

may have some fault.



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Hardware fault Disposing process

Monitor transmission and board alarms (TC board failure, A

interface PCM sync alarm, LAPD link disconnected, power amplifier

board, HPA, TRX alarm board, and CUI/FPU alarm).

Analyze whether the transmission is disconnected or the boards

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

Check whether there is a clock alarm.



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Congestion Objects needed to be analyzed

Cells with low incoming handover successful rate.

Neighbor of the cell with low incoming handover successful rate.

Analysis process

In incoming inter-cell handover Measurement function: check

whether many handover failures caused by congestion.

Low incoming handover successful rate: check the cells traffic .

Low outgoing handover successful 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 cell.



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Optimization Work Flow Drive Test

Traffic statistics



Trouble shooting

Call Drop

Handover

SDCCH Congestion

Topics


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SDCCH congestion

Main causes

Transmission fault and Board fault

Excessive SDCCH location updating in location area boundary

More traffic

Improper setting of system parameters

Interference

Trouble ShootingSDCCH Congestion


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Transmission faultandBoard fault

Problem description

Massive location updates happen suddenly.

Solution:Check transmission

Check hardware



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Excessive SDCCH location updating in location area boundary

Problem description

The border of different location area is the street.

The border of different location area is at the high traffic area.

Solution:Modify location area selection

Modify CRH (Cell Reselect Hysteresis)

Modify the parameters of periodical area updating.(T3212)

Modify the frequent handover problem of the dual-frequency

network

Add more SDCCH channel



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More traffic

Problem description

Many location updates happen at the border of different location

areas.

Solution:

Hardware fault in adjacent cell cause to suddenly traffic

increase

Traffic balance

Reduce CRO to reduce C2

Add more SDCCH channel



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Improper setting of system parameters

Solution:

Increase RACH access threshold (for coping with interference)

Decrease maximum resend times MS MAX retrans

Increase extended transmission timeslots appropriately

T3101 3s (Used to limit the duration of immediate assignment.)

T3122 10s Wait indication time, defines the MS waiting time before the

MS attempts another channel request after IMMEDIATE ASSIGNMENT

REJECT.



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Interference

Problem description

RACH threshold is low. At the same time, there is some

interference in the system, which will bring a lot of illusory

SDCCH channel requests.Disposing process

Properly set the RACH threshold

Dispose interference



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Case study

Refer to Problem Investigation


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Review and Thanks

Documents

Trainning to Maintenance 4 (Trouble Shooting)