LTE Optimization
Guidelines
•
2016-09-30/2016-10-07
•
Anton Naratkin
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LTE Optimization Guidelines
RF Optimization
Physical RF Optimization is the first step to improve the performance of the
network in order to get the maximum benefits from any subsequent parameter
optimization.
Checking
• the coverage footprint,
• aiming for good dominance areas,
• avoiding cross feeders and
• looking for wrong/not optimized tilts and azimuths
are fundamental areas
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LTE Optimization Guidelines
RF Optimization
Electrical tilt poses an advantage over the mechanical as tilt is also applied on the back lobe
and because the shape of the main radiation lobe is kept constant. Mechanical tilt results in
the uptilting of the back lobe which might increase the interference in tower sites.
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LTE Optimization Guidelines
RF Optimization
Antenna tilt issues:
• Overshooting cells
• Coverage gaps
(undershooting) cells
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LTE Optimization Guidelines
RF Optimization
Crossed feeders
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LTE Optimization Guidelines
RF Optimization
Crossed feeders in case of MIMO configuration
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LTE Optimization Guidelines
RF Optimization
Crossed feeders
in case of MIMO
configuration
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LTE Optimization Guidelines
Feature Summary
Features aimed at improving downlink throughputs
Id
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LTE793
LTE43
LTE70
LTE703
LTE568
LTE1089
LTE1332
LTE1803
LTE2149
LTE1804
LTE2316
LTE2180
LTE1987
LTE1541
LTE2276
LTE2531
LTE2630
LTE2479
Name
Support of 16 QAM (DL)
Support of 64 QAM in DL
Downlink adaptive open loop MIMO for two antennas
DL adaptive closed loop MIMO for two antennas
DL Adaptive Closed Loop MIMO (4x2)
Downlink Carrier Aggregation - 20 MHz
Downlink carrier aggregation - 40 MHz
Downlink carrier aggregation 3 CC - 40 MHz
Supplemental Downlink Carrier
Downlink Carrier Aggregation 3 CC - 60 MHz
FDD-TDD downlink carrier aggregation 3CC
FDD-TDD Downlink Carrier Aggregation 2CC
Downlink Adaptive Closed Loop SU MIMO (4x4)
Advanced SCell measurement handling
Measurement-based SCell Selection
FDD Downlink Carrier Aggregation 4CC
Uplink Control Information Only Transmission
256QAM in Downlink
Software
Release
RL10
RL10
RL10
RL20
RL50
RL50
RL60
RL70
FL15A
FL15A
FL16
FL16
FL16
FL16
FL16A
FL16A
FL16A
FL16A
LTE Optimization Guidelines
Feature Summary
Features aimed at improving uplink throughputs
Id
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LTE27
LTE28
LTE788
LTE619
LTE829
LTE1034
LTE46
LTE979
LTE980
LTE1336
LTE1402
LTE1495
LTE1691
LTE44
LTE2470
LTE2564
LTE1092
LTE1130
Name
Open loop UL power control and DL power setting
Closed loop UL power control
Support of 16 QAM (UL)
Interference aware UL scheduling
Increased uplink MCS range
Extended UL Link Adaptation
Channel-aware Scheduler (UL)
IRC for 2 RX Paths
IRC for 4 RX Paths
Interference aware UL power control
Uplink Intra-eNB CoMP
Fast uplink link adaptation
Uplink intra-eNB CoMP 4Rx
64QAM in UL
Centralized RAN for FL16
Centralized RAN CL16A Release
Uplink Carrier Aggregation – 2CC
Dynamic PUCCH Allocation
Software
Release
RL10
RL10
RL10
RL30
RL30
RL30
RL40
RL40
RL50
RL60
RL60
RL60
RL70
FL16
FL16
FL16A
FL16A
FL16A
LTE Optimization Guidelines
Feature Summary
Features aimed at improving CS Fallback and Release with Redirection
Id
LTE736
LTE1073
LTE984
LTE498
LTE1196
Name
CS Fallback to UTRAN
Measurement-based Redirect to UTRAN
GSM Redirect with System Information
