2002-03-11 1

TEMS INVESTIGATION

GSM

How do we use it

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Performing TEMS Measurements

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?

Clear objective

Why should this measurement be done

Preparations Collect Data Analyze

Check equipment

Get input files

Prepare route

External Antenna?

Save logfile

Take notes

Monitor

Find problem areas

Find solutions

What should be changed?

Report

Give answer to objective

Changes in Network

TEMS Measurement & Analyzing Process

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?

Clear objective

Why should this measurement be done

Preparations

Check equipment

Get input files

Prepare route

External antenna?

Possible Objectives

• Coverage analysis• Trouble shooting• Scanning• Verify network changes

Measurement Will Depend on Objective

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Drive Test

• Large areas

• Specific areas

Walk Test

Scanning

Performing Measurements with TEMS

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INPUT

Plots & Report

- Signal Strength

- Quality

Trouble Report /

Area for further investigation

Acceptance

New sites on air

Frequency Re-plan

BSC Re-homing

OUTPUTINPUT MEASUREMENT

Drive defined route/area

Record Logfile

Long / Short calls

Assure no data loss

Drive Test - Large area

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Manipulate

- Forced handover

- Lock on to Frequency

- Layer 3 messages

Analysis on-spot

Rectify & Verify on-spot

OUTPUTINPUT Measurement

Statistics

Customer complain

Large area drive test Trouble Report

Trouble Report

- Identified problem

- Solution

Drive Test- Specific area

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Statistics

Customer complain

Micro cell planning

Indoor cell planning

OUTPUTINPUT Measurement

Add file marks (GPS)

Scanning

Trouble Report

Planning Report

- Antenna location

- Frequency

Walk Test

* TEMS Light is the preferred tool for indoor cell planning

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Finding a new frequency

Area Network

Scanning

OUTPUTINPUT Measurement

Received SS on different ARFCN plot

New frequency

TEMS INV in scanning mode

Set ARFCN to scan

Scanning

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ANALYZING TEMS MEASUREMENTS

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Post-Processing TEMS Logfiles

TEMSLogfiles

Statistics Report

Geographical Presentation

Analysis

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Low Signal Strength• Interference• Handover • Call Setup Failure• Dropped Call• Misc.

Problem Cases

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Signal Strength Case

INPUT

Large area DT

Specific area DT

Post-Processing

Analysis

TEMSLogfiles

• Identify areas with low signal strength e.g. SS < -100dBm (outdoor)

• Look at RxLev distribution (for acceptance)

• Compare with design level or new requirements

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• Shadowed Antenna

• Antenna Direction

• Antenna Height / down tilt

• Output Power

• Missing Neighbor Relation

• Site Location

• Faulty Hardware e.g. antenna

• Cell is down

Signal Strength Case – Possible Reasons

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Shadowed Antenna Faulty Hardware

Height/down Tilt

Output Power

Visit site

Check antenna installation

Is there a better antenna position at same site?

Add reduce down tilt?

Can antenna be placed lower or higher to give better coverage?

Check output power

Parameters

BSPWRT - NON BCCH FREQ

BSPWRB - BCCH FREQ

Site Location

Possible to move site?

New antenna location at same site? Is it necessary to expand and build a new site?

Check alarm & BTS Error log

Visit site

Signal Strength Case – Analysis

Missing Neighbor

Is the call dragged?

Is low SS due to missing neighbor relations

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• Change parameter BSPWR , BSPWRT.

• Add neighbor relation.

• Physical changes:

• Antenna direction

• Antenna height, tilt or position

• New site as last option.

Signal Strength Case – Possible Solutions

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INPUT

Large area DT

Identify areas with Rxqual > 5

Identify source using Map and STS

New drive test around problem area?

Specific area DT

Post-Processing

Analysis

Interference Case

TEMSLogfiles

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From logfile & map:

What channel group suffer from interference? HOP or Non HOP?

• Check Current channel information in TEMS INV, hopping channel and hopping frequency.

Where does the interference come from? Cell name?

• Study map and logfile, look for co-channel or adjacent channel interference.

Does the interference lead to lower SQI?

• Look at SQI measurement during high RxQual.

Interference Case – Logfile analysis

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BCCH 590BCCH 590

High site

BCCH 590BCCH 590

BCCH 595

BCCH 600 CASE 1

CASE 2

Types of Interference

• Co - Channel interference• Adjacent Interference

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• Poor frequency plan• No dominant cell --> low C/I ---> increased Rxqual• Frequency Hopping is off• External interference e.g. jammer

Example of high Rxqual due to low Signal Strength

Interference Case – Possible Reasons

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Interference Case – Possible solutions

• Enable Frequency Hopping or add frequencies to Hopping group.

• Enable BTS Power Control, MS power control and make it less aggressive.

• Change frequency of interferer or interfered cell:

– Possible to find new frequency by using TEMS Scanning.

• Down tilt or change antenna of interferer.

• Redo frequency plan.

• Add new site.

