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8/7/2019 31685422 UMTS Optimization Example Dr Hatem MOKHTARI
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Radio Network Tuning andOptimization for Universal
Mobile TelecommunicationsSystem (UMTS)
Dr. Hatem MOKHTAR
Senior Wireless Consultant
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AGENDA
• Motivation
• 2G-3G, What is different
• Tuning Process Flow
• Tools used for Tuning Activity
• Equipments Configuration
• Pilot Tuning
• UE Tuning
• Final Words
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MOTIVATION
• 3G networks are becoming commercially available all over
the world
• To check the functionality of the networks beforecommercial launch
• Network designs are based on propagations models and
simulations (coverage verification)
• 3G technology (WCDMA) is different from 2G
• Tools and methods for 3G Networks
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Differences compared to 2G
• In General
- The Technology is more complicated (Overlapping cells, soft
hand over, power control, cell breathing etc)
- High performance requirements on products (UE & Networknodes)
- In Particular for Tuning & Optimzation
- Process & tools are under development
- Co-located GSM/3G sites- Shared Antenna System
- Inter-working with GSM
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Tuning or Optimization, What is the difference
• During Tuning
No traffic in the network, No subscribers
Network tuned only based on drive test data
Labour intensive with repeated drive testAll is about Pre-launch activities
• During Optimization
Commercial traffic, subscribers using the network
Statistics used widely to monitor network performance
Drive testing just in case
All is about Post–launch activities
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Tuning Process Flow
Radio Network Initial Tuning for WCDMA
Preparations Parameter
Audit
CommercialLaunch
Drive Testing &Post
Processing
ChangeVerification& Reporting
Analysis &Change
Proposals
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Tuning Process Flowchart
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Tools For Tuning/Optimization & Data Post
ProcessingActive measurement needed due to lack of statistics
• TEMS Investigation for WCDMA (Software)
• TEMS Scanner (Software + HW)
• External GPS
• User Equipment (UE)
• TEMS DeskCat for post processing• MCOM3g/Mapinfo
• MS Access/Excel based tools
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USB2USB1
Com 1
scanner
Short call Long Call
USB1
CS64
GPS
USB1
PS
Drive Test Equipments for Voice, CS64 & PS call
Drive test tools configuration
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Drive Test Routes
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PILOT TUNING
The basic measurements of scanner are
• CPICH_RSCP (received signal code power)
• CPICH_Ec/No (received energy per chip divided by the
power density in the band)• RSSI (received signal strength indicator)
What can you achieve with scanner?
• Crossed feeder issues (DL)
• Coverage verification
• Interference problems (overshooting cell, pilot pollution)
• Missing neighbours
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COVERAGE VERIFICATION - Primary Common Pilot
Channel
Verify P-CPICH detection to minimize coverage holes
• P-CPICH RSCP
• P-CPICH Ec/No
Coverage level RSCP [dBm] E c /N
0[dB]
Sufficient RSCP ≥ −100 E c /N
0 ≥ −14
Poor −115 ≤ RSCP <−100 −16 ≤ E c /N 0 < −14
No coverage RSCP < −115 E c /N
0<−16
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Best Server Signal Strength (RSCP)
• Yellow is
good
• Blue can
generateproblems
• Grey is bad
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Pilot Ec/No Measurements
• Green is
good
• Blue cangenerate
problems
• Orange is
bad
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INTERFERNECE
-100
-90
-80
-70
-60
-50
-40
-30
-25 -20 -15 -10 -5 0 5
Ec/Io [dB]
R S C P [ d B m ]
High interference
By correlating low Ec/No with high RSCP, areas with high
interference can be detected
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INTERFERENCE (RSCP > -90 dBm AND Ec/No < -9 dB)
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Primary Common Pilot Channel (P-CPICH) –
OVERSHOOTING
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Primary Common Pilot Channel (P-CPICH) – PILOT
POLLUTION
• P-CPICH RSCP
• P-CPICH Ec/No
High CPICH reception levels from many
Cells, (more than MAX_ACTIVE_SET)
size
serving
cc AS threshold N
E
N
E count Pilot >−≥ )(
00
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PILOT POLLUTION
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PILOT POLLUTION
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PILOT POLLUTION