RAN Information Management for GSM
RAN Information Management for WCDMA
Software
Release
RL40
RL40
RL40
RL60
FL15A
Features associated with DRX
Id
LTE42
LTE473
LTE585
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Name
DRX in RRC connected mode
Extended DRX settings
Smart DRX
Software
Release
RL30
RL30
RL50
LTE Optimization Guidelines
Feature Summary
Features aimed at improving VoLTE performance
Id
LTE11
LTE571
LTE907
LTE1406
LTE1127
LTE2112
LTE64
LTE2430
LTE2098
LTE1569
LTE2832
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Name
Robust header compression
Controlled uplink packet segmentation
TTI Bundling
Extended VoLTE talk time
Service Based Mobility Trigger
Dedicated Mobility Thresholds for SRVCC
Service-based Handover Thresholds
QCI1 Establishment Triggered Protection Timer
VoLTE uplink coverage boosting
QCI 1 specific RLF and re-establishment control
SRVCC Due to Admission Control Rejection
Software
Release
RL20
RL30
RL50
RL70
RL70
RL70
FL15A
FL15A
FL16
FL16
FL16A
LTE Optimization Guidelines
Feature Summary
Features associated with RRC Connection Re-establishment
Id
Name
LTE735
LTE1617
LTE2206
RRC Connection Re-establishment
RLF Triggered Handover
Extended RLF Handling
Software
Release
RL30
RL70
FL16
Features associated with RSRQ based mobility
Id
LTE1036
LTE1407
LTE1198
LTE2572
LTE2551
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Name
RSRQ Based Cell Reselection
RSRQ Based Redirect
RSRQ triggered mobility
RSRQ-based B2
RSRQ-based A5
Software
Release
RL50
RL50
RL60
FL16A
FL16A
LTE Optimization Guidelines
Feature Summary
Features associated with Traffic Management
Id
LTE1387
LTE487
LTE1170
LTE1531
LTE1677
LTE1894
LTE1140
LTE1841
LTE2050
LTE1357
LTE2051
LTE1536
LTE2275
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Name
Intra-eNB Inter-frequency Load Balancing
Idle Mode Mobility Load Balancing
Inter - frequency Load Balancing
Inter-frequency Load Balancing Extension
Idle Mode Mobility Balancing Extensions
Reference Signal Power De-boosting
Intra-Frequency Load Balancing
Inter-Frequency Load Equalization
Load triggered Idle Mode Load Balancing
LTE-UTRAN Load Balancing
Measurement based Idle Mode Load Balancing
RRC connection rejection with deprioritisation
PCell Swap
Software
Release
RL40
RL50
RL50
RL60
RL60
RL70
RL70
RL70
RL70
FL15A
FL15A
FL16
FL16
LTE Optimization Guidelines
Feature Summary
Features associated with Hardware Overload Management
Id
LTE1047
LTE2023
Name
Control plane overload handling
User Plane Overload Handling
Software
Release
RL60
FL15A
Features associated with Interference Management
Id
LTE1113
LTE1496
LTE1800
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Name
eICIC - macro
eICIC - micro
Downlink interference shaping
Software
Release
RL70
RL70
RL70
LTE Optimization Guidelines
Parameter Optimization
Parameter optimization can be initiated
after RF optimization has been
completed.
Parameter optimization can involve
enabling new features or tuning the
configuration of existing features.
All radio network parameters are stored
within the eNodeB. The structure of the
relevant parameter objects is illustrated
here
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LTE Optimization Guidelines
Parameter Optimization
Network layer
is congested
1. Do other LTE network layers have capacity available?
No
Yes
Idle Mode Mobility Typical Issues:
•
Inadequate hysteresis to avoid ping-pong
•
Overloading a network layer
•
Not selecting the highest priority layer
•
Triggering band scans
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2.
OPTION 1
Adjust Cell Reselection
Thresholds
OPTION 2
Enable Idle Mode Mobility
Load Balancing feature
3. Can traffic be offloaded to
other technologies?