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INPUT

Large area DT

Specific area DT

Post-Processing

Analysis

Look for:

Repeated handover (Ping Pong)

Repeated Intra-cell handover

Handover failure,

Unrealistic handover

Handover Case

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Repeated Handover (Ping Pong)- Examples

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Repeated Handover (Ping Pong) - Possible Reason 1

Merry-go-round Handover, Offset > Hysterisis

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Repeated Handover (Ping Pong) - Possible Reason 2

• Offset only in one direction e.g A-B for Inter BSC relation

BSCBSC

CELL A CELL B

A -> B OFFSET = -5dB

BSC 2BSC 1

No B -> A OFFSET

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No dominant Server

Repeated Handover (Ping Pong) – Other Possible Reasons

• No dominant server• Locating penalty settings e.g.

PSSBQ, PTIMBQ• Too small hysterisis setting

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Antenna direction

Antenna Tilts

Plan for new site

Change Locating Parameter e.g. KHYST or LHYST

Repeated Handover (Ping Pong) – Possible Solutions

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Change Parameter, KHYST or LHYST

Hysterisis

CELL A CELL B

Handover From A to B

Repeated Handover (Ping Pong) – Possible Solution

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Check layer 3 message

Handover command BSC correct?

Check reason for handover SS, RXQUAL

Target cell?

Handover Case – Handover Reversion

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Duplicates of BSIC BCCH combinations in neighboring list

610_31610_31

610_12

606_33

608_32

608_32

Serving cell

Neighbor cell 1

Road

Neighbor cell 2

BSCHandover command?

Handover Reversion – Common Reason

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Uplink interference in target cell

Downlink interference at MS

Solutions

Interference Investigation

• Statistics

• Scanning

Handover Reversion – Other Reasons

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Possible Reasons

Wrong intra-cell handover settings

External Uplink Interference

Possible Solutions

Consider to change parameters:

• SSOFFSETUL, SSOFFSETDL

• QOFFSETUL, QOFFSETDL

A wrong setting of parameters will cause “unnecessary” IHO

Turn off Intra-cell Handover?

Handover Case – Repeated Intra-cell Handover

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Handover Case – Unrealistic Handover

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Possible Reasons

Wrong locating settings, in Serving or Target cell

Note: Could be on purpose e.g. Dual Band network with HCS

Solution

• Fix locating settings e.g. MSRXSUFF, BSRXSUFF

Unrealistic Handover – Reason & Solution

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Call Setup Failure

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Call Setup Failure – Input Activities, Initial Tuning

Activities

Initial Tuning(Acceptance Test)

Troubleshooting (Customer

complaint etc.)

Measurement Type•Large Area Drive Test•Short Call Sequences

Post-Processing Output•Statistics Report•Geographical Report showing failure positions

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Call Setup Failure– Input Activities, Troubleshooting

Input Activities

Initial Tuning(Acceptance Test)

Troubleshooting (Customer

complaint etc.)

Measurement Type•Small Area Drive Test•Lock on problem cell’s BCCH•Force handover to the cell

Post-Processing Output•Geographical Report (if necessary)

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Call Setup Failure Analysis- Initial Tuning Scenario

• Check the TEMS statistics report (Blocked Call) if there is Call Setup Failure.

• If yes, identify the problem cells and which logfile from geographical report.

• Replay the logfile and jump to the Blocked Call event.• Check if there is any successful call setup to the problem

cell.

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Call Setup Failure Analysis- Initial Tuning Scenario cont.

• Review the layer 3 messages to check at which sequence the failure occur (random access, SDCCH, TCH assignment etc.).

• Is there any traffic (SDCCH & TCH) in the cell, SDCCH & TCH seizures, congestion etc.

• Check fault report

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Call Setup Failure Analysis- Troubleshooting Scenario

• Before performing drive test, check STS report & fault report.

• If can not identify the problem, perform drive test.• During measurement, lock the BCCH of the problem cell.• Review the layer 3 messages to check at which sequence

the failure occur (random access, SDCCH, TCH assignment etc.).

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Call Setup Failure Analysis- Possible reasons with ranking

• Low Signal Strength• Interference• High Congestion on SDCCH • High Congestion on TCH• Transmission Fault• Faulty TRU/Hardware • Central Processor Overload• Software File Congestion• Cell is not defined in MSC.

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Call Setup Failure Analysis- Possible solutions

• Low signal strength Signal strength analysis.• Interference Interference analysis.• High Congestion on SDCCH:

Define more SDCCHs. Activate adaptive configuration of logical channel feature and

immediate assignment to TCH.

• High Congestion on TCH:Add capacity/Tune coverage array.Activate assignment to worse cell.

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Failed Call Setup (Blocked Call) Example

Multiple Channel Requests.

Successful Random Access after the third try.

Congestion in SDCCH.

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Dropped Call Case- Input

• Statistics Report • Note from drive test.

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Dropped Call Case- Analysis

• From plot, identify which & where in logfile the dropped call occurs.

• In the log file, Jump the drop call event. • Check if there is a disrupt in the recording. If yes could

be a false drop due to TEMS mobile disconnection during recording!!!

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Dropped Call Case- Analysis (cont)

• Check the Radio environment just before drop:– If High Rxqual for a longer period of time and RLINKT expire

Interference problem.– If Low SS DL, SSDL < MSSENS ( -104dBm) low signal strength

problem.– If TA > 63 too far from the cell.

• If DL radio is good, check the TX power. If there is MS power down regulation when the MS is close to the cell. If full power suspect uplink interference or antenna, TMA problem.

• Verify or isolate the problem using STS (Drop call and reasons).