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GSM DT
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STTTelkom, 17-18 November 2006 GSM Drive Test & GSM Drive Test & Network Network Optimization Optimization
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Transcript of GSM DT
STTTelkom, 17-18 November 2006
GSM Drive Test & GSM Drive Test & Network Network
OptimizationOptimization
Page - 2
How do we use it
TEMS INVESTIGATION GSMTEMS INVESTIGATION GSM
Page - 3
?
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 TEMS Measurement & Analyzing ProcessProcess
Page - 4
?
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 Measurement Will Depend on ObjectiveObjective
Page - 5
Drive Test
• Large areas
• Specific areas
Walk Test
Scanning
Performing Measurements Performing Measurements with TEMSwith TEMS
Page - 6
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 Drive Test - Large area- Large area
Page - 7
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 TestDrive Test- Specific area- Specific area
Page - 8
Statistics
Customer complain
Micro cell planning
Indoor cell planning
OUTPUTINPUT Measurement
Add file marks (GPS)
Scanning
Trouble Report
Planning Report
- Antenna location
- Frequency
Walk TestWalk Test
* TEMS Light is the preferred tool for indoor cell planning
Page - 9
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
ScanningScanning
ANALYZING TEMS ANALYZING TEMS MEASUREMENTSMEASUREMENTS
Page - 11
Post-Processing TEMS Post-Processing TEMS LogfilesLogfiles
TEMSLogfiles
Statistics Report
Geographical Presentation
Analysis
Page - 12
Problem CasesProblem CasesLow Signal Strength Interference Handover Call Setup Failure Dropped Call Misc.
Page - 13
Signal Strength CaseSignal 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
Page - 14
• 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 Signal Strength Case – – Possible ReasonsPossible Reasons
Page - 15
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
– – AnalysisAnalysis
Missing Neighbor
Is the call dragged?
Is low SS due to missing neighbor relations
Signal Strength CaseSignal Strength Case
Page - 16
• Change parameter BSPWR , BSPWRT.
• Add neighbor relation.
• Physical changes:
• Antenna direction
• Antenna height, tilt or position
• New site as last option.
Signal Strength Case Signal Strength Case – – Possible SolutionsPossible Solutions
Page - 17
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
TEMSLogfiles
Interference Case Interference Case
Page - 18
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 Interference Case – Logfile analysis– Logfile analysis
Page - 19
BCCH 590BCCH 590
High site
BCCH 590BCCH 590
BCCH 595
BCCH 600 CASE 1
CASE 2
Types of InterferenceTypes of Interference Co - Channel interference Adjacent Interference
Page - 20
• 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 Interference Case – Possible Reasons– Possible Reasons
Page - 21
Interference Case Interference Case – Possible solutions– 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.
Page - 22
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 Handover Case
Page - 23
Repeated Handover (Ping Repeated Handover (Ping Pong)Pong)- Examples- Examples
Page - 24
Repeated Handover (Ping Repeated Handover (Ping Pong) Pong) - Possible Reason 1- Possible Reason 1Merry-go-round Handover, Offset > Hysterisis
Page - 25
Repeated Handover (Ping Repeated Handover (Ping Pong) Pong) - Possible Reason 2- 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
Page - 26
No dominant Server
Repeated Handover (Ping Repeated Handover (Ping Pong) Pong) – Other Possible Reasons– Other Possible Reasons No dominant server Locating penalty settings e.g. PSSBQ,
PTIMBQ Too small hysterisis setting
Page - 27
Antenna direction
Antenna Tilts
Plan for new site
Change Locating Parameter e.g. KHYST or LHYST
Repeated Handover (Ping Repeated Handover (Ping Pong) Pong) – Possible Solutions – Possible Solutions
Page - 28
Change Parameter, KHYST or LHYST
HysterisisCELL A CELL B
Handover From A to B
Repeated Handover (Ping Repeated Handover (Ping Pong) Pong) – Possible Solution – Possible Solution
Page - 29
Check layer 3 message Handover command BSC correct?
Check reason for handover SS, RXQUAL
Target cell?
Handover Case Handover Case – Handover Reversion– Handover Reversion
Page - 30
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 Handover Reversion – Common Reason – Common Reason
Page - 31
Uplink interference in target cell
Downlink interference at MS
Solutions
Interference Investigation
• Statistics
• Scanning
Handover Reversion Handover Reversion – Other Reasons– Other Reasons
Page - 32
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 Handover Case – Repeated Intra-cell – Repeated Intra-cell HandoverHandover
Page - 33
Handover Case Handover Case – Unrealistic Handover– Unrealistic Handover
Page - 34
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 Unrealistic Handover – Reason & Solution– Reason & Solution
Page - 35
Call Setup FailureCall Setup Failure
Page - 36
Call Setup Failure Call Setup Failure – – Input Activities, Initial Input Activities, Initial TuningTuning
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
Page - 37
Call Setup FailureCall Setup Failure– – Input Activities, Input Activities, TroubleshootingTroubleshooting
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)
Page - 38
Call Setup Failure AnalysisCall Setup Failure Analysis- Initial Tuning Scenario- 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.
Page - 39
Call Setup Failure AnalysisCall Setup Failure Analysis- Initial Tuning Scenario - Initial Tuning Scenario cont.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
Page - 40
Call Setup Failure AnalysisCall Setup Failure Analysis- Troubleshooting Scenario- 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.).
Page - 41
Call Setup Failure AnalysisCall Setup Failure Analysis- Possible reasons with - Possible reasons with rankingranking 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.
Page - 42
Call Setup Failure AnalysisCall Setup Failure Analysis- Possible solutions- 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.
Page - 43
Failed Call Setup (Blocked Failed Call Setup (Blocked Call) ExampleCall) Example
Multiple Channel Requests.
Successful Random Access after the third try.
Congestion in SDCCH.
Page - 44
Dropped Call CaseDropped Call Case- Input- Input Statistics Report Note from drive test.
Page - 45
Dropped Call CaseDropped Call Case- Analysis- 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!!!
Page - 46
Dropped Call CaseDropped Call Case- Analysis (cont)- 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).
Page - 47
The EndThe EndGSM Drive Test & Network Optimization
