microsoft powerpoint - 09 oeo300010 lte network tuning issue1

LTE Network Tuning

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Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved.

LTE Network Tuning


Objectives

� Upon completion of this course, you will be able to:

� Describe the basic process of LTE network tuning

� Understand the different steps in the process of LTE network

tuning

� Understand the coverage problem analysis and handover

problem analysis during LTE network tuning

Page1

LTE Network Tuning




Contents

1. Basic Process of LTE Network Tuning

2. Test Preparations for LTE Network Tuning

3. Data Collection for LTE Network Tuning

4. Coverage Problem Analysis

5. Handover Problem Analysis

Page2


Basic Process of Network Optimization

Page3

LTE Network Tuning




The Basic Process of Network Tuning

Page4


Contents






Page5

LTE Network Tuning




Test Preparations: Set Optimization

Target

� Coverage is the most import requirement of network tuning. The

following is a example of coverage target:

Page6

Acceptance Content

Reference Value Remarks

RSRP ≥ –110 dBm

≥ 95% (urban area)

This is the result of a scanner test conducted without outdoor load in the planned coverage areas. The test routes are of grid structure, covering all cells. ≥ 90% (suburb)

SINR ≥ 5 dB ≥ 95%

This is the result of a UE test conducted without outdoor load in the planned coverage areas. The test routes are of grid structure, covering all cells.


RSRP & SINR

� RSRP (Reference signal received power):

� RSRP is defined as the linear average over the power

contributions of the resource elements that carry cell-specific

reference signals within the considered measurement

frequency bandwidth.

� SINR (Signal-to-Interference plus Noise Ratio) = S / (I + N)

� Signal (S): power of effective signal

� Interference (I): power of interference

� Noise (N): Thermal noise of receiver

Page7

LTE Network Tuning




Some Other KPI for Drive Test

� For some network tuning projects, maybe some other KPIs more

than coverage KPI are needed. The following are some examples:

Page8

LTE/SAE Attach success rate

E-RAB setup success rate

Call drop rate

Intra-LTE handover success rate

intra-LTE handover delay

FTP download average throughput

FTP upload average throughput


Test Preparation: Partition of Cluster� Network tuning is performed in a group/cluster of eNodeBs, rather

than for each single eNodeB separately.

� Some considerations for cluster division:

� Terrain

� Traffic

� Route line

� …

Page9

0102

03

04

0506

0708

• 01 is a highway coverage area.• 03 and 04 are dense urban areas.• 02, 05, 06 and 07 are ordinary urban areas.• 08 is a suburban area.• Each cluster includes 18 to 22 eNodeB.

An example of cluster division

LTE Network Tuning




Test Preparations: Determine Test Routes

� Some considerations of

test route plan:

� Cover main streets and

important places

� Cover all cells if possible

� Cover the borders of

neighboring clusters

� …

Page10

Test routes of a cluster of a project


Test Preparations: Preparing Tools and

Materials

Page11

Recommended

software:• GENEX probe• GENEX assistant

• Map info• Google earth• …

Recommended

hardware:• Frequency scanner• GPS• Test terminal

• Laptop• …

Materials:• Engineering

parameters• Mapinfo map• Network configuration parameters• …

LTE Network Tuning




Contents






Page12


Date collection

� Before network tuning:

� Collecting planned neighboring cell data and the data

configured in eNodeB

� Checking the consistency between the current configured data

and the planned data

� Drive test result

� The result of outdoor/indoor drive test should be saved for

analysis

Page13

LTE Network Tuning




Contents






Page14


Overview of Coverage Analysis

� Coverage problem analysis is a key task of RF optimization,

which focuses on signal distribution.

� The following are some typical coverage problems:

Page15

weak

coverage

cross

coverage

Lack of

dominant cell

LTE Network Tuning




Overview of Coverage Analysis (cont.)

� Weak coverage means the RSRP of the reference signal in a

coverage is smaller than a threshold (The typical threshold is -

110dBm).

� Cross coverage generally means that the coverage area of an

eNodeB goes beyond the planned scope, and generates

discontinuous dominant areas in the coverage areas of other

eNodeBs.

� Lack of dominant cell means a type of area where there is no

dominant cell or the dominant cell is changed frequently.

Page16


Factors Affecting Coverage

Page17

For downlink:

• Downlink Tx power

• Path loss in downlink• Carrier frequency• Distance between UE receiver and eNodeBtransmitter

• Propagation environment• Antenna gain• Height of antenna• Tilt of antenna• Azimuth of antenna

For uplink:• Uplink Tx power• Path loss in uplink• Carrier frequency• Distance between UE transmitter and eNodeBreceiver• Propagation environment

• Gain of Rx diversity in eNodeB

LTE Network Tuning




Solutions for Weak Coverage

� Optimize coverage by adjusting the azimuth and tilt of the

antenna, increasing the height of the antenna, and using an

antenna with higher gain. The preferential measure is

electrical tilt, followed by mechanical adjustment tilt, and

then adjustment of azimuth.

