TroubleShooting RNO

TROUBLE SHOOTING

Series 4

TROUBLE SHOOTING

Series 4

Optimization Work Flow

Drive Test

Traffic statistics

• Brief Introduction

• Limitation of statistics

• Traffic statistics analysis

Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

Monitor Network Performance

Monitor Network Performance

ProposeAction Plan

ProposeAction Plan

Trouble TicketTrouble TicketDrive TestDrive TestNetwork StatisticNetwork Statistic

Is Performance OK?Is Performance OK?

YesYes

NoNo

Parameter, Configuration and Hardware Changes

Parameter, Configuration and Hardware Changes

Implement Action PlanImplement Action Plan

Optimization Work FlowOptimization Work Flow

STEP 1: Identify Problem

Customer Complaints Drive Test

Traffic Statistics

Alarm

What Problem ?


STEP 2: Analyze Problem

How to solve?Any activity? Alarm / Hardware

Call Statistics

Drive Test


STEP 3: Implement Solutions

Change what?Re-configurationHardware Change/Antenna tilting

Parameter Change

Software Upgrades


STEP 4: Monitor Performance

Change Success? Alarm

Call Statistics

Drive test

CustomerFeedback



Drive Test

Traffic statistics




Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

Standard for Drive Test

Define Route drive test

Specific drive test measurement tools

Time period for Drive Test

Summary drive test results

Drive Test

Standard for Drive Test

Used external ANT outdoor mounted on rooftop of drive test

car.

Trace mode drive test

Drive test same direction in each route

Drive Test

Define Route drive test

Main road level 1

Normal road level 2

Route in city

Drive Test

Specific drive test measurement tools

TEMS 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 pr

ocessing software) to Mapinfo table .

Drive Test

Time period for Drive Test

For optimization perform drive test after launched in each batch

For trouble shooting drive test

Drive Test

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 <= 4 compare with base line in each

route.

Summary drive test results.

Trouble shooting drive test

The 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.


Drive Test

Traffic statistics




Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

BM1

Call process data

BM data

Hardware data

Signaling data

BM

AM/CM

BAM

¡ ¡ WS1 WSn

OMC SERVERHUB

Brief Introduction to BSC Traffic Statistics Item


MTP Measurement Function

Cell Measurement Function

Power-control Measurement

Call Drop Measurement

Site Initialization Measurement

Function

BSC Cell Broadcast

Measurement Function

BSC Measurement Function

SCCP Measurement Function

A-interface Operation and

management statistic

A-interface Equipment

Maintenance statistic

A-interface Trunk Board

message statistic

CPU Measurement Function

Demo

BTS Initialization

Measurement

Cell Broadcast Statistic

Outgoing Inter-cell handover


Incoming Inter-cell handover


Undefined Adjacent Cell


GPRS Measurement Function

Defined Adjacent Cell


Receiving Quality Measurement

Function

Receiving Level Measurement

Function

Link Balance Measurement

Function

LAPD Link Measurement Function

Cell Frequency Scan


Demo


Drive Test

Traffic statistics




Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

Limitation of statisticsLimitation of statistics

1. Traffic statistics task occupies some of the system resources. If too many

tasks 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 task

equals 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".

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.



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

handover measurement function task

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

Outgoing inter cell handover measurement function and Incoming inter cell

handover measurement function only support 16 cells in one task.

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



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 percentage

GPRS Related Measurement Function Max num. of available PDCH

GPRS Related Measurement Function Min num. of available PDCH


3. Do not modify the time of BAM and OMC Server.

Since the management and time of traffic statistics are closely related, if the time

is modified, the result of this cycle that outputted may be incorrect.


Drive Test

Traffic statistics




Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

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

BSC Measurement Function

High call drop rate High congestion rate Low handover successful rate

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General method for traffic analysis

Traffic Statistics Analysis

TCH call drop analysis ( Analysis diagram )

Cell with high call drop rate

Cell performance statistics

Call drop measurementHandovermeasurement

Call drop times

Interference band

Causes of call drop

Average uplink level at TCH call drops

Average down link level atTCH call drop

Average uplink quality atTCH call drop

Average downlink quality at TCH call drop

Average TA value atTCH call drop

Outgoing-cell handover success rate

Incoming inter cell handover successful rate

Handover failure and re-establish

failure

Alarm and hardware fault

Traffic Statistics Analysis-TCH Call Drop

Low Handover Success Rate

Handover Measurement Function

Alarm (Clock),Hardware FaultTCH Measurement Function

Outgoing-Cell Failure Incoming-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)


Drive Test

Traffic statistics




Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

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 DropTrouble shooting--Call Drop

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


Call drop types

Edge call drop: low receiving signaling strength, large TA.

Short distance call drop: low receiving signal strength and

small TA.

Bad Qual 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.

• 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..


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.


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.


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 can’t work).


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.

Note ： First, we shall know the type of the call drop.


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


SDCCH call drop Refer to TCH call drop analysis.

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

same as TCH.



Drive Test

Traffic statistics




Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

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)

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).


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.


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.


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.


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 cell’s traffic .

• Low outgoing handover successful rate: check the neighbor cell’s

traffic.


Congestion

Disposing process

• Adjust the cell’s 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.



Drive Test

Traffic statistics




Trouble shooting

•Call Drop

•Handover

•SDCCH Congestion

Topics

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 Shooting—SDCCH Congestion

Transmission fault and Board fault

Problem description

Massive location updates happen suddenly.

Solution:

Check transmission

Check hardware


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


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


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.


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


Thank You for Attention

TroubleShooting RNO

Documents

Transcript of TroubleShooting RNO