Change Proposals
Site
Name
Sector
Number
SC of
Pilot
Height of
Antenna
(meters)
Antenna
Tilts
(degree)
Proposed
Antenna
Tilts
(degree)
A 1 173 38 2 5
A 2 76 38 2 4
D1
485 47.3 2 8
C 2 24 39.2 3 5
B 3 79 27 2 3
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0
5
10
15
20
25
30
35
Numbers of
Samples
173 76 485 79 24
SC of Pilots
0
5
10
15
20
25
30
35
40
Number of
Samples
173 76 79 24
SC of Pilots
PILOT POLLUTION
Initial Drive Test (before tuning)
Verification Drive Test (after tuning)
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UE TUNING
• Voice /Video/PS calls
– Long calls
– short calls
• Identify problem areas
– Blocked calls
– Dropped calls
– Delay/Throughput
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Short Calls Analysis
Set-up a call and maintain it for a pre-defined time duration
(for 15-60 s)
Call set-up failure and drops during short calls can be mainly
used to analysis Accessibility failure due to:
• UE Failure
• Unsuitable Parameters Setting• Coverage Problem
• Interference
• Others
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Long Calls Analysis
Drops during long call can be used to identify:
• Missing Neighbor Relation
• Coverage Problem
• UE Problems
• Network Characteristics
• Best Parameter Setting
• Others
Set-up a call and maintain it until it is drop (used for
the analysis of Retainability performace)
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KEY PERFORMANCE INDICATORS
• Accessability (Call set-up success rate)
• Retainability (Dropped calls)
• Mobility (Handover success rate)
• Integrity (BLER and throughput)
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Case 1: Drop due to missing neighbor
Problem: Detected Nighbor (DN)
• UE sends a Measurement Report that contains an event1a
means adding a new RL (cell) to Active Set• If the reported cell is not in the current neighbor cell list and
the reported Ec/No is better than the best serving cell
Ec/No in AS by some dBs (set by a RNC parameter)
• If for any reason the new cell can not be added to AS, callwill be released
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Case 1: Drop due to missing neighbor
“DN” cell better than the serving cell
DL BLERgets worse
“DN” cell better than the serving cell
DL BLERgets worse
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Case 2: Drop due to Poor Coverage (low RSCP)
Problem: Poor DL coverage
When UE gets to an area with low RSCP ( < -105 dBm)
regardless Ec/No values there is high risk for drop.
UE will likely ramp up the transmitted power and reach its
max power. The DL BLER will probably increase and SIR
target cannot maintain anymore, finally the call drops.
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Case 2: Drop due to DL Poor Coverage
Very bad RSCP
UE max Tx power
and
high DL BLERVery bad RSCP
UE max Tx power
and
high DL BLER
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Case 3:
PS: Session Error due to Poor DL CoverageUE enters a very low coverage area (RSCP < – 105 dBm).
The packet connection is carried on a 64/64 DCH Channel
as consequence of the low coverage conditions.
The UE will likely ramp up its power to the maximum, goes
to Idle Mode and the Application and RLC throughputs go
to zero.
At this point the RAS application will start the SessionTimeout timer, if the throughput is not resumed the Session
Error event is triggered with cause “session timeout”.
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PS: Session Error due to Poor DL Coverage
App throughput ~64kbps
Very low RSCP
App throughput ~64kbps
Very low RSCP
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FINAL WORDS
• For network tuning, we need to relay on field measurements whichrequire extensive drive tests
• Finding the best possible configuration for antenna heights, tilts,azimuths and parameter setting for all the present cells/sectors in thenetwork and also for any new sites that might be needed to improvecoverage
•Power adjustment can also be used for network tuning but can becomecomplicated and result in poor network performance
• Use of Remote Electrical Tilt (RET) Antenna is preferred over mechanicaltilt antenna
• Neighbour definition is of prime importance in UMTS network (Softhandover gain and interference reduction). Keep neighbour list upto 20.
• Automated tools are needed that could suggest the best possibleneighbour relations, antenna heights and tilts by using both the fieldmeasurements and the propagation models & simulations
• Skilled people, right methods and advanced tools are needed to perform3G tuning and optimisation
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Comparison of Mechanical and Electrical Down-tilts