Yes
4.
OPTION 1
Adjust Cell Reselection
Thresholds
OPTION 2
Enable Idle Mode Mobility
Load Balancing feature
No
5. Apply Capacity
Solutions Guidelines
UE log files indicate that maximum
number of PRACH preambles is
reached without a response
LTE Optimization Guidelines
Parameter Optimization
1. Check that MSG1 & MSG2
parameters are configured
correctly
Random Access Typical Issues:
2. Root Cause selection
• Antenna radiating beyond the planned maximum
cell range (PrachCS)
• PRACH root sequence clashes and Ghost Calls
• Unreliable reception of MSG3 (first PUSCH
transmission)
Root Cause 1
UE is outside the
maximum cell range
3. Cell range
optimisation
Root Cause 2
eNode B is not
receiving MSG1
4. MSG1 power
control optimisation
• eNodeB processing capability
• PDCCH congestion
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Complete RACH Setup Success Rate
• Unreliable reception of MSG5 (second PUSCH
transmission)
Root Cause 3
UE is not
receiving MSG2
5. MSG2 PDCCH
optimisation
6. MSG2 optimisation
- Resource allocation
- Wait time
15 km
22 km
LTE Optimization Guidelines
Parameter Optimization
Performance Monitoring indicates:
- maximum RRC connections is reached, AND/OR
- admission control blocking is experienced
Radio Admission Control Typical Issues:
1. Is capacity limited by admission
thresholds or by PUCCH dimensioning
• Inadequate PUCCH dimensioning
• Admission thresholds set too low
• Inactivity timer set too long
Thresholds
5. Can actHighRrc
be enabled?
No
• Aggressive Traffic Management
No
Yes
6. Enable actHighRrc
Performance Monitoring indicates:
- maximum number of active UE is reached, AND/OR
- admission control blocking is experienced
1. Has the maximum number of active UE
been set equal to the maximum number of
RRC connections?
No
2. Set the maximum number
of active UE equal to the
maximum number of RRC
connections
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Yes
3. Trigger the RRC connection
optimisation procedure
Return to Performance Monitoring
2. Can thresholds be
increased?
Yes
9. Will the PUCCH overhead become
unacceptable if increased?
3. Increase thresholds
4. Does the PUCCH need
to be re-dimensioned?
7. Evaluate parameter changes:
-offload traffic by changing the
traffic management strategy
- reduce RRC inactivity timer
PUCCH Dimensioning
No
No
Yes
10. Re-dimension the PUCCH
with existing parameter set
Yes
11. Re-dimension the PUCCH
with updated parameter set
Parameter changes
not possible
8. Evaluate hardware changes:
-add cell by new RF carrier,
sectorisation or new site
Return to Performance Monitoring
LTE Optimization Guidelines
Parameter Optimization
PDCCH Capacity to
be increased
Physical Downlink Control Channel
Typical Issues:
• Dynamic Allocation Triggering based
upon Blocking
• General lack of Capacity
• Dependence upon Traffic Profile
• Blocks causing other procedures to fail
PDCCH Performance
to be improved
1.
Verify that the following are enabled:
Adaptive Modulation and Coding (AMC) enableAmcPdcch
Outer Loop Link Adaptation (LA) actOlLaPdcch
Power Control (PC) enablePcPdcch
Load based Symbol allocation actLdPdcch
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2.
Evaluate reduction to CQI Shift (pdcchCqiShift)
Evaluate reduction in BLER target (pdcchHarqTargetBler)
1.
Verify maxNrSymPdcch is set to maximum for
channel bandwidth
5. Do other LTE network layers
have capacity available?
Yes
2.
Verify that the following are enabled:
Adaptive Modulation and Coding (AMC) enableAmcPdcch
Outer Loop Link Adaptation (LA) actOlLaPdcch
Power Control (PC) enablePcPdcch
Load based Symbol allocation actLdPdcch
3.