Page18


Solutions for Weak Coverage (cont.)

� For the non-overlapped parts of the coverage areas of two

adjacent eNodeBs, if they have plenty of users or are large

in size, a new eNodeB should be built or the coverage of

adjacent eNodeBs should be enlarged, so as to deepen the

overlaps of the coverage of the two eNodeBs. Meanwhile,

attention should be paid to intra-frequency interference as a

possible result of increase of coverage scope.

Page19

LTE Network Tuning




Solutions for Weak Coverage (cont.)

� For a weak coverage area caused by a hollow and back of a

hill, the coverage scope can be extended with a new

eNodeB or RRU.

� For a dead zone inside an elevator shaft, tunnel,

underground garage or basement, and high building, the

measures include use of RRU, indoor distribution systems,

leakage cables, and directional antennas.

Page20


Solutions for Cross Coverage

� For cross coverage, try to prevent an antenna from

transmitting signal right towards a road, or use the adjacent

buildings to produce a blocking effect to decrease cross

coverage.

� For a high eNodeB, changing its address is an effective

method. Generally, however, it is always very difficult to find

a suitable substitute for new site. So adjusting the pilot

power or using an electrical tilt antenna to reduce the

eNodeB coverage scope is a possible solution.

Page21

LTE Network Tuning




Solutions for Lack of Dominant Cell

� For an area without a dominant cell, a typical method is to

strengthen the coverage of a cell with strong signal (or a

short-distance cell) and weaken the coverage of other cells

with weak signal (or long-distance cells) by adjusting the

antenna tilt and azimuth.

Page22


Coverage Analysis Process

� Normally coverage analysis process includes downlink

coverage analysis and uplink coverage analysis.

Page23

Downlink coverage analysis: RSRP

Uplink coverage analysis: UE Tx Power

LTE Network Tuning




RSRP for Downlink Coverage Analysis� Downlink coverage analysis is to analyze the RSRP.

� The RSRP quality standard must be combined with the

optimization standard. The following is a example of the

optimization standard of RS RSRP:

� The corresponding quality standards can be defined as:

� Good: RSRP ≥ –90 dBm

� Fair: –110 dBm ≤ RSRP < –90 dBm

� Poor: RSRP < –110 dBm

Page24

RSRP >= –110 dBm >= 95%Result of test by using scanner, with the

UE antenna placed outdoor.


Basic Process of Downlink Coverage

Analysis

Page25

RS Coverage Strength Analysis

• Check the RSRP distribution and find the weak

coverage areas

Dominant Cell Analysis

• Check PCI (physical cell identifier) information and

find the areas where the best PCI changes frequently

LTE Network Tuning




An Example of RS Coverage Strength

Analysis

Page26

Area with poor coverage


An Example of Dominant Cell Analysis

Page27

PCI of the best cell changes frequently

because of lack of dominant cell

LTE Network Tuning




UE Tx Power for Uplink Coverage

Analysis

� The main method of uplink coverage analysis is the analyze

the distribution of UE transmission power.

� UE Transmission power can reflect the uplink path loss

and uplink interference.

Page28


An Example of UE Tx Power Distribution

Page29

Areas where UETx power is high

LTE Network Tuning




Case 1(Cross Coverage): Symptom

Page30

Over coverage by cell with PCI 288


Case 1(Cross Coverage): Analysis

� As shown in Figure, the most possible reason for this over

coverage is either excessive height of the antenna or

improper setting of the antenna tilt.

� In this case a check of the current engineering parameter

settings shows that the tilt is too small. It is recommended to

increase the tilt.

Page31

LTE Network Tuning




Case 1(Cross Coverage): Adjustment

� Adjust the tilt of cell with PCI 288 from 3 degree to 6 degree

� The result after adjustment

Page32

The problem of over coverage by cell with PCI 288 solved after adjustment.


Case 2(Wrong Connection of Antenna):

Symptom

Page33

The coverage of the three cells does not match the configuration.

LTE Network Tuning




Case 2(Wrong Connection of Antenna): Analysis & Adjustment� In this case, the antenna connection for the three cells is wrong. The

antenna for cell9 is connected to cell10. The antenna for cell10 is

connected to cell11. The antenna for cell11 is connected to cell9.

Page34

The problem is solved after changing the antenna connection.


Contents






Page35

LTE Network Tuning




Main Handover Problems During Network

Tuning

� During network tuning two main problems can affect the

handover:

Page36

Channel quality problem

Neighboring relationproblem


Channel Quality Problem

� Under multi-user or loading test scenario, the interference is

more serious; poor channel quality leads to signaling lost

and handover failure.

� Channel quality can be divided into UL and DL for analysis.

Page37

Uplink channel

problem

Downlink channel

problem

Uplink and downlink channelproblems are related.