Check scope for decreasing default aggregations:
pdcchAggMsg4, pdcchAggPaging, pdcchAggPreamb,
pdcchAggRaresp, pdcchAggSib
4.
Evaluate optimisation of pdcchAlpha
No
6.
Improve traffic balancing
7. Can traffic be offloaded to
other technologies?
Yes
8.
Offload traffic
LTE Optimization Guidelines
Parameter Optimization
Physical Uplink Control Channel Typical Issues:
• PUCCH is under dimensioned
• PUCCH is over dimensioned
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Cell Specific Reference Signal
LTE Optimization Guidelines
Parameter Optimization
1. Consider benefits and drawbacks associated
with Reference Signal transmit power boosting
Downlink Power Control Typical Issues:
2. Is Reference Signal transmit power
boosting justified?
• Reference Signal Power Boosting causes
excessive neighbour addition
• Reference Signal Power Boosting causes
maximum planned cell range to be exceeded
No
3. Leave Reference Signal without
transmit power boosting
• Reference Signal Power Boosting causes
increased downlink inter-cell interference
PDSCH
Main parameters:
• pMax
• dlCellPwrRed
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PDCCH
1. Verify that Reference Signal power boosting
is not reducing PDSCH transmit power
1. Verify that power control is enabled using
enablePcPdcch
2. Evaluate benefit of PDSCH boosting using
allowPbIndexZero (RL70)
3. Verify that power boosting of the PCFICH,
PHICH and Reference Signal are not reducing
the PDCCH transmit power
3. Verify that dlCellPwrRed and
dlpcMimoComp are not reducing PDSCH
transmit power
Yes
4. Identify impact upon other
downlink transmit powers
5. Determine requirement to
adjust idle mode and connected
mode RSRP thresholds
PRACH preamble reception
to be optimised
LTE Optimization Guidelines
Parameter Optimization
1. UE log file indicates high number of PRACH preambles
prior to reception of Random Access Response?
Yes
No
2. Evaluate whether initial target
power or PRACH step size can be
decreased
Uplink Power Control Typical Issues:
3. Evaluate whether initial target
power or PRACH step size should
be increased
• PRACH Preambles not received by eNodeB
• Unreliable MSG3 reception
PRACH preamble reception
to be optimised
• High uplink intercell interference
1. UE log file indicates that cell edge UE do not receive
response to PRACH preambles?
• Reduced uplink throughputs
No
2. No action necessary
PUSCH power control
target power
1. Check configured target power
against Nokia default value
5. Evaluate requirement to change target power accounting
for use of fractional and interference aware power control
3. Check that UE is within the maximum
planned cell range
Intercell interference to
be optimised
1. Is site density relatively high?
No
Yes
2. Evaluate performance with
both Fractional and Interference
Aware power control disabled
3. Select between Fractional and
Interference Aware power control
Fractional
4. Evaluate performance with
Fractional power control
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Yes
Interference
Aware
5. Evaluate performance with
Interference Aware power control
4. Identify RSRP at which UE become power
limited and determine whether or not PRACH
power control is too aggressive
LTE Optimization Guidelines
Parameter Optimization
MIMO Mode Control Typical Issues:
• Inappropriate selection between spatial diversity and spatial multiplexing
• Ping-Pong between spatial diversity and spatial multiplexing
Open loop MIMO used
1. Complete field trial
with Closed Loop MIMO
2. Complete field trial for
Fast MIMO mode switching
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Open or Closed Loop
MIMO used
1. Check configured MIMO mode switching
thresholds against Nokia default value
2. Evaluate requirement for field trial with
different switching thresholds
LTE Optimization Guidelines
Parameter Optimization
Downlink Throughput Typical Issues:
• Poor radio conditions
• Limited Transport Bandwidth
• Application Server
• Traffic Profile
• KPI Definition
Measurement Methods
1. Measure with TCP
2. Measure with multithread TCP session
Checks
1. Check transport
bandwidth
6. Check eNode B
databuild
11. Check feature
set
2. Check cell load
(users and PRB)
7. Check round trip
time
11. Check KPI
definition
3. Check QoS profile
8. Check uplink
throughput
4. Check application
server
9. Check
Transmission Mode
5. Check air-interface
conditions
10. Check Reference
Signal Boosting
3. Measure with UDP
4. Measure from different
Application Servers
4. Measure from network
counters / KPI
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LTE Optimization Guidelines
Parameter Optimization
Uplink Throughput Typical Issues:
Measurement Methods
• Poor radio conditions
1. Measure with TCP
• Inappropriate power control configuration
2. Measure with multithread TCP session
• Aggressive proactive scheduling strategy
3. Measure with UDP
• Over-dimensioning of PUCCH
4. Measure with different
Application Servers
• Lack of enabled features
4. Measure from network
counters / KPI
• Non-optimal packet scheduler and link
adaptation selection
• Application Server
• Traffic Profile
• KPI Definition
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Checks
1. Check transport
bandwidth
6. Check eNode B
databuild
11. Check PUCCH and
PRACH overheads
2. Check cell load
(users and PRB)
7. Check round trip
time
12. Check Scheduler
Type
3. Check QoS profile
8. Check downlink
throughput
13. Check use of IRC
/ MRC
4. Check application
server
9. Power Control
strategy
5. Check air-interface
conditions
10. Check Proactive
Scheduling
LTE Optimization Guidelines
Parameter Optimization
Interference Typical Issues:
1. RF Optimisation
• Reduced Uplink Throughput
2. Check Power Control Solution
5. Check Feature Impact
• Reduced Downlink Throughput
3. Check Scheduler Solution
6. Check eICIC Requirement
• Increased Drop Rate
4. Check Receiver Solution
1. RF Optimisation
2. Check Power Control Solution
3. Check Scheduler Solution
4. Check RSRQ Mobility
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5. Check eICIC Requirement
Monitor metrics:
Uplink Throughput
Uplink MCS
Uplink SINR
Uplink RSSI
UE Power Headroom
Monitor metrics:
Downlink Throughput
Downlink MCS
Downlink CQI
LTE Optimization Guidelines
Parameter Optimization
Latency Typical Issues:
• PING configuration
• Scheduling Request period
• DRX cycle duration
Proactive Scheduling
1. Evaluate Proactive
Scheduling for SRB and data
Scheduling Request Period
1. Evaluate reduced
Scheduling Request Period
Consider PUCCH overhead
2. Evaluate Proactive
Scheduling for SRB only
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Consider uplink interference
and uplink throughput
DRX Cycle Duration
1. Evaluate reduced DRX
cycle durations
Consider UE battery life
LTE Optimization Guidelines
Parameter Optimization
Connection Setup Typical Issues:
• Relatively long paging DRX cycle
• Multiple PRACH preamble transmissions
• Congestion
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LTE Optimization Guidelines
Parameter Optimization
Inactivity Timer Typical Issues:
• Admission Control blocking due to number of RRC Connections
• Ping-Pong between RRC Idle and Connected modes
1. Reduce Inactivity Timer
2. Quantify impact upon:
• signalling load at eNB
• signalling load at MME
• RRC connection load
• drop ratio
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LTE Optimization Guidelines
Parameter Optimization
With dummy LAC – TAC
mapping in MME
With correct LAC – TAC
mapping in MME
CS Fallback Typical Issues:
• No coverage on target layer
Without
Measurements
• Weak coverage on target layer
Release with
Redirection
Improve
Reliability
1. Ensure proper LAC/TAC
mapping within MME
3. Enable Deferred
Measurement Control
Reading on 3G network
5. Enable CSFB with
Measurement based
Redirection
2. Consider inclusion of
System Information within
RRC Release
4. Evaluate Paging DRX
cycle duration
6. Enable CSFB with
Inter-System Handover
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With
Measurements
Release with
Redirection
• Increased Call Setup Delays
Reduce Call
Setup Delay
Options for CS Fallback
With System
Information
Without System
Information
With System
Information
Without System
Information
ISHO
LTE Optimization Guidelines
Parameter Optimization
Network Strategy
• Codec/GBR Selection
• Network Layer Allocation
• Load Balancing Solution
• Inter-System Mobility
• Neighbour Planning Solution
• Geographic Roll-Out Pattern
Feature Selection
VoLTE Typical Issues:
Parameter Design
Neighbour Planning
• Enabling VoLTE increases the LTE Drop Ratio
• Alerting Phase SRVCC not supported/enabled in the Core Network
• Call Setup Failures due to ongoing Handover Procedure
• Release with Redirection causing Dropped Calls
• Releases due to Inactivity during Ringing causing Setup Failures
• IP Counters generate unexpected results
• KPI definitions
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Capacity Planning
RF Planning and Coverage Checks
LTE Optimization Guidelines
Role of SON within LTE Network Optimization
SON:
• centralized SON (algorithms executed in the O&M System)
• distributed SON (algorithms executed at eNodeB level)
• hybrid SON (some algorithms are executed within the O&M system while others are executed at
eNodeB level).