LTE Network Tuning




Typical Parameters for Channel Quality

Page38

RSRP• RSRP is the basic requirement for downlink signal coverage.

SINR• SINR indicates the downlink channel quality.

IBLER• IBLER indicates the data block error ratio.

PDCCH DL/UL Grant• PDCCH DL/UL grant indicates the scheduling result which is affected by channel quality.


Neighboring Relation Problem

� During network tuning the basic problem of neighboring

relation is missing neighboring cells.

� Because of configuration mistakes maybe some neighboring

cells are missed. It can result in call drop.

� ANR (automatic neighbor relation) can help to solve this

problem, but some terminals don’t support ANR. So ANR is not

fully verified in commercial networks.

Page39

LTE Network Tuning




Case 1(Missing Neighboring cells):

Symptom

Page40

Measurement report has been sent to eNodeB but no handover command from eNodeB.


Case 1(Missing Neighboring cells): Analysis

� UE sent measurement report to eNodeB. But eNodeB didn’t

send handover command. Missing neighboring cell is a

possible reason.

� To confirm that the problem is caused by missing

neighboring cell:

� At first, check measurement report to find which cell are

reported.

� Next step is to check whether the reported cell is included in

RRC connection reconfiguration (measurement control).

Page41

LTE Network Tuning



Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved. Page42

In measurement report A3 event for cell with PCI 64 is reported.


Analysis (cont.): Measurement Report



Analysis (cont.): Measurement Control

Page43

In RRC connection reconfiguration (measurement control) cell with PCI 64 is not in the neighboring cell list. So the problem is confirmed which is missing neighboring cell.

LTE Network Tuning




Case 2(Interference): Symptom

� During the test, the handover from cell with PCI 281 to cell

with PCI 279 fails.

Page44

The handover failure area is covered by the cells with PCI 281, PCI 279 and PCI 178,


Case 2(Interference): Analysis

� In this case, the interference from the cell with PCI 178 is

too strong. So the UE can not receive the handover

command correctly, then handover failed.

Page45

Strong interference from the cell with PCI 178

causes handover failure.

LTE Network Tuning




Case 2(Interference): Adjustment

� In this case, to control the interference from the cell with PCI

178, we can increase the antenna tilt of the cell with PCI

178. Then in the handover area the signal strength from the

cell with PCI 178 is reduced.

Page46

The adjustment reduces the signal strength of the cell with PCI 178, so the strong interference disappear and problem is solved.


Case 3(Bad DL Channel Quality):

Symptom

� Handover fails and call drop happens. The following is the

signaling trace result in eNodeB side.

Page47

eNodeB received

measurement report.

eNodeB sent handover

command.

Uu signaling in eNodeB side

X2 signaling in eNodeB side

eNodeB sent handover request

to the target eNodeB.

LTE Network Tuning





Symptom (cont.)

� The signaling trace result in UE side.

Page48

UE sent measurement

reports to eNodeB.

UE didn’t receive

handover command.



Analysis� The complete handover procedure through X2 interface:

Page49

LTE Network Tuning





Analysis (cont.)

� What is the possible reason for handover failure?

� Is it because of missing neighboring cell?

� No. eNodeB sent RRC CONNECTION

RECONFIGURATION(handover command) to the UE. It means

the neighboring cell is configured, not missing.

� From the signaling trace result we can see eNodeB sent

handover command to the UE but UE didn’t receive it. Is it

because of bad channel quality?

Page50



Analysis (cont.)

� Check the RSRP in serving cell and target cell. The following is

the result:

Page51

Target cell RSRP

Serving cell RSRP

LTE Network Tuning





Analysis (cont.)

� In this case the downlink channel quality in serving cell

decreased too fast. So the handover procedure can not be

completed in time.

� If the handover can be triggered earlier. Maybe the

problem can be solved.

Page52


Case 3(Bad DL Channel Quality): A3

Event for Intra-frequency Handover

� A3 event is used to trigger intra-frequency handover. To trigger

handover earlier, some parameters in A3 event can be modified.

Page53

� For A3 event:

� Entering condition: Mn + Ofn

+ Ocn – Hys > Ms + Ofs +

Ocs + Off

� Leaving condition: Mn + Ofn

+ Ocn + Hys < Ms + Ofs +

Ocs + Off

LTE Network Tuning





Adjustment

� Two parameters in A3 event can be modified to trigger

handover earlier:

� 1. Modify the intra-frequency handover offset to 1dB

� This method will affect handover between the serving cell and all

the neighboring cells. So it is not good.

� 2. Modify the CIO (cell individual offset) between the

serving cell and the target cell

� Try this method and the problem is solved.

Page54

Thank youwww.huawei.com

microsoft powerpoint - 09 oeo300010 lte network tuning issue1

Documents

huawei technologies

lte network tuning4

lte network tuning3

lte network tuningcopyright

network tuning projects

test preparations

test routes

coverage problem analysis5