SON functions:
 Self – configuration
 Self – healing
 Self – optimization
 Self - planning
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LTE Optimization Guidelines
Role of SON within LTE Network Optimization
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LTE Optimization Guidelines
Role of SON within LTE Network Optimization
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LTE Optimization Guidelines
Counters and KPI monitoring
Set of radio related counter tables generated by the eNodeB
M8000 S1 Application Protocol
M8001 Cell Load
M8004 Transport Load
M8005 Uplink Power and Quality
M8006 EPS Bearer
M8007 Radio Bearer
M8008 RRC
M8009 Intra eNodeB Handover
M8010 Downlink Power and Quality
M8011 Cell Resource
M8012 Cell Throughput
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M8013 UE State
M8014 Inter eNodeB Handover
M8015 Neighbour cell related
Handover
M8016 Inter System Handover
M8017 LTE Inter System Handover to
UTRAN per Neighbour Cell
M8018 eNodeB Load
M8019 LTE Inter System Handover to
GSM per Neighbour Cell
M8020 Cell Availability
M8021 LTE HO
M8022 X2 AP
M8023 UE and Service Differentiation
LTE Optimization Guidelines
Measurements and Network Logging
Control plane messages and user plane traffic can be traced from various
interfaces. To trace all control messages related to call establishment
following interfaces should be traced: S1 – MME, S6a, S11
User plane traffic can be traced from S1-U interface. X2 interface tracing can
be used to follow handover process and data forwarding during handovers.
Evolved UTRAN (E-UTRAN)
Evolved
NodeB
(eNodeB)
Evolved Packet Core (EPC)
HSS
S6a
MME
X2
S1-MME
LTE-UE
LTE-Uu
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MME: Mobility Management
Entity
S11
cel
l
S1-U
Evolved
NodeB
(eNodeB)
Serving Gateway
Gateway
S10
S7
SAE
Gateway
S5/S8
PDN Gateway
PCRF
SGi
Rx+
PDN
LTE Optimization Guidelines
Measurements and Network Logging
Network logging tools for troubleshooting:
 TTI traces
 BTS-log
 Emil
 RF-Unit Console
 Memory Dumper
 Wireshark
 NetHawk
 JDSU
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LTE Optimization Guidelines
Measurements and Network Logging
Real case example.
TEMS logging for
throughput limitation
troubleshooting
5 MHz bandwidth
CINR: 28
MCS: 26
#PRB: 6
RI: 2 (MIMO 2 streams)
DL throughput: 5.3 Mbps
Backhaul issue
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LTE Optimization Guidelines
Measurements and Network Logging
Real case example. Wireshark tracing for throughput limitation troubleshooting
MW configuration settings 60 Mbps
MW configuration settings changed to 116 Mbps
eNB S1
eNB S1
UDP DL
UDP
DL
Speed >90Mbps
13mbps ≤ speed ≥
19mbps
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UDP UL
FTP оп DL
FTP оп
UL
FTP мп
DL
FTP мп. UL
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